Improving the SO2 tolerance of CO2 reduction electrocatalysts using a polymer/catalyst/ionomer heterojunction design

The high concentrations of CO2 in industrial flue gases make these point sources attractive candidates for renewably powered electrocatalytic conversion of CO2 to products. However, trace SO2 in common flue gases rapidly and irreversibly poisons catalysts. Here we report that limiting hydrogen adsorption in the vicinity of electrochemically active sites deactivates SO2 to enable efficient CO2 conversion. We realize this approach via a polymer/catalyst/ionomer heterojunction design with combined hydrophobic and highly charged hydrophilic domains that diminish hydrogen adsorption and promote CO2 over SO2 transport. We develop an SO2-tolerant system that maintains ~50% faradaic efficiency towards multi-carbon products for over 150 h (at 100 mA cm–2). Extending this strategy to a high-surface-area composite catalyst, we achieve faradaic efficiencies of 84%, partial current densities of up to 790 mA cm–2 and energy efficiencies of ~25% towards multi-carbon products with a CO2 stream containing 400 ppm SO2, a performance that is competitive with the best reports using pure CO2.