Fine Tuning of Torus-Shaped Mo-Doped Ni₂P Nanorings for Enhanced Seawater Electrolysis

Seawater, as one of nature's most plentiful resources, provides a virtually inexhaustible source for generating hydrogen via water electrolysis. Developing an efficient bifunctional electrocatalyst for direct seawater splitting is challenging but highly desirable. Herein, a donut-shaped Mo-doped Ni₂P nanoring electrocatalyst is developed, which is promising for direct overall seawater splitting. The optimized Mo_0.1Ni_1.9P catalyst shows low overpotentials and Tafel slopes in addition to high turnover frequencies, mass activities, and exchange current densities. The Mo_0.1Ni_1.9P||Mo_0.1Ni_1.9P couple-based electrolyzer requires a cell voltage of only 1.45 V in 1.0 m KOH and 1.47 V in untreated alkaline real seawater electrolysis at 10 mA cm^-2 current density. Industrially required current densities of 500 and 1000 mA cm^-2 are achieved at record low voltages of 1.81 and 1.86 V, respectively, at 25 °C and 1.77 and 1.82 V, respectively, at 75 °C for overall alkaline seawater splitting. The catalyst exhibited long-term stability at 400 mA cm^-2 during alkaline seawater electrolysis. The synergy between Mo ions with multiple oxidation states and Ni ions, and nanoring morphology play a crucial role in increasing active sites for enhanced seawater dissociation. This work highlights the potential of Mo-doped Ni₂P nanorings as unique catalysts for seawater electrolysis.