Here are some frequently asked questions about fuel cells and hydrogen.
What is a fuel cell?
A fuel cell is an electrochemical device that produces electricity without combustion. The optimal energy carrier for fuel cells is hydrogen (which can be extracted for example from water, methanol, natural gas or petroleum products). When hydrogen is combined with oxygen (from air) it produces electrical energy. The conversion process is environmentally benign: only heat and water are emitted as by-products. Environmentally, hydrogen is the optimal energy carrier for fuel cells, because fuel cells that run on hydrogen have zero emissions.
By the nature of its electrochemical reaction, a fuel cell can be more than twice as efficient as an internal combustion engine. A conventional engine burns fuel to create heat and in turn converts heat into mechanical energy and finally electricity. A fuel cell produces electricity, water and heat directly from hydrogen and oxygen. Fuel cells are like batteries in that they are electrochemical devices, but unlike batteries do not need recharging and will continue to operate as long as they are provided with fuel (hydrogen).
A fuel cell stack is a number of fuel cells stacked together like a sandwich using bipolar plates (an anode and cathode combined in one). One advantage of fuel cell technology is that it is both scalable and modular. To achieve desired power output, you only need to stack cells together.
A fuel cell power system is the complete set of components that integrate with the fuel cell stack so that electricity is produced. The fuel cell requires other systems to make it a complete power source, including air, fuel and control systems.
PEM is an acronym meaning Proton Exchange Membrane. In a PEM fuel cell the electrolyte is a proton (H+) conducting solid polymer membrane. They are also known as PEFC (polymer electrolyte fuel cell) or SPFC (solid polymer fuel cell).
PEM fuel cells display the highest power densities of any of the fuel cell types, which makes them particularly attractive for transportation and portable applications where minimum size and weight are required. They contain no corrosive liquid electrolyte and are robust in construction and are modular and scalable in design. They are low temperature fuel cells which usually operate below 100 degrees oC.
This means that unlike high temperature fuel cells such as solid oxide, which operate at ~600 degrees oC they can be fabricated from cheaper, less exotic materials. The low temperature of PEM fuel cells can also be an advantage when low thermal signature is desired. PEM fuel cells also have the advantage of potential application across a very wide range; from portable power at a few watts to hundreds of kilowatts for vehicular and stationary power.
PEM fuel cells can be used in portable electronic and electrical devices, such as laptops or power tools, to generate heat and power for domestic and distributed generation, to provide auxiliary and back-up power in a wide range stationary and transport applications and to provide propulsion power to motorbikes, cars, vans, trucks, buses, submarines, drones, UAVs and light aircraft.
Where does the hydrogen come from to fuel PEM fuel cells?
Hydrogen is an energy carrier not a naturally occurring fuel and must be produced from hydrogen containing feedstock. Hydrogen can be produced from an extremely wide range of sources, but most of the world’s hydrogen is presently produced by reformation of natural gas. Hydrogen is also commonly produced by the electrolysis of water. Electrolysis requires electricity, if that electricity is produced by renewable means; the hydrogen produced is as low carbon as it is possible to be.
What about using hydrocarbon fuels to produce hydrogen gas?
The reformation (cracking) of natural gas produces much less pollution than burning it. The key thing is the energy conversion at the point of power production. If the hydrogen is burned in an internal combustion engine there is no real benefit. If the hydrogen is fed into a PEM fuel cell, with its much higher efficiencies, the amount of carbon dioxide produced can be much less. Well-to-wheel, using hydrogen produced from natural gas to feed a fuel cell produces 30% – 50% less carbon dioxide than just burning the fuel to provide the same amount of energy.
Hydrogen is no more or less dangerous than other flammable fuels, including petrol, LPG and natural gas. In fact, some of hydrogen’s properties actually provide safety benefits compared to petrol or other fuels, for example it dissipates very quickly and is much less likely to explode in open air because of its high buoyancy and diffusivity. This contrasts sharply with much heavier gases such as natural gas and gasoline vapour which carry a greater danger of explosion because they hover close to the ground and do not disperse quickly enough. However, all flammable fuels must be handled responsibly. Like petrol and natural gas, hydrogen is flammable and can behave dangerously under specific conditions. Hydrogen can be handled safely when guidelines are observed and the user has an understanding of its behaviour.
Over 50 million tons of hydrogen are produced every year and hydrogen’s safety record is excellent.