Hydrogen from solar energy and water?

Industrialization has been largely driven by the continued discovery of oil reserves. However, the number of oil findings is decreasing. A future with no oil left to use is a reality we have to face. Apart from the obvious problem of scarcity the fuels such as oil, coal and gas have been known to contribute to the problem of global warming. The situation is further complicated by the growing need for energy from users who are yet to start using the energy resources.

Many alternative strategies such as solar energy, wind, nuclear, tidal, geothermal etc have been proposed to solve these problems. Although these alternative sources might be able to provide energy, it might not be possible to use them effectively as fuels for transportation systems. Transportation systems being the major consumer of fuels today may need a different approach. Loss of energy during the conversion process has made it necessary to have a direct product which can be used as a fuel.

Use of solar energy to produce fuels such as hydrogen has gained importance in this context. Hydrogen could be directly used as a fuel and lack of carbon in the fuel source makes it a rather clean source of energy. The problem of scarcity and global warming can be tackled with this interesting approach. Two main approaches are being pursued to achieve this goal of using water to produce hydrogen using solar energy. The first approach is the photo biological method which aims to create or alter a biological system to convert solar energy into hydrogen using water as raw material. The second approach is the chemical method, which uses photo systems or molecules that imitate photo systems coupled to other molecules to drive reaction that convert water into hydrogen.

Photosystem II uses solar energy to oxidize water releasing electrons. This reaction is rather efficient although the other steps happening in the biological systems are not as efficient. Hence, the aim is to mimic just this step of the process from nature. The chemical approach has used molecules such as ruthenium linked to the photo systems to act as electron acceptor from Manganese. This is used to drive the reaction to produce hydrogen from water. The enzyme hydrogenase which can catalyse the reaction to produce hydrogen is used in this second step of the reaction.

Biological systems such as Nostoc produce hydrogen in special cells from nitrogenase. Currently large and small scale reactors are being developed to produce hydrogen from such biological systems and make them as effective as possible.

The direct methods of producing fuels have been found to be much more effective than the indirect methods which require the energy to be converted to electricity which is then used to split the water molecules by electrolysis.