Mesoporous cerium oxide decorated nickel-based metal–organic frameworks for diffusion-driven charge storage in symmetric aqueous supercapacitors

Abstract

Mesoporous cerium oxide (CeO2) decorated nickel-based metal–organic framework (Ni-MOF) composites were synthesised by varying the CeO2 : Ni-MOF weight ratios, using ratios of 1 : 8, 2 : 8 and 3 : 8, following the optimization process. The corresponding composites are denoted as NC1, NC2 and NC3, respectively. The structural, microstructural, and BET analysis confirmed the formation of mesoporous CeO2@Ni-MOF composites, which are beneficial for electrolyte ion diffusion and electrochemical accessibility. The synthesised composites are used as electrodes in the fabricated symmetric aqueous supercapacitor devices. The NC2 electrode showed a specific capacitance of 1004 F g−1 at a current density of 1 A g−1 in a three-electrode system. The improved electrochemical performance of NC2 is attributed to the enhanced active sites, which facilitates the charge-transfer and ion-transport processes. Kinetic analysis showed a predominantly diffusion-controlled charge-storage behaviour with improved faradaic redox participation. The estimated energy density of the NC2//NC2 symmetric supercapacitor is 21.66 Wh kg−1 with a power density of 699.7 W kg−1, showing 80.7% capacitance retention after 7000 charge–discharge cycles. The obtained results show that the electrochemical characteristics of MOF-based electrodes can be improved by the controlled incorporation of CeO2 into Ni-MOFs, which is a promising strategy for aqueous supercapacitors.