Preparation of nickel/copper sulfides from metal-organic frameworks. Applications to energy storage in a symmetric supercapacitor and electrocatalytic methanol oxidation

A hybrid of nickel and copper sulfides was synthesized by using metal-organic frameworks. The prepared composite (Ni3S2/CuxS) was then mixed with multi-walled carbon nanotubes to form MWCNTs@Ni3S2/CuxS. Several methods were used for characterization of the prepared composite. Electrochemical studies showed a great improvement in capacitive properties of graphite foil (GF) when modified by MWCNTs@Ni3S2/CuxS. In a three-electrode system, the specific capacitance was estimated from galvanostatic charge-discharge experiments to be 1388.7 F g-1 at a current density of 1 A g-1 with cycling stability of - 100% (10,000 cycles). In two electrode system (symmetric supercapacitor, SSC), a wide working voltage range (2.4 V) was obtained in aqueous alkaline solution. Moreover, MWCNTs@Ni3S2/CuxS showed great electrocatalytic effect in methanol oxidation reaction (current density 346.7 mA cm-1 in methanol, 0.5 M). Chronoamperometric oxidation of methanol on MWCNT@Ni3S2/CuxS/GCE showed a current lose < 16% after 14,000 s (- 4 h). Chronopotentiometry at a constant current density (22.3 mA cm-2) showed a highly stable potential after 14,000 s (drift < 8%). The excellent capacitive and electrocatalytic properties of MWCNTs@Ni3S2/CuxS were attributed to deposition of metal sulfides on metal-organic frameworks which prevented their agglomeration, and effective synergy among Ni3S2, MOF-derived-CuxS and MWCNTs. (c) 2022 Elsevier B.V. All rights reserved.