Se-doped cobalt-nickel sulfide hollow nanospheres with heterostructure and engineered defects as high-performance electrode for supercapacitors

Porous structures with heterogeneous interfaces and defects are an important way to enhance electrochemically active sites and facilitate electron transfer, while also improving the permeability of the electrolyte and the rate of ion transport. In this study, Se-doped cobalt-nickel sulfide (Se-CoNi2S4) hollow nanospheres with heterostructure and defects were prepared from CoNi metal-organic framework (MOF) as substrate by sequential sulfidation and selenization treatments. Notably, the hollow structure not only offers additional ion transport channels to promote rapid transfer of ions in the electrolyte but also provides an increased number of electrochemically active sites. The morphology and electrochemical performance of Se-CoNi2S4 nanospheres with different levels of Se doping were compared. From the results, Se doping not only enhances the conductivity of CoNi2S4 but also increases its charge storage capacity. As an electrode material, the synthesized Se-CoNi2S4 composite that was synthesized demonstrated a notable specific capacitance of 1260 F g(-1) at 1 A g(-1). Additionally, when Se-CoNi2S4 was utilized as the anode and activated carbon served as the cathode in an asymmetric supercapacitor, it achieved an energy density of 44.6 Wh kg(-1) at a power density of 827 W kg(-1). After undergoing 10,000 cycles, this device demonstrated exceptional cycling stability, retaining 80.2 % of its initial capacitance. Therefore, the synthesized electrode material Se-CoNi2S4 has significant potential for energy storage applications.