Tailoring the catalytic microenvironment of large-scale Cu foil with polyaniline to enhance CH4 selectivity in CO2 electroreduction

Abstract

Electrochemical conversion of CO₂ into liquid fuels and value-added chemicals is a promising approach for closing the carbon cycle. Copper (Cu) is considered one of the most effective catalysts for the electrocatalytic CO₂ reduction reaction (CO₂RR). However, its utilization potential is limited by poor selectivity for hydrocarbon products and the competing hydrogen evolution reaction (HER). In this study, we present a strategy to suppress the HER process and enhance the CH₄ selectivity of large-scale Cu foil toward the CO₂RR. By coating the Cu foil surface with a porous polyaniline (PANI) layer, the H₂ faradaic efficiency (FE) reduces from 60% to 18%. Moreover, the FE of hydrocarbons increases dramatically from 25% to 80%, and the FE of the dominant product CH₄ is high up to 62%. In situ electrochemical attenuated total reflection Fourier transform infrared spectroscopy (in situ ATR-FTIR) and density functional theory (DFT) calculations are conducted to elucidate the mechanism. The enhanced performance of Cu-PANI in the CO₂RR is mainly attributed to the porous PANI layer, which facilitates CO₂ adsorption and mass transport. This leads to a reversal in the energy barrier for the rate-determining steps between the HER and the CO₂RR, significantly inhibiting the HER and enhancing the CO₂RR activity. Additionally, Cu–PANI promotes the hydrogenation of *CO to *CHO, resulting in higher methane selectivity. This work provides a promising strategy for designing efficient large-scale Cu-based catalysts with high CH₄ catalytic activity and selectivity.