Water in polymer electrolyte fuel cells: Friend or foe?

Almost a billion years ago, Nature engineered an ingenious solution to the problem of converting chemical energy to mechanical energy in living things: the creation of a gradient in the concentration of protons across mitochondrial membranes. Human beings came up with a radically different solution just prior to the Industrial Revolution: the heat engine and its conversion of thermal energy from a chemical reaction into work. Steam engines, first patented in 1698, could provide vast amounts of power for locomotives and industrial processes. The trouble was that the steam engine’s need for large amounts of water as a working fluid limited its practical use to large installations. It wasn’t until Nikolaus Otto in 1861 and Rudolf Diesel in 1897 devised the two earliest variants of the internal combustion engine that engineers could circumvent the need to carry around tons of water. Engine sizes shrank in response, which kick-started the motor-vehicle...