Structure‐Dependent Impact of Organic Water Contaminants on Nickel Surface Chemistry and Water Splitting Performance

Anion exchange membrane water electrolysis (AEMWE) is a promising technology for sustainable hydrogen production but currently relies on highly purified water. Its large‐scale implementation would benefit from alternative water sources. However, the effects of dissolved contaminants, particularly organic compounds such as aromatic amines, remain poorly understood. We therefore investigated structurally distinct aromatic amines as model contaminants to evaluate their effects on the water splitting performance of nickel electrodes. Electrochemical measurements, product analysis, and operando interfacial characterization were combined to identify structure‐dependent effects and mechanisms of catalyst deactivation and recovery. Aniline severely suppressed the oxygen evolution reaction, whereas its methyl‐substituted derivatives had negligible effects. Complementary analyses attributed this inhibition to the potential‐dependent accumulation of an aniline‐derived, polyaniline‐like surface layer. This layer progressively modified the NiOOH/electrolyte interface, impeded interfacial charge transfer, and reduced oxygen evolution. These findings contribute to fundamental insights into how organic contaminants originating from feedwater or the degradation of polymeric electrolyzer components interact with nickel‐based electrodes, providing valuable guidance for defining feedwater‐quality requirements of future AEMWE systems.