High energy density supercapacitor electrode materials based on mixed metal MOF and its derived C@bimetal hydroxide embedded onto porous support

Abstract

In the recent years, metal-organic frameworks (MOFs) and their derived mixed metal hydroxides/oxides structures have emerged as an engrossing category of functional materials with some unique properties such as high porosity and high specific surface area for energy storage applications. Here, a cathodic electrodeposition strategy was utilized to prepare a bimetallic NiCo metal-organic framework (NiCo-MOF) with flower-like morphology consisting of nanopetals onto Ni foam (NF) as free-standing electrode. Structural characterization revealed that Ni2+ and Co2+ metal ions are uniformly distributed on the deposited films on the nickel foam. Post-chemical treatment of NiCo-MOF/Ni foam electrode under basic condition (i.e. 4 M KOH) was concluded carbon coated hierarchical mixed hydroxide (i.e. C@Ni1-xCox(OH)2) structures onto Ni-foam with similar morphology as its pristine binary MOF. Both ready-to-use fabricated electrodes were characterized with various techniques of X-ray diffraction (XRD), Fourier-transform infrared (FT-IR), Field-emission scanning electron microscope (FE-SEM), Energy dispersive X-ray analysis (EDAX), Energy dispersive spectroscopy (EDS) mapping and Thermogravimetric-differential scanning calorimetry (TG-DSC). Supercapacitive behaviors of pristine NiCo-MOF/NF and its derived C@NiCo-hydroxide/NF electrodes were also measured using cyclic voltammetry (CV), galvanostatic charge/discharge, and electrochemical impedance spectroscopy (EIS) measurements in 2 M KOH as electrolyte. The C@NiCo-hydroxide/NF electrode exhibited better performance as compared to pristine sacrificial binary metallic MOF electrode, which was 1825 F g–1 at a discharge current density of 1 A g–1 which still preserved 66.5% of its initial capacitance even at a high-rate load of 15 A g–1. Additionally, the C@NiCo-hydroxide/NF showed 87.6% of its capacitance at the end of 8000th cycle.