Fossil fuels as energy sources are coming, sooner or later, to end. Hence, trials to find c alternatives including chemical, photochemical and biological production of hydrogen are continually running but each of them has its problems. Hydrogen gas as a fuel is extremely fascinating not least because it is absolutely clean with water being the sole combustion product. Also, it produces the highest energy output compared with other fuels. The capability to photoevolve hydrogen has been recorded in several photosynthetic bacteria, blue green algae and algae. The basic requirements for biological hydrogen evolution can be summarized, in general terms, into an electron source and an enzyme system. Photosynthesis, respiration and fermentation have been proved to supplement electrons for proton reduction.
Almost 60 years ago, it was first observed that the anaerobically adapted unicellular alga Scendesmus is capable of evolving H2 gas in a photochemical reaction. Since that time, algae and blue green algae are used in experiments to produce hydrogen gas on a large scale.
The major problem in the photoproduction of hydrogen is the sensitivity of the catalysing enzymes (nitrogenases and hydrogenases) to oxygen. Mother problem is that the evolved hydrogen comes out in a mixture with other gases such as nitrogen, oxygen and carbon dioxide.