<i>Operando</i> Identification of Dual Active Sites in Ca<sub>2</sub>IrO<sub>4</sub> Nanocrystals with Yttrium Substitutions Boosting Acidic Oxygen Evolution Reaction
Yuying Liu, Liang Cai, Qianqian Ji, Chao Wang, Ziyi Liu, Liyang Lv, Bing Tang, Hengli Duan, Fengchun Hu, Huijuan Wang, Na Li, Zhihu Sun, Wensheng Yan
Abstract
Non-noble metal substitutions of the iridium sites in iridium-based complex oxides while boosting acidic oxygen evolution reaction (OER) is a promising method for developing efficient electrocatalysts, but this remains a huge challenge. Herein, we report yttrium substitution of iridium in Ca2IrO4 (Ca2YxIr1–xO4) nanocrystals for the first time, which is demonstrated by detailed structural characterizations using X-ray absorption spectra, X-ray diffraction patterns, and elemental mapping images. The synthesized Ca2Y0.2Ir0.8O4 catalyst requires a low overpotential of only 213 mV, achieving an acidic OER current density of 10 mA cm–2, which represents an approximately 203.7-fold improvement in iridium mass activity and 204.4-fold improvement in turnover frequency in comparison to that of IrO2 at 1.5 V vs RHE, respectively. Systematic characterizations of electronic structures reveal the synergistic effects between high-valence iridium sites and increased lattice oxygen concentration induced by Y3+ substitutions, which greatly enhance the intrinsic OER activity of Ca2Y0.2Ir0.8O4. Operando X-ray absorption spectra and Raman spectra reveal the iridium and yttrium dual active sites during acidic OER. Our results provide a method for designing dual active sites in iridium-based complex oxides for highly active acidic OER electrocatalysts.