Atomically dispersed Ni–N₄ species and Ni nanoparticles constructing N-doped porous carbon fibers for accelerating hydrogen evolution

Single-atom catalysis has aroused enormous attention due to the highly exposed active sites and nearly 100% atomic utilization. However, the relatively low metal atoms loading limits their catalytic activities. Herein, we report N-doped carbon fibers supported Ni single atoms and nanoparticles hybrid (Ni SA/NP-NCF-800) by the combined strategies comprising electrospinning, pyrolysis, and etching. The in-situ formed SiO₂ and Ni particles serve as the hard templates to create highly porous architecture throughout the entire fibers, enabling the Ni species to efficiently anchor on carbon matrix to generate a high single atoms loading of 1.83 wt%, as well as provide accessible channels for mass transport and electrolyte diffusion. The unique configuration endows the hybrid with outstanding hydrogen evolution performance along with the low overpotential and robust long-term durability in 1 M KOH. The synchrotron radiation analysis and density functional theory calculations experimentally and theoretically reveal the isolated Ni was coordinated with neighboring four N atoms, which could lead to the re-arranged electron structure of Ni nanoparticles. The synergistic effect of atomically dispersed Ni and nanoparticles leads to the significantly enhanced water adsorption/dissociation abilities and optimized H adsorption free energy in alkaline media, thus paving a new avenue to design single atoms based electrocatalysts.