Direct Electrochemistry of Hydrogenase, Formate Dehydrogenase, CO Dehydrogenase, and Nitrogenase: Wiring Strategies and Mechanistic Insights into Metalloenzymes That Produce Solar Fuels

century as a powerful tool to investigate redox enzymes. In this review we focus on the electrochemistry of metalloenzymes that are involved in the conversion of biological solar fuels. We summarize the strategies that made it possible to wire them to electrodes, from their mere physisorption onto friendly electrodes to more sophisticated covalent attachment. We then describe a number of qualitative and quantitative electrochemical investigations of their mechanisms. These studies have disclosed the functional diversity within each family of enzymes considered here, suggesting that structural features that are remote from the active site play a major role in determining catalytic properties such as catalytic directionality, reversibility, and resistance to oxygen. DET electrochemistry contributed to elucidating some of these outer sphere effects, which are crucial in molecular catalysis, and also to discovering and characterizing new enzymes, which have the properties and robustness required in solar fuel devices.