Finding connections between light-activated excited state chemistry and bond-making/breaking steps in catalysis is of great importance as a means for elucidating fundamental mechanisms, structures, and design features for solar-to-fuels energy conversion. The cobalt-phosphate (CoPi) electrocatalyst has garnered much attention due to its robust water-splitting catalytic reactivity at neutral pH and analogous functionality to the oxygen-evolving complex of Photosystem II. While the structures and electrocatalytic performance of CoPi have been well-explored, the photocatalytic properties of CoPi are poorly understood and embody an area of growing interest. This talk will feature an operando time-resolved study of the photo-electrochemical responses of CoPi excited by two wavelengths corresponding to three overlapping transitions comprised of oxygen-to-metal charge transfer and metal-bridged hybridized states (415 nm excitation), as well as ligand field charge transfer states or 3d-3d multiplets (623 nm excitation). Both photo-oxidation and photo-reduction voltage-dependent electronic responses are observed, where the photocurrent responses strikingly diverge for the different excitation wavelengths. Our photocurrent measurements distinguish charge transfer versus macroscopic thermal (heat)-driven processes and suggest that excitation of charge transfer resonances can activate electronic and structural dynamics underlying oxygen-evolving reaction (OER) catalytic function. The photo-excited charge transfer coupled redox states collectively act to energetically lower the onset of water-splitting potentials and drive the production of solvated O<sub>2</sub>. The findings are anticipated to have profound impact on artificial photosynthesis and renewable energy applications on the timescales of seconds to femtoseconds.

Interplay between structural and electronic dynamics: Elucidating the photo-electrochemical effect in the water oxidation catalyst cobalt-phosphate (CoPi)

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ACS Fall 2022

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