Operando Direct Observation of Stable Water-Oxidation Intermediates on Ca2- xIrO4 Nanocrystals for Efficient Acidic Oxygen Evolution

Na Li; Liang Cai; Guoping Gao; Yue Lin; Chao Wang; Hengjie Liu; Yuying Liu; Hengli Duan; Qianqian Ji; Wei Hu; Hao Tan; Zeming Qi; Lin-Wang Wang; Wensheng Yan

doi:10.1021/acs.nanolett.2c01777

Operando Direct Observation of Stable Water-Oxidation Intermediates on Ca_{2- x}IrO₄ Nanocrystals for Efficient Acidic Oxygen Evolution

Nano Lett. 2022 Sep 14;22(17):6988-6996. doi: 10.1021/acs.nanolett.2c01777. Epub 2022 Aug 25.

Authors

Na Li^{1

2}, Liang Cai^{3

2}, Guoping Gao^{3

4}, Yue Lin⁵, Chao Wang¹, Hengjie Liu¹, Yuying Liu¹, Hengli Duan¹, Qianqian Ji¹, Wei Hu¹, Hao Tan¹, Zeming Qi¹, Lin-Wang Wang³, Wensheng Yan¹

Affiliations

¹ National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei, Anhui 230029, China.
² Department of Materials Science and Engineering, National University of Singapore, 117575 Singapore.
³ Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States.
⁴ MOE Key Laboratory for Non-equilibrium Synthesis and Modulation of Condensed Matter, Shaanxi Province Key Laboratory of Advanced Functional Materials and Mesoscopic Physics, School of Physics, Xi'an Jiaotong University, Xi'an, Shaanxi 710049, China.
⁵ Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, Anhui 230029, China.

PMID: 36005477
DOI: 10.1021/acs.nanolett.2c01777

Abstract

We report Ca_2-xIrO₄ nanocrystals exhibit record stability of 300 h continuous operation and high iridium mass activity (248 A g_Ir^-1 at 1.5 V_RHE) that is about 62 times that of benchmark IrO₂. Lattice-resolution images and surface-sensitive spectroscopies demonstrate the Ir-rich surface layer (evolved from one-dimensional connected edge-sharing [IrO₆] octahedrons) with high relative content of Ir⁵⁺ sites, which is responsible for the high activity and long-term stability. Combining operando infrared spectroscopy with X-ray absorption spectroscopy, we report the first direct observation of key intermediates absorbing at 946 cm^-1 (Ir⁶⁺═O site) and absorbing at 870 cm^-1 (Ir⁶⁺OO- site) on iridium-based oxides electrocatalysts, and further discover the Ir⁶⁺═O and Ir⁶⁺OO- intermediates are stable even just from 1.3 V_RHE. Density functional theory calculations indicate the catalytic activity of Ca₂IrO₄ is enhanced remarkably after surface Ca leaching, and suggest IrOO- and Ir═O intermediates can be stabilized on positive charged active sites of Ir-rich surface layer.

Keywords: acidic oxygen evolution reaction; electrocatalysis; iridium-based oxides; iridium-rich surface layer; key intermediates.