It is increasingly important to synthesize a low-cost and high-efficiency bifunctional electrocatalyst for overall water splitting. Herein, a unique line-sphere layered superstructure Ag/CoO is prepared via a facile alternating electrodeposition method. Compared to electrocatalysts with CoO as the innermost layer, the Ag/CoO catalysts with Ag nanowires (NWs) as initial layer take more advantages of the low conductance for water splitting. Electrochemical tests reveal that the layered superstructure material with n+1 layers of Ag NWs and n layers of CoO (An+Cn) exhibits excellent catalytic activities and stabilities for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). In addition, when the catalyst consisting of 3 layers of Ag NWs and 2 layers of CoO (A3C2) used as a dual-function electrode, only a potential of 1.90 V is needed for current density of 10 mA cm(-2). Based on the kinetics and thermodynamic measurements of the catalytic processes, a reasonable catalytic mechanism of overall water splitting has been proposed for different electrocatalysts. The results show that the diffusion of hydrogen-containing species may be the rate-determining step. (c) 2019 Elsevier Ltd. All rights reserved.