Three-Dimensional Core-Branch α-Fe2O3@NiO/Carbon Cloth Heterostructured Electrodes for Flexible Supercapacitors

Bifunctional properties of Ag/α-Fe2O3/rGO nanocomposite for supercapacitor and electrochemical nitrate sensing using tetradodecyl ammonium nitrate as ion-selective membrane

Noble metal nanoparticles incorporated in hybrid nanocomposites are considered as promising candidates for electrochemical applications owing to their physicochemical properties. In this work, we demonstrated the preparation of Fe2O3/rGO nanocomposite by hydrothermal method, followed by in situ Ag binding synthesis for the fabrication of hybrid nanocomposite (Ag/α-Fe2O3/rGO). The crystallographic structure of the hybrid nanocomposite is examined by X-ray diffraction (XRD) analysis which confirms the characteristics of Ag, Fe2O3, and rGO. The microscopic studies and energy-dispersive X-ray analysis (EDS) spectra confirmed the presence and formation of hybrid nanostructures. Raman analysis results further corroborate the formation of composite with significant D and G bands in Fe2O3/rGO and Ag/α-Fe2O3/rGO samples, which follow XRD results. Cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) studies were carried out to analyze the faradaic capacitor behavior. A specific capacitance of 209.09 F/g was observed by GCD studies for Ag/α-Fe2O3/rGO composites at a current density of 1 A/g, which exhibited good capacitance retention of 94% for 5000 cycles at 7 A/g. Furthermore, the Ag/α-Fe2O3/rGO electrode was used for the electrochemical detection of nitrate ions in soil by utilizing an ion-selective membrane over the surface of the Ag/α-Fe2O3/rGO electrode. The fabricated nanocomposite electrode showed a significant change in the peak current values with the concentration of nitrate in a linear range from 10 to 450 μM with the sensitivity to be calculated 1.426 μA μM-1 cm-2 and limit of detection (LOD) calculated to be 0.18 μM. The reproducibility and interference studies showed a promising result to be utilized for detecting nitrate ions in soil and in real-time applications.

Highly Stable Electrochemical Supercapacitor Performance of Self-Assembled Ferromagnetic Q-Carbon

Novel phase Q-carbon thin films exhibit some intriguing features and have been explored for various potential applications. Herein, we report the growth of different Q-carbon structures (i.e., filaments, clusters, and microdots) by varying the laser energy density from 0.5 to 1.0 J/cm² during pulsed laser annealing of amorphous diamond-like carbon films with different sp³-sp² carbon compositions. These unique nano- and microstructures of Q-carbon demonstrate exceptionally stable electrochemical performance by cyclic voltammetry, galvanostatic charging-discharging, and electrochemical impedance spectroscopy for energy applications. The temperature-dependent magnetic studies (magnetization vs magnetic field and temperature) reveal the ferromagnetic nature of the Q-carbon microdots. The saturation magnetization and coercive field values decrease from 132 to 14 emu/cc and 155 to 92 Oe by increasing the temperature from 2 to 300 K, respectively. The electrochemical performances of Q-carbon filament, cluster, and microdot thin-film supercapacitors were investigated by two-electrode configurations, and the highest areal specific capacitance of ∼156 mF/cm² was observed at a current density of 0.15 mA/cm² in the Q-carbon microdot thin film. The Q-carbon microdot electrodes demonstrate an exceptional capacitance retention performance of ∼97.2% and Coulombic efficiency of ∼96.5% after 3000 cycles due to their expectational reversibility in the charging-discharging process. The kinetic feature of the ion diffusion associated with the charge storage property is also investigated, and small changes in equivalent series resistance of ∼9.5% and contact resistance of ∼9.1% confirm outstanding stability with active charge kinetics during the stability test. A high areal power density of ∼5.84 W/cm² was obtained at an areal energy density of ∼0.058 W h/cm² for the Q-carbon microdot structure. The theoretical quantum capacitance was obtained at ∼400 mF/cm² by density functional theory calculation, which gives an idea about the overall capacitance value. The obtained areal specific capacitance, power density, and impressive long-term cyclic stability of Q-carbon thin-film microdot electrodes endorse substantial promise in high-performance supercapacitor applications.

Synthesis and Characterization of Ternary α-Fe2O3/NiO/rGO Composite for High-Performance Supercapacitors

Herein, pure α-Fe₂O₃, binary α-Fe₂O₃/NiO, and ternary α-Fe₂O₃/NiO/rGO composites were prepared by a hydrothermal method. The properties of the prepared materials were studied by powder X-ray diffraction, scanning electron microscopy, TEM, XPS, and Brunauer-Emmett-Teller techniques. The clusters of smaller α-Fe₂O₃ nanoparticles (∼30 nm) along with conducting NiO was freely covered by the rGO layer sheet, which offer a higher electrode-electrolyte interface for improved electrochemical performance. The ternary composite has shown a higher specific capacitance of 747 F g^-1@ a current density of 1 A g^-1 in a 6 M KOH solution, when compared with that of α-Fe₂O₃/rGO (610 F g^-1@1 A g^-1) and α-Fe₂O₃ (440 F g^-1@1 A g^-1) and the nanocomposite. Moreover, the ternary α-Fe₂O₃/NiO/rGO composite exhibited a 98% rate capability @ 10 A g^-1. The exceptional electrochemical performance of ternary composites has been recognized as a result of their well-designed unique architecture, which provides a large surface area and synergistic effects among all three constituents. The asymmetric supercapacitor (ASC) device was assembled using the ternary α-Fe₂O₃/NiO/rGO composite as the anode electrode (positive) material and activated carbon as the cathode (negative) material. The ASC device has an energy density of 35.38 W h kg^-1 at a power density of 558.6 W kg^-1 and retains a 94.52% capacitance after 5000 cycles at a 1 A g^-1 current density.

