Fuel cells were first used in manned space flight. By combining hydrogen and oxygen chemically electricity can be produced without harmful emissions, only water vapor is produced besides energy. Fuel cells today aren't very efficient and they are very bulky. They are also very expensive, but there are new ways being researched to make fuel cells smaller, more efficient, and less costly.
In a fuel cell there is a gas-permeable plastic membrane with a catalytic platinum foil on both sides. The membrane is sandwiched between 2 electrode plates. Hydrogen gas flows between the anode plate and the membrane, and compressed oxygen flows between the membrane and the cathode plate. The catalytic platinum causes the hydrogen gas to separate into hydrogen ions (protons) and electrons, thereby creating a negative charge at the anode. The protons create a positive charge on the other side near the cathode. When current is allowed to flow, the oxygen molecules separate and combine with the hydrogen protons and the incoming electrons to form water and heat.
