This seminar will describe some of our efforts to understand and control the processes determining the efficiency of energy conversion systems. Specifically, the behavior of metal oxide thin films for photoelectrochemical (PEC) water oxidation will be discussed.
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 states will be elucidated and its role in controlling water oxidation discussed. Surface state recombination can generally be mitigated through introduction of electrocatalysts on metal oxide semiconductor surfaces which generally leads to improved performance. We have found that some semiconductor/catalyst combinations result in similar or worse performance compared to the bare electrode, however. 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 significant insight into the role of the catalyst and the electron-transfer reactions at the interface on the performance of PEC water oxidation.