An Overview of Hierarchical Design of Textile-Based Sensor in Wearable Electronics

Smart textiles have recently aroused tremendous interests over the world because of their broad applications in wearable electronics, such as human healthcare, human motion detection, and intelligent robotics. Sensors are the primary components of wearable and flexible electronics, which convert various signals and external stimuli into electrical signals. While traditional electronic sensors based on rigid silicon wafers can hardly conformably attach on the human body, textile materials including fabrics, yarns, and fibers afford promising alternatives due to their characteristics including light weight, flexibility, and breathability. Of fundamental importance are the needs for fabrics simultaneously having high electrical and mechanical performance. This article focused on the hierarchical design of the textile-based flexible sensor from a structure point of view. We first reviewed the selection of newly developed functional materials for textile-based sensors, including metals, conductive polymers, carbon nanomaterials, and other two-dimensional (2D) materials. Then, the hierarchical structure design principles on different levels from microscale to macroscale were discussed in detail. Special emphasis was placed on the microstructure control of fibers, configurational engineering of yarn, and pattern design of fabrics. Finally, the remaining challenges toward industrialization and commercialization that exist to date were presented.

Flexible FeVOx porous nanorods on carbon cloth for long-life aqueous energy storage

We report the FeVO_x porous nanorods on carbon cloth as a novel cathode material for flexible aqueous energy storage. It exhibits excellent electrochemical properties and cycling stability in supercapacitors and zinc-ion batteries. Moreover, this work makes significant progress for developing high-performance electrodes and provides a foundation for future research.

Well-designed sophisticated structure of sandwich-like CC@NiAl-LDH@GO@NiCo-LDH material with unique advantages for high performance and practicality hybrid quasi-solid-state supercapacitors

A sandwich-like flexible architecture electrode material composed of NiAl-LDH nanoplates grown on carbon cloths (CC), coupled with GO interlayer and NiCo-LDH nanowire on the interlayer was successfully assembled via hydrothermal and chemical bath deposition (denoted as CC@NiAl-LDH@GO@NiCo-LDH). The promising combination of NiAl-LDH, graphene and NiCo-LDH forming a multilayer structure through electrostatic absorption and in-situ growth process which endow a high mass loading superiority and synergistic effect for supercapacitors. In addition, the interspace inside the sandwich-like architecture constructed by the graphene and the NiAl-LDH/ NiCo-LDH nano-flakes contribute to alleviate of the volume expansion during the cycling process and promote the diffusion rate of ions. The CC@NiAl-LDH@GO@NiCo-LDH material demonstrates excellent electrochemical performance which exhibit remarkable specific capacitance of 2359.8F·g^-1 (14.2F·cm^-2) at 1 A·g^-1 (6 mA·cm^-2) and outstanding capacitance retentions of 93.1% after 1500 cycles. Subsequently, the CC@NiAl-LDH@GO@NiCo-LDH material was used as cathode material to fabricate a hybrid quasi-solid-state supercapacitor that exhibits a high energy density of 52.0 Wh·kg^-1 at 796.7 W·kg^-1 and 38.4 Wh·kg^-1 at 12015 W·kg^-1, revealing its potential and viability for commercial applications. Furthermore, the hybrid quasi-solid-state supercapacitor can be applied under different extreme operating conditions such as bending, twisting, sour/alkali soaking, ice bathing, warm bathing, hammering and cutting conditions. It is predictable that the unique sandwich-like structure will be an extremely promising electrode material for high-performance supercapacitors.

Porous Fe2O3 Nanorods on Hierarchical Porous Biomass Carbon as Advanced Anode for High-Energy-Density Asymmetric Supercapacitors

In this study, a novel negative electrode material was prepared by aligning α-Fe₂O₃ nanorods on a hierarchical porous carbon (HPC) skeleton. The skeleton was derived from wheat flour by a facile hydrothermal route to enhance conductivity, improve surface properties, and achieve substantially good electrochemical performances. The α-Fe₂O₃/HPC electrode exhibits enhanced specific capacitance of 706 F g⁻¹, which is twice higher than that of α-Fe₂O₃. The advanced α-Fe₂O₃/HPC//PANI/HPC asymmetrical supercapacitor was built with an expanded voltage of 2.0 V in 1 M Li₂SO₄, possessing a specific capacitance of 212 F g⁻¹ at 1 A g⁻¹ and a maximum energy density of 117 Wh kg⁻¹ at 1.0 kW kg⁻¹, along with an excellent stability of 5.8% decay in capacitance after 5,000 cycles. This study affords a simple process to develop asymmetric supercapacitors, which exhibit high electrochemical performances and are applicable in next-generation energy storage devices, based on α-Fe₂O₃ hybrid materials.