High-Performance 3D Nanostructured Silver Electrode for Micro-Supercapacitor Application

In the current energy crisis scenario, the development of renewable energy forms such as energy storage systems among the supercapacitors is an urgent need as a tool for environmental protection against increasing pollution. In this work, we have designed a novel 3D nanostructured silver electrode through an antireplica/replica template-assisted procedure. The chemical surface and electrochemical properties of this novel 3D electrode have been studied in a 5 M KOH electrolyte. Microstructural characterization and compositional analysis were studied by SEM, energy-dispersive X-ray spectroscopy, XRD technique, and Kripton adsorption at -198 °C, together with cyclic voltammetry and galvanostatic charge-discharge cycling measurements, Coulombic efficiency, cycle stability, and their leakage current drops, in addition to the self-discharge and electrochromoactive behavior, were performed to fully characterize the 3D nanostructured electrode. Large areal capacitance value of 0.5 F/cm2 and Coulombic efficiency of 97.5% are obtained at a current density of 6.4 mA/cm2 for a voltage window of 1.2 V (between -0.5 and 0.8 V). The 3D nanostructured silver electrode exhibits excellent capacitance retention (95%) during more than 2600 cycles, indicating a good cyclic stability. Additionally, the electrode delivers a high energy density of around 385.87 μWh/cm2 and a power density value of 3.82 μW/cm2 and also displays an electrochromoactive behavior. These experimental results strongly support that this versatile combined fabrication procedure is a suitable strategy for improving the electrochemical performances of 3D nanostructured silver electrodes for applications as micro-supercapacitors or in electrochemical devices.

Simultaneous Electrodeposition of Ternary Metal Oxide Nanocomposites for High-Efficiency Supercapacitor Applications

Complex oxides and hydroxides of Ni, Co, and Mn from a precursor mixture were electrochemically deposited on both a cathode and an anode. On the Ni foam cathode, the complex metal hydroxides precipitated as nanolayers at -0.9 V. Simultaneously, the metal ions were oxidized and deposited as blocks on the Ni foam anode. While the concentrations of Ni(NO₃)₂ and Mn(NO₃)₂ were constant (80 mM for Ni²⁺ and 40 mM for Mn²⁺, respectively), the concentration of Co(NO₃)₂ was varied from 20 to 120 mM, which affected the morphology and electrochemical properties of the electrode: a Co:Ni:Mn molar ratio resulted in the highest specific capacitance (at a scan rate of 5 mV s^-1, 1800 F g^-1 for the cathode material and 720 F g^-1 for the anode material). This cathode material was assembled into symmetric supercapacitors, which demonstrated an excellent energy density of 39 Wh kg^-1 at a power density of 1300 W kg^-1 and a high capacitance retention of 90% after 3000 charge/discharge cycles. This high electrochemical performance was attributed to the optimized ratio of metal oxides, and this simple preparation strategy can be applied to other nanocomposites of complex metal oxides/hydroxides with desired characteristics for various applications.

Engineering triangular bimetallic metal-organic-frameworks derived hierarchical zinc-nickel-cobalt oxide nanosheet arrays@reduced graphene oxide-Ni foam as a binder-free electrode for ultra-high rate performance supercapacitors and methanol electro-oxidation

The rigorous fabrication of electrode materials using upper-ranked porous precursor especially metal organic frameworks (MOFs) are challenging but appealing task to procure electrochemical energy storage and conversion system with altitudinous performance. Herein, we replenish the rational construction of atypical electrode of hollow Zn-Ni-Co-oxide (ZNCO) nanosheet arrays onto rGO garnished Ni foam (rGO/NF) via two step solution based method. Firstly, 2D Zn-Co-MOFs derived nanoleave arrays are prepared by co-precipitation method. Next, hollow and porous ZNCO nanostructure from 2D solid nanoleave arrays are achieved by ion-exchange and etching process conjoined with post annealing treatment. The as-fabricated hierarchical ZNCO nanosheet arrays offer large numbers of electroactive sites with short ion-diffusion pathways, reflecting the outstanding electrochemical performance in-terms of excellent specific capacity (267 mAh g^-1) ultra-high rate capability (83.82% at 50 A/g) and long-term cycling life (~90.16%) in three electrode configuration for supercapacitor (SCs). Moreover, the hollow and porous ZNCO nanostructure responds as immensely active and substantial electrocatalyst for methanol oxidation with lowest onset potential of 0.27 V. To demonstrate the practicability, hybrid supercapacitor (HSC) device is constructed using ZNCO@rGO-NF nanostructure as positive and rGO decorated MOF derived porous carbon (rGO-MDPC) as negative electrode. The as-assembled ZNCO//rGO-MDPC ASC device delivers higher energy density of 61.25 Wh kg^-1 at the power density of 750 W kg^-1 with long-term cyclic stability (<6% to its initial specific capacity value) after 6000 cycles.

