Strategies for solar fuel generation

Abstract

Solar production and use of fuels (hydrogen, reduced carbon compounds) is an integral part of any large scale solar energy strategy. Technically, the most promising pattern of implementation is the decentralised generation of photovoltaic energy on buildings, interconnection with the public electricity grid and centralized electrolytic generation of fuels. A complementary strategy could be solar electrochemical generation of simple inorganic energy carriers (e.g. Fe2+ from Fe3+) which serve as the energy source for bacteria (e.g.Thiobacillus ferrooxidans), which fix carbon dioxide via the Calvin cycle. Direct photo-electrochemical generation of solar fuels (in analogy to photosynthesis) is a complex frontier with many unsolved problems, some of which are discussed. The most promising route appears to be development of photoactive transition metal electrocatalysts, which are able to induce interfacial coordination chemical mechanisms. In addition it may be necessary to develop far-from-equilibrium electrochemical mechanisms to facilitate cooperative electron transfer processes during photocatalysis.At the long term, solar fuel generation may gradually become economical with increasing consideration of social and environmental costs in the price of fossil energy.