Direct photoelectrochemical (PEC) water splitting is a promising solution for solar energy conversion; however, there is a pressing bottleneck to address the intrinsic charge transport for the enhancement of PEC performance. Herein, a versatile coupling strategy was developed to engineer atomically dispersed Ni-N4 sites coordinated with an axial direction oxygen atom (Ni-N4-O) incorporated between oxygen evolution cocatalyst (OEC) and semiconductor photoanode, boosting the photogenerated electron-hole separation and thus improving PEC activity. This state-of-the-art OEC/Ni-N4-O/BiVO4 photoanode exhibits a record high photocurrent density of 6.0 mA cm-2 at 1.23 V versus reversible hydrogen electrode (vs RHE), over approximately 3.97 times larger than that of BiVO4, achieving outstanding long-term photostability. From X-ray absorption fine structure analysis and density functional theory calculations, the enhanced PEC performance is attributed to the construction of single-atomic Ni-N4-O moiety in OEC/BiVO4, facilitating the holes transfer, decreasing the free energy barriers, and accelerating the reaction kinetics. This work enables us to develop an effective pathway to design and fabricate efficient and stable photoanodes for feasible PEC water splitting application.