Unraveling the electron dynamics at semiconductor/liquid and semiconductor/catalyst interfaces is critical for the development of design rules for efficient photoelectrochemical (PEC) reactions. Metal oxides comprise an interesting class of photoanode materials for photoelectrochemical (PEC) water oxidation; a key reaction for the realization of solar fuels. Under PEC water oxidation conditions, many metal oxides have been shown to accumulate holes in surface states which can recombine with conduction band electrons and thus limit the performance. The nature of such surface accumulated holes was studied with in-situ spectroelectrochemical and operando infrared (IR) spectroscopy measurements which indicate that the surface trapped holes correspond to oxidized surface states which mediate PEC water oxidation. Results of several materials will be presented which establish a general framework to understand the mechanism of PEC water oxidation on metal oxides and rate limiting steps. Surface state recombination can be mitigated through the introduction of electrocatalysts on the metal oxide semiconductor surface. In most cases this leads to improved performance. We have found that some semiconductor/catalyst combinations result in similar or worse performance compared to the bare electrode, however. We will also present recent results which deepen the understanding of the energetics and electron-transfer processes at semiconductor/electrocatalyst interface which control the performance of such systems. Through rigorous comparison of cyclic voltammetry, current transient and electrochemical impedance spectroscopy (EIS), intensity modulated photocurrent spectroscopy (IMPS), and dual-working electrode experiments measurements, we have been able to gain a significant insight into the role of the catalyst and the electron-transfer at the interface on the performance of PEC water oxidation. General lessons and design rules for efficient PEC water splitting will finally be discussed.

Electron dynamics at metal oxide surfaces and interfaces

2019 Fall National Meeting

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