Cobalt–nickel sulfide nanosheets modified by nitrogen-doped porous reduced graphene oxide as high-conductivity cathode materials for supercapacitor

Tailoring vinegar residue-derived all-carbon electrodes for efficient electrocatalytic carbon dioxide reduction to formate through heteroatom doping and defect enrichment

Electrocatalytic carbon dioxide reduction (ECO2R) to formate is the most technically and economically feasible approach to achieve electrochemical CO2 value addition. Here, a few-layer graphene is prepared from vinegar residue. Then a series of heteroatom-doped vertical graphene electrodes (X-rGO, X=P/S/N/B/, NS/NP/NB, NSP/NSB/NPB/NSPB) are prepared. The NS-rGO has improved ECO2R to formate selectivity (Faraday Efficiency (FEHCOO-) = 78.7 %) thanks to the synergistic effect between N and S. Carbon quantum dots (CQDs) are introduced into the electrode, the doped heteroatoms are further removed by high-temperature to form the defects-rich electrode (NS-CQDs-rGO-1100), which has better catalytic performance (FEHCOO-=90 %, stability over 10 h) with electrochemical double layer capacitance of 12.5 mF cm-2. The intrinsic effect of heteroatom doping and defects on the ECO2R activity of the electrodes are explored by density functional theory calculation. This work broadens the field of preparation of graphene and opens the door to the development of cost-effective electrocatalysts for efficient ECO2R.

Citric acid-capped NiWO4/Bi2S3 and rGO-doped NiWO4/Bi2S3 nanoarchitectures for photocatalytic decontamination of emerging pollutants from the aqueous environment

Herein, we describe the successful synthesis of NiWO4/Bi2S3 and reduced graphene oxide (rGO-NiWO4/Bi2S3) nanocomposites through a simple green sol-gel approach. The fabricated composites were subsequently characterized by Fourier transform infrared (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), Energy Dispersive X-Ray Analysis (EDX) and ultraviolet-visible spectroscopy (UV-VIS) spectroscopic analyses. Dielectric properties were done by a precision impedance analyzer. Tanδ and dielectric constant for NiWO4/Bi2S3 and rGO-NiWO4/Bi2S3 were 1.811, 292818, and 0.2970, 344574, respectively, at 20 Hz. The photocatalytic performance of NiWO4/Bi2S3 and rGO-NiWO4/Bi2S3 was investigated against methylene blue and methyl orange dyes in an aqueous medium. NiWO4-Bi2S3 showed degradation of methylene blue 15.52% after 20 min, 21.8% after 30 min and 46.8% after 40 min. Similarly, for methyl orange dye it was 18.1% after 20 min, 54% after 30 min and 59.36% after 40 min. Compared to NiWO4/Bi2S3, rGO-NiWO4/Bi2S3 exhibited superior degradation efficiency of 7.5% (20 min), 25.24% (30 min) and 57.71% (40 min) for methylene blue, and 35.7% (20 min), 56.98% (30 min) and 72.42% (40 min) for methyl orange under sunlight. This enhancement in photocatalytic and dielectric properties might be attributed to the presence of graphene in rGO-NiWO4/Bi2S3 nanococomposite. Different factors such as effect of time, pH, dose of catalyst, concentration of dye were optimized and the reusability of superior catalyst rGO-NiWO4/Bi2S3 was also checked for four cycles. In conclusion, promising photocatalytic and dielectric properties of rGO-NiWO4/Bi2S3 suggest its potential applications in the photocatalytic degradation of organic pollutants and energy storage materials. This study provides a well-developed route to exploit metal sulphide/oxide nanocomposites in environmental remediation and energy storage devices.

Micro/Nano Energy Storage Devices Based on Composite Electrode Materials

It is vital to improve the electrochemical performance of negative materials for energy storage devices. The synergistic effect between the composites can improve the total performance. In this work, we prepare α-Fe2O3@MnO2 on carbon cloth through hydrothermal strategies and subsequent electrochemical deposition. The α-Fe2O3@MnO2 hybrid structure benefits electron transfer efficiency and avoids the rapid decay of capacitance caused by volume expansion. The specific capacitance of the as-obtained product is 615 mF cm−2 at 2 mA cm−2. Moreover, a flexible supercapacitor presents an energy density of 0.102 mWh cm−3 at 4.2 W cm−2. Bending tests of the device at different angles show excellent mechanical flexibility.

