Bioelectrocatalysis of Hydrogen Oxidation/Reduction by Hydrogenases

Hydrogenases are the enzymatic biocatalysts that catalyze the reversible interconversion of hydrogen to protons and electrons. A number of hydrogenases have been immobilized at electrode surfaces, and their electrocatalytic properties investigated, both to understand the fundamental mechanisms of these enzymes and to optimize either fuel production or power output in a hydrogen fuel cell. This chapter discusses the basic enzymology of hydrogenases, and the advantages and limitations of their application in electro-catalysis. It focuses on the bio-inspired small inorganic catalyst mimics that have been designed, with the hope of being cheaper and more robust, to reproduce the functionality of these enzymes in technological applications. The chapter considers only the [NiFe]- and [FeFe]-hydrogenases, because they have been demonstrated to be active in electrocatalytic applications. Hydrogenases can generally be thought of as models of biological multielectron catalysis with earth-abundant transition metals, and, on that front, there is still much to be learned.