期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2021
卷号：118
期号：36
DOI：10.1073/pnas.2101817118
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Significance
The efficiency with which renewable fuels and feedstocks are synthesized from electrical sources is largely limited by the sluggish water oxidation reaction. We show that the optimal water oxidation catalyst could be achieved by systematically modulating the coordination of the Ir active sites using an in situ cryogenic–photochemical reduction synthesis method. We achieved a highly oxidized Ir single site (Ir
+5.3) in the best atom utilization by single-atom catalysts on electrochemically stable supports. The origin of water oxidation activity in an Ir single-atom catalyst is revealed experimentally and theoretically. The concept and strategy of this work are expected to pioneer novel approaches to engineer single-atom catalysts.
The efficiency of the synthesis of renewable fuels and feedstocks from electrical sources is limited, at present, by the sluggish water oxidation reaction. Single-atom catalysts (SACs) with a controllable coordination environment and exceptional atom utilization efficiency open new paradigms toward designing high-performance water oxidation catalysts. Here, using operando X-ray absorption spectroscopy measurements with calculations of spectra and electrochemical activity, we demonstrate that the origin of water oxidation activity of IrNiFe SACs is the presence of highly oxidized Ir single atom (Ir
5.3+) in the NiFe oxyhydroxide under operating conditions. We show that the optimal water oxidation catalyst could be achieved by systematically increasing the oxidation state and modulating the coordination environment of the Ir active sites anchored atop the NiFe oxyhydroxide layers. Based on the proposed mechanism, we have successfully anchored Ir single-atom sites on NiFe oxyhydroxides (Ir
0.1/Ni
9Fe SAC) via a unique in situ cryogenic–photochemical reduction method that delivers an overpotential of 183 mV at 10 mA ⋅ cm
−
2 and retains its performance following 100 h of operation in 1 M KOH electrolyte, outperforming the reported catalysts and the commercial IrO
2 catalysts. These findings open the avenue toward an atomic-level understanding of the oxygen evolution of catalytic centers under in operando conditions.
关键词：enhighly oxidized Ir sites;water oxidation;operando X-ray absorption spectroscopy;DFT calculations
