Tsyganok Anton, Ghigna Paolo, Minguzzi Alessandro, Naldoni Alberto, Murzin Vadim, Caliebe Wolfgang, Rothschild Avner, Ellis David S
Department of Materials Science and Engineering, Technion--Israel Institute of Technology, Haifa 3200003, Israel.
Dipartimento di Chimica, Università di Pavia, and Unità INSTM di Pavia, V.le Taramelli 16, I2700 Pavia, Italy.
Langmuir. 2020 Oct 6;36(39):11564-11572. doi: 10.1021/acs.langmuir.0c02065. Epub 2020 Sep 22.
An FeNi (oxy)hydroxide cocatalyst overlayer was photoelectrochemically deposited on a thin-film hematite (α-FeO) photoanode, leading to a cathodic shift of ∼100 mV in the photocurrent onset potential. Operando X-ray absorption spectroscopy (XAS) at the Fe and Ni K-edges was used to study the changes in the overlayer with potential in the dark and under illumination conditions. Potential or illumination only had a minor effect on the Fe oxidation state, suggesting that Fe atoms do not accumulate significant amount of charge over the whole potential range. In contrast, the Ni K-edge spectra showed pronounced dependence on potential in the dark and under illumination. The effect of illumination is to shift the onset for the Ni oxidation because of the generated photovoltage and suggests that holes that are photogenerated in hematite are transferred mainly to the Ni atoms in the overlayer. The increase in the oxidation state of Ni proceeds at potentials corresponding to the redox wave of Ni, which occurs immediately prior to the onset of the oxygen evolution reaction (OER). Linear combination fitting analysis of the obtained spectra suggests that the overlayer does not have to be fully oxidized to promote oxygen evolution. Cathodic discharge measurements show that the photogenerated charge is stored almost exclusively in the Ni atoms within the volume of the overlayer.
在薄膜赤铁矿（α-Fe₂O₃）光阳极上通过光电化学沉积法制备了一层氢氧化铁镍（氧）助催化剂覆盖层，这使得光电流起始电位发生了约100 mV的阴极偏移。利用Fe和Ni K边的原位X射线吸收光谱（XAS）来研究覆盖层在黑暗和光照条件下随电位的变化。单独的电位或光照对Fe的氧化态影响较小，这表明在整个电位范围内Fe原子不会积累大量电荷。相比之下，Ni K边光谱在黑暗和光照条件下对电位表现出明显的依赖性。光照的作用是由于产生的光电压使Ni氧化的起始点发生偏移，这表明在赤铁矿中光生的空穴主要转移到覆盖层中的Ni原子上。Ni氧化态的增加发生在与Ni的氧化还原波相对应的电位处，该氧化还原波紧接在析氧反应（OER）起始之前出现。对所得光谱进行的线性组合拟合分析表明，覆盖层不必完全氧化就能促进析氧。阴极放电测量表明，光生电荷几乎完全存储在覆盖层体积内的Ni原子中。
