(Keynote) Electrochemistry for Studying and Using Biological and Synthetic Catalysts of Hydrogen Oxidation and Production

Abstract

Direct electrochemistry has proved invaluable for studying natural and synthetic catalysts of redox reactions that are of interest in the context of solar fuels production, including H2 oxidation and production. With the catalyst either attached to the electrode or free to diffuse in solution, the current response to changing the electrochemical driving force, the so-called voltammetric signature, can be interpreted to learn about various aspects of the mechanism that are difficult to probe using more conventional methods: long-range electron transfer, diffusion along gas channels, redox-driven (in)activations, active site chemistry and photoreactivity under conditions of turnover. It can also be used to define the sequence of events in the catalytic cycle and to benchmark the performances of the catalyst in terms of rate, directionality and reversibility. This approach contrasts with and complements the usual strategy which aims at stabilizing species that are presumed to be catalytic intermediates, and determining their structure using spectroscopic or structural methods. Embedding the enzyme in a film of redox polymer provides further opportunities for stabilising the enzyme-electrode and tuning its apparent properties, particularly the resistance to oxygen, making it possible to achieve long-term aerobic hydrogen oxidation using enzymes that are notoriously oxygen sensitive. Exemples will be given that illustrate electrochemical studies and applications of hydrogenase enzymes and synthetic catalysts. [1] M. Del Barrio, Melisa and M. Sensi and C. Orain and C. Baffert and S. Dementin and V. Fourmond and C. Leger, “Electrochemical investigations of hydrogenases and other enzymes that produce and use solar fuels” Acc. Chem. Res. 51 769 (2018) [2] M Sensi, M del Barrio, C Baffert, V Fourmond, C Leger “New perspectives in hydrogenase direct electrochemistry”, Curr. Op. Electrochem 1:5 135 (2017) [3] V Fourmond and C. Leger, “Modelling the voltammetry of adsorbed enzymes and molecular catalysts”, Curr. Op. Electrochem 1:1, 110 (2017) [4] Vincent Fourmond, Eric S. Wiedner, Wendy J. Shaw and Christophe Léger, “On the design of molecular catalysts of reversible and bidirectional H2 oxidation/production”, submitted. [5] Huaiguang Li, Darren Buesen, Christophe Léger, Vincent Fourmond and Nicolas Plumeré, in preparation. Figure 1