The Role of Transition Metal and Nitrogen in Metal–N–C Composites for Hydrogen Evolution Reaction at Universal pHs

For the first time, we demonstrated that transition metal and nitrogen codoped carbon nanocomposites synthesized by pyrolysis and heat treatment showed excellent catalytic activity toward hydrogen evolution reaction (HER) in both acidic and alkaline media. The overpotential at 10 mA cm^–2 was 235 mV in a 0.5 M H₂SO₄ solution at a catalyst loading of 0.765 mg cm^–2 for Co–N–C. In a 1 M KOH solution, the overpotential was only slightly increased by 35 mV. The high activity and excellent durability (negligible loss after 1000 cycles in both acidic and alkaline media) make this carbon-based catalyst a promising alternative to noble metals for HER. Electrochemical and density functional theory (DFT) calculation results suggested that transition metals and nitrogen played a critical role in activity enhancement. The active sites for HER might be associated with metal/N/C moieties, which have been also proposed as reaction centers for oxygen reduction reaction

Polymer-Embedded Fabrication of Co₂P Nanoparticles Encapsulated in N,P-Doped Graphene for Hydrogen Generation

We developed a method to engineer well-distributed dicobalt phosphide (Co₂P) nanoparticles encapsulated in N,P-doped graphene (Co₂P@NPG) as electrocatalysts for hydrogen evolution reaction (HER). We fabricated such nanostructure by the absorption of initiator and functional monomers, including acrylamide and phytic acid on graphene oxides, followed by UV-initiated polymerization, then by adsorption of cobalt ions and finally calcination to form N,P-doped graphene structures. Our experimental results show significantly enhanced performance for such engineered nanostructures due to the synergistic effect from nanoparticles encapsulation and nitrogen and phosphorus doping on graphene structures. The obtained Co₂P@NPG modified cathode exhibits small overpotentials of only −45 mV at 1 mA cm^–2, respectively, with a low Tafel slope of 58 mV dec^–1 and high exchange current density of 0.21 mA cm^–2 in 0.5 M H₂SO₄. In addition, encapsulation by N,P-doped graphene effectively prevent nanoparticle from corrosion, exhibiting nearly unfading catalytic performance after 30 h testing. This versatile method also opens a door for unprecedented design and fabrication of novel low-cost metal phosphide electrocatalysts encapsulated by graphene