Alkaline fuel cell. Using fuel cells to power buildings. Types of chemical fuel cells

Benefits of fuel cells/cells

A fuel cell/cell is a device that efficiently generates D.C. and heat from hydrogen-rich fuel by electrochemical reaction.

A fuel cell is similar to a battery in that it generates direct current through a chemical reaction. The fuel cell includes an anode, a cathode and an electrolyte. However, unlike batteries, fuel cells/cells cannot store electrical energy, do not discharge and do not require electricity to recharge. Fuel cells/cells can continuously generate electricity as long as they have a supply of fuel and air.

Unlike other power generators such as internal combustion engines or turbines powered by gas, coal, oil, etc., fuel cells/cells do not burn fuel. This means no noisy rotors high pressure, loud exhaust noise, vibration. Fuel cells/cells generate electricity through a silent electrochemical reaction. Another feature of fuel cells/cells is that they convert the chemical energy of the fuel directly into electricity, heat and water.

Fuel cells are highly efficient and do not produce large amounts of greenhouse gases such as carbon dioxide, methane and nitrous oxide. The only products emitted during operation are water in the form of steam and a small amount of carbon dioxide, which is not emitted at all if pure hydrogen is used as fuel. Fuel cells/cells are assembled into assemblies and then into individual functional modules.

History of fuel cell/cell development

In the 1950s and 1960s, one of the biggest challenges for fuel cells was born out of the US National Aeronautics and Space Administration's (NASA) need for energy sources for long-duration space missions. NASA's Alkaline Fuel Cell/Cell uses hydrogen and oxygen as fuel, combining the two in an electrochemical reaction. The output is three by-products of the reaction useful in spaceflight - electricity to power the spacecraft, water for drinking and cooling systems, and heat to keep the astronauts warm.

The discovery of fuel cells dates back to the beginning of the 19th century. The first evidence of the effect of fuel cells was obtained in 1838.

In the late 1930s, work began on alkaline fuel cells, and by 1939 a cell using high pressure nickel-plated electrodes had been built. During the Second World War, fuel cells/cells for British Navy submarines were developed and in 1958 a fuel assembly consisting of alkaline fuel cells/cells just over 25 cm in diameter was introduced.

Interest increased in the 1950s and 1960s and also in the 1980s when the industrial world experienced a shortage of fuel oil. In the same period, world countries also became concerned about the problem of air pollution and considered ways to generate environmentally friendly electricity. At present, fuel cell/cell technology is undergoing rapid development.

How fuel cells/cells work

Fuel cells/cells generate electricity and heat through an ongoing electrochemical reaction using an electrolyte, a cathode and an anode.

On the anode catalyst, molecular hydrogen dissociates and loses electrons. Hydrogen ions (protons) are conducted through the electrolyte to the cathode, while electrons are passed through the electrolyte and through an external electrical circuit, creating a direct current that can be used to power equipment. On the cathode catalyst, an oxygen molecule combines with an electron (which is supplied from external communications) and an incoming proton, and forms water, which is the only reaction product (in the form of vapor and / or liquid).

Below is the corresponding reaction:

Anode reaction: 2H 2 => 4H+ + 4e -
Reaction at the cathode: O 2 + 4H+ + 4e - => 2H 2 O
General element reaction: 2H 2 + O 2 => 2H 2 O

Types and variety of fuel cells/cells

Similar to the existence of different types of internal combustion engines, there are different types of fuel cells - the choice of the appropriate type of fuel cell depends on its application.

Fuel cells are divided into high temperature and low temperature. Low temperature fuel cells require relatively pure hydrogen as fuel. This often means that fuel processing is required to convert the primary fuel (such as natural gas) to pure hydrogen. This process consumes additional energy and requires special equipment. High temperature fuel cells do not need this additional procedure as they can "internally convert" the fuel when elevated temperatures, which means there is no need to invest in hydrogen infrastructure.

Fuel cells/cells on molten carbonate (MCFC)

The operation of RCFC is different from other fuel cells. These cells use an electrolyte from a mixture of molten carbonate salts. Currently, two types of mixtures are used: lithium carbonate and potassium carbonate or lithium carbonate and sodium carbonate. To melt carbonate salts and achieve a high degree of mobility of ions in the electrolyte, the operation of fuel cells with molten carbonate electrolyte occurs at high temperatures(650°C). The efficiency varies between 60-80%.

When heated to a temperature of 650°C, salts become a conductor for carbonate ions (CO 3 2-). These ions pass from the cathode to the anode where they combine with hydrogen to form water, carbon dioxide and free electrons. These electrons are sent through an external electrical circuit back to the cathode, generating electrical current and heat as a by-product.

Anode reaction: CO 3 2- + H 2 => H 2 O + CO 2 + 2e -
Reaction at the cathode: CO 2 + 1/2O 2 + 2e - => CO 3 2-
General element reaction: H 2 (g) + 1/2O 2 (g) + CO 2 (cathode) => H 2 O (g) + CO 2 (anode)

The high operating temperatures of molten carbonate electrolyte fuel cells have certain advantages. At high temperatures, the natural gas is internally reformed, eliminating the need for a fuel processor. In addition, the advantages include the ability to use standard materials of construction, such as stainless steel sheet and nickel catalyst on the electrodes. The waste heat can be used to generate high pressure steam for various industrial and commercial purposes.

High reaction temperatures in the electrolyte also have their advantages. The use of high temperatures takes a long time to reach optimal operating conditions, and the system reacts more slowly to changes in energy consumption. These characteristics allow the use of fuel cell systems with molten carbonate electrolyte in constant power conditions. High temperatures prevent damage to the fuel cell by carbon monoxide.

Molten carbonate fuel cells are suitable for use in large stationary installations. Thermal power plants with an output electric power of 3.0 MW are industrially produced. Plants with an output power of up to 110 MW are being developed.

Fuel cells/cells based on phosphoric acid (PFC)

Fuel cells based on phosphoric (orthophosphoric) acid were the first fuel cells for commercial use.

Fuel cells based on phosphoric (orthophosphoric) acid use an electrolyte based on orthophosphoric acid (H 3 PO 4) with a concentration of up to 100%. The ionic conductivity of phosphoric acid is low at low temperatures, for this reason, these fuel cells are used at temperatures up to 150–220°C.

The charge carrier in fuel cells of this type is hydrogen (H+, proton). A similar process occurs in proton exchange membrane fuel cells, in which hydrogen supplied to the anode is split into protons and electrons. The protons pass through the electrolyte and combine with oxygen from the air at the cathode to form water. The electrons are directed along an external electrical circuit, and an electric current is generated. Below are the reactions that generate electricity and heat.

Reaction at the anode: 2H 2 => 4H + + 4e -
Reaction at the cathode: O 2 (g) + 4H + + 4e - \u003d\u003e 2 H 2 O
General element reaction: 2H 2 + O 2 => 2H 2 O

The efficiency of fuel cells based on phosphoric (orthophosphoric) acid is more than 40% when generating electrical energy. In the combined production of heat and electricity, the overall efficiency is about 85%. In addition, given operating temperatures, waste heat can be used to heat water and generate steam at atmospheric pressure.

The high performance of thermal power plants on fuel cells based on phosphoric (orthophosphoric) acid in the combined production of heat and electricity is one of the advantages of this type of fuel cells. The plants use carbon monoxide at a concentration of about 1.5%, which greatly expands the choice of fuel. In addition, CO 2 does not affect the electrolyte and the operation of the fuel cell, this type of cell works with reformed natural fuel. Simple design, low electrolyte volatility and increased stability are also advantages of this type of fuel cell.

Thermal power plants with an output electric power of up to 500 kW are industrially produced. Installations for 11 MW have passed the relevant tests. Plants with an output power of up to 100 MW are being developed.

Solid oxide fuel cells/cells (SOFC)

Solid oxide fuel cells are the fuel cells with the highest operating temperature. The operating temperature can vary from 600°C to 1000°C, which allows the use of various types of fuel without special pre-treatment. To handle these high temperatures, the electrolyte used is a thin ceramic-based solid metal oxide, often an alloy of yttrium and zirconium, which is a conductor of oxygen (O 2-) ions.

A solid electrolyte provides a hermetic gas transition from one electrode to another, while liquid electrolytes are located in a porous substrate. The charge carrier in fuel cells of this type is the oxygen ion (O 2-). At the cathode, oxygen molecules are separated from the air into an oxygen ion and four electrons. Oxygen ions pass through the electrolyte and combine with hydrogen to form four free electrons. Electrons are directed through an external electrical circuit, generating electrical current and waste heat.

Reaction at the anode: 2H 2 + 2O 2- => 2H 2 O + 4e -
Reaction at the cathode: O 2 + 4e - \u003d\u003e 2O 2-
General element reaction: 2H 2 + O 2 => 2H 2 O

The efficiency of the generated electrical energy is the highest of all fuel cells - about 60-70%. High operating temperatures allow for combined heat and power generation to generate high pressure steam. Combining a high temperature fuel cell with a turbine creates a hybrid fuel cell for increase efficiency generation of electrical energy up to 75%.

Solid oxide fuel cells operate at very high temperatures (600°C-1000°C), resulting in a long time to reach optimal operating conditions, and the system is slower to respond to changes in power consumption. At such high operating temperatures, no converter is required to recover hydrogen from the fuel, allowing the thermal power plant to operate with relatively impure fuels from coal gasification or waste gases, and the like. Also, this fuel cell is excellent for high power applications, including industrial and large central power plants. Industrially produced modules with an output electrical power of 100 kW.

