Ion-selective interface engineering for durable electrolysis of impure water

Electrolysis of low-grade impure water offers a sustainable approach to hydrogen production. However, unstable interfacial pH caused by electrochemical reactions accelerates ion-induced electrode degradation. Here, we show an ion-selective gate strategy, in which ion-conducting polymer coatings are applied onto commercial platinum carbon and iridium oxide catalysts to enable selective ion transport and to stabilize the interfacial pH. Compared with conventional aqueous electrolytes, this solid-state configuration effectively suppresses local pH fluctuations and blocks the migration of detrimental impurity ions. The ion-selective gate achieves nearly complete rejection of common ions found in seawater, river and lake water, and industrial wastewater, demonstrating broad adaptability to impurity-rich environments. In untreated seawater, the ion-selective gate engineered electrode operates stably for 1500 h at 200 mA cm^-2, with a degradation rate of 5.2 mV kh^-1, approaching the durability of pure water electrolysis. This design is compatible with both proton exchange membrane and anion exchange membrane electrolyzers, providing a scalable route for sustainable hydrogen generation from natural water sources.