Growth of bimodal NiCo2O4·MnO2 nanorods in situ on carbon fiber paper synergistically affects their electrochemical properties

Bimodal NiCo₂O₄·MnO₂ (NCM) nanorods were grown on carbon fiber paper (CFP) using a hydrothermal process.

Single-Crystal α-Fe2O3 with Engineered Exposed (001) Facet for High-Rate, Long-Cycle-Life Lithium-Ion Battery Anode

Designing electrode materials with engineered exposed facets provides a novel strategy to improve their electrochemical properties. However, the controllability of the exposed facet remains a daunting challenge, and a deep understanding of the correlation between exposed facet and Li⁺-transfer behavior has been rarely reported. In this work, single-crystal α-Fe₂O₃ hexagonal nanosheets with an exposed (001) facet are prepared with the assistance of aluminum ions through a one-step hydrothermal process, and structural characterizations reveal an Al³⁺-concentration-dependent-growth mechanism for the α-Fe₂O₃ nanosheets. Furthermore, such α-Fe₂O₃ nanosheets, when used as lithium-ion battery anodes, exhibit high specific capacity (1261.3 mAh g^-1 at 200 mA g^-1), high rate capability (with a reversible capacity of approximately 605 mAh g^-1 at 10 A g^-1), and excellent cyclic stability (with a capacity of over 900 mAh g^-1 during 500 cycles). The superior electrochemical performance of α-Fe₂O₃ nanosheets is attributed to the pseudocapacitive behavior, Al-doping in the α-Fe₂O₃ structure, and improved Li⁺-transfer property across the (001) facet, as elucidated by first-principles calculations based on density functional theory. These results reveal the underlying mechanism of Li⁺ transfer across different facets and thus provide insights into the understanding of the excellent electrochemical performance.

Facile Synthesis of Mesoporous Carbon Spheres Using 3D Cubic Fe-KIT-6 by CVD Technique for the Application of Active Electrode Materials in Supercapacitors

Mesoporous carbon spheres (MCS-750, MCS-800, MCS-850, MCS-900, and MCS-950) have been synthesized by a facile strategy with low temperature and rapid chemical vapor deposition technique. The synthesized MCS possess relatively large surface area (570-670 m² g^-1), good graphitization, remarkable porosity, and redox functionalities on the surface of the synthesized MCS. Combination of these structural and surface properties of the synthesized MCS as an electrode material (MCS-850) showed an excellent charge-storage capacity with a specific capacitance of 338 F/g at 1 mV/s, 217 F/g at 0.5 A/g. MCS-850 shows long-term cycling stability with capacitive retention of more than 96% after 2000 cycles in 6 M KOH electrolyte. In addition, a fabricated two-electrode symmetric cell obtained 86% retention after 2000 cycles. The two-electrode symmetric device exhibited a specific capacitance of 63 F/g at 5 mV/s with an energy density of 7.1 Wh/kg.

Vertically-oriented graphene nanosheet as nano-bridge for pseudocapacitive electrode with ultrahigh electrochemical stability

A hierarchical structure consisting of Ni-Co hydroxide nanosheets (NCHN) electrodeposited on vertically-oriented graphene nanosheets (GN) on carbon cloth (CC) was fabricated for high-performance pseudocapacitive electrodes. NCHN was uniformly distributed on GN, forming a sheet-on-sheet hierarchical structure. Such NCHN/GN/CC hybrid electrodes exhibit high capacitance and ultrahigh electrochemical-stability that structure and electrochemical properties of hybrid electrodes are not affected by the cyclic low-rate scanning (at 5 mV s-1 even over 1000 cycles). GN vertically grown on CC is used as nano-bridge between NCHN active materials and CC current collector, which effectively facilitates ion/charge transfer between the electrolyte and electrode, consequently leading to the ultrahigh electrochemical-stability of hybrid electrodes. To assess functional behavior, two-terminal flexible asymmetric supercapacitor devices with NCHN/GN/CC as positive electrode and GN/CC as negative electrode were assembled and electrochemically treated to demonstrate the ultrahigh electrochemical stability.