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It is of great significance to develop highly active and cost-effective electrocatalysts for the oxygen evolution reaction and hydrogen evolution reaction in alkaline solution. Herein, we report an interface engineering strategy to fabricate 3D hierarchical CuCo2O4@CuCo2S4 heterostructure catalysts with efficient synergistic effects for water splitting. Owing to the special nano-architectures with abundant active interfaces, the as-prepared CuCo2O4@CuCo2S4 catalysts exhibit superior electrochemical activity and prominent electrochemical stability, with a small overpotential of 240 and 101 mV for oxygen and hydrogen evolution reactions to deliver a current density of 10 mA cm−2, respectively. Remarkably, the CuCo2O4@CuCo2S4 materials directly applied as both anode and cathode electrode demonstrate excellent water splitting performance, achieving 10 mA cm−2 at a low cell voltage of only 1.53 V, outperforming the integrated state-of-the-art RuO2||Pt/C couple (1.56 V). Moreover, density functional theory calculations suggest that the excellent overall water splitting property of CuCo2O4@CuCo2S4 is attributed to a large amount of hierarchical hetero-interfaces, giving rise to effective adsorption and cleavage of H2O molecules on the catalyst surface. This work represents a general strategy to exploit efficient and stable hybrid electrocatalysts for renewable energy applications by rational catalyst interface engineering.