Green hydrogen, the most sustainable and eco-friendly form of hydrogen energy, stands at the forefront of the global energy transition. However, its production heavily depends on catalysts, currently dominated by expensive precious metals, which hinders its large-scale commercial utilization. In this respect, cobalt-based phosphides are promising alternatives given their excellent catalytic activity, low cost, and abundance. Particularly, the construction of Co₂P/CoP heterostructures is expected to yield even more efficient catalysts. However, critical challenges persist in the synthesis of Co₂P/CoP heterostructures, including atomic-level interface engineering, compositional homogeneity, and long-term operational stability. Encouragingly, metal–organic frameworks (MOFs), composed of metal centers and organic ligands, are promising precursors for constructing Co₂P/CoP based catalysts. During pyrolysis, MOFs with metal–nitrogen coordination tend to form Co–N_x and Co, whereas oxygen-coordinated MOFs preferentially generate CoO_x with the potential coformation of Co. Because the favorable thermodynamic conditions for the conversion of CoO_x to corresponding phosphides have been confirmed, employing oxygen-coordinated MOFs as precursors can enable the precise construction of well-defined Co₂P/CoP heterostructures via the preformation of Co/CoO_x, followed by phosphidation.

An oxygen-coordinated MOF was fabricated on nickel foam via potentiostatic electrochemical deposition, followed by a two-step process involving pyrolysis and subsequent phosphidation under a nitrogen atmosphere to obtain the target catalyst. Comprehensive structural characterization was conducted using X-ray diffraction, Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy to analyze the catalyst’s crystalline structure, morphology, and elemental composition. The electrochemical performance was systematically evaluated using a standard three-electrode system connected to an electrochemical workstation. The prepared catalyst served as the working electrode, with a graphite rod as the counter electrode and a saturated Ag/AgCl electrode as the reference. Measurements were performed under acidic, neutral, and alkaline conditions to assess the catalyst’s catalytic behaviors.

As revealed by the aforementioned characterizations, MOF crystals were successfully grown on the nickel foam and subsequently converted into well-dispersed Co₂P/CoP heterostructures through pyrolysis and phosphidation. The resulting catalyst exhibited exceptional catalytic performance in the hydrogen evolution reaction across all pH conditions (acidic, neutral, and alkaline), demonstrating an activity superior to that of commercial Pt/C at high current densities, along with favorable reaction kinetics. The catalyst maintained excellent stability under high-current operation after 20-hour continuous testing in different electrolytes. Electrochemical impedance spectroscopy revealed its low charge transfer resistance in all pH media, with particularly outstanding performance in acidic and alkaline solutions. These results highlight the catalyst’s exceptional activity, stability, and charge transfer properties across a wide pH range.

The comprehensive experiment conducted in this study developed a carbon-supported Co₂P/CoP heterostructure catalyst via a “Co/CoO preconstruction–post phosphidation” strategy using oxygen-coordinated Co-gallate MOF. It was designed as a leading-edge scientific endeavor, integrating MOF synthesis, electrochemical synthesis, Co₂P/CoP heterostructure construction, structural characterization, and electrocatalytic testing. This experiment not only equips students with technical mastery and research intelligence but also systematically cultivates their potential, fostering innovation in materials science.