Fuel cells/cells with direct methanol oxidation (DOMTE)

The technology of using fuel cells with direct oxidation of methanol is undergoing a period of active development. It has successfully established itself in the field of powering mobile phones, laptops, as well as for creating portable power sources. what the future application of these elements is aimed at.

The structure of fuel cells with direct oxidation of methanol is similar to fuel cells with a proton exchange membrane (MOFEC), i.e. a polymer is used as an electrolyte, and a hydrogen ion (proton) is used as a charge carrier. However, liquid methanol (CH 3 OH) is oxidized in the presence of water at the anode, releasing CO 2 , hydrogen ions and electrons, which are guided through an external electrical circuit, and an electric current is generated. Hydrogen ions pass through the electrolyte and react with oxygen from the air and electrons from the external circuit to form water at the anode.

Reaction at the anode: CH 3 OH + H 2 O => CO 2 + 6H + + 6e -
Reaction at the cathode: 3/2O 2 + 6 H + + 6e - => 3H 2 O
General element reaction: CH 3 OH + 3/2O 2 => CO 2 + 2H 2 O

The advantage of this type of fuel cells is their small size, due to the use of liquid fuel, and the absence of the need to use a converter.

Alkaline fuel cells/cells (AFC)

Alkaline fuel cells are one of the most efficient elements used to generate electricity, with power generation efficiency reaching up to 70%.

Alkaline fuel cells use an electrolyte, i.e. water solution potassium hydroxide contained in a porous stabilized matrix. The concentration of potassium hydroxide may vary depending on the operating temperature of the fuel cell, which ranges from 65°C to 220°C. The charge carrier in an SFC is a hydroxide ion (OH-) moving from the cathode to the anode where it reacts with hydrogen to produce water and electrons. The water produced at the anode moves back to the cathode, again generating hydroxide ions there. As a result of this series of reactions taking place in the fuel cell, electricity is produced and, as a by-product, heat:

Reaction at the anode: 2H 2 + 4OH - => 4H 2 O + 4e -
Reaction at the cathode: O 2 + 2H 2 O + 4e - => 4 OH -
General reaction of the system: 2H 2 + O 2 => 2H 2 O

The advantage of SFCs is that these fuel cells are the cheapest to produce, since the catalyst needed on the electrodes can be any of the substances that are cheaper than those used as catalysts for other fuel cells. SCFCs operate at relatively low temperatures and are among the most efficient fuel cells - such characteristics can respectively contribute to faster power generation and high fuel efficiency.

One of the characteristic features of SHTE is its high sensitivity to CO 2 , which can be contained in fuel or air. CO 2 reacts with the electrolyte, quickly poisons it, and greatly reduces the efficiency of the fuel cell. Therefore, the use of SFCs is limited to closed spaces such as space and underwater vehicles, they must operate on pure hydrogen and oxygen. Moreover, molecules such as CO, H 2 O and CH4, which are safe for other fuel cells and even fuel for some of them, are detrimental to SFCs.

Polymer electrolyte fuel cells/cells (PETE)

In the case of polymer electrolyte fuel cells, the polymer membrane consists of polymer fibers with water regions in which there is a conduction of water ions (H 2 O + (proton, red) attached to the water molecule). Water molecules present a problem due to slow ion exchange. Therefore, a high concentration of water is required both in the fuel and on the exhaust electrodes, which limits the operating temperature to 100°C.

Solid acid fuel cells/cells (SCFC)

In solid acid fuel cells, the electrolyte (CsHSO 4 ) does not contain water. The operating temperature is therefore 100-300°C. The rotation of the SO 4 2- oxy anions allows the protons (red) to move as shown in the figure. Typically, a solid acid fuel cell is a sandwich in which a very thin layer of solid acid compound is sandwiched between two tightly compressed electrodes to ensure good contact. When heated, the organic component evaporates, leaving through the pores in the electrodes, retaining the ability of numerous contacts between the fuel (or oxygen at the other end of the cell), electrolyte and electrodes.

Various fuel cell modules. fuel cell battery

Fuel Cell Battery
Other high temperature equipment (integrated steam generator, combustion chamber, heat balance changer)
Heat resistant insulation

fuel cell module

Comparative analysis of types and varieties of fuel cells

Innovative energy-saving municipal heat and power plants are typically built on solid oxide fuel cells (SOFCs), polymer electrolyte fuel cells (PEFCs), phosphoric acid fuel cells (PCFCs), proton exchange membrane fuel cells (MPFCs) and alkaline fuel cells (APFCs) . They usually have the following characteristics:

Solid oxide fuel cells (SOFC) should be recognized as the most suitable, which:

operate at a higher temperature, which reduces the need for expensive precious metals (such as platinum)
can work for various types hydrocarbon fuels, mainly natural gas
have a longer start-up time and therefore are better suited for long-term operation
demonstrate high efficiency of power generation (up to 70%)
due to high operating temperatures, the units can be combined with heat recovery systems, bringing the overall system efficiency up to 85%
have near-zero emissions, operate silently and have low operating requirements compared to existing power generation technologies

Fuel cell type	Working temperature	Power Generation Efficiency	Fuel type	Application area
RKTE	550–700°C	50-70%		Medium and large installations
FKTE	100–220°C	35-40%	pure hydrogen	Large installations
MOPTE	30-100°C	35-50%	pure hydrogen	Small installations
SOFC	450–1000°C	45-70%	Most hydrocarbon fuels	Small, medium and large installations
POMTE	20-90°C	20-30%	methanol	portable
SHTE	50–200°C	40-70%	pure hydrogen	space research
PETE	30-100°C	35-50%	pure hydrogen	Small installations

Since small thermal power plants can be connected to a conventional gas supply network, fuel cells do not require a separate hydrogen supply system. When using small thermal power plants based on solid oxide fuel cells, the generated heat can be integrated into heat exchangers for heating water and ventilation air, increasing the overall efficiency of the system. This innovative technology is best suited for efficient power generation without the need for expensive infrastructure and complex instrument integration.

Fuel cell/cell applications

Application of fuel cells/cells in telecommunication systems

With the rapid spread of wireless communication systems around the world, as well as the growing social and economic benefits of mobile phone technology, the need for reliable and cost-effective backup power has become critical. Power grid losses throughout the year due to bad weather conditions, natural Disasters or limited network capacity present a persistent challenge for network operators.

Traditional telecom power backup solutions include batteries (valve-regulated lead-acid battery cell) for short-term backup power and diesel and propane generators for longer backup power. Batteries are a relatively cheap source of backup power for 1 to 2 hours. However, batteries are not suitable for longer backup periods as they are expensive to maintain and become unreliable after long service life, are temperature sensitive and hazardous to the environment after disposal. Diesel and propane generators can provide continuous backup power. However, generators can be unreliable, require extensive maintenance, and release high levels of pollutants and greenhouse gases into the atmosphere.

In order to eliminate the limitations of traditional backup power solutions, an innovative green fuel cell technology has been developed. Fuel cells are reliable, quiet, contain fewer moving parts than a generator, have a wider operating temperature range than a battery from -40°C to +50°C and, as a result, provide extremely high levels of energy savings. In addition, the lifetime cost of such a plant is lower than that of a generator. Lower fuel cell costs are the result of just one maintenance visit per year and much more high performance installation. After all, the fuel cell is an environmentally friendly technology solution with minimal environmental impact.

Fuel cell units provide backup power for critical communications network infrastructures for wireless, permanent and broadband communications in the telecommunications system, ranging from 250W to 15kW, they offer many unrivaled innovative features:

RELIABILITY– Few moving parts and no standby discharge
ENERGY SAVING
SILENCE– low noise level
STABILITY– operating range from -40°C to +50°C
ADAPTABILITY– outdoor and indoor installation (container/protective container)
HIGH POWER– up to 15 kW
LOW MAINTENANCE NEED– minimum annual maintenance
ECONOMY- attractive total cost of ownership
CLEAN ENERGY– low emissions with minimal environmental impact

The system senses the DC bus voltage all the time and smoothly accepts critical loads if the DC bus voltage drops below a user-defined setpoint. The system runs on hydrogen, which enters the fuel cell stack in one of two ways - either from a commercial source of hydrogen, or from a liquid fuel of methanol and water, using an on-board reformer system.

Electricity is produced by the fuel cell stack in the form of direct current. The DC power is sent to a converter that converts the unregulated DC power from the fuel cell stack into high quality, regulated DC power for the required loads. A fuel cell installation can provide backup power for many days, as the duration is limited only by the amount of hydrogen or methanol/water fuel available in stock.

Fuel cells offer superior energy efficiency, increased system reliability, more predictable performance in a wide range of climates, and reliable service life compared to industry standard valve regulated lead acid battery packs. Lifecycle costs are also lower due to significantly less maintenance and replacement requirements. Fuel cells offer the end user environmental benefits as disposal costs and liability risks associated with lead acid cells are a growing concern.

The performance of electric batteries can be adversely affected by a wide range of factors such as charge level, temperature, cycles, life and other variables. The energy provided will vary depending on these factors and is not easy to predict. Performance characteristics Proton exchange membrane fuel cells (PEMFCs) are relatively unaffected by these factors and can provide critical power as long as fuel is available. Increased predictability is an important benefit when moving to fuel cells for mission-critical backup power applications.

