Asymmetric supercapacitor based on novel coal fly ash derived metal–organic frameworks as positive electrode and its derived carbon as negative electrode

Please read abstract in the article.The South African Department of Science and Innovation (DSI) for research activities under the HySA Infrastructure, South African Research Chairs Initiatives (SARChI) of the Department of Science and Technology and the National Research Foundation (NRF) of South Africa.https://link.springer.com/journal/10800hj2023Physic

A study of Co-Mn phosphate supported with graphene foam as promising electrode materials for future electrochemical capacitors

Please read abstract in the article.The South African Research Chairs Initiative (SARChI) of the Department of Science and Technology and the National Research Foundation (NRF) of South Africa.http://wileyonlinelibrary.com/journal/erhj2023Physic

Effect of growth-time on electrochemical performance of birnessite manganese oxide (δ-MnO2) as electrodes for supercapacitors : an insight into neutral aqueous electrolytes

Please read abstract in the article.South African Research Chairs Initiative of the Department of Science and Technology; National Research Foundation (NRF) of South Africa and the University of Pretoria.https://www.elsevier.com/locate/est2022-03-02hj2022Physic

Fabrication and characterization of clay-polyethylene composite opted for shielding of ionizing radiation

This study fabricated and characterized a self-sustaining hydrogenous content claypolyethylene composite opted for ionizing radiation shielding. Composites designated A–G were fabricated each containing 0–30 wt% of recycled low density polyethylene (LDPE), respectively. To know the effects of the incorporated LDPE on the morphology, microstructural, compressive strength, thermal property and displacement effect on the vital elements were studied using scanning electron microscopy (SEM), X-ray diffractometry (XRD), universal mechanical testing machine, differential thermal analysis (DTA), Rutherford backscattering (RBS) technique and particle induced X-ray emission (PIXE), respectively. The bulk densities of the clay composites ranged between 1.341 and 2.030 g/cm3. The samples’ XRD analysis revealed similar patterns, with a sharp and prominent peak at angle 2 equals ~26.11 , which matched with card number 16-0606 of the Joint Committee on Powder Diffraction Standards (JCPDS) that represents Aluminum Silicate Hydroxide (Al2Si2O5(OH)4), a basic formula for Kaolin clay. The compressive strength ranged between 2.52 and 5.53 MPa. The ratio of Si to Al in each composite is about 1:1. The dehydroxylation temperature for samples ranged between 443.23 C and 555.23 C.http://www.mdpi.com/journal/crystalsam2022Physic

Effect of hydrothermal and chemical treatment on the optical and electrical properties of reduced graphene oxide deposited on ITO glass

In this work, the effect of hydrothermal and chemical treatment on the optical and electrical properties of reduced graphene oxide (RGO) was investigated. Reduced graphene oxide was synthesized by both hydrothermal route using a locally fabricated Teflon lined autoclave and chemical method using hydrazine monohydrate. The thin film was obtained by depositing RGO on Indium Tin Oxide (ITO) glass via spray pyrolysis technique. In RGO hydrothermal, the Raman spectroscopy analysis showed greater restoration of the conjugated networks in graphene sheet. The optical transmittance of RGO hydrothermal and RGO hydrazine decreased after the reduction methods unlike in highly oxidized graphene oxide (HOGO) where eighty percent transmittance was observed at 600 nm and above. For RGO hydrothermal and RGO hydrazine; the optical analysis gave an energy band gap value of 2.1 eV and 2.4 eV respectively, while the resistivity were calculated to be 0.3 Ω m and 0.09 Ω m respectively. This research showed a correlation between the band gap value of RGO and the electrical conductivity. This finding can improve the functionality of RGO as sensing materials. The improved electrical and optical properties of RGO hydrothermal makes it suitable in fiber-optic and opto-electronic applications.http://iopscience.iop.org/2053-1591am2021Physic

