Selenium-vacancy-engineered NiSe2-Vse@Ni-Co PBA heterojunctions with work-function-driven interfacial electron redistribution for asymmetric supercapacitors

A pretreatment method can simultaneously achieve the removal of the surface passivation layer and vacancy engineering. • The difference in work function drives electron injection, resulting in a redistribution of electrons at the interface. • A multi-scale evidence chain verified the vacancy construction and directional charge transfer in a closed-loop manner. • Ion-intercalation pseudocapacitive storage provides high capacitance, wide voltage window, and persistent ASC performance. Owing to sluggish kinetic processes, the development of high-energy-density supercapacitors still faces major challenges. Herein, a NiSe 2 -Vse@Ni-Co PBA heterojunction synthesized through a sodium borohydride (NaBH 4 ) pretreatment-assisted assembly strategy is reported. The novelty of this work lies in the fact that the NaBH 4 treatment simultaneously depassivates the NiSe 2 surface, introduces a high density of selenium vacancies, and weakens the electrostatic repulsion between NiSe 2 and negatively charged Ni-Co PBA, thereby facilitating closer interfacial contact. Electron paramagnetic resonance (EPR) measurements confirm the successful generation of selenium vacancies. Density functional theory (DFT) calculations further reveal a pronounced work-function difference between NiSe 2 and Ni-Co PBA, while selenium vacancies increase the d-orbital states near the Fermi level in NiSe 2 -Vse. Together, these factors favour directional electron donation from the vacancy-rich NiSe 2 side to the PBA side after interfacial contact. Combined with the XPS results, this interfacial electron redistribution is consistent with the partial reduction of Co species and the markedly improved charge-transfer behaviour. As a result, the optimised electrode delivers a high specific capacitance of 1631.14 F g −1 and retains 80.37% of its initial capacitance after 5000 cycles. The assembled asymmetric supercapacitor operates stably at 1.7 V, achieving an energy density of 52.19 Wh kg −1 at a power density of 739.64 W kg −1 , and maintains 78.71% of its initial capacitance after 5500 cycles. This work shows that a simple pretreatment step can integrate surface depassivation, vacancy engineering, and work-function-driven interfacial electron redistribution into a single heterojunction system, offering a practical route to high-performance supercapacitor electrodes. Download: Download high-res image (189KB) Download: Download full-size image