Rajan Wilcox
Fuel cells are devices that generate electricity through an electrochemical reaction, not combustion. They use hydrogen and oxygen to generate electricity, heat, and water. Hydrogen does not exist in its natural state on Earth, so it must be generated from other sources such as natural gas or biogas. Fuel cells can also be designed to run on other fuels, provided they contain hydrogen, such as hydrocarbons (natural gas and methane) or alcohols like ethanol and methanol. This means that the amount of natural gas used by a fuel cell depends on the type of fuel cell and its specific requirements.
| Characteristics | Values |
|---|---|
| How fuel cells work | Fuel cells generate electricity by combining oxygen and hydrogen (or a hydrogen-rich fuel source) in a chemical reaction. |
| Fuel cell types | PEMFCs, MCFCs, SOFCs, AFCs |
| Fuel cell fuel sources | Natural gas, biogas, methane, propane, butane, diesel, methanol, chemical hydrides, ethanol, etc. |
| Fuel cell efficiency | PEMFCs: 40-60% efficiency; MCFCs: 50-60% efficiency, 70-80% in CHP applications; SOFCs: N/A; AFCs: 60% electrical efficiency, 80-90% in CHP applications |
| Fuel cell applications | PEMFCs: cars, forklifts, telecommunications, data centers, residential markets; MCFCs: stationary applications for utilities and businesses; SOFCs: N/A; AFCs: NASA Apollo mission |
| Fuel cell benefits | Clean, efficient, reliable, quiet, safe, modular, small footprint, low emissions, less maintenance |
| Fuel cell challenges | High operating temperatures, long start-up times, potential for carbon dust build-up, sensitive to carbon dioxide |
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What You'll Learn
Natural gas as a hydrogen source
Hydrogen is an essential fuel for fuel cells, and it can be produced from many different sources in various ways. Natural gas is one of the most common sources for hydrogen production. The process of converting natural gas into hydrogen is called steam-methane reforming or natural gas reforming. This process involves heating the natural gas, which is mostly methane (CH4), to very high temperatures between 700°C and 1,100°C (1,300°F and 2,000°F) in the presence of steam and a catalyst, such as nickel. This triggers an endothermic reaction that produces carbon monoxide and molecular hydrogen (H2). The carbon monoxide then undergoes a water-gas shift reaction, reacting with more steam to produce additional hydrogen and carbon dioxide.
Natural gas reforming is a well-established and efficient process, building upon the existing natural gas pipeline infrastructure. It is faster than steam reforming and requires a smaller reactor vessel. This process is used by commercial hydrogen producers and petroleum refineries to separate hydrogen atoms from carbon atoms in methane. While this process does emit carbon dioxide, it is significantly less than that of traditional gasoline vehicles. Additionally, the Department of Energy (DOE) expects that hydrogen production from natural gas will be supplemented with renewable, nuclear, and other low-carbon sources in the future.
Another method for producing hydrogen from natural gas is through methane pyrolysis, which does not produce carbon dioxide as a byproduct. This process is referred to as turquoise hydrogen when derived from natural gas with zero greenhouse gas emissions. Electrolysis, which involves splitting water molecules using electricity, is another way to produce hydrogen. While electrolysis using renewable energy sources is considered green hydrogen, electrolysis powered by the electric grid, which includes a mix of energy sources, is referred to as grey hydrogen.
Fuel cells, such as MCFCs (Molten Carbonate Fuel Cells), can directly use natural gas as a fuel source. MCFCs operate at high temperatures, allowing them to reform natural gas into hydrogen internally. This process enables MCFCs to achieve efficiencies of 50-60% in regular applications and up to 80% in CHP (Combined Heat and Power) applications. These fuel cells are commonly used in stationary settings to provide primary and backup power to utilities and businesses.
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Fuel cell efficiency
Fuel cells are a clean and efficient energy source that can be used to power a variety of applications, from vehicles to homes and businesses. They generate electricity through an electrochemical reaction between hydrogen and oxygen, producing water and heat as by-products. This electrochemical process allows fuel cells to avoid the energy losses associated with combustion and mechanical conversion, resulting in high electrical efficiency and reduced emissions.
