Electrocatalysis for the hydrogen economy

Abstract

This chapter deals with the concept of "hydrogen economy", which was introduced by John O.M' Bockris in 1972. We summarize the fundamental principles and the progress for the reactions relevant to the hydrogen economy, namely the hydrogen and oxygen evolution for water electrolyzers, and the hydrogen oxidation and oxygen reduction for fuel cells. The activity of each reaction can be correlated to a single descriptor, i.e. the adsorption energy of a key reaction intermediate, following a volcano-type relationship. Highly active materials can be prepared with the aid of modern computational and experimental tools. Nevertheless, to develop catalysts that are substantially more active and reach the performance of ideal catalysts, the focus must be placed on materials that can break the energetic scaling relations between intermediates. The systems of choice are acidic water electrolyzers or fuel cells, using noble metals for the catalytic material, despite the great progress made in the field of alkaline systems. However, to realize the concept of hydrogen economy on a large scale, the electrode material for either reaction must combine activity, stability and abundance.