Renewable pine cone biomass derived carbon materials for supercapacitor application

The environmental degradation and hazard to human life caused by the depletion of fossils fuels and the urgent need for sustainable energy sources to meet the rising demand in energy has led to the exploration of novel materials that are environmentally friendly, low cost and less hazardous to human life for energy storage application using the green chemistry approach. Herein, we report on the transformation of the readily abundant pine cone biomass into porous carbon via KOH activation and carbonization at 800 C as electrode materials for supercapacitors. The porous carbon material exhibited a mesoporous framework with a specific surface area of 1515 m2 g 1, a high voltage window of 2.0 V, a gravimetric capacitance of 137 F g 1, energy density of 19 W h kg 1 and excellent cyclability in neutral 1 M Na2SO4 electrolyte for a symmetric carbon/carbon electrode cell. The result shows that the material is robust and shows great promise with neutral electrolytes in high-performance energystorage devices.South African Research Chairs Initiative of the Department of Science and Technology and National Research Foundation of South Africa (Grant No. 97994).http://www.rsc.orgadvances2017-07-31hb2016Institute of Applied MaterialsPhysic

Coniferous pine biomass : a novel insight into sustainable carbon materials for supercapacitors electrode

Low-cost biomass-derived activated porous carbon from natural pine cones is synthesized using hydrothermal approach followed by KOH activation and carbonization. The produced carbon materials have a high surface area of 1515 m2 g1 with a well-developed meso/micropores structure which is advantageous and favorable for mass transfer and ion accommodation for fast rate performance by providing pathways for electrolyte permeation and contact probability. Symmetric device fabricated using the obtained carbon material as electrode, exhibited good electrochemical performance with no degradation of capacitance after voltage holding at 1 V for about 60 h demonstrating good rate capability of the fabricated device. The results demonstrate the exciting potential of the pine cone derived carbons as a promising candidate for high-performance electrode materials for supercapacitors if fully explored.The South African Research Chairs Initiative of the Department of Science and Technology and National Research Foundation of South Africa (Grant No. 97994).http://www.elsevier.com/locate/matchemphys2017-10-31hb2016Physic

High performance hybrid supercapacitor device based on cobalt manganese layered double hydroxide and activated carbon derived from cork (Quercus Suber)

Thin Co-Mn layered double hydroxide (LDH) nanoflakes and Activated carbon (AC) from cork raw material (Quercus Suber) with highly porous structure and good textural properties was synthesized by a facile solvothermal and two-step eco-friendly hydrothermal syntheses routes respectively. A hybrid device was successfully fabricated using Co-Mn LDH as the positive electrode and AC as negative electrode. The device exhibited a high energy density of 20.3 W h kg−1 and corresponding power density of up to 435 W kg−1 at 0.5 A g−1 current density in 1 M KOH aqueous electrolyte. The device also displayed a very high stability with 99.7% capacitance retention after 10,000 continuous charge-discharge cycles and negligible degradation after subsequently subjecting it to voltage holding test at its maximum operating voltage for 70 hours. These results showcase the potential use of this hybrid device as possible electrodes for high energy density supercapacitor application.The South African Research Chairs Initiative (SARChI) of the Department of Science and Technology and the National Research Foundation (NRF) of South Africa (Grant No. 61056).http://www.elsevier.com/locate/electacta2018-10-20hj2017Physic

High electrochemical performance of hierarchical porous activated carbon derived from lightweight cork (Quercus suber)

Activated carbon (AC) derived from biomass lightweight cork (Quercus suber) material was synthesized by KOH activation with different mass ratios of Q. suber: KOH in order to investigate the electrochemical properties of the AC in relation to KOH concentration. A well-defined porous activated carbon was obtained with a high surface area of 1081 m2 g−1 and a high pore volume of 0.66 cm3 g−1 when the Q. suber: KOH mass ratio was fixed at 1:2. A specific capacitance of 166 F g−1 was obtained for the symmetric device at 0.5 A g−1 in 1 M Na2SO4 with energy and power densities of 18.6 and 449.4 W Kg−1, respectively. The device displays good cycling stability after floating test for 200 h at 1.8 V and also displays 99.8% capacitance retention after cycling for 5000 cycles. The excellent electrochemical performance of the device makes it a potential material for supercapacitor application.National Research Foundation (NRF) of South Africahttp://link.springer.com/journal/10853Lightweight cork (Quercus suber)2018-09-30hj2017Physic

Activated carbon derived from tree bark biomass with promising material properties for supercapacitors

