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-Fe₂O₃, in contact with one of the fastest known water oxidation catalysts, Ni_0.8Fe_0.2O_x, by directly measuring/controlling the current and/or voltage at the Ni_0.8Fe_0.2O_x catalyst layer using a second working electrode. The measurements demonstrate that the majority of photogenerated holes in α-Fe₂O₃ directly transfer to the catalyst film over a wide range of conditions and that the Ni_0.8Fe_0.2O_x is oxidized by photoholes to an operating potential sufficient to drive water oxidation at rates that match the photocurrent generated by the α-Fe₂O₃. The Ni_0.8Fe_0.2O_x 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-Fe₂O₃|Ni_0.8Fe_0.2O_x interface is significantly decreased by the oxidation of Ni²⁺ to Ni³⁺ and the associated increase in the Ni_0.8Fe_0.2O_x electrical conductivity. In sum, the results illustrate the underlying operative charge-transfer and photovoltage generation mechanisms of catalyzed photoelectrodes, thus guiding their continued improvement.

中文翻译：

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催化赤铁矿光电化学水氧化过程中电荷转移过程的直接原位测量

电催化剂提高了光吸收性半导体光阳极驱动氧释放反应的效率，但是电催化剂的精确功能仍然不清楚。我们直接测量，对于第一次，一个典型的可见光吸收半导体的界面载流子传输性能，的α-Fe ₂ Ó ₃，在以最快的已知水的氧化催化剂中的一种，镍接触_0.8铁_0.2 ø _X，通过使用第二工作电极直接测量/控制Ni _0.8 Fe _0.2 O _x催化剂层上的电流和/或电压。测量结果表明，α-Fe中大部分光生空穴₂ ö ₃直接传送到催化剂膜在宽范围的条件和在Ni _0.8铁_0.2 ø _X是由光穴氧化成工作电势足以在匹配由所产生的光电流，利率以驱动水氧化的α-Fe ₂ O ₃。因此，Ni _0.8 Fe _0.2 O _x既充当空穴收集接触又充当光电化学水氧化过程的催化剂。单独的测量结果表明，在整个被照明的光电压结的α-Fe ₂ ö ₃ |的Ni _0.8铁_0.2 ø通过Ni ²⁺氧化为Ni ³⁺以及相关的Ni _0.8 Fe _0.2 O _x电导率的增加， _x界面显着降低。总而言之，结果说明了催化光电极的潜在有效电荷转移和光电压产生机理，从而指导了它们的持续改进。