Tailoring Mesopores on Ultrathin Hollow Carbon Nanoarchitecture with N₂O₂ Coordinated Ni Single-Atom Catalysts for Hydrogen Evolution

Single-atom catalysts (SACs) offer exceptional atomic utilization and catalytic efficiency, particularly in the hydrogen evolution reaction (HER), where effective mass transport and electronic structure control are critical. However, many SACs suffer from suboptimal hydrogen adsorption energies and limited synergy with the support matrix, which restrict their intrinsic activity and durability. Overcoming these limitations requires an integrated strategy that simultaneously optimizes both the atomic coordination environment and the support architecture. Here, we present a dual-template strategy for synthesizing ultrathin mesoporous hollow carbon (MHC) with tunable mesopores, which enhances ion transport and structural accessibility. Ni single atoms are stabilized within the MHC framework via a tailored N₂O₂ coordination environment, which fine-tunes the electronic structure of Ni and facilitates efficient hydrogen adsorption and HER kinetics. This coordination environment and the hierarchical porous framework collectively enhance HER activity, significantly reducing the overpotential to 68 mV at 10 mA cm^-2 and resulting in remarkable mass activity (5 A mg_Ni^-1 at 50 mV) and enhanced durability over 5000 cycles. Spectroscopic analyses and density functional theory calculations reveal that the N₂O₂ coordination fine-tunes the electronic structure of Ni, promoting efficient hydrogen adsorption and evolution. These findings highlight the synergistic effects of atomic-level Ni dispersion and tailored support, offering a robust strategy for fabricating single-atom electrocatalysts for sustainable hydrogen production.