A Dual‐Functional Inherent Hydroxyl Chainmail on Defective La(OH) 3 for Robust Electrocatalytic Hydrogenation in Extreme Aqueous Matrices

ABSTRACT Electrocatalytic hydrogenation of carbon‐heteroatom bonds promises sustainable chemical synthesis and water remediation, yet practical deployment is challenged by both sluggish proton supply from water dissociation in alkaline media and rapid catalyst poisoning by dissolved organic matter (DOM). Herein, we show that the defective La(OH) 3 nanorods bearing an inherent hydroxyl chainmail circumvent these two bottlenecks simultaneously. The chainmail is proposed to be capable of reconstructing the interfacial hydrogen‐bond continuum into a proposed proton‐relay highway that accelerates water‐dissociation‐limited proton delivery, while acting as a proposed biomimetic, multisite hydrogen‐bonding shield that sequesters macromolecular DOM to protect active sites from fouling. Demonstrated for the electrocatalytic hydrodechlorination reaction, the catalyst achieves highly effective dechlorination of florfenicol across pH 3.0–13.0 and sustains exceptional stability in high‐chemical oxygen demand (COD) matrices (1000 mg L −1 humic acid), outperforming most state‐of‐the‐art catalysts. Continuous‐flow treatment of real aquaculture and pharmaceutical effluents confirms sustained dechlorination efficiency and pronounced toxicity abatement. By revealing how this seemingly passive OH − chainmail orchestrates proton transfer and molecular sieving, this work establishes a broadly applicable design paradigm for fouling‐resistant electrocatalysts operating in complex aqueous environments.