▎ 摘　　要

Developing an efficient electrocatalyst with the desired architectural and electronic properties is paramount for water splitting. Here, we apply theoretical calculations to experimental studies to uncover the influence of structure engineering (quantizing and support coupling) on the HER catalytic activity and develop an optimized C3N4 hybrid catalyst. Impressively, the desired atom-thick C3N4 quantum dots on graphene (CNQDs@G) has been successfully obtained and achieves HER performance with low overpotential (110 mV) at 10 mA cm(-2), large exchange current density (3.67 mu A cm(-2)), and long-term durability, better than those of many metallic catalysts. In combination with the experimental results, DFT calculations also disclose that the HER catalytic activity of CNQD5@G originates from bisynergetic effects: one between G and CNQDs and another between the edge and the molecular sieve structure.