Designing ionomers to control water content for low-voltage ethylene production from CO2 electrolysis

Electrochemical CO₂ reduction (eCO₂R) holds promise for decarbonizing industrial sectors by producing valuable commodities, such as ethylene. Incorporating polymer electrolyte ionomers onto Cu-based eCO₂R cathodes is crucial for enhancing eCO₂R efficiency. These ionomers control mass transport, surface chemistry, and water uptake at the cathode, enabling selectivity tuning toward desired C₂ products. Complexities and interdependence of interfacial properties have led to challenges within the field to define design properties of catalyst layer ionomers that can enhance the performance of Cu-based catalysts. Herein, we present a systematic investigation into ionomer properties and their relationship to electrochemical performance and demonstrate a 14.3% energy efficiency for ethylene selectivity at 200 mA cm⁻². Through multiphysics modeling, we elucidated that the role of the water content of the ionomer is to mitigate flooding and control the local water concentration at the catalyst surface. Translating knowledge from this study will stimulate the synthesis of ionomers tailored for eCO₂R.