The efficiency of fuel cells varies depending on the type and operating temperature. Phosphoric acid fuel cells (PAFCs), for example, typically operate at efficiencies of 40-50%, but this can be increased to about 80% through cogeneration, where the waste heat is captured and used for other purposes. High-temperature fuel cells, such as molten carbonate fuel cells, can achieve even higher efficiencies of more than 60%, outperforming similar-sized conventional energy sources.
Proton-exchange membrane fuel cells (PEMFCs), which operate at cooler temperatures, have an efficiency range of 40-60%. This type of fuel cell is well-suited for vehicles like cars and forklifts due to its ability to handle large and sudden shifts in power output. Alkaline fuel cells (AFCs) are another efficient type, with electrical efficiency potentials of 60% and up to 90% in cogeneration applications. AFCs, however, are highly sensitive to carbon dioxide and are primarily used in controlled aerospace and underwater applications.
Fuel cells also offer scalability and cost savings. Their modular design allows for precise engineering to meet specific power requirements, and their high efficiency results in lower fuel consumption and reduced operating costs. Additionally, the waste heat from fuel cells can be captured and reused, further increasing their overall efficiency and reducing emissions.
In summary, fuel cell efficiency can range from 40% to over 60%, depending on the type and operating conditions. The high efficiency, low emissions, and scalability of fuel cells make them a sustainable and attractive alternative energy source for a growing number of applications.
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Fuel cell applications
Fuel cells are unique in the variety of their potential applications. They can be used to power systems ranging from laptops to utility power stations. They have several benefits over conventional combustion-based technologies, including higher efficiency and the ability to convert chemical energy directly to electrical energy.
One of the most common applications of fuel cells is in specialty vehicles such as forklifts. Fuel cells offer several advantages over traditional lead-acid batteries in this context, including rapid refuelling, constant voltage delivery, and the elimination of the need for battery chargers, storage, and changing areas.
Fuel cells are also well-suited for use in cars and other vehicles that require quick startup or acceleration, such as buses, trucks, trains, and specialty vehicles. Proton Exchange Membrane Fuel Cells (PEMFCs), in particular, are a good fit for these applications due to their ability to operate at cooler temperatures and handle large and sudden shifts in power output.
Another important application of fuel cells is in providing backup power and enhancing grid reliability. Fuel cells can replace grid electricity for dedicated, on-site, premium-power generation at critical load facilities, such as data centres, financial processing centres, defence communications facilities, air traffic control centres, hospital intensive care units, and remote law enforcement campuses. In these settings, fuel cells offer high-quality, reliable, grid-independent power with reduced emissions. Additionally, the waste heat from fuel cells can be captured to provide heating and cooling, further increasing energy efficiency.
Fuel cells also have applications in residential settings, providing heat and power to homes. Solid Oxide Fuel Cells (SOFCs) are commonly used in small residential auxiliary power units, while also being versatile enough to be used in large-scale stationary power generation for larger buildings and businesses. Phosphoric Acid Fuel Cells (PAFCs) are also used in residential settings, particularly in cogeneration mode, where they produce electricity and heat to assist with heating and cooling.
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Fuel cell construction
Fuel cells are electrochemical energy conversion devices that use hydrogen and oxygen to generate electricity, heat, and water. They are composed of an anode, cathode, and electrolyte membrane. The basic operation of all fuel cells is the same, but there are different types of fuel cells that use different electrolytes and fuel sources.
The first step in building a fuel cell is to determine the power requirements needed for the particular device or application. The output voltage of a single cell is less than 1 V under realistic operating conditions, but most fuel cell developers use a voltage of 0.6 to 0.7 V at nominal power. Fuel cell systems can be designed at nominal voltages of 0.8 V per cell or higher if the correct design, materials, operating conditions, balance-of-plant, and electronics are selected.
