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Although single-atom catalysts (SACs) have been at the vanguard of energy conversion research, the selection of suitable substrates and single-atom specification permits remains ambiguous. Herein, we fabricated Co-g-C3N4/rGO SACs (Co-CNG) by coupling the suitable single-atom Co with a promising substrate of g-C3N4/rGO. Remarkably, Co-CNG exhibits even comparable HER performance (10 mA cm–2 at ∼47 mV) with commercially available Pt/C (10 mA cm–2 at ∼48 mV) and outperformed non-noble transition-metal SACs under alkaline conditions since its mass activity is about 4 times that of Pt/C with the long-term durability of 500 h. Athena fitting of Co-CNG was conducted, revealing its two types of coordination structure, including 20% of Co-N and 80% of Co-3N. Notably, the Co-N coordination structure is responsible for boosting HER due to its downshift d-band center, unique electronic structures, and low free energy barriers based on density functional theory. This study not only reveals that Co-CNG shows HER performance due to its unique SACs coordination of Co-N but also proves a way for catalyst optimization by specifically coordination engineering for particular applications.
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