Unraveling Sequential Oxidation Kinetics and Determining Roles of Multi-Cobalt Active Sites on Co<sub>3</sub>O<sub>4</sub> Catalyst for Water Oxidation
Wanchao Kang, Ruifang Wei, Heng Yin, Dongfeng Li, Zheng Chen, Qinge Huang, Pengfei Zhang, Huanwang Jing, Xiuli Wang, Can Li
Abstract
The multi-redox mechanism involving multi-sites has great implications to dictate the catalytic water oxidation. Understanding the sequential dynamics of multi-steps in oxygen evolution reaction (OER) cycles on working catalysts is a highly important but challenging issue. Here, using quasi-operando transient absorption (TA) spectroscopy and a typical photosensitization strategy, we succeeded in resolving the sequential oxidation kinetics involving multi-active sites for water oxidation in OER catalytic cycle, with Co 3 O 4 nanoparticles as model catalysts. When OER initiates from fast oxidation of surface Co 2+ ions, both surface Co 2+ and Co 3+ ions are active sites of the multi-cobalt centers for water oxidation. In the sequential kinetics (Co 2+ → Co 3+ → Co 4+ ), the key characteristic is fast oxidation and slow consumption for all the cobalt species. Due to this characteristic, the Co 4+ intermediate distribution plays a determining role in OER activity and results in the slow overall OER kinetics. These insights shed light on the kinetic understanding of water oxidation on heterogeneous catalysts with multi-sites.