High Mass Loading Asymmetric Micro-supercapacitors with Ultrahigh Areal Energy and Power Density

High mass loading asymmetric micro-supercapacitors (MSCs) are key components for the development of high-performance energy and power supply systems. Here, a concept for achieving high mass loading electrodes is presented and applied to high mass loading micro-supercapacitors with ultrahigh areal energy and power density. The positive electrode is made from porous carbon with birnessite coverage and multiwalled carbon nanotubes (CNTs) as conducting additives (PIC-CNTs-MnO₂). The negative electrode is prepared from hierarchically porous active carbon mixed with CNTs (PICK-CNTs). Both positive and negative electrode materials are tailored to ensure a high content of macro- and mesopores. MSCs with an optimized mass loading of 13.9 mg·cm^-2 (maximum: 23.6 mg·cm^-2) provide an ultrahigh areal capacitance of 1.13 F·cm^-2 (volumetric capacitance: 22.6 F·cm^-3), an outstanding energy of 627.8 μWh·cm^-2, and a maximum power density of 64 mW·cm^-2. About 85% of the initial capacitance remained after 5000 cycles. Moreover, shunt and tandem device testing confirmed a high uniformity of these MSCs, meeting the requirements of adjustable output currents and voltages in microchips.

Realizing high performance flexible supercapacitors by electrode modification

It is well known that the structure of an electrode material seriously affects its electrochemical performance. In this study, we prepare hybrid structured NiCo₂S₄@PPy nanoarchitectures by a hydrothermal method and subsequent electrodeposition process. The specific capacitance of the obtained sample is 1733.23 C g⁻¹ at 1 A g⁻¹. The assembled asymmetric device presents an energy density of 59.59 W h kg⁻¹ at 1404.04 W kg⁻¹. The excellent electrochemical performance can be attributed to the synergistic effect between the high theoretical specific capacitance of the NiCo₂S₄ sheets and the superior cycling stability of the PPy film. The device also shows an outstanding mechanical flexibility at different bending angles.

We prepare hybrid structured NiCo₂S₄@PPy nanoarchitectures by a hydrothermal method and subsequent electrodeposition process. The assembled asymmetric device presents an energy density of 59.59 W h kg⁻¹ at 1404.04 W kg⁻¹.

Enhanced Supercapacitor Performance Using a Co3 O4 @Co3 S4 Nanocomposite on Reduced Graphene Oxide/Ni Foam Electrodes

To avoid an enormous energy crisis in the not-too-distant future, it be emergent to establish high-performance energy storage devices such as supercapacitors. For this purpose, a three-dimensional (3D) heterostructure of Co₃ O₄ and Co₃ S₄ on nickel foam (NF) that is covered by reduced graphene oxide (rGO) has been prepared by following a facile multistep method. At first, rGO nanosheets are deposited on NF under mild hydrothermal conditions to increase the surface area. Subsequently, nanowalls of cobalt oxide are electro-deposited on rGO/Ni foam by applying cyclic-voltammetry (CV) under optimized conditions. Finally, for the synthesis of Co₃ O₄ @Co₃ S₄ nanocomposite, the nanostructure of Co₃ S₄ was fabricated from Co₃ O₄ nanowalls on rGO/NF by following an ordinary hydrothermal process through the sulfurization for the electrochemical application. The samples are characterized by using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The obtained sample delivers a high capacitance of 13.34 F cm^-2 (5651.24 F g^-1 ) at a current density of 6 mA cm^-2 compared to the Co₃ O₄ /rGO/NF electrode with a capacitance of 3.06 F cm^-2 (1230.77 F g^-1 ) at the same current density. The proposed electrode illustrates the superior electrochemical performance such as excellent specific energy density of 85.68 W h Kg^-1 , specific power density of 6048.03 W kg^-1 and a superior cycling performance (86% after 1000 charge/discharge cycles at a scan rate of 5 mV s^-1 ). Finally, by using Co₃ O₄ @Co₃ S₄ /rGO/NF and the activated carbon-based electrode as positive and negative electrodes, respectively, an asymmetric supercapacitor (ASC) device was assembled. The fabricated ASC provides an appropriate specific capacitance of 79.15 mF cm^-2 at the applied current density of 1 mA cm^-2 , and delivered an energy density of 0.143 Wh kg^-1 at the power density of 5.42 W kg^-1 .