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 carbon efficiency. 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 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. The high energy efficiency of 37 % and carbon utilization of 77 % ±2.4 at a total current density of 375 mA cm −2 were achieved using an optimal Ag/buffer electrode when performing acidic MEA electrolysis. Effectively regulating the cathode surface in an acidic membrane-electrode assembly (MEA) electrolyzer by fabricating a polymer hydrogel buffering layer shows impressive carbon efficiency, meeting the industrial electro-conversion of CO 2 requirements. • A series of hydrogel layers with tunable porosity and aerophobicity were fabricated. • The hydrogel buffering layer keeps a favorable alkaline environment at the catalyst surface. • The hydrogel buffering layer effectively manages the dynamic behavior of the regenerated CO 2 . • The optimization of the PEI hydrogel achieves an industrial carbon utilization of 80 %.