Electrode surface wettability is critically important for heterogeneous electrochemical reactions taking place in aqueous and nonaqueous media. Herein, electrochemically inert g-C 3 N 4 (GCN) is successfully demonstrated to significantly enhance water oxidation by constructing a superhydrophilic catalyst surface and promoting substantial exposure of active sites. As a proof-of-concept application, superhydrophilic GCN/Ni(OH) 2 (GCNN) hybrids with monodispersed Ni(OH) 2 nanoplates strongly anchored on GCN are synthesized for enhanced water oxidation catalysis. Owing to the superhydrophilicity of functionalized GCN, the surface wettability of GCNN (contact angle 0°) is substantially improved as compared with bare Ni(OH) 2 (contact angle 21°). Besides, GCN nanosheets can effectively suppress Ni(OH) 2 aggregation to help expose more active sites. Benefiting from the well-defined catalyst surface, the optimal GCNN hybrid shows significantly enhanced electrochemical performance over bare Ni(OH) 2 nanosheets, although GCN is electrochemically inert. In addition, similar catalytic performance promotion resulting from wettability improvement induced by incorporation of hydrophilic GCN is also successfully demonstrated on Co(OH) 2 . The present results demonstrate that, in addition to developing new catalysts, building efficient surface chemistry is also vital to achieve extraordinary water oxidation performance.