Max Planck Institute for Chemical Energy Conversion , Mülheim a.d. Ruhr, Germany.
Department of Inorganic Chemistry, Fritz-Haber-Institut der Max-Planck-Gesellschaft , Faradayweg 4-6, 14195 Berlin, Germany.
J Am Chem Soc. 2017 Aug 30;139(34):12093-12101. doi: 10.1021/jacs.7b07079. Epub 2017 Aug 18.
Hydrogen production by electrocatalytic water splitting will play a key role in the realization of a sustainable energy supply. Owing to their relatively high stability and activity, iridium (hydr)oxides have been identified as the most promising catalysts for the oxidation of water. Comprehensive spectroscopic and theoretical studies on the basis of rutile IrO have provided insight about the electronic structure of the active X-ray amorphous phase. However, due to the absence of long-range order and missing information about the local arrangement of structural units, our present understanding of the active phase is very unsatisfying. In this work, using a combination of real-space atomic scale imaging with atomic pair distribution function analysis and local measurements of the electronic structure, we identify key structural motifs that are associated with high water splitting activity. Comparison of two X-ray amorphous phases with distinctively different electrocatalytic performance reveals that high activity is linked to the ratio between corner- and edge-sharing IrO octahedra. We show that the active and stable phase consists of single unit cell sized hollandite-like structural domains that are cross-linked through undercoordinated oxygen/iridium atoms. In the less active phase, the presence of the rutile phase structural motif results in a faster structural collapse and deactivation. The presented results provide insight into the structure-activity relationship and promote a rational synthesis of X-ray amorphous IrO hydroxides that contain a favorable arrangement of structural units for improved performance in catalytic water splitting.
通过电催化水分解生产氢气将在实现可持续能源供应方面发挥关键作用。由于铱（氢）氧化物具有相对较高的稳定性和活性，因此被确定为水氧化的最有前途的催化剂。基于金红石 IrO 的综合光谱和理论研究提供了有关活性 X 射线非晶相电子结构的深入了解。然而，由于缺乏长程有序和结构单元局部排列的信息，我们目前对活性相的理解非常令人不满意。在这项工作中，我们使用实空间原子尺度成像与原子配分函数分析以及局部电子结构测量相结合的方法，确定了与高水分解活性相关的关键结构基序。两种具有明显不同电催化性能的 X 射线非晶相的比较表明，高活性与顶角和边缘共享 IrO 八面体的比例有关。我们表明，活性和稳定相由单胞大小的类水铁矿结构域组成，这些结构域通过配位不足的氧/铱原子交联。在活性较低的相中，金红石相结构基序的存在导致更快的结构塌陷和失活。所提出的结果提供了对结构-活性关系的深入了解，并促进了 X 射线非晶 IrO 氢氧化物的合理合成，这些氢氧化物具有有利于提高催化水分解性能的结构单元的有利排列。
