Qiu Jingjing, Hajibabaei Hamed, Nellist Michael R, Laskowski Forrest A L, Hamann Thomas W, Boettcher Shannon W
Department of Chemistry and Biochemistry, Materials Science Institute, University of Oregon, Eugene, Oregon 97403, United States.
Department of Chemistry, Michigan State University, East Lansing, Michigan 48824, United States.
ACS Cent Sci. 2017 Sep 27;3(9):1015-1025. doi: 10.1021/acscentsci.7b00310. Epub 2017 Aug 17.
Electrocatalysts improve the efficiency of light-absorbing semiconductor photoanodes driving the oxygen evolution reaction, but the precise function(s) of the electrocatalysts remains unclear. We directly measure, for the first time, the interface carrier transport properties of a prototypical visible-light-absorbing semiconductor, α-FeO, in contact with one of the fastest known water oxidation catalysts, NiFeO , by directly measuring/controlling the current and/or voltage at the NiFeO catalyst layer using a second working electrode. The measurements demonstrate that the majority of photogenerated holes in α-FeO directly transfer to the catalyst film over a wide range of conditions and that the NiFeO is oxidized by photoholes to an operating potential sufficient to drive water oxidation at rates that match the photocurrent generated by the α-FeO. The NiFeO therefore acts as both a hole-collecting contact and a catalyst for the photoelectrochemical water oxidation process. Separate measurements show that the illuminated junction photovoltage across the α-FeO|NiFeO interface is significantly decreased by the oxidation of Ni to Ni and the associated increase in the NiFeO electrical conductivity. In sum, the results illustrate the underlying operative charge-transfer and photovoltage generation mechanisms of catalyzed photoelectrodes, thus guiding their continued improvement.
电催化剂可提高驱动析氧反应的吸光半导体光阳极的效率，但电催化剂的确切功能仍不清楚。我们首次通过使用第二个工作电极直接测量/控制NiFeO催化剂层处的电流和/或电压，直接测量了典型的可见光吸收半导体α-FeO与已知最快的水氧化催化剂之一NiFeO接触时的界面载流子传输特性。测量结果表明，在很宽的条件范围内，α-FeO中大多数光生空穴直接转移到催化剂薄膜上，并且NiFeO被光生空穴氧化到足以驱动水氧化的工作电位，其速率与α-FeO产生的光电流相匹配。因此，NiFeO既是空穴收集接触层，也是光电化学水氧化过程的催化剂。单独的测量表明，Ni氧化为Ni以及NiFeO电导率的相关增加会显著降低α-FeO|NiFeO界面上的光照结光电压。总之，这些结果阐明了催化光电极潜在的电荷转移和光电压产生机制，从而指导它们的持续改进。
