A simple chemical reaction is the basis of fuel cell technology. Fuel cells run on hydrogen to provide electricity. The only byproduct is water vapour. Clean, environment-friendly, exciting. But haven't we heard too much about them already without anything happening? No. Till now, only environmentalists were interested. Now, big business is really keen to develop stakes in the hydrogen economy of the future. LIAN CHAWII appraises the history, potential, politics and science of fuel cells