Triphasic Ni₂P–Ni₁₂P₅–Ru with Amorphous Interface Engineering Promoted by Co Nano-Surface for Efficient Water Splitting

This research designs a triphasic Ni₂P–Ni₁₂P₅–Ru heterostructure with amorphous interface engineering strongly coupled by a cobalt nano-surface (Co@Ni_mP_n–Ru) to form a hierarchical 3D interconnected architecture. The Co@Ni_mP_n–Ru material promotes unique reactivities toward hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline media. The material delivers an overpotential of 30 mV for HER at 10 mA cm⁻² and 320 mV for OER at 50 mA cm⁻² in freshwater. The electrolyzer cell derived from Co@Ni_mP_n–Ru_(+,−) requires a small cell voltage of only 1.43 V in alkaline freshwater or 1.44 V in natural seawater to produce 10 mA cm⁻² at a working temperature of 80 °C, along with high performance retention after 76 h. The solar energy-powered electrolyzer system also shows a prospective solar-to-hydrogen conversion efficiency and sufficient durability, confirming its good potential for economic and sustainable hydrogen production. The results are ascribed to the synergistic effects by an exclusive combination of multi-phasic crystalline Ni₂P, Ni₁₂P₅, and Ru clusters in presence of amorphous phosphate interface attached onto cobalt nano-surface, thereby producing rich exposed active sites with optimized free energy and multi open channels for rapid charge transfer and ion diffusion to promote the reaction kinetics.