Operando Spectroscopic Insights into the Triple Role of Cu Doping in Enhancing the Catalytic Efficiency of CoFe Hydroxides

Abstract

Directly monitoring stabilization mechanisms at the electrocatalytic solid–liquid interface presents a critical measurement challenge. While Fe incorporation significantly enhances the oxygen evolution reaction (OER) activity of transition-metal catalysts, elucidating how dopants stabilize these active Fe sites exceeds the capabilities of conventional ex situ techniques, which fail to capture dynamic chemical states under operating conditions. To address this analytical bottleneck, we developed an operando multimodal diagnostic platform integrating in situ Raman spectroscopy, in situ X-ray absorption spectroscopy (XAS), and differential electrochemical mass spectrometry (DEMS) with density functional theory (DFT) to track the active-site evolution process in real time. This integrated framework successfully unraveled a triple stabilization effect induced by copper doping in CoFe-layered hydroxides. In situ XAS and Raman spectroscopy enabled the tracking of chemical states of metal sites, revealing that Cu doping stabilizes iron in the +3 oxidation state under anodic polarization, preventing the formation of soluble high-valent Fe species. Furthermore, DEMS combined with DFT demonstrates that Cu doping reduces O 2p hole density near the Fermi level, thereby inhibiting the lattice oxygen oxidation pathway and enhancing structural stability. Correlation with DFT calculations supported these operando observations by revealing a significantly increased bulk Fe migration energy barrier by Cu doping from 1.55 eV in CoFe hydroxide to 3.07 eV. This work underscores the pivotal role of operando spectroscopic techniques in unraveling complex electrocatalytic stabilization mechanisms and provides a validated analytical framework for the rational design of durable, high-performance OER electrocatalysts.