Charge Self‐Regulation of Metallic Heterostructure Ni2P@Co9S8 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 (Ni2 P@Co9 S8 ) composite. The charge transfer between active Ni sites of Ni2 P and Co─Co bonds of Co9 S8 efficiently enhances the active electronic states of Ni sites, and consequently, Ni2 P@Co9 S8 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 Ni2 P@Co9 S8 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║RuO2 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.