Inert is not inactive: origin of carbon dioxide electroreduction activity over a carbon current collector-based electrode

Abstract

Electrocatalyst is commonly regarded as the primary source of activity in electrochemical reactions, while the other modules of the catalysis electrode, such as the current collector, are typically assumed to be electrochemically inert. We herein demonstrated that commercial carbon paper (CP), a classical current collector utilized in a wide array of electrochemical processes, does not remain inert as authoritative wisdom suggested when subjected to CO₂ electroreduction in non-aqueous electrolytes. In supporting electrolytes featuring fluorine-containing anions, CP undergoes a self-activation procedure via in situ fluorination. This activation process is intricately influenced by the proportion of H₂O in electrolytes and the surface hydroxy content of CP. In the optimized electrolyte of 1-butyl-2,3-dimethylimidazolium hexafluorophosphate (0.3 M) containing 5 wt% H₂O, pristine CP electrode delivered 99.7% CO selectivity with a current density of up to 150 mA cm⁻² in an H-type cell. It was disclosed that F-dopants activate the adjacent C sites for CRR. The stabilizing effect of C4/5 protons on the imidazolium cations toward *COOH intermediate further enhances the intrinsic activity for CO₂-to-CO conversion. This self-activation phenomenon is universal for various carbon materials and fluorine-containing ILs.