Synthesis and Supercapacitive Properties of Ni/Co-S Derived from MOF-74

Abstract

Supercapacitors have been considered as one of the most promising energy storage devices for developing renewable energy with increasing demands of energy and environmental protection. Binary transition metal sulfides have captured tremendous interests in the field of supercapacitors due to intrinsically high electrical conductivity and superior capacitive properties. In this work, MOF-74 with Ni, Co and different ratios of Ni/Co (2:3, 1:1, 3:2) are synthesized by a facile solvothermal method, and then adopted as templates to derive Ni3S4, Co3S4 and NiCo sulfides by a heat treatment and subsequently solvothermal sulphidation. Electrochemical measurements indicate that the obtained rod-like sulfides have excellent capacitance properties. Notably, Co3S4 exhibits a high specific capacitance of 1843 F g-1 at 1 A g-1, which decreases to 930 F g-1 at 20 A g-1 with a retention of circa 50%. While NiCo-S derived from NiCo-MOF-74 (Ni/Co=2:3) displays superior specific capacitance of 1910 F g-1 and 1160 F g-1 at 1 A g-1 and 20 A g-1, respectively, with a retention of above 60%. It shows that NiCo-S has higher specific capacitance and superior rate capability, which can be attributed to synergistic effects accompanying with the introduction of Ni.