Fuel cells are energy generators which provide a combination of high efficiency combined with low pollutant emissions, based on the direct electrochemical oxidation of hydrogen or hydrocarbon fuels to provide an electric current, and at the same time forming water. They can be built in a wide range of sizes ranging from power for mobile telephones and laptop computers, through to multi-megawatt power stations. After decades of development and large scale trials, fuel cell generators are now entering commercial service to provide electricity and heat for individual homes, or district schemes. In addition, virtually all the world’s major vehicle manufacturers are demonstrating electrically propelled passenger vehicles or municipal buses.