Fabrication of Nanoneedle and Nanograss Array of Ni-Mixed CuCo₂S₄@Ni-Foam as Binder-Free Electrode Materials for High-Performance Supercapacitor Applications

Abstract

The surface morphologies of the active electrode materials have a significant impact on the electrochemical performance of supercapacitors. The Ni-mixed CuCo2S4 materials were successfully prepared on Ni-Foam using the hydrothermal method followed by the sulfidation process. CuCo1.5Ni0.5S4 has a nanoneedle structure, whereas CuCo1.0Ni1.0S4 has a vertically aligned nanograss structure. Due to the high theoretical capacity and redox behavior of Ni, Co, and Cu elements, the low electronegativity of S atoms, favorable structural behavior, and low hydration sphere radius with high ionic mobility character of OH– ions, the resulting CuCo1.0Ni1.0S4 nanograss was used as a binder-free electrode for supercapacitor application. It has delivered outstanding specific capacity, rate capability, and cycle performance characteristics. The CuCo1.0Ni1.0S4 electrode produced a maximum specific capacity of 325.5 mA h/g at a current density of 1 A/g, while maintaining good rate capability. After 5000 cycles at 20 A/g, the CuCo1.0Ni1.0S4 electrode retains 86% of its initial capacity. Furthermore, the asymmetric supercapacitor device is made with CuCo1.0Ni1.0S4 as the positive electrode material and activated carbon as the negative electrode material. The fabricated ASC has a maximum energy density of 38.5 W h/kg at a power density of 356 W/kg. In summary, the CuCo1.0Ni1.0S4 electrode is a promising material for electrochemical energy storage and conversion applications.

MOF-Derived Nickel–Cobalt Sulfide Nanoflakes Wrapped Carbon Nanotubes for Hybrid Supercapacitors

“…Energy density and power density are important indexes for evaluating the performance of supercapacitor devices, and the Ragone plot of the CNTs/Ni–Co–S-3//AC HSC was shown in Figure g. The CNTs/Ni–Co–S-3//AC HSC possessed a high energy density of 42.15 Wh kg –1 at 852 W kg –1 power density and 16.54 Wh kg –1 at 8506 W kg –1 power density, which was superior in the bimetal sulfide-based supercapacitors reported previously, such as GRH-NiCo 2 S 4 //AC, NF/NiCo 2 S 4 //AC, Ni–Co–S 4 //AC, NiCo 2 S 4 //AC, NiCo 2 S 4 /CF//PCF, NiCo 2 S 4 /PRGO//AC, CuCo 1.0 Ni 1.0 S 4 //AC, NiCo 2 S 4 /BPC//BPC, and NC/Ni–Ni 3 S 4 /CNTs//CNTs Table compared the electrochemical performance of CNTs/Ni–Co–S-3 composites with previously reported electrode materials of similar composition as supercapacitor electrodes, which well indicated the favorable charge storage properties of the material obtained in this work.…”

Hierarchical MnO2/NiS–MnS with Rich Electro-Microstructural Physiognomies for Highly Efficient All-Solid-State Hybrid Supercapacitors

“…This signifies a linear increase in the required overpotential to execute the synchronized oxidation–reduction reactions at higher rate conditions . This clearly suggests the linearly facile surface/bulk (of MnO 2 /Ni–Mn–S) accessibility of the electroactive ions at elevated rate redox conditions, which is ascribed to the ion accessible microstructure of MnO 2 /Ni–Mn–S . Inset II in Figure A presents the extremely linear ( R 2 = 0.99) i (anodic, A g –1 ) vs (ν) 1/2 Randles–Sevcik (R–S) plot for MnO 2 /Ni–Mn–S, which demonstrates facile diffusibility of electrolyte ions into the material bulk at all scan rates. , The intercept of the R–S plot on the “ i ” axis represents the current contribution due to non-Faradaic chemical processes occurring majorly on the conductive carbon and sparingly on MnO 2 /Ni–Mn–S .…”

“…This can be ascribed to Ni 2+ /Ni 3+ , Ni 3+ /Ni 4+ , Mn 2+ /Mn 3+ , and Mn 3+ /Mn 4+ major redox oscillations during the oxidation–reduction processes in MnO 2 /Ni–Mn–S. The chemical reactions involved during the redox oscillations in the CV process are presented in reaction . ,, …”

“…This can be ascribed to Ni 2+ /Ni 3+ , Ni 3+ /Ni 4+ , Mn 2+ /Mn 3+ , and Mn 3+ /Mn 4+ major redox oscillations during the oxidation–reduction processes in MnO 2 /Ni–Mn–S. The chemical reactions involved during the redox oscillations in the CV process are presented in reaction . ,, .25ex2ex NiS + O H − ⇌ NiSOH + e − NiSOH + O H − ⇌ NiSO + e − + H 2 O MnS + O H − ⇌ MnSOH + e − MnSOH + O H − ⇌ MnSO + e − + H 2 O Mn O 2 + O H − ⇌ MnOOH + e − …”

“…In this regard, hybrid supercapacitor systems with redox-active positive electrodes and double-layer prompting negative electrodes show promising Ragone efficiency (high power and energy density) and have become ominously important in modern-day technologies . Fundamentally, the enhanced energy density of hybrid supercapacitor systems arises due to superior specific capacitance of the integrated redox-active (Faradaic) electrode material and the wide potential window of the device arising due to the assimilated non-Faradaic material, which shows the highest efficiency when operated in a broader potential window. , Further, the deliverable specific capacitance of the Faradaic electrode material in a hybrid supercapacitor can be enhanced by amending the number of redox reactions during the charging and discharging of the device. , In essence, the added number of redox-active metal ions and nonstoichiometric oxidation states of metal ions in the Faradaic electrode materials bring about supplementary redox oscillations and charge transfer during the operation of the device. , Further, intrinsically high conductivity of the electrode materials (Faradaic as well as non-Faradaic) facilitates lowly impeded charge transfer, which decreases the redox overpotential and improves the concerted efficiency of electrochemical processes. , In the overall context, transition multimetal (mostly first row) chalcogenides with chalcogen ion vacancy in the lattice offer rich distribution of redox-active metal ions and nonstoichiometric oxidation states of the corresponding metal ions. , Amongst, Ni and Mn-based oxides are the most efficient class of Faradaic electrode materials as they possess several inherent oxidation states and produce supplementary oxidation states during the redox processes. − In particular, Mn-based oxides produce supplementary oxidation states during the redox processes and are investigated as electrode materials, which can deliver high specific capacitance/capacity and Ragone efficiency. , However, the poor electronic conductivity of transition metal oxides at the ambient operating temperature is responsible for their subpar utilization in tangible hybrid systems . Research shows that transition metal sulfides possess labile sulfur and lattice S 2– vacancy, which fundamentally induce flexible conductivity and facile redox activity in the materials. ,, Perspectively, transition multimetal sulfides are considered as highly efficient electrode materials for supercapacitive energy storage in the hybrid systems. − In the overall context, it may be fundamentally proposed that transition multimetal sulfides would induce supplementary electronic conductivity and facilitate redox activity in transition metal oxide electrode materials in a heterotransition multimetal oxide/sulfide system.…”