Engineering the Morphology and Microenvironment of a Graphene-Supported Co-N-C Single-Atom Electrocatalyst for...

Graphene-supported single-atom catalysts (SACs) are promising alternatives to precious metals for catalyzing the technologically important hydrogen evolution reaction (HER), but their performances are limited by the low intrinsic activity and insufficient mass transport. Herein, a highly HER-active graphene-supported Co-N-C SAC is reported with unique design features in the morphology of the substrate and the microenvironment of the single metal sites: i) the crumpled and scrolled morphology of the graphene substrate circumvents the issues encountered by stacked nanoplatelets, resulting in improved exposure of the electrode/electrolyte interfaces (≈10 times enhancement); ii) the in-plane holes in graphene preferentially orientate the Co atoms at the edge sites with low-coordinated Co-N₃ configuration that exhibits enhanced intrinsic activity (≈2.6 times enhancement compared to the conventional Co-N₄ moiety), as evidenced by detailed experiments and density functional theory calculations. As a result, this catalyst exhibits significantly improved HER activity with an overpotential (η) of merely 82 mV at 10 mA cm^-2 , a small Tafel slope of 59.0 mV dec^-1 and a turnover frequency of 0.81 s^-1 at η = 100 mV, ranking it among the best Co-N-C SACs.