High-Entropy Phosphide CrMnFeCoNiP Nanosheets as Bifunctional Electrocatalysts for Anion-Exchange Membrane Seawater Electrolyzers

Abstract Seawater electrolysis is an attractive route to large-scale hydrogen production, yet practical implementation is hindered by sluggish anodic kinetics, chloride-induced corrosion and catalyst deactivation, competing chlorine chemistry, and ion-transport limitations in alkaline anion exchange membrane (AEM) devices. Here, we report a high-entropy phosphide (HEP), CrMnFeCoNiP, as a stable bifunctional electrocatalyst for overall seawater splitting in alkaline AEM water electrolyzers (AEMWEs). Incorporation of five transition metals into a single crystalline phosphide lattice induces lattice distortion and charge redistribution, tuning intermediate adsorption to promote water dissociation and multi-electron transfer while suppressing Cl– adsorption. Consequently, CrMnFeCoNiP delivers ultra-low overpotentials of 146 mV for HER and 279 mV for OER at 100 mA cm−2 in 1 M KOH. In a single-cell AEMWE operated at 60 °C, a HEP||HEP configuration achieves low cell voltages of 1.82 V (alkaline saline) and 1.97 V (alkaline seawater) at 1 A cm−2, enabling energy efficiencies of ∼81 and ∼75% relative to the thermoneutral voltage (1.48 V), respectively. Moreover, the cell sustains stable operation for 400 h at 1 A cm−2 without noticeable degradation, highlighting long-term chloride tolerance. Overall, these results establish high-entropy phosphide electrocatalysts as a scalable, corrosion-resistant, and energy-efficient platform for hydrogen production from abundant natural saline resources.