Effect of incorporating graphene oxide in ZnS and study of the thermistor applications of ZnS-RGO film

We report the effect of incorporating graphene oxide in ZnS and developed a ZnS-RGO hybrid film with negative temperature coefficient (NTC) for thermistor application towards temperature sensing in this study. The light sensing properties of the films were also investigated by exposing the film to light sources from mercury and tungsten lamp and recording the photo resistance. As the composition of ZnS in ZnS-RGO increased, sharper diffraction peaks were observed thus confirming improved crystallinity. The crystallite size of ZnS-RGO hybrid decreased from 4.02 to 1.87 nm while the lattice strain increased from 0.0086 to 0.0185 as the composition of ZnS in the hybrid increased. ZnS-RGO recorded a maximum sensor response of 1.91 which is approximately twice the maximum value obtained for pure ZnS in literature. The negative temperature coefficient (NTC) for ZnS-RGO (0.00174825/K) was higher than values obtained in literature for ZnS and Ag nanoparticles coated RGO. Furthermore, the sensitivity value of ZnS-RGO (0.00769 Ω/ K) was five times that of ZnS while the activation energy (0.0352 eV) was about seven times the value reported for ZnS. The increase in activation energy of ZnS-RGO compared to ZnS is responsible for the improved sensing response of the hybrid while the intercalation of ZnS in GO created reactive sites that resulted in activation energy, sensing response and an NTC much higher than in pure ZnS thus favoring utilization of ZnS-RGO as thermistors. This research has shown that ZnS, intercalated in the matrix of GO improved the thermal and photo sensing properties of ZnS and is thus suitable in thermistor applications. These properties can be used to suggest the application of ZnS-RGO in optoelectronic applications such as EM detectors, solar cells and temperature monitoring devices

Electrochemical analysis of nanoporous carbons derived from activation of polypyrrole for stable supercapacitors

In this study, activated carbon was derived from polypyrrole (PPY) using a K2CO3 activating agent with varying mass ratios of the activating agent to PPY polymer (AA:PP), for the optimization of the hierarchical pore structure necessary for improved electrochemical performance. The textural study of the as-synthesized samples (AC-PPY) displayed an increase in the specific surface area (SSA) and pore volume with increase in the amount of the activating agent up to a threshold for AA:PP of 6:1. The increase in the SSA was due to the presence of hierarchical pores in the material structure for efficient ion penetration. Initial half-cell electrochemical tests performed on the different activated carbon samples with varying SSA revealed superior charge storage capability for the 6:1 sample in both negative and positive operating potentials. The highest current response value was obtained from the signatory EDLC-type cyclic voltammogram, along with the longest discharge time from the chronopotentiometry plot as a result of the lowest ion diffusion length for successful fast ion transport reported from the impedance spectroscopy analysis. A full symmetric device (AC-PPY-6) assembled from the best material using KNO3 neutral electrolyte yielded a specific capacitance of 140 F g−1, 12.4 Wh kg−1 energy density at 0.5 A g−1 gravimetric current. An energy density of 7.12 Wh kg−1 was still maintained at a specific current of 2 A g−1. Interestingly, after the ageing test to ascertain device stability, the device energy density increased back to 12.2 Wh kg−1 as a result of the creation of additional active pores within the nanostructured material for charge storage via voltage holding tests which also led to the enhancement in specific capacitance to 137.5 F g−1 at 2 A g−1. A 99.0% capacitance retention was recorded even after 10000 cycles at a moderate specific current of 2 A g−1. A substantial approach was used to elucidate the degradation phenomena from the device self-discharge profile, which showcased the device retaining up to 70% of its operating potential after 80 h (> 3 days) on open circuit. The results obtained demonstrate the potential of adopting the AC-PPY material in potential device for energy storage purposes.The South African Research Chairs Initiative of the Department of Science and Technology, Republic of South Africa, and National Research Foundation of South Africa (Grant No. 61056).http://link.springer.com/journal/108532019-04-18hj2018Physic

