Combined In Situ X‐Ray Spectroscopic and Theoretical Study on Trimetal Synergistic Enhancement of Water Oxidation

Trimetal synergistic enhancement of OER activity is observed in CaCu₃Co₂Ru₂O₁₂ catalyst, which exhibits a low overpotential of 198 mV at 10 mA cm^‒2. In situ X-ray absorption spectra reveal that the Co and Ru ions are active sites. Although Cu is not the active sites, it optimizes the electronic structure at the E_F, leading to a synergistic enhancement of OER activity by the Cu-Co-Ru network.

Abstract

Electrochemical water-splitting is vital in energy storage and conversion applications. However, the sluggish kinetics of the oxygen evolution reaction (OER) hinders the electrochemical water-splitting. Therefore, developing efficient catalysts and understanding the OER mechanism are highly desirable. This study successfully synthesized a new quadruple perovskite oxide CaCu₃Co₂Ru₂O₁₂ (CCCRO) catalyst exhibiting high OER activity with overpotential 198 mV at 10 mA cm⁻², a Tafel slope of 37 mV dec⁻¹, and long-term operational stability with a current density of 500 mA cm⁻² for >500 h. The in situ X-ray absorption near-edge structure (XANES) indicated that a part of high-spin (HS) Co³⁺ ions and low-spin (LS) Ru⁵⁺ ions transitioned to the tetravalent Co (IV) and hexavalent Ru (VI) valence states under OER. However, the Cu²⁺ valence state remained unchanged. Furthermore, the density functional theory (DFT) calculations reveal that the lattice-oxygen oxidation mechanism (LOM) rather than conventional adsorbate evolution mechanism (AEM) is responsible for high OER activity in Ru (VI)-O-Co (IV) network, and that the Cu(A’)/Co(B)/Ru(B’) three sites synergistically facilitate the OER activity for CCCRO.