Fuel cells generate energy only when fuel is supplied, like a gas turbine generator, but do not have moving parts in the generation zone. Therefore, unlike a generator, they are not subject to rapid wear and do not require constant maintenance and lubrication.

The fuel used to drive the Extended Duration Fuel Converter is a mixture of methanol and water. Methanol is a widely available, commercially produced fuel that currently has many applications, including windshield washer, plastic bottles, engine additives, emulsion paints. Methanol is easy to transport, miscible with water, has good biodegradability and is sulfur free. It has a low freezing point (-71°C) and does not decompose during long storage.

Application of fuel cells/cells in communication networks

Security networks require reliable backup power solutions that can last hours or days at a time. emergency situations if the power grid is no longer available.

With few moving parts and no standby power reduction, the innovative fuel cell technology offers an attractive solution compared to currently available backup power systems.

The most compelling reason for using fuel cell technology in communications networks is the increased overall reliability and security. During events such as power outages, earthquakes, storms, and hurricanes, it is important that systems continue to operate and have a reliable backup power supply for an extended period of time, regardless of the temperature or age of the backup power system.

The range of fuel cell power supplies is ideal for supporting secure communications networks. Thanks to their energy saving design principles, they provide an environmentally friendly, reliable backup power with extended duration (up to several days) for use in the power range from 250 W to 15 kW.

Application of fuel cells/cells in data networks

Reliable power supply for data networks, such as high-speed data networks and fiber optic backbones, is of key importance throughout the world. Information transmitted over such networks contains critical data for institutions such as banks, airlines or medical centers. A power outage in such networks not only poses a danger to the transmitted information, but also, as a rule, leads to significant financial losses. Reliable, innovative fuel cell installations that provide standby power provide the reliability you need to ensure uninterrupted power.

Fuel cell units operating on a liquid fuel mixture of methanol and water provide a reliable backup power supply with extended duration, up to several days. In addition, these units feature significantly reduced maintenance requirements compared to generators and batteries, requiring only one maintenance visit per year.

Typical application characteristics for the use of fuel cell installations in data networks:

Applications with power inputs from 100 W to 15 kW
Applications with battery life requirements > 4 hours
Repeaters in fiber optic systems (hierarchy of synchronous digital systems, high speed internet, voice over IP…)
Network nodes of high-speed data transmission
WiMAX Transmission Nodes

Fuel cell standby installations offer numerous advantages for critical data network infrastructures over traditional battery or diesel generators, allowing for increased on-site utilization:

Liquid fuel technology solves the problem of hydrogen storage and provides virtually unlimited backup power.
Due to their quiet operation, low weight, resistance to temperature extremes and virtually vibration-free operation, fuel cells can be installed outdoors, in industrial premises/containers or on rooftops.
On-site preparations for using the system are quick and economical, and the cost of operation is low.
The fuel is biodegradable and represents an environmentally friendly solution for the urban environment.

Application of fuel cells/cells in security systems

The most carefully designed building security and communication systems are only as reliable as the power that powers them. While most systems include some type of back-up uninterruptible power system for short-term power losses, they do not provide for the longer power outages that can occur after natural disasters or terrorist attacks. This could be a critical issue for many corporate and government agencies.

Vital systems such as CCTV monitoring and access control systems (ID card readers, door closing devices, biometric identification technology, etc.), automatic fire alarm and fire extinguishing systems, elevator control systems and telecommunication networks, are at risk in the absence of a reliable alternative source of continuous power supply.

Diesel generators are noisy, hard to locate, and are well aware of their reliability and maintenance issues. In contrast, a fuel cell back-up installation is quiet, reliable, has zero or very low emissions, and is easy to install on a rooftop or outside a building. It does not discharge or lose power in standby mode. It ensures continuous operation of critical important systems, even after the institution ceases operation and the building is abandoned by people.

Innovative fuel cell installations protect expensive investments in critical applications. They provide environmentally friendly, reliable backup power with extended duration (up to many days) for use in the power range from 250 W to 15 kW, combined with numerous unsurpassed features and, especially, a high level of energy saving.

Fuel cell power backup units offer numerous advantages for mission critical applications such as security and building management systems over traditional battery or diesel generators. Liquid fuel technology solves the problem of hydrogen storage and provides virtually unlimited backup power.

Application of fuel cells/cells in domestic heating and power generation

Solid oxide fuel cells (SOFCs) are used to build reliable, energy-efficient and emission-free thermal power plants to generate electricity and heat from widely available natural gas and renewable fuel sources. These innovative units are used in a wide variety of markets, from domestic power generation to power supply to remote areas, as well as auxiliary power sources.

Application of fuel cells/cells in distribution networks

Small thermal power plants are designed to operate in a distributed power generation network, consisting of a large number small generator sets instead of one centralized power plant.

The figure below shows the loss in efficiency of electricity generation when it is generated by CHP and transmitted to homes through the traditional transmission networks currently in use. Efficiency losses in district generation include losses from the power plant, low and high voltage transmission, and distribution losses.

The figure shows the results of the integration of small thermal power plants: electricity is generated with a generation efficiency of up to 60% at the point of use. In addition, the household can use the heat generated by the fuel cells for water and space heating, which increases the overall efficiency of fuel energy processing and improves energy savings.

Using Fuel Cells to Protect the Environment - Utilization of Associated Petroleum Gas

One of the most important tasks in the oil industry is the utilization of associated petroleum gas. The existing methods of utilization of associated petroleum gas have a lot of disadvantages, the main one being that they are not economically viable. Associated petroleum gas is flared, which causes great harm to the environment and human health.

Innovative fuel cell heat and power plants using associated petroleum gas as a fuel open the way to a radical and cost-effective solution to the problems of associated petroleum gas utilization.

One of the main advantages of fuel cell installations is that they can operate reliably and sustainably on variable composition associated petroleum gas. Due to the flameless chemical reaction underlying the operation of a fuel cell, a reduction in the percentage of, for example, methane only causes a corresponding reduction in power output.
Flexibility in relation to the electrical load of consumers, differential, load surge.
For the installation and connection of thermal power plants on fuel cells, their implementation does not require capital expenditures, because The units are easily mounted on unprepared sites near fields, are easy to operate, reliable and efficient.
High automation and modern remote control do not require the constant presence of personnel at the plant.
Simplicity and technical perfection of the design: the absence of moving parts, friction, lubrication systems provides significant economic benefits from the operation of fuel cell installations.
Water consumption: none at ambient temperatures up to +30 °C and negligible at higher temperatures.
Water outlet: none.
In addition, fuel cell thermal power plants do not make noise, do not vibrate, do not emit harmful emissions into the atmosphere

Part 1

This article discusses in more detail the principle of operation of fuel cells, their design, classification, advantages and disadvantages, scope, efficiency, history of creation and modern prospects for use. In the second part of the article, which will be published in the next issue of the ABOK magazine, provides examples of facilities where various types of fuel cells were used as sources of heat and electricity (or only electricity).

Introduction

Fuel cells are a very efficient, reliable, durable and environmentally friendly way to generate energy.

Initially used only in the space industry, fuel cells are now increasingly used in a variety of areas - as stationary power plants, autonomous sources of heat and power for buildings, vehicle engines, power supplies for laptops and mobile phones. Some of these devices are laboratory prototypes, some are undergoing pre-series testing or are used for demonstration purposes, but many models are mass-produced and used in commercial projects.

A fuel cell (electrochemical generator) is a device that converts the chemical energy of fuel (hydrogen) into electrical energy in the process of an electrochemical reaction directly, unlike traditional technologies that use the combustion of solid, liquid and gaseous fuels. Direct electrochemical conversion of fuel is very efficient and attractive from an environmental point of view, since the minimum amount of pollutants is released during operation, and there are no loud noises and vibration.

From a practical point of view, a fuel cell resembles a conventional galvanic battery. The difference lies in the fact that initially the battery is charged, i.e. filled with “fuel”. During operation, "fuel" is consumed and the battery is discharged. Unlike a battery, a fuel cell uses fuel supplied from an external source to generate electrical energy (Fig. 1).

For the production of electrical energy, not only pure hydrogen can be used, but also other hydrogen-containing raw materials, such as natural gas, ammonia, methanol or gasoline. Ordinary air is used as a source of oxygen, which is also necessary for the reaction.

When pure hydrogen is used as a fuel, the reaction products, in addition to electrical energy, are heat and water (or water vapor), i.e. no gases are emitted into the atmosphere that cause air pollution or cause a greenhouse effect. If a hydrogen-containing feedstock, such as natural gas, is used as a fuel, other gases, such as oxides of carbon and nitrogen, will be a by-product of the reaction, but its amount is much lower than when burning the same amount of natural gas.

The process of chemical conversion of fuel in order to produce hydrogen is called reforming, and the corresponding device is called a reformer.

Advantages and disadvantages of fuel cells

Fuel cells are more energy efficient than internal combustion engines because there is no thermodynamic limitation on energy efficiency for fuel cells. The efficiency of fuel cells is 50%, while Engine efficiency internal combustion is 12-15%, and the efficiency of steam turbine power plants does not exceed 40%. By using heat and water, the efficiency of fuel cells is further increased.

In contrast to, for example, internal combustion engines, the efficiency of fuel cells remains very high even when they are not operating at full power. In addition, the power of fuel cells can be increased by simply adding separate blocks, while the efficiency does not change, i.e. large installations are as efficient as small ones. These circumstances allow a very flexible selection of the composition of equipment in accordance with the wishes of the customer and ultimately lead to a reduction in equipment costs.

