title: Spectroelectrochemical analysis of the mechanism of (photo)electrochemical hydrogen evolution at a catalytic interface.
abstract: Multi-electron heterogeneous catalysis is a pivotal element in the (photo)electrochemical generation of solar fuels. However, mechanistic studies of these systems are difficult to elucidate by means of electrochemical methods alone. Here we report a spectroelectrochemical analysis of hydrogen evolution on ruthenium oxide employed as an electrocatalyst and as part of a cuprous oxide-based photocathode. We use optical absorbance spectroscopy to quantify the densities of reduced ruthenium oxide species, and correlate these with current densities resulting from proton reduction. This enables us to compare directly the catalytic function of dark and light electrodes. We find that hydrogen evolution is second order in the density of active, doubly reduced species independent of whether these are generated by applied potential or light irradiation. Our observation of a second order rate law allows us to distinguish between the most common reaction paths and propose a mechanism involving the homolytic reductive elimination of hydrogen.
authors.affiliation: Department of Chemistry, Imperial College London, South Kensington Campus, London SW7 2AZ, UK.
authors.forename: Ernest
authors.initials: E
authors.lastname: Pastor
authors.affiliation: Department of Chemistry, Imperial College London, South Kensington Campus, London SW7 2AZ, UK.
authors.forename: Florian
authors.identifier: 0000-0001-7074-7001
authors.initials: F
authors.lastname: Le Formal
authors.affiliation: Institut des Sciences et Ingénierie Chimiques, Ecole Polytechnique Fédérale de Lausanne (EPFL), Laboratory of Photonics and Interfaces, Station 6, CH-1015 Lausanne, Switzerland.
authors.forename: Matthew T
authors.identifier: 0000-0001-5379-2775
authors.initials: MT
authors.lastname: Mayer
authors.affiliation: Institut des Sciences et Ingénierie Chimiques, Ecole Polytechnique Fédérale de Lausanne (EPFL), Laboratory of Photonics and Interfaces, Station 6, CH-1015 Lausanne, Switzerland.
authors.forename: S David
authors.initials: SD
authors.lastname: Tilley
authors.affiliation: Department of Chemistry, Imperial College London, South Kensington Campus, London SW7 2AZ, UK.
authors.forename: Laia
authors.initials: L
authors.lastname: Francàs
authors.affiliation: Department of Chemistry, Imperial College London, South Kensington Campus, London SW7 2AZ, UK.
authors.forename: Camilo A
authors.initials: CA
authors.lastname: Mesa
authors.affiliation: Institut des Sciences et Ingénierie Chimiques, Ecole Polytechnique Fédérale de Lausanne (EPFL), Laboratory of Photonics and Interfaces, Station 6, CH-1015 Lausanne, Switzerland.
authors.forename: Michael
authors.initials: M
authors.lastname: Grätzel
authors.affiliation: Department of Chemistry, Imperial College London, South Kensington Campus, London SW7 2AZ, UK.
authors.forename: James R
authors.initials: JR
authors.lastname: Durrant