Designed mesoporous hollow sphere architecture metal (Mn, Co, Ni) silicate: A potential electrode material for flexible all solid-state asymmetric supercapacitor

The high performance of a supercapacitor device relies largely on the nanoarchitectures scrupulous designed and electrode material used. In this work, by utilizing Stöber method-prepared SiO2 sphere as a template, porous hollow spherical nanostructured metal silicates (MnSi, CoSi and NiSi) were synthesized by a hydrothermal method. When MnSi, CoSi and NiSi were used as effective positive materials for asymmetric supercapacitor, they exhibited a battery-type redox behavior and a relatively high charge storage property (517.0, 452.8, 66.7 F g−1 at 0.5 A g−1) in an aqueous alkaline electrolyte. The excellent electrochemical performance is mainly based on the large surface area of metal silicates, and the porous hollow spherical structure facilitates fast electrolyte ions and electrons transportation. More importantly from the practical applications, three high capacity performance, flexible asymmetric solid-state supercapacitor devices were assembled by employing metal silicates as an effective positive electrode and activated carbon as negative material in PVA-KOH gel electrolyte. The MnSi//AC, CoSi//AC and NiSi//AC device showed an areal capacitance of 1048.3, 375.5 and 120.9 F cm−2, corresponding to a high energy density of 4.6, 2.6 and 0.93 mWh cm−3, respectively. The detailed formation mechanism and electrochemical mechanism of metal silicate is performed experimentally and theoretically. The results reveal that MnSi, CoSi and NiSi have a potential application in energy storage.