Hydrophilic-hydrophobic Janus polybenzimidazole membrane electrode assemblies regulate hydrogen evolution for high efficient electrochemical CO2 reduction

The membrane Electrode Assemblies (MEAs) electrolyzers are the most attractive systems for the electrolytic conversion of CO2 into commodity chemicals and fuels at commercially relevant current densities. Suppressing the hydrogen evolution reaction (HER) is vital to the highly efficient electrochemical CO2 reduction reaction (CO2RR). However, little attention has been paid to the HER. Herein, polybenzimidazole (PBI) Janus membranes with significant hydrophobic/hydrophilic asymmetric surface wettability were constructed for regulating the HER in CO2RR. The HER was modulated by adjusting the microstructure and surface hydrophobicity of the membrane as well as the CO2 feeding method. The p-PBI-HCF MEA showed a significant suppression of HER and a 6-fold improvement in CO selectivity over p-PBI MEA. The p-PBI-HCF exhibited superior CO2RR performance in MEA compared to commercial membranes (FAA-3-50 and Nafion115). At 2.0–3.0 V, the CO Faraday efficiency (FECO) of the p-PBI-HCF MEA electrolyzer remained above 92%. The optimal energy efficiency range was between 2.0 and 2.4 V when the FECO was close to 100%. The p-PBI-HCF provided 92% FECO and a current density of 225 mA cm−2 at 3 V. This work provides guidelines for the development of viable PBI membranes and MEAs for CO2RR.