Engineering the catalyst interface enables high carbon efficiency in both cation-exchange and bipolar membrane electrolyzers

The formation of (bi)carbonate in alkaline and neutral membrane-electrode assembly (MEA) electrolyzers poses an unsatisfactorily low upper-bound of CO 2 single-pass utilization rate (SPU) and single-pass conversion rate (SPC) in CO 2 electrolyzers. Electrolyzing CO 2 in acidic MEA has been regarded as an effective strategy to prevent carbonate formation and CO 2 loss but poses challenges due to the competitive hydrogen evolution reaction. Here we report the preparation of a hydrogel buffering layer on an Ag-coated gas diffusion electrode (GDE) to prevent the (bi)carbonate formation and break the theoretical limitation of 50% SPU in neutral-media electrolyzers. Through precise control of the porosity within the buffering layer, while maintaining superaerophobicity, we found that the hydrogel enhances the mass transfer of regenerated CO 2 at the interface between the buffering layer and the cation-exchange layer. We demonstrate a high energy efficiency of 37% and high SPU of 77% at a total current density of 375 mA cm − 2 when performing acidic electrolysis using an optimal Ag/buffer GDE within a Nafion-based MEA cell.