Impact of an Incompatible Atomic Nickel-Incorporated Metal–Organic Framework on Phase Evolution and Electrocatalytic Activity of Ni-Doped Cobalt Phosphide for the Hydrogen Evolution Reaction

The development of efficient, cost-effective, and durable electrocatalysts for sustainable hydrogen production is highly desirable, yet it has several challenges. Designing a metal–organic framework (MOF) as an exceptional precursor benefiting from its structural flexibility and permissible pore modulation is crucial for developing efficient metal-supported carbon electrocatalysts. Herein, we report a highly efficient bimetallic (Ni/Co–P) phosphide electrocatalyst, derived from a Ni-doped Co-based zeolitic imidazole framework (ZIF-67) precursor, for the hydrogen evolution reaction (HER). Ni doping modulates the pore structure and surface chemistry of ZIF-67 by increasing the (meso)pore size and the number of Ni sites selectively occupying the surfaces of ZIF-67 crystals. This occurs due to the incompatible coordination between the d8 configuration of Ni2+ (planar structure) and the three-dimensional structure of ZIF-67 (tetrahedral structure). Phase engineering of a post-converted phosphide was achieved using a Ni-doped ZIF-67 precursor, which facilitated effective phosphidation via enhanced diffusion of the reactant in the mesopore, thus forming a Ni-doped Co2P/CoP hybrid draped with a nitrogen-doped carbon (N–C), compared to undoped ZIF-67 that formed a metallic Co/Co2P hybrid. Ni-doped Co2P/CoP@N–C exhibited superior HER activity under alkaline conditions, requiring an overpotential of 161 mV to attain a current density of 10 mA cm–2 (η10) with a Tafel slope of 94 mV dec–1, compared to undoped Co2P/Co requiring η10 of 187 mV. The superior performance of Ni-doped Co2P/CoP@N–C is attributed to the synergistic effects of integrated (semiconducting)Co2P/(conducting)CoP, Ni-driven HER activity, and the N–C component with high nitrogen contents that offer abundant catalytically active sites, fast charge transport, and enhanced electronic conductivity. Our study thus provides insights into altering pore/surface properties of an MOF precursor as a strategy to fabricate MOF-derived metal salt@carbon-based catalysts for electrochemical water splitting.