Designing and constructing bifunctional electrocatalysts is vital for water splitting. Particularly, the rational interface engineering can effectively modify the active sites and promote the electronic transfer, leading to the improved splitting efficiency. Herein, free‐standing and defect‐rich heterogeneous MoS₂/NiS₂ nanosheets for overall water splitting are designed. The abundant heterogeneous interfaces in MoS₂/NiS₂ can not only provide rich electroactive sites but also facilitate the electron transfer, which further cooperate synergistically toward electrocatalytic reactions. Consequently, the optimal MoS₂/NiS₂ nanosheets show the enhanced electrocatalytic performances as bifunctional electrocatalysts for overall water splitting. This study may open up a new route for rationally constructing heterogeneous interfaces to maximize their electrochemical performances, which may help to accelerate the development of nonprecious electrocatalysts for overall water splitting.

Highlights Freestanding Mo-doped NiCoP nanosheets are designed as bifunctional electrocatalysts for overall water splitting. Remarkable electrocatalytic performances are achieved by Mo doping, where a low-water-splitting voltage of 1.61 V at 10 mA cm⁻² is obtained.

Strong chemical bonds between transition metal oxides and carbon materials which enable fast electron transfer kinetics are highly required in supercapacitor electrodes. Meanwhile, hollow transition metal oxide nanostructures have promising potential for advanced energy storage applications. Herein, an oxygen vacancy assisted hydroxyl modification method is proposed to encapsulate Mn₃O₄ hollow spheres with controlled shell numbers in reduced graphene oxide (Mn₃O₄–rGO). The strong bonds between Mn₃O₄ and graphene result in fast charge transport, uniform distribution, increased active sites and enhanced structural stability. Originating from the structural features, when these materials were evaluated as electrodes for supercapacitors, Mn₃O₄–rGO shows a high specific capacitance of 561.5 C g⁻¹ with good rate performance and excellent stability with 98% retention after 10 000 cycles. In order to widen the potential application of supercapacitors, asymmetric supercapacitors (ASCs) are assembled using Mn₃O₄–rGO as positive electrodes and active carbon as negative electrodes. The ASCs exhibit a high specific capacitance of 180.2 F g⁻¹, delivering a high energy density of 72.3 W h kg⁻¹ at a power density of 864 W kg⁻¹. This surface-confined strategy may pave a way for realizing strong chemical bonds between hollow oxides and carbon-based materials for high performance supercapacitors.