Abstract
The formation of (bi)carbonate in alkaline and neutral membrane-electrode assembly (MEA) electrolyzers poses an unsatisfactorily low upper-bound of carbon efficiency. Electrolyzing CO2 in acidic MEA has been regarded as an effective strategy to prevent carbonate formation and CO2 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 CO2 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.