An important advantage of fuel cells is their environmental friendliness. Air emissions from fuel cells are so low that in some parts of the United States they do not require special permission from government agencies that control the quality of the air environment.

Fuel cells can be placed directly in the building, thus reducing energy transmission losses, and the heat generated as a result of the reaction can be used to supply heat or hot water to the building. Autonomous sources of heat and electricity can be very beneficial in remote areas and in regions that are characterized by a shortage of electricity and its high price, but at the same time there are reserves of hydrogen-containing raw materials (oil, natural gas).

The advantages of fuel cells are also the availability of fuel, reliability (there are no moving parts in the fuel cell), durability and ease of operation.

One of the main shortcomings of fuel cells today is their relatively high cost, but this shortcoming can be overcome soon - more and more companies produce commercial samples of fuel cells, they are constantly being improved, and their cost is decreasing.

The most efficient use of pure hydrogen as a fuel, however, this will require the creation of a special infrastructure for its generation and transportation. Currently, all commercial designs use natural gas and similar fuels. Vehicles can use ordinary gasoline, which will allow maintaining the existing developed network of gas stations. However, the use of such fuel leads to harmful emissions into the atmosphere (albeit very low) and complicates (and therefore increases the cost of) the fuel cell. In the future, the possibility of using environmentally friendly renewable energy sources (for example, solar energy or wind power) to decompose water into hydrogen and oxygen by electrolysis, and then convert the resulting fuel in a fuel cell. Such combined plants operating in a closed cycle can be a completely environmentally friendly, reliable, durable and efficient source of energy.

Another feature of fuel cells is that they are most efficient when using both electrical and thermal energy at the same time. However, the possibility of using thermal energy is not available at every facility. In the case of using fuel cells only for generating electrical energy, their efficiency decreases, although it exceeds the efficiency of “traditional” installations.

History and modern uses of fuel cells

The principle of operation of fuel cells was discovered in 1839. The English scientist William Grove (1811-1896) discovered that the process of electrolysis - the decomposition of water into hydrogen and oxygen by means of an electric current - is reversible, i.e. hydrogen and oxygen can be combined into water molecules without combustion, but with the release of heat and electric current. Grove called the device in which such a reaction was carried out a "gas battery", which was the first fuel cell.

The active development of fuel cell technologies began after the Second World War, and it is associated with the aerospace industry. At that time, searches were conducted for an efficient and reliable, but at the same time quite compact source of energy. In the 1960s, NASA specialists (National Aeronautics and Space Administration, NASA) chose fuel cells as a power source for spacecraft of the Apollo (manned flights to the Moon), Apollo-Soyuz, Gemini and Skylab programs. . The Apollo used three 1.5 kW units (2.2 kW peak power) using cryogenic hydrogen and oxygen to produce electricity, heat and water. The mass of each installation was 113 kg. These three cells worked in parallel, but the energy generated by one unit was enough for a safe return. During 18 flights, the fuel cells have accumulated a total of 10,000 hours without any failures. Currently, fuel cells are used in the space shuttle "Space Shuttle", which uses three units with a power of 12 W, which generate all the electrical energy on board the spacecraft (Fig. 2). Water obtained as a result of an electrochemical reaction is used as drinking water, as well as for cooling equipment.

In our country, work was also underway to create fuel cells for use in astronautics. For example, fuel cells were used to power the Soviet Buran space shuttle.

Development of methods for the commercial use of fuel cells began in the mid-1960s. These developments were partially funded by government organizations.

Currently, the development of technologies for the use of fuel cells goes in several directions. This is the creation of stationary power plants on fuel cells (for both centralized and decentralized energy supply), power plants of vehicles (samples of cars and buses on fuel cells have been created, including in our country) (Fig. 3), and as well as power sources of various mobile devices(laptops, mobile phones, etc.) (Fig. 4).

Examples of the use of fuel cells in various fields are given in Table. one.

One of the first commercial models of fuel cells designed for autonomous heat and power supply of buildings was the PC25 Model A manufactured by ONSI Corporation (now United Technologies, Inc.). This fuel cell with a nominal power of 200 kW belongs to the type of cells with an electrolyte based on phosphoric acid (Phosphoric Acid Fuel Cells, PAFC). The number "25" in the name of the model means the serial number of the design. Most of the previous models were experimental or test pieces, such as the 12.5 kW "PC11" model that appeared in the 1970s. The new models increased the power taken from a single fuel cell, and also reduced the cost per kilowatt of energy produced. Currently, one of the most efficient commercial models is the PC25 Model C fuel cell. Like model "A", this is a fully automatic fuel cell of the PAFC type with a power of 200 kW, designed to be installed directly on the serviced object as an independent source of heat and electricity. Such a fuel cell can be installed outside the building. Outwardly, it is a parallelepiped 5.5 m long, 3 m wide and 3 m high, weighing 18,140 kg. The difference from previous models is an improved reformer and a higher current density.

Table 1
Scope of fuel cells

Region applications	Rated power	Examples of using
Stationary installations	5–250 kW and above	Autonomous sources of heat and power supply for residential, public and industrial buildings, uninterruptible power supplies, backup and emergency power supplies
Portable installations	1–50 kW	Road signs, refrigerated trucks and railroads, wheelchairs, golf carts, spacecraft and satellites
Mobile installations	25–150 kW	Cars (prototypes were created, for example, by DaimlerCrysler, FIAT, Ford, General Motors”, “Honda”, “Hyundai”, “Nissan”, “Toyota”, “Volkswagen”, VAZ), buses (for example, “MAN”, “Neoplan”, “Renault”) and other vehicles, warships and submarines
Microdevices	1-500W	Mobile phones, laptops, PDAs, various consumer electronic devices, modern military devices

In some types of fuel cells, the chemical process can be reversed: by applying a potential difference to the electrodes, water can be decomposed into hydrogen and oxygen, which are collected on porous electrodes. When a load is connected, such a regenerative fuel cell will begin to generate electrical energy.

A promising direction for the use of fuel cells is their use in conjunction with renewable energy sources, such as photovoltaic panels or wind turbines. This technology allows you to completely avoid air pollution. A similar system is planned to be created, for example, at the Adam Joseph Lewis Training Center in Oberlin (see ABOK, 2002, No. 5, p. 10). Currently, solar panels are used as one of the energy sources in this building. Together with NASA specialists, a project was developed to use photovoltaic panels to produce hydrogen and oxygen from water by electrolysis. The hydrogen is then used in fuel cells to generate electricity and hot water. This will allow the building to maintain the performance of all systems during cloudy days and at night.

The principle of operation of fuel cells

Let us consider the principle of operation of a fuel cell using the simplest element with a proton exchange membrane (Proton Exchange Membrane, PEM) as an example. Such an element consists of a polymer membrane placed between the anode (positive electrode) and the cathode (negative electrode) together with the anode and cathode catalysts. A polymer membrane is used as the electrolyte. The diagram of the PEM element is shown in fig. 5.

A proton exchange membrane (PEM) is a thin (approximately 2-7 sheets of plain paper thick) solid organic compound. This membrane functions as an electrolyte: it separates matter into positively and negatively charged ions in the presence of water.

An oxidative process occurs at the anode, and a reduction process occurs at the cathode. The anode and cathode in the PEM cell are made of a porous material, which is a mixture of particles of carbon and platinum. Platinum acts as a catalyst that promotes the dissociation reaction. The anode and cathode are made porous for free passage of hydrogen and oxygen through them, respectively.

The anode and cathode are placed between two metal plates, which supply hydrogen and oxygen to the anode and cathode, and remove heat and water, as well as electrical energy.

Hydrogen molecules pass through the channels in the plate to the anode, where the molecules decompose into individual atoms (Fig. 6).

	Figure 5 () Schematic diagram of a proton exchange membrane (PEM) fuel cell
	Figure 6 () Hydrogen molecules through the channels in the plate enter the anode, where the molecules are decomposed into individual atoms
	Figure 7 () As a result of chemisorption in the presence of a catalyst, hydrogen atoms are converted into protons
	Figure 8 () Positively charged hydrogen ions diffuse through the membrane to the cathode, and the electron flow is directed to the cathode through an external electrical circuit to which the load is connected.
	Figure 9 () Oxygen supplied to the cathode, in the presence of a catalyst, enters into a chemical reaction with hydrogen ions from the proton-exchange membrane and electrons from the external electrical circuit. Water is formed as a result of a chemical reaction

Then, as a result of chemisorption in the presence of a catalyst, hydrogen atoms, each donating one electron e - , are converted into positively charged hydrogen ions H +, i.e. protons (Fig. 7).

Positively charged hydrogen ions (protons) diffuse through the membrane to the cathode, and the electron flow is directed to the cathode through an external electrical circuit to which the load (consumer of electrical energy) is connected (Fig. 8).

Oxygen supplied to the cathode, in the presence of a catalyst, enters into a chemical reaction with hydrogen ions (protons) from the proton exchange membrane and electrons from the external electrical circuit (Fig. 9). As a result of a chemical reaction, water is formed.

The chemical reaction in a fuel cell of other types (for example, with an acidic electrolyte, which is a solution of phosphoric acid H 3 PO 4) is absolutely identical to the chemical reaction in a fuel cell with a proton exchange membrane.

