Gas Crossover Regulation by Porosity‐Controlled Glass Sheet Achieves Pure Hydrogen Production by Buffered Water Electrolysis at Neutral pH

Near‐neutral pH water electrolysis driven by renewable electricity can reduce the costs of clean hydrogen generation, but its low efficiency and gas crossover in industrially relevant conditions remain a challenge. Here, it was shown that electrolyte engineering could suppress the crossover of dissolved gases such as O2 by regulating their diffusion flux. In addition, a hydrophilized mechanically stable glass sheet was found to block the permeation of gas bubbles, further enhancing the purity of evolved gas from water electrolysis. This sheet had a lower resistance than conventional diaphragms such as Zirfon due to its high porosity and small thickness. A saturated K‐phosphate solution at pH 7.2 was used as an electrolyte together with the hydrophilized glass sheet as a gas‐separator. This led to a near‐neutral pH water electrolysis with 100 mA cm−2 at a total cell voltage of 1.56 V with 99.9 % purity of produced H2. Caution, gas crossing: Successful regulation of gas crossover during water electrolysis is achieved by using a porous silica sheet as a gas separator in a saturated potassium phosphate buffer solution. Electrocatalytic testing of water electrolysis with the separator in the phosphate solutions under practical conditions at high rates demonstrates comparable performance to existing alkaline water electrolyzers.