Biohydrogen

Hydrogen gas is an interesting alternative fuel because it completely eliminates carbon as an energy carrier.Therefore it obviously cannot contribute to the green house effect. Although hydrogen is currently being produced by either thermally decomposing natural gas or by electrolysis of water there is also a potential for biological hydrogen production. The enzyme which is responsible for the production of hydrogen, hydrogenase, however is extremely sensitive to oxygen so that hydrogen is only produced in anaerobic habitats. Although the capacity to produce hydrogen is generally acknowledged in anaerobic, fermentative bacteria like Clostridium , there are also examples of green algae who produce oxygen under anaerobic and dark conditions like Chlamydomonas reinhardtii which is currently under development by Melis Energy in the United States.

Hydrogen is envisioned to be used in a very different way to generate energy than conventional fuels. Whereas bioethanol and biodiesel are interesting because they can be directly used in an existing technology, the internal combustion engine, hydrogen has the potential to be used in a far more efficient way in the hydrogen fuel cell. In a conventional engine all the energy is released in an explosive way by burning. In a fuel cell however the oxidation is accomplished in steps at an electrode in a process which closely resembles the functioning of an everyday battery. In this process the energy is not explosively released as heat but produces an electric current with high efficiency which can be used to run an electric engine. However because hydrogen is one of the smallest molecules known a number of engineering problems arise with storing and transporting it. Because it is a gas it takes up a greater volume than an equivalent bioethanol or biodiesel. Although it can be adsorbed by certain metals, these metals themselves like platinum are toxic and prohibitively expensive for large scale use. It represents a bigger danger for explosions and because of its small size it can get lodged in crystal defects in the metal pipes through which it is conducted making them brittle.