Metal-Organic Framework derived α-MnS MWCNT composite as a promising pseudocapacitive material in a flexible quasi-solid state asymmetric supercapacitor device

Abstract

The low conductivity of traditionally used pseudocapacitive materials like transition metal oxides has forced researchers to look for alternative materials. Transition metal sulfides are being investigated as viable alternative materials which have shown promising results. In this work, α-MnS MWCNT composite is selected as the active material for supercapacitor application. α-MnS has better conductivity than many transition metal oxides but has an extremely low specific surface area (10.5 m2 g-1), which reduces its specific capacitance. Metal-organic framework (MOF) derived materials are known to possess higher specific surface area and favorable pore size distribution. Herein, α-MnS MWCNT composite is synthesized via two routes: conventional solvothermal technique and MOF route and their performance is compared. It is proved that α-MnS MWCNT composite synthesized through the MOF route shows a favorable porous structure and better performance than the composite synthesized through the conventional route. It shows a specific surface area of 47.6 m2 g-1 and a specific capacitance of 546.3 F g-1 at 1 A g-1 with a mass loading of 1.5 mg cm-2 in 3 M KOH under the 3-electrode configuration. A flexible quasi-solid state asymmetric supercapacitor device is fabricated with MOF derived α-MnS MWCNT as the positive electrode material and the device achieved 1.4 V, showed a specific capacitance of 82.5 F g-1 at 1 A g-1 and a capacitance retention of 90.1% after 5000 cycles at 10 A g-1. The results clearly indicate that transition metal sulfides like MOF–derived α-MnS can be a viable alternative to traditional materials like transition metal oxides. The assembled device has the potential to power flexible, wearable electronics.