The reduction in λ negatively impacts the transport of all the species, which explains the strong dependency of a (d) and (e) respectively). Since pH OHP is always quite high (see Figure ), it is reasonable to think that the acidic HER will be relatively lower than in the liquid electrolyte case at low V RHE , and the FE would be high even if we included H + -based mechanisms. Ultimately, we show that in hydrophilic membranes water content is a key parameter for optimizing eCO 2 R, and that both the fixed background charge and the inorganic cation contributes to the overall performances of the system.