Bullet-like microstructured nickel ammonium phosphate/graphene foam composite as positive electrode for asymmetric supercapacitors

Unique microstructured nickel ammonium phosphate Ni(NH4)2(PO3)4$4H2O and Ni(NH4)2(PO3)4$4H2O/GF composite were successfully synthesized through the hydrothermal method with different graphene foam (GF) mass loading of 30, 60 and 90 mg as a positive electrode for asymmetric supercapacitors. The crystal structure, vibrational mode, texture and morphology of the samples were studied with X-ray diffraction (XRD), Raman spectroscopy, Brunauer–Emmett–Teller (BET) surface area analysis and scanning electron microscopy (SEM). The prepared materials were tested in both 3-and 2-electrode measurements using 6 M KOH electrolyte. The composite material Ni(NH4)2(PO3)4$4H2O/60 mg exhibited a remarkable gravimetric capacity of 52 mA h g 1, higher than the 34 mA h g 1 obtained for the Ni(NH4)2(PO3)4$4H2O pristine sample, both at 0.5 A g 1. For the fabrication of the asymmetric device, activated carbon from pepper seed (ppAC) was used as a negative electrode while Ni(NH4)2(PO3)4$4H2O/60 mg GF was adopted as the positive electrode. The Ni(NH4)2(PO3)4$4H2O/60 mg GF//ppAC asymmetric device delivered a specific energy of 52 Wh kg 1 with an equivalent specific power of 861 W kg 1 at 1.0 A g 1 within a potential range of 0.0–1.5 V. Moreover, the asymmetric device displayed a capacity retention of about 76% for over 10 000 cycles at a high specific current of 10.0 A g 1.The South African Research Chairs Initiative (SARChI) of the Department of Science and Technology, the National Research Foundation (NRF) of South Africa and the University of Pretoria.http://pubs.rsc.org/en/journals/journalissues/raam2021Physic

Novel thermally reduced graphene oxide microsupercapacitor fabricated via mask free axidraw direct writing

We demonstrate a simple method to fabricate all solid state, thermally reduced graphene oxide (TRGO) microsupercapacitors (µ-SCs) prepared using the atmospheric pressure chemical vapor deposition (APCVD) and a mask-free axiDraw sketching apparatus. The Fourier transform infrared spectroscopy (FTIR) shows the extermination of oxygen functional groups as the reducing temperature (RT) increases, while the Raman shows the presence of the defect and graphitic peaks. The electrochemical performance of the µ-SCs showed cyclic voltammetry (CV) potential window of 0–0.8 V at various scan rates of 5–1000 mVs−1 with a rectangular shape, depicting characteristics of electric double layer capacitor (EDLC) behavior. The µ-SC with 14 cm−2 (number of digits per unit area) showed a 46% increment in capacitance from that of 6 cm−2 , which is also higher than the µ-SCs with 22 and 26 cm−2 . The TRGO-500 exhibits volumetric energy and power density of 14.61 mW h cm−3 and 142.67 mW cm−3 , respectively. The electrochemical impedance spectroscopy (EIS) showed the decrease in the equivalent series resistance (ESR) as a function of RT due to reduction of the resistive functional groups present in the sample. Bode plot showed a phase angel of −85◦ for the TRGO-500 µ-SC device. The electrochemical performance of the µ-SC devices can be tuned by varying the RT, number of digits per unity area, and connection configuration (parallel or series).The National Research Foundation (NRF) of South Africa, the South African Research Chairs Initiative (SARChI) of the Department of Science and Technology and the University of Pretoria.http://www.mdpi.com/journal/nanomaterialspm2022Physic

High-energy asymmetric supercapacitor based on nickel cobalt oxide (NiCo2O4) nanostructure material and activated carbon derived from cocoa pod

Please read abstract in the article.http://pubs.acs.org/journal/enfuem2022-12-01hj2022Physic