CoWO4-based Oxygen-Evolving Catalysts for Electrochemical and Photoelectrochemical Water Oxidation

Electrochemical and photochemical water splitting has drawn great attentions because it allows production of chemical fuels in carbon-neutral manner. However, water oxidation reaction acts as a rate determining step, requiring development of efficient water oxidation catalysts (WOCs) and simple strategy for their integration on the desired electrode surface. To address these issues, we developed a simple method to synthesize and integrate efficient WOCs for electrochemical and photoelectrochemical water oxidation. Simple heat treatment of cobalt-based polyoxometalate led to the formation of CoWO4 nanoparticles, of which the structure and catalytic activity can be controlled by varying annealing temperature. At 400 ??C, it was converted to amorphous CoWO4 with a high catalytic activity. Besides, at above 500??C, crystalline CoWO4 was formed with a degraded catalytic activity. According to X-ray photoelectron spectroscopy and density functional theory analyses, a large amount of oxygen vacancies were generated at 400 ??C, leading to the formation of a high population of Co2+-Co2+ couples with an optimum interatomic distance for water oxidation