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Designing the transition metal oxide-based electrode with hollow nanostructure is of great importance for high-performance supercapacitors. Here, the hollow NiO encapsulated in a nitrogen-doped carbon matrix (NiO/NC) is synthesized by using the precursor of Ni-based metal–organic complex based on the Kirkendall effect. With the same precursor, the hollow NC is obtained by removing the Ni element through an acid etching method. Density functional theory (DFT) calculations convince that both hollow NiO/NC and NC have high electrical conductivity and adsorption energy for OH^–, demonstrating their high practicability for supercapacitor applications. In a three-electrode system, the NiO/NC sample prepared under 700 °C displays a high specific capacitance (1026 F g⁻¹ at 1 A g⁻¹) and excellent cycle stability (80.2% capacity retention over 8000 cycles). Importantly, a high energy density of 40.2 Wh kg⁻¹ was …