In any fuel cell, part of the energy of a chemical reaction is released as heat.

The flow of electrons in an external circuit is a direct current that is used to do work. Opening the external circuit or stopping the movement of hydrogen ions stops the chemical reaction.

The amount of electrical energy produced by a fuel cell depends on the type of fuel cell, geometric dimensions, temperature, gas pressure. A single fuel cell provides an EMF of less than 1.16 V. It is possible to increase the size of the fuel cells, but in practice several cells are used, connected in batteries (Fig. 10).

Fuel cell device

Let's consider the fuel cell device on the example of the PC25 Model C model. The scheme of the fuel cell is shown in fig. eleven.

The fuel cell "PC25 Model C" consists of three main parts: the fuel processor, the actual power generation section and the voltage converter.

The main part of the fuel cell - the power generation section - is a stack composed of 256 individual fuel cells. The composition of the fuel cell electrodes includes a platinum catalyst. Through these cells, a direct electric current of 1,400 amperes is generated at a voltage of 155 volts. The dimensions of the battery are approximately 2.9 m in length and 0.9 m in width and height.

Since the electrochemical process takes place at a temperature of 177 ° C, it is necessary to heat the battery at the time of start-up and remove heat from it during operation. To do this, the fuel cell includes a separate water circuit, and the battery is equipped with special cooling plates.

The fuel processor allows you to convert natural gas into hydrogen, which is necessary for an electrochemical reaction. This process is called reforming. The main element of the fuel processor is the reformer. In the reformer, natural gas (or other hydrogen-containing fuel) reacts with steam at high temperature (900 °C) and high pressure in the presence of a nickel catalyst. The following chemical reactions take place:

CH 4 (methane) + H 2 O 3H 2 + CO

(reaction endothermic, with heat absorption);

CO + H 2 O H 2 + CO 2

(the reaction is exothermic, with the release of heat).

The overall reaction is expressed by the equation:

CH 4 (methane) + 2H 2 O 4H 2 + CO 2

(reaction endothermic, with heat absorption).

To provide the high temperature required for natural gas conversion, a portion of the spent fuel from the fuel cell stack is directed to a burner that maintains the reformer at the required temperature.

The steam required for reforming is generated from the condensate formed during the operation of the fuel cell. In this case, the heat removed from the fuel cell stack is used (Fig. 12).

The fuel cell stack generates an intermittent DC current that differs low voltage and high current. A voltage converter is used to convert it to industrial standard AC. In addition, the voltage converter unit includes various control devices and safety interlock circuits that allow the fuel cell to be turned off in the event of various failures.

In such a fuel cell, approximately 40% of the energy in the fuel can be converted into electrical energy. Approximately the same amount, about 40% of the fuel energy, can be converted into thermal energy, which is then used as a heat source for heating, hot water supply and similar purposes. Thus, the total efficiency of such a plant can reach 80%.

An important advantage of such a source of heat and electricity is the possibility of its automatic operation. For maintenance, the owners of the facility on which the fuel cell is installed do not need to maintain specially trained personnel - periodic maintenance can be carried out by employees of the operating organization.

Fuel cell types

Currently, several types of fuel cells are known, which differ in the composition of the electrolyte used. The following four types are most widespread (Table 2):

1. Fuel cells with proton exchange membrane (Proton Exchange Membrane Fuel Cells, PEMFC).

2. Fuel cells based on orthophosphoric (phosphoric) acid (Phosphoric Acid Fuel Cells, PAFC).

3. Fuel cells based on molten carbonate (Molten Carbonate Fuel Cells, MCFC).

4. Solid oxide fuel cells (Solid Oxide Fuel Cells, SOFC). Currently, the largest fleet of fuel cells is built on the basis of PAFC technology.

One of the key features different types fuel cell is operating temperature. In many ways, it is the temperature that determines the scope of fuel cells. For example, high temperatures are critical for laptops, so proton exchange membrane fuel cells with low operating temperatures are being developed for this market segment.

For autonomous power supply of buildings, fuel cells of high installed capacity are required, and at the same time it is possible to use thermal energy, therefore, fuel cells of other types can also be used for these purposes.

Proton Exchange Membrane Fuel Cells (PEMFC)

These fuel cells operate at relatively low operating temperatures (60-160°C). They are characterized by high power density, allow you to quickly adjust the output power, and can be quickly turned on. The disadvantage of this type of elements is the high requirements for fuel quality, since contaminated fuel can damage the membrane. The nominal power of fuel cells of this type is 1-100 kW.

Proton exchange membrane fuel cells were originally developed by the General Electric Corporation in the 1960s for NASA. This type of fuel cell uses a solid state polymer electrolyte called a Proton Exchange Membrane (PEM). Protons can move through the proton exchange membrane, but electrons cannot pass through it, resulting in a potential difference between the cathode and anode. Due to their simplicity and reliability, such fuel cells were used as a power source on the Gemini manned spacecraft.

This type of fuel cell is used as a power source for a wide range of different devices, including prototypes and prototypes, from mobile phones to buses and stationary power systems. The low operating temperature allows such cells to be used to power various types of complex electronic devices. Less efficient is their use as a source of heat and power supply for public and industrial buildings, where large amounts of thermal energy are required. At the same time, such elements are promising as an autonomous source of power supply for small residential buildings such as cottages built in regions with a hot climate.

table 2
Fuel cell types

Item type	workers temperature, °С	efficiency output electrical energy), %	Total Efficiency, %
Fuel cells with proton exchange membrane (PEMFC)	60–160	30–35	50–70
fuel cells based on orthophosphoric (phosphoric) acid (PAFC)	150–200	35	70–80
Fuel cells based molten carbonate (MCFC)	600–700	45–50	70–80
Solid state oxide fuel cells (SOFC)	700–1 000	50–60	70–80

Phosphoric Acid Fuel Cells (PAFC)

Tests of fuel cells of this type were already carried out in the early 1970s. Operating temperature range - 150-200 °C. The main area of application is autonomous sources of heat and power supply of medium power (about 200 kW).

The electrolyte used in these fuel cells is a solution of phosphoric acid. The electrodes are made of paper coated with carbon, in which a platinum catalyst is dispersed.

The electrical efficiency of PAFC fuel cells is 37-42%. However, since these fuel cells operate at a sufficiently high temperature, it is possible to use the steam generated as a result of operation. In this case, the overall efficiency can reach 80%.

To generate energy, the hydrogen-containing feedstock must be converted to pure hydrogen through a reforming process. For example, if gasoline is used as a fuel, then sulfur compounds must be removed, since sulfur can damage the platinum catalyst.

PAFC fuel cells were the first commercial fuel cells to be economically justified. The most common model was the 200 kW PC25 fuel cell manufactured by ONSI Corporation (now United Technologies, Inc.) (Fig. 13). For example, these elements are used as a source of heat and electricity in a police station in New York's Central Park or as an additional source of energy for the Conde Nast Building & Four Times Square. The largest plant of this type is being tested as an 11 MW power plant located in Japan.

Fuel cells based on phosphoric acid are also used as an energy source in vehicles. For example, in 1994, H-Power Corp., Georgetown University, and the US Department of Energy equipped a bus with a 50 kW power plant.

Molten Carbonate Fuel Cells (MCFC)

Fuel cells of this type operate at very high temperatures - 600-700 °C. These operating temperatures allow the fuel to be used directly in the cell itself, without the need for a separate reformer. This process is called "internal reforming". It allows to significantly simplify the design of the fuel cell.

Fuel cells based on molten carbonate require a significant start-up time and do not allow to quickly adjust the output power, so their main area of application is large stationary sources of heat and electricity. However, they are distinguished by high fuel conversion efficiency - 60% electrical efficiency and up to 85% overall efficiency.

In this type of fuel cell, the electrolyte consists of potassium carbonate and lithium carbonate salts heated to about 650 °C. Under these conditions, the salts are in a molten state, forming an electrolyte. At the anode, hydrogen interacts with CO 3 ions, forming water, carbon dioxide and releasing electrons that are sent to the external circuit, and at the cathode, oxygen interacts with carbon dioxide and electrons from the external circuit, again forming CO 3 ions.

Laboratory samples of fuel cells of this type were created in the late 1950s by the Dutch scientists G. H. J. Broers and J. A. A. Ketelaar. In the 1960s, engineer Francis T. Bacon, a descendant of a famous 17th-century English writer and scientist, worked with these elements, which is why MCFC fuel cells are sometimes referred to as Bacon elements. NASA's Apollo, Apollo-Soyuz, and Scylab programs used just such fuel cells as a power source (Fig. 14). In the same years, the US military department tested several samples of MCFC fuel cells manufactured by Texas Instruments, in which army grades of gasoline were used as fuel. In the mid-1970s, the US Department of Energy began research to develop a stationary molten carbonate fuel cell suitable for practical applications. In the 1990s, a number of commercial units rated up to 250 kW were put into operation, such as at the US Naval Air Station Miramar in California. In 1996, FuelCell Energy, Inc. launched in trial operation 2 MW pre-series plant in Santa Clara, California.

Solid state oxide fuel cells (SOFC)

Solid-state oxide fuel cells are simple in design and operate at very high temperatures - 700-1000 °C. Such high temperatures allow the use of relatively "dirty", unrefined fuel. The same features as in fuel cells based on molten carbonate determine a similar area of application - large stationary sources of heat and electricity.

