Traditional electrolyzer membranes, namely Nafion, face challenges regarding scalability, environmental impact, and the overall cost of water electrolysis as a feasible method for hydrogen generation. Zero-gap electrolyzers incorporating PFAS-free, proton-conducting silicon oxide (SiO2) membranes produced by atomic layer deposition (ALD) offer a promising alternative, exhibiting lower porosity for hydrogen transport and reduced susceptibility to swelling and creep. Although SiO2 has lower intrinsic proton conductivity than Nafion, reducing membrane thickness to the nanoscale (<1 µm) minimizes ionic resistances, thereby enabling higher system efficiency with lower capital expenditure compared to conventional Nafion membranes. Though these structural advantages underscore the feasibility of SiO2 membranes, their overall performance is governed by oxide matrix’s fundamental transport mechanism. Electrochemical impedance spectroscopy (EIS) revealed that achieving appreciable ionic conductivity requires the presence of a supporting electrolyte, with the conductivity level dependent on the ion identity; this underscores the role of specific ions in mediating proton transport. In addition, safe electrolyzer operation requires low hydrogen permeability. 250 nm SiO₂ membranes achieve gas crossover rates an order of magnitude below Nafion-117 as a result of their dense microstructure, but are also highly prone to defects that serve as highways for crossover. To address defects, our team has developed a method to deposit nanoscopic plugs that are able to effectively seal these defects and lower gas crossover rates by 99.999% compared to identical membranes lacking the plugs. Performance can be further optimized by designing the membrane-catalyst interface to enhance ion transport while maintaining low resistance. These results demonstrate the fundamental feasibility of ALD-grown SiO2 membranes to serve as efficient and cost effective replacements of Nafion membranes in PEM electrolyzers.
