Surface-derived phosphate layer on NiFe-layered double hydroxide realizes stable seawater oxidation at the current density of 1 A·cm⁻²

Seawater electrolysis, especially in coastlines, is widely considered as a sustainable way of making clean and high-purity H₂ from renewable energy; however, the practical viability is challenged severely by the limited anode durability resulting from side reactions of chlorine species. Herein, we report an effective Cl⁻ blocking barrier of NiFe-layer double hydroxide (NiFe-LDH) to harmful chlorine chemistry during alkaline seawater oxidation (ASO), a pre-formed surface-derived NiFe-phosphate (Pi) outer-layer. Specifically, the PO₄³⁻-enriched outer-layer is capable of physically and electrostatically inhibiting Cl⁻ adsorption, which protects active Ni³⁺ sites during ASO. The NiFe-LDH with the NiFe-Pi outer-layer (NiFe-LDH@NiFe-Pi) exhibits higher current densities (j) and lower overpotentials to afford 1 A·cm⁻² (η₁₀₀₀ of 370 mV versus η₁₀₀₀ of 420 mV) than the NiFe-LDH in 1 M KOH + seawater. Notably, the NiFe-LDH@NiFe-Pi also demonstrates longer-term electrochemical durability than NiFe-LDH, attaining 100-h duration at the j of 1 A·cm⁻². Additionally, the importance of surface-derived PO₄³⁻-enriched outer-layer in protecting the active centers, γ-NiOOH, is explained by ex situ characterizations and in situ electrochemical spectroscopic studies.