Solid oxide fuel cells are structurally different from fuel cells based on PAFC and MCFC technologies. The anode, cathode and electrolyte are made of special grades of ceramics. Most often, a mixture of zirconium oxide and calcium oxide is used as the electrolyte, but other oxides can be used. The electrolyte forms a crystal lattice coated on both sides with a porous electrode material. Structurally, such elements are made in the form of tubes or flat boards, which makes it possible to use technologies widely used in the electronics industry in their manufacture. As a result, solid-state oxide fuel cells can operate at very high temperatures, so they can be used to produce both electrical and thermal energy.

At high operating temperatures, oxygen ions are formed at the cathode, which migrate through the crystal lattice to the anode, where they interact with hydrogen ions, forming water and releasing free electrons. In this case, hydrogen is released from natural gas directly in the cell, i.e. there is no need for a separate reformer.

The theoretical foundations for the creation of solid-state oxide fuel cells were laid back in the late 1930s, when Swiss scientists Bauer (Emil Bauer) and Preis (H. Preis) experimented with zirconium, yttrium, cerium, lanthanum and tungsten, using them as electrolytes.

The first prototypes of such fuel cells were created in the late 1950s by a number of American and Dutch companies. Most of these companies soon abandoned further research due to technological difficulties, but one of them, Westinghouse Electric Corp. (now "Siemens Westinghouse Power Corporation"), continued work. The company is currently accepting pre-orders for a commercial model of tubular topology solid oxide fuel cell expected this year (Figure 15). The market segment of such elements is stationary installations for the production of heat and electric energy with a capacity of 250 kW to 5 MW.

SOFC type fuel cells have shown very high reliability. For example, a Siemens Westinghouse fuel cell prototype has logged 16,600 hours and continues to operate, making it the longest continuous fuel cell life in the world.

The high temperature, high pressure operating mode of SOFC fuel cells allows the creation of hybrid plants, in which fuel cell emissions drive gas turbines used to generate electricity. The first such hybrid plant is in operation in Irvine, California. The rated power of this plant is 220 kW, of which 200 kW from the fuel cell and 20 kW from the microturbine generator.

The traditional internal combustion engine (ICE) has a number of significant drawbacks, which forces scientists to look for a worthy replacement for it. The most popular option for such an alternative is the electric motor, but it is not the only one that can compete with internal combustion engines. This article will focus on the hydrogen engine, which is rightfully considered the future of the automotive industry and can solve the problem of harmful emissions and the high cost of fuel.

Short story

Despite the fact that the preservation of the environment has only now become a mass problem, about changing standard engine internal combustion, scientists have thought about it before. So, a hydrogen-powered motor “saw the world” back in 1806, which was facilitated by the French inventor Francois Isaac de Rivaz (he produced hydrogen by electrolysis of water).

Several decades passed, and in England the first patent for a hydrogen engine was issued (1841), and in 1852 German scientists designed an internal combustion engine that could run on an air-hydrogen mixture.

A little later, during the blockade of Leningrad, when gasoline was a scarce product, and hydrogen was available in fairly large quantities, technician Boris Shelishch suggested using an air-hydrogen mixture for the operation of barrage balloons. After that, all internal combustion engines of balloon winches were transferred to hydrogen power, and the total number of hydrogen-powered machines reached 600 units.

In the first half of the 20th century, public interest in hydrogen engines was not great, but with the advent of the fuel and energy crisis of the 1970s, the situation changed dramatically. In particular, in 1879, BMW released the first car that ran quite successfully on hydrogen (without explosions and water vapor escaping from the exhaust pipe).

Following BMW, others began to work in this direction major automakers, and by the end of the last century, almost every self-respecting car company already had the concept of developing a car on hydrogen fuel. However, with the end of the oil crisis, public interest in alternative fuel sources has also faded, although in our time it is starting to awaken again, fueled by environmentalists fighting to reduce the toxicity of car exhaust gases.

Moreover, energy prices and the desire to gain fuel independence only contribute to theoretical and practical research by scientists from many countries of the world. The most active companies are BMW, General Motors, Honda Motor, Ford Motor.

Interesting fact! Hydrogen is the most common element in the universe, but it will be very difficult to find it in its pure form on our planet.

The principle of operation and types of hydrogen engine

The main difference between a hydrogen plant and traditional engines is the method of supplying the fuel liquid and subsequent ignition of the working mixture. At the same time, the principle of transformation of the reciprocating movements of the crank mechanism into useful work remains unchanged. Considering that the combustion of petroleum fuel occurs rather slowly, the fuel-air mixture fills the combustion chamber before the piston reaches its extreme upper position (the so-called top dead center).

The rapid reaction of hydrogen makes it possible to move the injection time closer to the moment when the piston begins to return to bottom dead center. It should be noted that the pressure in the fuel system will not necessarily be high.

If ideal operating conditions are created for a hydrogen engine, then it can have a closed-type fuel supply system, when the mixture formation process will take place without the participation of atmospheric air currents. In this case, after the compression stroke, water vapor remains in the combustion chamber, which, passing through the radiator, condenses and turns back into ordinary water.

However, the use of this type of device is possible only when the vehicle has an electrolyzer that separates hydrogen from water for its re-reaction with oxygen. At the moment, it is extremely difficult to achieve such results. For stable operation of engines, it is used, and its evaporation is part of the exhaust gases.

Therefore, the trouble-free launch of the power plant and its stable operation on explosive gas without the use of atmospheric air is still an impossible task. There are two options for automotive hydrogen plants:units operating on the basis of hydrogen fuel cells, and hydrogen internal combustion engines.

Power plants based on hydrogen fuel cells

The principle of operation of fuel cells is based on physical and chemical reactions. In fact, these are the same lead batteries, only the efficiency of a fuel cell is slightly higher than that of a battery, and is about 45% (sometimes more).

A membrane (conducts only protons) is placed in the body of the hydrogen-oxygen fuel cell, separating the chamber with the anode and the chamber with the cathode. Hydrogen enters the anode chamber, and oxygen enters the cathode chamber. Each electrode is pre-coated with a catalyst layer, which is often platinum. When exposed to it, molecular hydrogen begins to lose electrons.

At the same time, protons pass through the membrane to the cathode and, under the influence of the same catalyst, combine with electrons coming from outside. As a result of the reaction, water is formed, and the electrons from the anode chamber move to the electrical circuit connected to the motor. Simply put, we get an electric current, which feeds the engine.

Fuel cell-based hydrogen engines are currently used on Niva vehicles equipped with the Antel-1 power plant and Lada 111 vehicles with the Antel-2 unit, which were developed by Ural engineers. In the first case, one charge is enough for 200 km, and in the second - for 350 km.

It should be noted that due to the high cost of metals (palladium and platinum) included in the design of such hydrogen engines, such installations are very expensive, which significantly increases the price of the vehicle on which they are installed.

Do you know?Toyota began working with fuel cell technology 20 years ago. Around that time, the Prius hybrid car project also started.

Hydrogen internal combustion engines

This type of power plant is very similar to propane engines common today, so to switch from propane to hydrogen fuel, it is enough to simply reconfigure the engine. There are already many examples of such a transition, but it must be said that in this case the efficiency will be somewhat lower than when using fuel cells. At the same time, less hydrogen energy is required to obtain 1 kW of hydrogen energy, which fully compensates for this disadvantage.

The use of this substance in a conventional internal combustion engine will cause a number of problems. Firstly, the high compression temperature will "cause" the hydrogen to react with the metal parts of the engine or even engine oil. Secondly, even a small leak on contact with hot exhaust manifold will definitely cause a fire.

For this reason, only rotary-type power units are used to create hydrogen structures, since their design reduces the risk of fire due to the distance between the intake and exhaust manifolds. In any case, all problems have so far been overcome, which makes it possible to consider hydrogen as a fairly promising fuel.

A good example of a hydrogen-powered vehicle is the experimental BMW 750hL sedan, a concept that was unveiled back in the early 2000s. The car is equipped with a twelve-cylinder engine that runs on rocket fuel and allows you to accelerate the car to 140 km / h. Hydrogen in liquid form is stored in a special tank, and one supply is enough for 300 kilometers. If it is completely consumed, the system automatically switches to gasoline power.

Hydrogen engine in today's market

Recent research by scientists in the field of operating hydrogen engines has shown that not only are they very environmentally friendly (like electric motors), but they can be very efficient in terms of performance. Moreover, according to technical indicators, hydrogen power plants bypass their electric counterparts, which has already been proven (for example, Honda Clarity).

Also It should be noted that, unlike Tesla Powerwall systems, hydrogen analogues have one significant drawback: it will no longer be possible to charge the battery using solar energy, but instead you will have to look for a special gas station, which today, even on a global scale, there are not so many.

Now Honda Clarity is released in a fairly limited batch, and you can buy a car only in the Country rising sun, since in Europe and America the vehicle will appear only at the end of 2016.

Interesting to know!Power Exporter 9000 generator (may be part of complete set of Honda Clarity) is able to feed the entire home appliances almost a whole week.

Also in our time, other vehicles using hydrogen fuel are being produced. These include the Mazda RX-8 hydrogen and BMW Hydrogen 7 (hybrids running on liquid hydrogen and gasoline), as well as the Ford E-450 and MAN Lion City Bus buses.

