Direct fabrication of mixed metal–organic frameworks (Ni/Cu-MOF) and C@NiCu₂O₄ onto Ni foam as binder-free high performance electrode for supercapacitors

Abstract

Cathodic electrodeposition has recently attracted considerable attention in the fabrication of porous materials such as metal–organic frameworks (MOFs) because of its advantages including controllability, simplicity, product continuously and mild synthesis conditions. Here, we report fabrication of the porous mixed metal oxides through in situ cathodic electrodeposition of pristine Ni,Cu-MOF onto Ni-foam followed by its calcination strategy. The as-prepared materials are characterized via structural and chemical analyses (i.e. XRD, FE-SEM, FT-IR, BET and TG-DSC) and also electrochemical tests (i.e. CV, GCD and EIS). The analyses results indicated that calcination of pristine MOF under at 650 °C in dry air atmosphere concludes mixed Ni/Cu-oxide with similar morphology to its MOF precursor. The results of electrochemical tests showed that the fabricated MOF-derived Ni/Cu-oxide electrode is capable to deliver a highest specific capacitance of 1525 F g⁻¹ at a current density of 1 A g⁻¹, which was higher than that of pristine Ni,Cu-MOF electrode (i.e. 942 F g⁻¹). Rate capability of MOF-derived oxide was as high as 69.1% which was higher than that of Ni,Cu-MOF electrode (57%) by increasing the current density to 20 times. Excellent capacity retentions of 92.35% and 87.25% were also observed after 9000 GCD cycling at the current load of 5 A g⁻¹, respectively, for Ni,Cu-MOF and Ni,Cu-oxide electrodes. Furthermore, MOF-derived oxide electrode displayed lower Rs and Rct values (0.36 Ω and 2.21 Ω, respectively) as compared with those of Ni,Cu-MOF electrode (i.e. 0.56 Ω and 2.54 Ω, respectively) verifying that the MOF-derived oxide electrode has high electrical conductivity and smaller kinetic barrier.