The number of cells in a stack is determined by the maximum voltage requirement and the desired operating voltage. The fuel cell stack power output can be designed by calculating the highest possible power and voltage spike that may occur during device operation and then putting a safety factor into the power design calculation. After the initial power requirements have been estimated, the fuel cell parts and materials can be prepared.
The essential parts of a fuel cell are:
- Proton Exchange Membrane (PEM): PEM helps the chemical reaction inside the fuel cell by allowing the flow of hydrogen protons through the membrane.
- Electrode Backing Layers: These layers allow fuel and oxidant to travel to the catalyst while collecting electrons.
- Catalyst: The catalyst breaks the fuel into protons and electrons.
- Flow Field Plates: These distribute the gases and liquids throughout the fuel cell.
- Gaskets: Gaskets prevent fuel leakage and help distribute pressure in the stack.
- Current Collectors: These collect the electrons from the flow field plates.
- End Plates: End plates provide support and apply compression to the components.
- Clamping Mechanism: This holds the stack together.
To make a low-temperature proton exchange membrane fuel cell (PEMFC), the basic materials needed for constructing your first fuel cell stack are:
- Proton exchange membrane, such as Nafion® 117.
- Nafion® solution.
- Carbon fabric or paper.
- Catalyst, which is usually platinum.
- Graphite or another type of flow field plate.
- Gasket material to seal the gases into the flow field area.
- Metal to create current collectors.
- End plates.
- Clamping mechanism such as nuts and bolts.
- Hydrogen source.
- Testing instruments such as a multimeter and oscilloscope.
- Method for pressing the MEA together.
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Fuel cell emissions
Fuel cells are often touted as a more environmentally friendly alternative to traditional combustion-based technologies. They can operate at higher efficiencies than combustion engines and can convert chemical energy in the fuel directly into electrical energy.
When pure hydrogen is used as fuel, the only byproducts are heat and water, with no harmful emissions at all. However, hydrogen does not exist in its natural state on Earth and must be derived from compounds such as water (H2O) or hydrocarbons. This extraction process is energy-intensive and can emit harmful pollution and greenhouse gases, especially when hydrogen is extracted from hydrocarbons.
Fuel cells can also be designed to run on other fuels, such as hydrocarbons (e.g., natural gas and methane) or alcohols (e.g., ethanol and methanol). In these cases, the hydrogen needed to power the cell is extracted from the fuel using a reformer. When using fuels other than pure hydrogen, fuel cells emit some carbon pollution and trace amounts of other pollutants, but still substantially less than combustion-based engines. For example, Bloom Energy Servers release 773 pounds of CO2 per megawatt-hour, while the average US grid emission rate is 1,555 pounds.
FuelCell Energy's carbon capture platform can run on natural gas or biogas, both of which contain methane. Inside the fuel cell, methane is steam-reformed at 600 degrees Celsius and converted into hydrogen and CO2. The fuel cell produces electricity, heat, water, and CO2, which can be exhausted or captured and recycled into valuable end-products. Their carbon capture method can also concentrate CO2 from external sources, such as fossil fuel emissions from industrial plants.
Overall, fuel cells offer a promising avenue for reducing emissions, especially when coupled with carbon capture technologies. They can extend the life of existing fossil-fueled power plants while generating a return on investment and reducing emissions.
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Frequently asked questions
The amount of natural gas used by a fuel cell depends on the type of fuel cell and the application it is used for. Fuel cells can be designed to run on different fuels, including natural gas, as long as they can extract hydrogen from the fuel source.
Molten Carbonate Fuel Cells (MCFCs) can use natural gas directly as fuel, reforming it into hydrogen within the system itself. Solid Oxide Fuel Cells (SOFCs) can also use natural gas as fuel, but they are still in the early stages of development.
MCFCs have an efficiency of 50-60%, which can increase to 70-80% when used for combined heat and power (CHP) applications. SOFCs operate at very high temperatures, which can improve efficiency, but they are challenging to use in mobile applications due to long start-up times.
