Restructuring of Benzimidazole-Based Copper Complexes during Electrochemical CO2Reduction

Abstract

Copper-based molecular catalysts have been widely used for the electrochemical reduction of carbon dioxide (ERCO2). However, establishing a correlation between structure and catalytic performance has been challenging due to the dynamic nature of these materials under ERCO2working conditions. Here, we report on the restructuring of the copper complexes [Cu(bzimpy)Cl2] and [Cu(pyrben)2(NO3)]NO3during ERCO2in an acidic medium, evidencing its effects on the observed activity, selectivity, and stability. In situ X-ray absorption spectroscopy (XAS) suggested that, at sufficiently negative potentials, the Cu2+centers of both complexes are reduced to undercoordinated Cu0species. Pb underpotential deposition of post-ERCO2samples indicated that such Cu0species also present a dominant contribution of the (100) domain, which is in line with the high Faradaic efficiency toward C2products (∼45%) shown by both complexes at −1.24 V vs RHE. By combining online electrochemical mass spectrometry, in situ XAS, electron paramagnetic resonance (EPR), and quantitative product analysis, we found that [Cu(bzimpy)Cl2] exhibits a partially reversible restructuring, regenerating the main complex moiety, [Cu(bzimpy)]2+, and its geometry.