Light induced electron transfer from a photoelectrode to a molecular catalyst represents the first mechanistic step for proton or CO2 reduction catalysis to form solar fuels. In this presentation, a Marcus-Gerischer theoretical analysis will be provided that allows for the extraction of the reorganization energy, λ, and the electronic coupling matrix element, Hab, for this interfacial electron transfer step. A family of four photocatalysts were anchored to tin-doped indium oxide (ITO) electrodes and used to initiate the desired electron transfer reaction ITO(e-)|-PC+ → ITO|-PC. The degenerately doped ITO allowed the thermodynamic driving force (-ΔG°) for electron transfer to be continuously controlled, -ΔG° = eE°' - EF, where E°' is the formal reduction potential of the photocatalyst (Bangle, R; Schneider, J; Meyer, G.J.; J. Am. Chem. Soc. 2020, 142, 674−679). The electronic coupling, Hab, was small and consistent with non-adiabatic electron transfer for all four photocatalysts. Surprisingly, the reorganization energies were sensitive to the E°' , increasing from 0.40 to 0.60 eV as the photocatalyst formal reduction potential increased from 1.20 to 1.60 V vs NHE. This behavior was rationalized based on the molecular orbital location within the electric double layer. The impact of these findings on photoelectrocatalysis at molecular-oxide interfaces will be discussed.

Marcus-Gerischer analysis of interfacial electron transfer kinetics at metal oxide interfaces

ACS Spring 2022

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