Oxyanion-regulated Fe–NiMoN electrocatalyst for efficient and durable alkaline seawater electrolysis: Advancing energy chemistry through interface engineering

Electrochemical water splitting using seawater as a feedstock offers a promising strategy for large-scale, sustainable hydrogen production, but electrolysis is fundamentally challenged by sluggish reaction kinetics, chloride-induced corrosion, and catalyst instability. Addressing these limitations requires not only advanced catalyst design but also a deeper understanding of the energy chemistry at the catalyst–electrolyte interface under harsh operating conditions. Here, we present a bifunctional Fe-doped NiMo nitride (Fe–NiMoN) electrocatalyst that integrates transition metal synergy with oxyanion-regulated surface chemistry to achieve highly efficient and durable hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline seawater. The Mo-based electrocatalyst can produce in situ MoO₄²⁻, in addition, OER activity is increased and stabilizes the active phase of Fe–NiOOH, which plays the critical role in seawater electrolysis to shield the electrode from chloride ion (Cl⁻) corrosion and extend its stability. As a result, Fe–NiMoN exhibits low overpotentials of 24 and 88 mV for HER and 245 and 285 mV for OER at 10 and 100 mA cm⁻² in alkaline seawater, with strong resistance to Cl⁻-induced degradation. To bridge fundamental insights with practical applications, we assembled an anion-exchange membrane (AEM) electrolyzer using Fe–NiMoN as both the anode and cathode. The device delivers industrially relevant current densities of 1 A cm⁻² at 1.84 V in 1 M KOH and 1.94 V in alkaline seawater, retaining 93.3 % of its initial current after 250 h of continuous operation at 1.7 V. This work contributes to the field of energy chemistry by elucidating a chloride-tolerant catalytic pathway enabled through oxyanion-surface interactions, offering a scalable and mechanistically informed approach for seawater electrolysis.