Proton exchange membrane (PEM) water electrolysis represents a feasible technology for ‘green’ hydrogen production. However, the efficiency of the electrolyzers can be compromised by foreign ions in the feed water. In particular, sodium ions (Na⁺), which are commonly found in water sources, poses a serious threat for the operation of PEM water electrolyzers. This work examines the effects of low-concentration Na⁺ on the performance of membrane electrode assemblies (MEAs). Results reveal that Na⁺ can diminish the H⁺ concentration (c_H+) and cation diffusion coefficient (D₀) in the isomer and PEM by substituting H⁺ sites, but doesn’t cause irreversible catalyst or structure damage. The reduced c_H+ can lead to a negative shift in equilibrium potential, particularly at the cathode. Concurrently, a lowered D₀ slows down the movement of cations, which serve as reactants at the cathode, resulting in impeded mass transport. Additionally, the work presents a methodology for recovering the performance of Na⁺ poisoned MEAs. Operating the electrolyzer at high current densities, viz. 6.0 A cm^-2, could aid in the re-equilibration of Na⁺/H⁺ and the expulsion of Na⁺ from the MEAs. With Pt-coated Ti porous transport layers employed, the poisoned MEAs can be recovered to their original performance levels. This work presents an effective countermeasure to manage the Na⁺ poisoning in PEM electrolyzers and overcome this prohibitive barrier to the commercial viability of this technology.

https://www.sciencedirect.com/science/article/pii/S000925092400383X