Phosphate-functionalized amorphous NiMoO4 nano-armor on hematite: Robust ligand-anchoring engineering for efficient corrosion-resistant seawater splitting

Photoelectrochemical seawater splitting is promising for renewable hydrogen, yet severe chloride corrosion remains a roadblock. Although amorphous catalysts improve hematite (α-Fe2O3) photoanode activity, their defect-enabled functionality inherently accelerates structural degradation, exacerbating chloride-induced corrosion. Here, a synergistic dual-functional nano-armor is designed by anchoring phosphate (PO43−) to active sites on amorphous NiMoO4 (a-NiMoO4@PO43−), achieving dual activity-stability enhancement. Detailed physicochemical characterization and density functional theory (DFT) calculations show that the successful and stable anchoring of phosphate is highly dependent on the amorphous structural properties of a-NiMoO4. Its rich disordered coordination environment provides sufficient highly reactive sites, allowing PO43− to be firmly bound through strong coordination bonds, which is the key for the dual role of PO43− coordination. As a dynamic Cl− shield, PO43− coordinates unsaturated Ni sites, forming an anionic layer that resists Cl− via steric-electrostatic blocking. As an electronic modulator, PO43− triggers metal-to-ligand charge transfer at Ni sites, depleting electron density to optimize the intermediate adsorption of oxygen evolution reaction (OER) and reduce kinetic barriers. Simultaneously, this charge redistribution induces a built-in electric field that accelerates hole-selective transport. Benefiting from these dual effects, the Fe2O3/a-NiMoO4@PO43− achieves 4 mA cm−2 at 1.23 VRHE with exceptional stability in seawater. This work leverages the unique coordination flexibility of amorphous structures to construct a phosphate-coordinated bifunctional nano-armor on hematite photoanodes, which simultaneously enables efficient chloride exclusion and electronic structure optimization. The synergistic mechanism, rooted in strong phosphate anchoring on amorphous carriers, establishes a new design paradigm for photoelectrochemical systems that integrate high activity with extreme environmental stability, providing an efficient pathway toward corrosion-resistant seawater splitting.