Defect-engineered CuCo2S4@Bi2O3 p-n heterojunction with enhanced built-in electric field for high-performance hybrid supercapacitors

To address the critical challenge of insufficient energy density of supercapacitors, this work reports a defect-engineered p-n heterojunction electrode based on sulfur vacancy-rich CuCo 2 S 4 (CCSv) and Bi 2 O 3 . In detail, a hierarchical 3D porous CCSv@Bi 2 O 3 (CCSvB) heterostructure is constructed by precisely controlling the morphology, starting with CuCo-precursor nanoneedles, followed by sulfidation, NaBH 4 reduction and Bi 2 O 3 electrodeposition. Mott-Schottky analysis and UV–vis spectroscopy identify CCSv as a p-type semiconductor and Bi 2 O 3 as an n-type semiconductor. The formation of a p-n junction in CCSvB is confirmed by the inverted V-shape of its Mott-Schottky curve, which leads to an enhanced built-in electric field and an expanded space charge region at the heterointerface, as revealed by density functional theory (DFT) calculations. This electronic-structure optimization facilitates rapid charge transfer and enables a high capacitance of 6.22 F cm −2 (2392.3 F g −1 ) at 5 mA cm −2 (1.92 A g −1 ), with 88.9% capacitance retention after 7000 cycles. The assembled CuCo 2 S 4 //CCSvB hybrid supercapacitor delivers an energy density of 54.1 Wh kg −1 at 797.87 W kg −1 . In brief, this work proposes a viable strategy for developing electrode materials applicable to advanced supercapacitors through the combination of defect engineering and heterojunction construction.