Proton-donating cations enable efficient and stable acidic CO2 reduction in membrane electrode assemblies
Shijia Feng, Ziang Liu, Dongfang Cheng, Yunfeng Hu, Sizhe Chen, Xinyuan Zhang, Jiabao Li, Xiaorui Dong, Tianyu Wang, Ziwei Wang, Yulun Wu, Ya Yin, Hongzhi Zheng, Philippe Sautet, Xiaojun Wang, Jia Zhu
Abstract
ABSTRACT Electrochemical CO2 reduction (CO2R) in acidic membrane electrode assemblies (MEAs) represents a promising pathway for sustainable chemical production, but achieving high selectivity, low cell voltage and long-term stability remains challenging. Current approaches using alkali cations can promote selectivity through cationic effects, but relying on H2O as a weak proton donor results in high overpotential and severe precipitation, causing elevated cell voltage and poor operational stability. Here, we introduce NH4+ as a proton-donating cation that simultaneously addresses these challenges in acidic MEAs. As a cation, it electromigrates to the catalyst surface, stabilizing *CO2 intermediates and reducing localized H+ concentration for high selectivity. As a proton donor, it provides superior proton-donating ability compared to H2O when H+ mass transport is limited, which decreases the protonation barrier and reduces CO2R overpotential on CoPc@CNT, resulting in a lower cell voltage. Furthermore, NH4+ effectively donates protons to bicarbonate, promoting its decomposition at significantly lower temperatures compared to KHCO3, thereby enabling easy removal of precipitates through mild heating and maintaining an NH3/NH4+ recirculation system for operational stability. As a result, this approach achieves an average CO2-to-CO selectivity of 86% in acidic MEAs at 100 mA cm−2 and 60°C using CoPc@CNT–NH2 catalyst, with stable performance over 110 h at an average cell voltage of 2.84 V, corresponding to a 40.6% energy efficiency. This strategy advances acidic MEA-based CO2R toward practical implementation by simultaneously achieving high selectivity, low overpotential and stable operation.