Fuel Cells: Biohydrogen

A relatively new concept is capturing the energy value of the biomass as H₂ gas. Although H₂ can be combusted to generate heat and electricity, the true value of H₂ comes from routing it to a fuel cell. Compared to combustion, using a fuel call can increase the energy capture to about 55% (from about 35%), while avoiding air pollution associated with combustion. The scientific and engineering bases for biohydrogen production are far from established today. One large problem is that most of the electrons and energy in biomass do not end up in H₂, but in organic products that cannot be used in a conventional fuel cell. Therefore, a major objective is to make the production of H₂ from biomass have a much higher H₂ yield. If this is achieved, H₂ can become a truly renewable and pollution-free fuel.

A very similar idea is also being pursued using natural enzymes as the source of creating reducing power from organic molecules. These enzymes reduce an intermediate compound called NADH which then, in turn donates electrons to the anode of a cell. At the cathode, protons are reduced to hydrogen, just as above.