Among passenger cars, the most prominent representatives of hydrogen vehicles today are cars Mercedes-Benz GLC F-Cell(there is the possibility of recharging from a conventional household network, and the total power reserve is about 500 km), Toyota Mirai(works only on hydrogen, and one refueling should be enough for 650 km of travel) and Honda FCX Clarity(the declared power reserve reaches 700 km). But that's not all, because hydrogen-powered vehicles are also produced by other companies, such as Hyundai (Tucson FCEV).

Advantages and disadvantages of hydrogen engines

With all its advantages, it cannot be said that hydrogen transport is devoid of certain disadvantages. In particular, it must be understood that the combustible form of hydrogen at room temperature and normal pressure is in the form of a gas, which causes certain difficulties in the storage and transportation of such fuel. That is, there is serious problem designing safe reservoirs for hydrogen used as a fuel for cars.

In addition, cylinders containing this substance require periodic inspection and certification, which can only be carried out by qualified and licensed personnel. Also, the high cost of servicing a hydrogen engine should be added to these problems, not to mention the very limited number of filling stations (at least in our country).

Don't forget that the hydrogen plant increases the weight of the car, which may make it not as maneuverable as you would like it to be. Therefore, given all of the above, think carefully: is it worth buying a hydrogen vehicle, or is it better to wait with it for now.

However, it must be said that there are many advantages in such a solution. Firstly, your car will not pollute the environment with toxic exhaust gases, Secondly, mass production of hydrogen could help solve the problem of fluctuating fuel prices and disruptions in the supply of conventional fuel liquids.

In addition, pipeline networks for methane have already been built in many countries, and it is not difficult to adapt them for pumping hydrogen with subsequent delivery to gas stations. Hydrogen can be produced both on a small scale, that is, at the local level, and massively, at large, centralized enterprises. The growth in hydrogen production will serve as an additional incentive to increase the supply of this substance for domestic purposes (for example, for heating houses and offices).

Subscribe to our feeds

fuel cell ( fuel cell) is a device that converts chemical energy into electrical energy. It is similar in principle to a conventional battery, but differs in that its operation requires a constant supply of substances from the outside for an electrochemical reaction to occur. Hydrogen and oxygen are supplied to the fuel cells, and the output is electricity, water and heat. Their advantages include environmental friendliness, reliability, durability and ease of operation. Unlike conventional batteries, electrochemical converters can operate virtually indefinitely as long as fuel is available. They do not need to be charged for hours until fully charged. Moreover, the cells themselves can charge the battery while the car is parked with the engine off.

Proton membrane fuel cells (PEMFC) and solid oxide fuel cells (SOFC) are the most widely used in hydrogen vehicles.

A fuel cell with a proton exchange membrane operates as follows. Between the anode and cathode are a special membrane and a platinum-coated catalyst. Hydrogen enters the anode, and oxygen enters the cathode (for example, from air). At the anode, hydrogen is decomposed into protons and electrons with the help of a catalyst. Hydrogen protons pass through the membrane and enter the cathode, while electrons are given off to the external circuit (the membrane does not let them through). The potential difference thus obtained leads to the appearance of an electric current. On the cathode side, hydrogen protons are oxidized by oxygen. As a result, water vapor is produced, which is the main element of car exhaust gases. Possessing a high efficiency, PEM cells have one significant drawback - their operation requires pure hydrogen, the storage of which is a rather serious problem.

If such a catalyst is found that will replace expensive platinum in these cells, then a cheap fuel cell will immediately be created to generate electricity, which means that the world will get rid of oil dependence.

Solid oxide cells

Solid oxide SOFC cells are much less demanding on fuel purity. In addition, thanks to the use of a POX reformer (Partial Oxidation - partial oxidation), such cells can consume ordinary gasoline as fuel. The process of converting gasoline directly into electricity is as follows. In a special device - a reformer, at a temperature of about 800 ° C, gasoline evaporates and decomposes into its constituent elements.

This releases hydrogen and carbon dioxide. Further, also under the influence of temperature and with the help of SOFC itself (consisting of a porous ceramic material based on zirconium oxide), hydrogen is oxidized by oxygen in the air. After obtaining hydrogen from gasoline, the process proceeds further according to the scenario described above, with only one difference: the SOFC fuel cell, in contrast to devices operating on hydrogen, is less sensitive to foreign impurities in the original fuel. So the quality of gasoline should not affect the performance of the fuel cell.

The high operating temperature of SOFC (650-800 degrees) is a significant drawback, the warm-up process takes about 20 minutes. However, excess heat is not a problem, since it is completely removed by the remaining air and exhaust gases produced by the reformer and the fuel cell itself. This allows the SOFC system to be integrated into the vehicle as a stand-alone device in a thermally insulated housing.

The modular structure allows you to achieve the required voltage by connecting a set of standard cells in series. And, perhaps most importantly, from the point of view of the introduction of such devices, there are no very expensive platinum-based electrodes in SOFC. It is the high cost of these elements that is one of the obstacles in the development and dissemination of PEMFC technology.

Types of fuel cells

Currently, there are such types of fuel cells:

A.F.C.– Alkaline Fuel Cell (alkaline fuel cell);
PAFC– Phosphoric Acid Fuel Cell (phosphoric acid fuel cell);
PEMFC– Proton Exchange Membrane Fuel Cell (fuel cell with a proton exchange membrane);
DMFC– Direct Methanol Fuel Cell (fuel cell with direct methanol decomposition);
MCFC– Molten Carbonate Fuel Cell (fuel cell of molten carbonate);
SOFC– Solid Oxide Fuel Cell (solid oxide fuel cell).

Ecology of knowledge. Science and technology: Hydrogen energy is one of the most highly efficient industries, and fuel cells allow it to remain at the forefront of innovative technologies.

A fuel cell is a device that efficiently generates direct current and heat from a hydrogen-rich fuel through an electrochemical reaction.

A fuel cell is similar to a battery in that it generates direct current through a chemical reaction. Again, like a battery, a fuel cell includes an anode, a cathode, and an electrolyte. However, unlike batteries, fuel cells cannot store electrical energy, do not discharge, and do not require electricity to be recharged. Fuel cells can continuously generate electricity as long as they have a supply of fuel and air. The correct term to describe a working fuel cell is cell system, as it requires some auxiliary systems to function properly.

Unlike other power generators such as internal combustion engines or turbines powered by gas, coal, oil, etc., fuel cells do not burn fuel. This means no noisy high pressure rotors, no loud exhaust noise, no vibrations. Fuel cells generate electricity through a silent electrochemical reaction. Another feature of fuel cells is that they convert the chemical energy of the fuel directly into electricity, heat and water.

Fuel cells are highly efficient and do not produce large amounts of greenhouse gases such as carbon dioxide, methane and nitrous oxide. The only products emitted by fuel cells are water in the form of steam and a small amount of carbon dioxide, which is not emitted at all if pure hydrogen is used as fuel. Fuel cells are assembled into assemblies and then into separate functional modules.

The principle of operation of fuel cells

Fuel cells generate electricity and heat due to the ongoing electrochemical reaction, using an electrolyte, a cathode and an anode.

The anode and cathode are separated by an electrolyte that conducts protons. After hydrogen enters the anode and oxygen enters the cathode, a chemical reaction begins, as a result of which electric current, heat and water are generated. On the anode catalyst, molecular hydrogen dissociates and loses electrons. Hydrogen ions (protons) are conducted through the electrolyte to the cathode, while electrons are passed through the electrolyte and through an external electrical circuit, creating a direct current that can be used to power equipment. On the cathode catalyst, an oxygen molecule combines with an electron (which is supplied from external communications) and an incoming proton, and forms water, which is the only reaction product (in the form of vapor and / or liquid).

Below is the corresponding reaction:

Anode reaction: 2H2 => 4H+ + 4e-
Reaction at the cathode: O2 + 4H+ + 4e- => 2H2O
General element reaction: 2H2 + O2 => 2H2O

Fuel cell types

Similar to the existence of different types of internal combustion engines, there are different types of fuel cells - the choice of the appropriate type of fuel cell depends on its application.Fuel cells are divided into high temperature and low temperature. Low temperature fuel cells require relatively pure hydrogen as fuel.

This often means that fuel processing is required to convert the primary fuel (such as natural gas) to pure hydrogen. This process consumes additional energy and requires special equipment. High temperature fuel cells do not need this additional procedure, as they can "internally convert" the fuel at elevated temperatures, which means there is no need to invest in hydrogen infrastructure.

Fuel elements on molten carbonate (MCFC).

Molten carbonate electrolyte fuel cells are high temperature fuel cells. The high operating temperature allows direct use of natural gas without a fuel processor and low calorific value fuel gas from process fuels and other sources. This process was developed in the mid 1960s. Since that time, manufacturing technology, performance and reliability have been improved.

The operation of RCFC is different from other fuel cells. These cells use an electrolyte from a mixture of molten carbonate salts. Currently, two types of mixtures are used: lithium carbonate and potassium carbonate or lithium carbonate and sodium carbonate. To melt carbonate salts and achieve a high degree of mobility of ions in the electrolyte, fuel cells with molten carbonate electrolyte operate at high temperatures (650°C). The efficiency varies between 60-80%.

When heated to a temperature of 650°C, the salts become a conductor for carbonate ions (CO32-). These ions pass from the cathode to the anode where they combine with hydrogen to form water, carbon dioxide and free electrons. These electrons are sent through an external electrical circuit back to the cathode, generating electrical current and heat as a by-product.

