Polycalmagite Coating Enables Long‐Term Alkaline Seawater Oxidation Over NiFe Layered Double Hydroxide

Abstract Renewable energy‐powered seawater electrolysis is a green and attractive technique for producing high‐purity hydrogen. However, severe chlorideions (Cl ⁻ ) and their derivatives tend to corrode anodic catalysts at ampere‐level current densities and hinder the application of seawater‐to‐H ₂ systems. Herein, a polycalmagite (PCM)‐coated NiFe layered double hydroxide is presented on Ni foam (NiFe LDH@PCM/NF) that exhibits exceptional stability in alkaline seawater. PCM not only acts as a conductive layer to reduce charge transfer resistance of the anodes but also as a polymer‐based protective layer to inhibit Cl ⁻ adsorption and stabilize metal ions oxidation due to its own anions and strong adhesion, thereby increasing activity and stability during alkaline seawater. Thus, NiFe LDH@PCM/NF only needs a low overpotential of 364 mV to reach up to 1000 mA cm ⁻² and maintains operation for 500 h without activity degradation. Moreover, a minimal amount of hypochlorite can be detected in electrolyte after a 500‐h stability test. This development affords a significant exploration in creating durable and efficient anodes, highlighting the importance of polymer coating toward anti‐corrosion in alkaline seawater oxidation.