Experimental and theoretical exploration of nickel ion-implanted metal-organic frameworks (ZIF-67) as free-standing electrodes for hybrid supercapacitors

Abstract

Ion beam irradiation is a non-destructive method to tune the composition and morphology of nanoarchitectures. It is a promising tool owing to the creation of crystal defects such as dislocations and vacancies in addition to ion implantation. Due to the advantages of structural versatility, tunability of chemical composition and high theoretical capacity, Metal organic frameworks are considered as a potential class of electrode materials for supercapacitors. We have in situ grown ZIF-67, without binder on carbon cloth and modified the interface by implanting with Ni ions. Benefiting from the Ni+ ion implanted ZIF-67 (CC/Ni@ZIF67-4) as a binder-free positive electrode delivered an areal capacitance of 1010 mF cm−2 at 1 mA cm−2 with profound cyclic retention of 93.5%. The hybrid supercapacitor assembled with CC/Ni@ZIF-67-4//CC/O,N,S@AC composition delivered a maximum voltage window of 1.5 V, exhibited a specific capacitance of 68 F g−1 at a current density of 2 Ag-1 energy density, an energy density of 21.26 Wh kg−1 and power density of 13,500 W kg−1 as well as a remarkable electrochemical stability up to 10,000 (96.4% retention at 10 Ag-1). The density functional theory calculations show a change in the Fermi level after the inclusion of Ni+ ions supporting the experimental data.