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[Display omitted] • The Zn@Co 3 C functional layer is constructed in this work for the first time. • Co 3 C acts as a powerful oxygen evolution co-catalyst on BiVO 4 photoanodes. • Zn provides strong driving force for the migration of photogenerated holes. Currently, the sluggish charge transfer kinetics and water oxidation kinetics are still the bottlenecks faced by BiVO 4 photoanodes at present. Herein, an excellent Zn@Co 3 C functional layer is reported for the first time to tackle these problems of BiVO 4 photoanode. Zn@Co 3 C was prepared using a facile electrochemical method with 1,2-dimethylimidazole as a carbon source. In the BiVO 4 /Zn@Co 3 C photoanode, Co 3 C acts as a novel oxygen evolution co-catalyst to significantly enhance water oxidation kinetics. An electron depletion layer formed around Zn species provides a strong driving force for the migration of photogenerated holes from BiVO 4 to Co 3 C catalytic sites. Furthermore, the alternating distribution of Co 3 C and Zn species on the surface of BiVO 4 photoanodes increases the utilization efficiency of Co 3 C co-catalyst. The BiVO 4 /Zn@Co 3 C system constructed in this work not only demonstrates good photoelectrochemical performance in electrolytes (4.6 mA cm−2 at 1.23 V vs. RHE without any hole scavengers), but also enables water splitting in natural seawater. This work demonstrates a novel functional layer that simultaneously facilitates photogenerated carrier transfer and water oxidation kinetics, which holds great promise for constructing high-performance water oxidation systems in various photoanodes. [ABSTRACT FROM AUTHOR]