Charge Self-Regulation of Metallic Heterostructure Ni 2 P@Co 9 S 8 for Alkaline Water Electrolysis with Ultralow Overpotential at Large Current Density.

Designing cost-effective alkaline water-splitting electrocatalysts is essential for large-scale hydrogen production. However, nonprecious catalysts face challenges in achieving high activity and durability at a large current density. An effective strategy for designing high-performance electrocatalysts is regulating the active electronic states near the Fermi-level, which can improve the intrinsic activity and increase the number of active sites. As a proof-of-concept, it proposes a one-step self-assembly approach to fabricate a novel metallic heterostructure based on nickel phosphide and cobalt sulfide (Ni 2 P@Co 9 S 8 ) composite. The charge transfer between active Ni sites of Ni 2 P and Co─Co bonds of Co 9 S 8 efficiently enhances the active electronic states of Ni sites, and consequently, Ni 2 P@Co 9 S 8 exhibits remarkably low overpotentials of 188 and 253 mV to reach the current density of 100 mA cm -2 for the hydrogen evolution reaction and oxygen evolution reaction, respectively. This leads to the Ni 2 P@Co 9 S 8 incorporated water electrolyzer possessing an ultralow cell voltage of 1.66 V@100 mA cm -2 with ≈100% retention over 100 h, surpassing the commercial Pt/C║RuO 2 catalyst (1.9 V@100 mA cm -2 ). This work provides a promising methodology to boost the activity of overall water splitting with ultralow overpotentials at large current density by shedding light on the charge self-regulation of metallic heterostructure.