Wang Yang, Ma Yuan, Li Xu-Bing, Gao Lei, Gao Xiao-Ya, Wei Xiang-Zhu, Zhang Li-Ping, Tung Chen-Ho, Qiao Lijie, Wu Li-Zhu
Key Laboratory of Photochemical Conversion and Optoelectronic Materials, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190, P. R. China.
School of Future Technology, University of Chinese Academy of Sciences, Beijing 100049, P. R. China.
J Am Chem Soc. 2020 Mar 11;142(10):4680-4689. doi: 10.1021/jacs.9b11768. Epub 2020 Feb 28.
Semiconductor quantum dots (QDs) in conjunction with non-noble 3d-metal ions (e.g., Fe, Co, and Ni) have emerged as an extremely efficient, facile, and cost-effective means of solar-driven hydrogen (H) evolution. However, the exact structural change of the active sites under realistic conditions remains elusive, and the mechanism of H evolution behind the remarkable activity is poorly understood. Here, we successfully track the structural variation of the catalytic sites in the typical H photogeneration system consisting of CdSe/CdS QDs and 3d-metal ions (i.e., Ni used here). That is, the nickel precursor of Ni(OAc) changes to Ni(HO) in neutral HO and eventually transforms to Ni(OH) nanosheets in alkaline media. Furthermore, the in operando spectroscopic techniques of electron paramagnetic resonance and X-ray absorption spectroscopy reveal the photoinduced transformation of Ni(OH) to a defective structure [Ni/Ni(OH)], which acts as the real catalytic species of H photogeneration. Density functional theory (DFT) calculations further indicate that the surface Ni-vacancies () on the Ni(OH) nanosheets enhance the adsorption and dissociation of HO molecules to enhance the local proton concentration, while the Ni clusters behave as H-evolution sites, thereby synergistically promoting the activity of H photogeneration in alkaline media.
半导体量子点（QDs）与非贵金属3d金属离子（如Fe、Co和Ni）相结合，已成为一种极其高效、简便且经济高效的太阳能驱动析氢手段。然而，在实际条件下活性位点的确切结构变化仍不清楚，且这种显著活性背后的析氢机制也了解甚少。在此，我们成功追踪了由CdSe/CdS量子点和3d金属离子（即此处使用的Ni）组成的典型析氢光生系统中催化位点的结构变化。也就是说，Ni（OAc）的镍前驱体在中性H₂O中变为Ni（H₂O）₆²⁺，并最终在碱性介质中转变为Ni（OH）₂纳米片。此外，电子顺磁共振和X射线吸收光谱的原位光谱技术揭示了Ni（OH）₂光致转变为缺陷结构[Ni⁰/Ni（OH）]，其作为析氢的真正催化物种。密度泛函理论（DFT）计算进一步表明，Ni（OH）₂纳米片上的表面Ni空位（VNi）增强了H₂O分子的吸附和解离，以提高局部质子浓度，而Ni簇作为析氢位点，从而协同促进碱性介质中的析氢活性。
