Fuel Cells Explained
What is a Fuel Cell?
Fuel cells are devices that produce electrical power. They operate by using the chemical properties of hydrogen and oxygen to create useable electrical current, heat and water vapour. In some ways they can be considered to be a continuously fuelled battery, although, unlike a battery, they do not store energy - they convert it from one form to another.
Fuel cells are significantly more efficient than equivalent internal combustion engines (ICEs) because they convert chemical energy directly to electrical current rather than via an efficiency sapping mechanical intermediate phase. They operate at maximum efficiency at part load (where most ICE generators operate) and their efficiency is unaffected by size. In addition, the modular design allows the fuel cells to be stacked in such a way to match the specific output power needs without significant additional design work or capital requirements.
The simple nature of their design and operation makes them highly reliable. They operate quietly and can operate on a variety of fuel types. If pure hydrogen is used as a fuel then the only outputs are electricity, heat and water vapour. In this way fuel cells are seen as being significantly more environmentally friendly than other hydrocarbon fuelled power sources.
The Chemistry of Operation
On one side (the anode side) of the fuel cell is fuel in the form of hydrogen gas, and on the other side (the cathode side) is oxygen (in air). Sandwiched between the anode and cathode is the very thin, gas tight, electrically insulating but ion conducting, electrolyte layer. An electrical circuit connects the anode to the cathode and provides the mechanism to power electrical devices.
The combination of the materials used to make the fuel cell components, the type of fuel used and the operating temperature allow electricity to be generated via a chemical reaction rather than burning the fuel. The reaction starts with the oxygen on the cathode side being ionised at the cathode and generating negatively charged oxygen ions that then flow through the cathode and across the electrolyte. At the anode side the oxygen ion combines with a positively charged hydrogen ion and releases an electron that then, because of the charge imbalance and the electron-impermeable electrolyte, flows around the electrical circuit to the cathode side generating direct current. This high quality, direct current will continue to be produced as long as there is a supply of fuel and air to the fuel cell.