Anode reaction: CO32- + H2 => H2O + CO2 + 2e-
Reaction at the cathode: CO2 + 1/2O2 + 2e- => CO32-
General element reaction: H2(g) + 1/2O2(g) + CO2(cathode) => H2O(g) + CO2(anode)

Molten carbonate fuel cells are suitable for use in large stationary installations. Thermal power plants with an output electric power of 2.8 MW are industrially produced. Plants with an output power of up to 100 MW are being developed.

Fuel cells based on phosphoric acid (PFC).

Fuel cells based on phosphoric (orthophosphoric) acid were the first fuel cells for commercial use. This process was developed in the mid-1960s and has been tested since the 1970s. Since then, stability, performance and cost have been increased.

Fuel cells based on phosphoric (orthophosphoric) acid use an electrolyte based on orthophosphoric acid (H3PO4) with a concentration of up to 100%. The ionic conductivity of phosphoric acid is low at low temperatures, for this reason these fuel cells are used at temperatures up to 150–220°C.

The charge carrier in fuel cells of this type is hydrogen (H+, proton). A similar process occurs in proton exchange membrane fuel cells (MEFCs), in which hydrogen supplied to the anode is split into protons and electrons. The protons pass through the electrolyte and combine with oxygen from the air at the cathode to form water. The electrons are directed along an external electrical circuit, and an electric current is generated. Below are the reactions that generate electricity and heat.

Anode reaction: 2H2 => 4H+ + 4e-
Reaction at the cathode: O2(g) + 4H+ + 4e- => 2H2O
General element reaction: 2H2 + O2 => 2H2O

The high performance of thermal power plants on fuel cells based on phosphoric (orthophosphoric) acid in the combined production of heat and electricity is one of the advantages of this type of fuel cells. The plants use carbon monoxide at a concentration of about 1.5%, which greatly expands the choice of fuel. In addition, CO2 does not affect the electrolyte and the operation of the fuel cell, this type of cell works with reformed natural fuel. Simple construction, low electrolyte volatility and increased stability are also advantages of this type of fuel cell.

Thermal power plants with an output electric power of up to 400 kW are industrially produced. Installations for 11 MW have passed the relevant tests. Plants with an output power of up to 100 MW are being developed.

Fuel Cells with Proton Exchange Membrane (PME)

Proton exchange membrane fuel cells are considered the best type of fuel cells for vehicle power generation, which can replace gasoline and diesel engines internal combustion. These fuel cells were first used by NASA for the Gemini program. Today, installations on MOPFC with a power of 1 W to 2 kW are being developed and demonstrated.

These fuel cells use a solid polymer membrane (thin plastic film) as the electrolyte. When impregnated with water, this polymer passes protons, but does not conduct electrons.

The fuel is hydrogen, and the charge carrier is a hydrogen ion (proton). At the anode, the hydrogen molecule is separated into a hydrogen ion (proton) and electrons. The hydrogen ions pass through the electrolyte to the cathode, while the electrons move around the outer circle and produce electrical energy. Oxygen, which is taken from the air, is fed to the cathode and combines with electrons and hydrogen ions to form water. The following reactions take place on the electrodes:

Anode reaction: 2H2 + 4OH- => 4H2O + 4e-
Reaction at the cathode: O2 + 2H2O + 4e- => 4OH-
General element reaction: 2H2 + O2 => 2H2O

Compared to other types of fuel cells, proton exchange membrane fuel cells produce more power for a given fuel cell volume or weight. This feature allows them to be compact and lightweight. In addition, the operating temperature is less than 100°C, which allows you to quickly start operation. These characteristics, as well as the ability to quickly change energy output, are just some of the features that make these fuel cells a prime candidate for use in vehicles.

Another advantage is that the electrolyte is a solid rather than a liquid substance. Keeping the gases at the cathode and anode is easier with a solid electrolyte and therefore such fuel cells are cheaper to produce. Compared with other electrolytes, when using a solid electrolyte, there are no such difficulties as orientation, there is less problems due to the appearance of corrosion, which leads to a longer durability of the element and its components.

Solid oxide fuel cells (SOFC)

A solid electrolyte provides a hermetic gas transition from one electrode to another, while liquid electrolytes are located in a porous substrate. The charge carrier in fuel cells of this type is the oxygen ion (О2-). At the cathode, oxygen molecules are separated from the air into an oxygen ion and four electrons. Oxygen ions pass through the electrolyte and combine with hydrogen to form four free electrons. Electrons are directed through an external electrical circuit, generating electrical current and waste heat.

Anode reaction: 2H2 + 2O2- => 2H2O + 4e-
Reaction at the cathode: O2 + 4e- => 2O2-
General element reaction: 2H2 + O2 => 2H2O

The efficiency of the generated electrical energy is the highest of all fuel cells - about 60%. In addition, high operating temperatures allow for combined heat and power generation to generate high pressure steam. Combining a high-temperature fuel cell with a turbine creates a hybrid fuel cell to increase the efficiency of electrical power generation by up to 70%.

Fuel cells with direct methanol oxidation (DOMTE)

The structure of fuel cells with direct oxidation of methanol is similar to fuel cells with a proton exchange membrane (MOFEC), i.e. a polymer is used as an electrolyte, and a hydrogen ion (proton) is used as a charge carrier. However, liquid methanol (CH3OH) is oxidized in the presence of water at the anode, releasing CO2, hydrogen ions and electrons, which are guided through an external electrical circuit, and an electric current is generated. Hydrogen ions pass through the electrolyte and react with oxygen from the air and electrons from the external circuit to form water at the anode.

Anode reaction: CH3OH + H2O => CO2 + 6H+ + 6e-
Reaction at the cathode: 3/2O2 + 6H+ + 6e- => 3H2O
General element reaction: CH3OH + 3/2O2 => CO2 + 2H2O

The development of these fuel cells began in the early 1990s. After the creation of improved catalysts and, thanks to other recent innovations, has been increased power density and efficiency up to 40%.

These elements were tested in the temperature range of 50-120°C. With low operating temperatures and no need for a converter, direct methanol fuel cells are the best candidate for applications ranging from mobile phones and other consumer products to automotive engines. The advantage of this type of fuel cells is their small size, due to the use of liquid fuel, and the absence of the need to use a converter.

Alkaline fuel cells (AFC)

Alkaline fuel cells (ALFCs) are one of the most studied technologies and have been used since the mid-1960s. by NASA in the Apollo and Space Shuttle programs. On board these spacecraft, fuel cells produce electricity and drinking water. Alkaline fuel cells are one of the most efficient elements used to generate electricity, with power generation efficiency reaching up to 70%.

Alkaline fuel cells use an electrolyte, i.e. an aqueous solution of potassium hydroxide, contained in a porous, stabilized matrix. The concentration of potassium hydroxide may vary depending on the operating temperature of the fuel cell, which ranges from 65°C to 220°C. The charge carrier in the SFC is a hydroxide ion (OH-) moving from the cathode to the anode, where it reacts with hydrogen to produce water and electrons. The water produced at the anode moves back to the cathode, again generating hydroxide ions there. As a result of this series of reactions taking place in the fuel cell, electricity is produced and, as a by-product, heat:

Anode reaction: 2H2 + 4OH- => 4H2O + 4e-
Reaction at the cathode: O2 + 2H2O + 4e- => 4OH-
General reaction of the system: 2H2 + O2 => 2H2O

The advantage of SFCs is that these fuel cells are the cheapest to produce, since the catalyst needed on the electrodes can be any of the substances that are cheaper than those used as catalysts for other fuel cells. In addition, SCFCs operate at a relatively low temperature and are among the most efficient fuel cells - such characteristics can respectively contribute to faster power generation and high fuel efficiency.

One of the characteristic features of SFC is its high sensitivity to CO2, which can be contained in fuel or air. CO2 reacts with the electrolyte, quickly poisons it, and greatly reduces the efficiency of the fuel cell. Therefore, the use of SFCs is limited to closed spaces such as space and underwater vehicles, they must operate on pure hydrogen and oxygen. Moreover, molecules such as CO, H2O and CH4, which are safe for other fuel cells and even fuel for some of them, are detrimental to SFCs.

Polymer electrolyte fuel cells (PETE)

In the case of polymer electrolyte fuel cells, the polymer membrane consists of polymer fibers with water regions in which the conduction of water ions H2O+ (proton, red) is attached to the water molecule. Water molecules present a problem due to slow ion exchange. Therefore, a high concentration of water is required both in the fuel and on the exhaust electrodes, which limits the operating temperature to 100°C.

Solid acid fuel cells (SCFC)

Typically, a solid acid fuel cell is a sandwich in which a very thin layer of solid acid compound is sandwiched between two tightly compressed electrodes to ensure good contact. When heated, the organic component evaporates, leaving through the pores in the electrodes, retaining the ability of numerous contacts between the fuel (or oxygen at the other end of the cell), electrolyte and electrodes.published

Fuel cell type	Working temperature	Power Generation Efficiency	Fuel type	Application area
RKTE	550–700°C	50-70%		Medium and large installations
FKTE	100–220°C	35-40%	pure hydrogen	Large installations
MOPTE	30-100°C	35-50%	pure hydrogen	Small installations
SOFC	450–1000°C	45-70%	Most hydrocarbon fuels	Small, medium and large installations
POMTE	20-90°C	20-30%	methanol	Portable units
SHTE	50–200°C	40-65%	pure hydrogen	space research
PETE	30-100°C	35-50%	pure hydrogen	Small installations

Join us at