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In the development of photoelectrochemical cells for water splitting or CO2 reduction, a major challenge is O2 evolution at photoelectrodes that, in behavior, mimic photosystem II. At an appropriate semiconductor electrode, a water oxidation catalyst must be integrated with a visible light absorber in a stable half-cell configuration. An electrode is described consisting of a light absorber, an intermediate electron donor layer, and a water oxidation catalyst for sustained light-driven water oxidation catalysis. In assembling the electrode on nanoparticle SnO2/TiO2 electrodes, a Ru(II) polypyridyl complex was used as the light absorber, NiO was deposited as an overlayer, and a Ru(II) 2,2′-bipyridine-6,6′-dicarboxylate complex was used as the water oxidation catalyst. In the final electrode, addition of the NiO overlayer enhanced performance toward water oxidation with the final electrode operating with a 1.1 mA/cm2 photocurrent density for 2 h without decomposition under one sun illumination in a pH 4.65 solution. The enhanced performance is attributed to the role of NiO as an electron transfer mediator between the light absorber and the catalyst.

Wang, D.; Niu, F.; Mortelliti, M. J.; Sheridan, M. V.; Sherman, B. D.; Zhu, Y.; McBride, J. R.; Dempsey, J. L.; Shen, S.; Dares, C. J.; Li, F.; Meyer, T. J. A stable dye-sensitized photoelectrosynthesis cell mediated by a NiO overlayer for water oxidation. Proc. Natl. Acad. Sci. USA 2020, 117 (23), 12564-12571.

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