Fuel cells are catorgized by the type of electrolyte that they utilize. Phosphoric acid 4. Molten carbonate 5. Since pure hydrogen and oxygen are expensive, substitutions are usually made.
Air is used as a source of oxygen.
Hydrogen is provided in the form of gaseous mixtures from natural gas, biomasses, or heavy hydrocarbon liquids such as fuel oil. Obviously this is where current fuel cell use needs more work. A possible solution to the problem may be to utilize the sun. For some time, we've known that the sun is a great source of energy, but there has been a significant problem. Sure, you can use batteries, but you need either several thousand batteries or some very large ones to store an appreciable amount of energy.