Advanced Light Source, Lawrence Berkeley National Laboratory , One Cyclotron Road, Berkeley, California 94720, United States.
Joint Center for Artificial Photosynthesis, Lawrence Berkeley National Laboratory , One Cyclotron Road, Berkeley, California 94720, United States.
J Am Chem Soc. 2017 Jul 5;139(26):8960-8970. doi: 10.1021/jacs.7b03211. Epub 2017 Jun 22.
Photoelectrochemical water splitting is a promising approach for renewable production of hydrogen from solar energy and requires interfacing advanced water-splitting catalysts with semiconductors. Understanding the mechanism of function of such electrocatalysts at the atomic scale and under realistic working conditions is a challenging, yet important, task for advancing efficient and stable function. This is particularly true for the case of oxygen evolution catalysts and, here, we study a highly active CoO/Co(OH) biphasic electrocatalyst on Si by means of operando ambient-pressure X-ray photoelectron spectroscopy performed at the solid/liquid electrified interface. Spectral simulation and multiplet fitting reveal that the catalyst undergoes chemical-structural transformations as a function of the applied anodic potential, with complete conversion of the Co(OH) and partial conversion of the spinel CoO phases to CoO(OH) under precatalytic electrochemical conditions. Furthermore, we observe new spectral features in both Co 2p and O 1s core-level regions to emerge under oxygen evolution reaction conditions on CoO(OH). The operando photoelectron spectra support assignment of these newly observed features to highly active Co centers under catalytic conditions. Comparison of these results to those from a pure phase spinel CoO catalyst supports this interpretation and reveals that the presence of Co(OH) enhances catalytic activity by promoting transformations to CoO(OH). The direct investigation of electrified interfaces presented in this work can be extended to different materials under realistic catalytic conditions, thereby providing a powerful tool for mechanism discovery and an enabling capability for catalyst design.
光电化学水分解是一种从太阳能中可再生生产氢气的有前途的方法，需要将先进的水分解催化剂与半导体相连接。在原子尺度和实际工作条件下理解这种电催化剂的功能机制是一个具有挑战性但又很重要的任务，这对于氧气析出催化剂尤其如此。在这里，我们通过在固/液电界面上进行的原位常压 X 射线光电子能谱研究了 Si 上的高活性 CoO/Co(OH) 双相电催化剂。光谱模拟和多谱拟合表明，催化剂随着施加的阳极电势发生化学结构转变，在预催化电化学条件下，Co(OH)完全转化，尖晶石 CoO 相部分转化为 CoO(OH)。此外，我们还观察到在 CoO(OH)上的氧气析出反应条件下，Co 2p 和 O 1s 芯能级区域出现新的光谱特征。原位光电子能谱支持将这些新观察到的特征分配给催化条件下的高活性 Co 中心。与纯相尖晶石 CoO 催化剂的结果进行比较，支持了这一解释，并表明 Co(OH)的存在通过促进向 CoO(OH)的转化来提高催化活性。本工作中提出的对带电界面的直接研究可以扩展到实际催化条件下的不同材料，从而为机制发现提供了强大的工具，并为催化剂设计提供了实现能力。
