The PEM fuel cell below uses platinum and is the leading contender for homes and cars. As oxygen is going in one side, hydrogen is going in the other, either pumped directly into the cells or stripped from a fossil fuel, usually natural gas, with an apparatus called a reformer. An ultrathin polymer membrane inside each fuel cell permits only hydrogen protons to pass through. Electrons are forced around the stack to make direct current, which is converted into alternating power by a power conditioner. The hydrogen protons combine with oxygen and the electrons to make warm water.
All fuel cells have the same basic internal structure.
Gwen Kinkead is a senior editor at Worth .