Deciphering and Countering Formic Acid Permeability in Zero-Gap Electrolyzers

In recent years, formic acid (FA) has garnered attention as a compelling molecule for various chemical and everyday applications. Additionally, with recent studies demonstrating direct FA generation through CO2 electrolysis, it can serve as a stable liquid hydrogen carrier. Nevertheless, FA-permeability via semi-permeable ion–exchange membranes (FA-crossover) still constitutes a major issue in scalable polymer-electrolyte separated zero-gap electrolyzers, limiting the breakthrough of the technology to the larger-scale. Herein we present a holistic route towards understanding the mechanism of FA-crossover in zero-gap electrolyzers. The gained know-how through formic acid solution uptake, gel-phase conductivity, and membrane permeability measurements allowed for the development of an easy-to-scale barrier layer, showing a FA-flux (JFA) decrease by 46 % at 200 mA cm-2 compared to bare Nafion-membranes.