Ni(OH)₂/NiSe Nanoparticles Supported on Carbon Microspheres for Long‐Life and High‐Performance Asymmetric Supercapacitors

Abstract

The application of Ni-MOF in supercapacitors has received widespread attention, but its poor conductivity and bad stability hinder its application. Therefore, Ni-MOF derived CMs@Ni(OH) 2 /NiSe with a core-shell structure was designed.Here, carbon microspheres (CMs) were explored as the conductive substrate to enhance the stability and in situ prepared Ni-MOF was anchored on the surface of CMs. Then, alkalitreatment and selenylation were carried out on CMs@NiÀ MOF to improve stability and conductivity. The obtained core-shell nanostructure material possesses a high contact area, excellent synergistic effect and can provide more reactive active sites. The prepared CMs@Ni(OH) 2 /NiSe shows a higher specific capacitance (2106 F g À 1 ) and excellent cycling performance with a capacitance retention of 95 % after 30000 cycles. Furthermore, the assembled CMs@Ni(OH) 2 /NiSe//AC device delivers a high energy density of 70.84 Wh kg À 1 at the power density of 756.8 W kg À 1 and maintains 100 % of the initial capacitance after 40000 cycles.

Phase-Dependent Energy Storage Performance of the NixSey Polymorphs for Supercapacitor-Battery Hybrid Devices

“…Transition-metal chalcogenides (most often, metal sulfides/selenides/tellurides), notably in the form of nanostructures, have been a hot topic of study in recent years due to their unique multiple oxidation states, reversible Faradaic reactions, and high theoretical specific capacities. − For the elements of the oxygen family, the metallic characteristic increases whereas electronegativity and ionization energy decrease while progressing down the group. , Thus, although transition-metal selenides (TMSe) have physicochemical properties similar to those of metal oxides and sulfides, they exhibit better metallic properties (e.g., a higher electrical conductivity) and so can be used in advanced energy storage devices. The high electrical conductivity of TMSe results from the covalent character of the metal–selenium connections, which is substantially different from the ionic nature of the metal–oxygen bonds in metal oxides. , This property stems from the selenium ions that have d-orbitals of accessible energy, whereas oxygen and sulfur anions do not, and this leads to wide valence bands and, hence, narrower band gaps compared to those of the corresponding oxides/sulfides .…”