Copper tungstate (CuWO4) has been realized as a promising photoanode material for driving oxygen evolution reaction (OER), also called water oxidation, a half-reaction of water splitting. It has been shown that surface state recombination limits the performance of the CuWO4 for photoelectrochemical (PEC) water oxidation. The integration of an electrocatalyst with a semiconductor photoanode is a well-adopted approach to eliminate surface recombination and improve the efficiency of water oxidation process. Unlike most demonstrated photoanodes for OER, the integration of an electrocatalyst with a CuWO4 electrode has been observed to be usually detriment, or at most, do not affect the photocatalytic water oxidation activity of this material. Because the interfacial processes control the overall reaction, unraveling the dynamic of the interface is an essential step for the principle design of the electrocatalyst for enhanced PEC water oxidation on CuWO4 photoanode. In this dissertation, I am seeking to gain a fundamental understanding of the role of surface states as well as the influence of electrocatalysts on the behavior of CuWO4 thin-film electrodes for PEC OER. Here we present results that deepen the understanding of the energetics and electron-transfer processes at the CuWO4/electrolyte and CuWO4/electrocatalyst interfaces, which controls the performance of such systems. Ni0.75Fe0.25Oy was chosen as a model electrocatalyst to investigate the CuWO4/electrocatalyst interface due to the high electrocatalytic activity. Through dual-working electrode experiments, current transient, and impedance spectroscopy measurements, we have been able to gain significant insight into the role of the electrocatalyst and the electron-transfer at the CuWO4/electrocatalyst interface. Our results indicate that the lack of efficiency improvement after deposition of electrocatalyst on CuWO4 is due to water oxidation on the CuWO4 surface kinetically outcompetes the electrocatalyst oxidation. Thus, water oxidation occurs primarily from the CuWO4 surface rather than the electrocatalyst. For the investigation of the role of CuWO4 surface states, we employed the operando ATR-IR spectroscopy under PER OER condition. Our results show growing of absorption peaks at 750 and 1100 cm-1, which can be attributed to the formation of surface oxo and superoxo water oxidation intermediates on the CuWO4 surface, respectively.
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