Construction of advanced zeolitic imidazolate framework derived cobalt sulfide/MXene composites as high-performance electrodes for supercapacitors

The Ti3C2Tx with excellent conductivity is used in a novel cobalt-based ZIF-67/Ti3C2Tx composites, sulfide derivative (Co3S4/Ti3C2Tx) of which is then applied as an active supercapacitor material. The specific capacitance of ZIF-67/Ti3C2Tx is significantly higher than that of unmodified ZIF-67. The sulfide-containing derivatives of these compounds demonstrated pseudocapacitance. The specific capacitance of an electrode containing Co3S4/Ti3C2Tx as an active material is very high and equal to 602F/g at 1 A/g, which is 2.6 times higher than of a ZIF-67/Ti3C2Tx-containing electrode. The supercapacitor based on Co3S4/Ti3C2Tx maintained 81.6% of its original capacitance even at 10 A/g current density. Thus, the introduction of Ti3C2Tx into the ZIF-67 improves not only the electrical conductivity of the hybrid material but also its structural stability, which allows to act as support. An asymmetric Co3S4/Ti3C2Tx//AC supercapacitor (ASC) containing activated carbon (AC) as an anode showed a high energy density equal to 44.9 Wh/kg at 800.3 W/kg power density. This ASC also demonstrated high rate-performance (equal to 79.2%) and excellent cycling stability (with 88.3% capacitance retention and 99.23% Coulombic efficiency after 5000 cycles). The excellent electrochemical performance of our novel composite and conductivity, as well as the stability of its three-dimensional (3D) structure, make it a very promising material for energy storage applications.