Suppressing Cathode Corrosion Induced by Impurity Cations in Alkaline Water Electrolyzers

In alkaline water electrolysis systems operated under industrial conditions, cations leaching from corrosive dissolution of the anode and balance‐of‐plant components progressively accumulate and contaminate the circulating electrolyte during prolonged operation. Here, we demonstrate for the first time that impurity cations, particularly Fe ions, compromise the long‐term structural stability of the Raney Ni cathode. The accumulation of Fe species on the cathode surface promotes the two‐electron reduction of crossover oxygen and the formation of HO 2 • radicals that drive oxidative corrosion of Ni sites. We then introduce a Lewis‐acidic CeO x layer on the cathode surface for protection. The layer effectively suppresses the reductive deposition of Fe on the cathode, while coordinatively unsaturated high‐valent Ce sites directly scavenge the reactive radicals. As a result, the protected Raney Ni cathode demonstrates marked stability in Fe‐containing electrolyte, maintaining stable operation over 3,500 h at 1.0 A cm −2 and 15,000 accelerated startup–shutdown cycles. Notably, this strategy exhibits strong feasibility and universality under practical operating conditions, maintaining stable cathode performance in the presence of up to 200 µM Fe(III) or various impurity cations derived from system components, including Co(II), Mn(II), Mo(VI), Cr(III), and Al(III).