In photoelectrochemical water decomposition field, it remains a key challenge to develop photoanodes with excellent charge separation and transfer, efficient solar collection and rapid surface reaction kinetics. Here, we report a new strongly coupled ternary hybrid system using a single atom as a "bridge" to achieve high efficiency water oxidation photoelectrochemical performance, by constructing a monoatomic transition metal tightly bound to the core-shell gap which formed by lamina g-C3N4 coating on the surface of porous carbon balls. Experimental results and density functional theory calculations show that the unique structure combines lots of beneficial features, that is efficient light trapping and photo generated charge separation, strong coupling effects, fast electron transport paths and improved surface reaction dynamics. Benefited from the ideal nanostructure, the photocurrent density reached 5.08 mA cm(-2) at 1.23 V and the IPCE value achieved 27.5% at 350 nm under AM 1.5 G illumination. This work has promoted a significant step of developing single-atom photoanodes with unique structure for solar water splitting, as well as the design of thermochemically stable catalysts. (C) 2019 Elsevier Inc. All rights reserved.