Activated carbon from tree bark (ACB) has been synthesized by a facile and environmentally friendly activation and carbonization process at different temperatures (600, 700 and 800 °C) using potassium hydroxide (KOH) pellets as an activation agent with different mass loading. The physicochemical and microstructural characteristics of the as-obtained material revealed interconnected microporous/mesoporous architecture with increasing trend in specific surface area (SSA) as carbonization temperatures rises. The SSA values of up to 1018 m2 g−1 and a high pore volume of 0.67 cm3 g−1 were obtained. The potential of the ACB material as suitable supercapacitor electrode was investigated in both a three and two-electrode configuration in different neutral aqueous electrolytes. The electrodes exhibited electric double-layer capacitor (EDLC) behaviour in all electrolytes with the Na2SO4 electrolyte working reversibly in both the negative (−0.80 V to −0.20 V) and positive (0.0 V to 0.6 V) operating potentials. A specific capacitance (Cs) of up to 191 F g−1 at a current density of 1 A g−1 was obtained for the optimized ACB electrode material in 1 M Na2SO4 electrolyte. A symmetric device fabricated exhibited specific Cs of 114 F g−1 at 0.3 A g−1 and excellent stability with a coulombic efficiency of a 100 % after 5000 constant charge–discharge cycles at 5.0 A g−1 and a low capacitance loss for a floating time of 70 h.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. 97994).http://link.springer.com/journal/100082018-03-30hb2016Physic

Stability studies of polypyrole- derived carbon based symmetric supercapacitor via potentiostatic floating test

This work present the synthesis and electrochemical performance of mesoporous carbon material derived from the activation and carbonisation of polypyrole (PPY). Electrochemical performance of the PPY derived carbon was investigated in a two electrode cell in a 6 M KOH alkaline electrolyte. The symmetric device was subjected to floating test (voltage holding) for ~200 h at a voltage of 1.2 V and the specific capacitance as well as the resistance of device was determined after every 10 h of floating. The device exhibited a specific capacitance of 179 F g-1 at 0.5 A g-1 and 158 F g-1 at 10 A g-1. In addition, after floating for ~120 h the resistance was constant with a very slow decrease in capacitance. Beyond ~120 h, a quick decrease in capacitance was observed with a corresponding increase in resistance, indicating a possible deterioration to the electrodes. Remarkably, at the end of floating, the specific capacitance calculated at 5 A g-1 was 120 F g-1 (~25% decay in capacitance from the initial value 160.5 F g-1 at 5 A g-1) suggesting good stability of the device over a long period of time (~8 days).South African Research Chairs Initiative of the Department of Science and Technology and National Research Foundation of South Africa (Grant No. 97994).http://www.elsevier.com/locate/electacta2017-09-30hb2016Physic

Electrochemical performance of two-dimensional Ti3C2-Mn3O4 nanocomposites and carbonized iron cations for hybrid supercapacitor electrodes

Please read abstract in the article.The South African Research Chairs Initiative of the Department of Science and Technology, South Africa and National Research Foundation of South Africa (Grant No. 61056). K. O. appreciates the financial assistance from the University of Pretoria, South Africa and National Research Foundation (NRF) of South Africa for studentship grants.http://www.elsevier.com/locate/electacta2020-04-01hj2019Physic

A facile hydrothermal reflux synthesis of Ni(OH)2/GF electrode for supercapacitor application

Ni(OH)2/graphene foam (GF) electrode was synthesized for electrochemical application by a facile hydrothermal reflux technique. The results obtained from the scanning electron microscopy showed that the Ni(OH)2 spheres successfully coated the entire surface area of the GF. Specific capacitance of 2420 F g-1 at a current density of 1 A g-1 was obtained for Ni(OH)2/GF composite electrode, as well as a capacitance retention of ~93% after 1000 charge-discharge cycles, demonstrating excellent cycle stability in 6.0 M KOH electrolyte. These results suggest that the composite could be a potential active material for high performance electrochemical applications.South African Research Chairs Initiative of the Department of Science and Technology, National Research Foundation of South Africa (Grant No. 97994) and University of Pretoria.http://link.springer.com/journal/108532017-06-30hb2016Physic

Effect of activated carbon on the enhancement of CO sensing performance of NiO

NiO/activated carbon (AC) composites were successfully synthesized via a hydrothermal reflux process as an electrode material for carbon monoxide (CO) gas sensor application. The X-ray diffraction (XRD) analysis was used to investigate the crystallinity of the samples while gas sorption analysis was used to probe the specific surface area of both the pristine NiO and NiO/AC composite. The sensors were subjected to continuous cycles of different CO concentrations and were purged with air after each cycle, followed by variations in a normalized resistance study. The results obtained from the gas sensing analysis disclose that the incorporation of AC into NiO increased the conductivity and surface area of NiO/ AC composite and subsequently enhancing the CO sensing performance of NiO/AC based sensor. These results imply that the NiO/AC composite could be an excellent nanomaterial for CO gas sensors.http://www.elsevier.com/locate/jalcom2018-02-28hb2017Physic

Synthesis of nickel oxide/hydroxides and their nanocomposites with carbon materials for supercapacitor and gas sensing applications

The goal of this thesis is to produce NiO- and Ni(OH)2-carbon based nanocomposites and explore their possible adoption as active electrode materials in supercapacitor and gas sensing applications. Field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), X-ray powder diffraction (XRD), Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy, thermal gravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS) and gas adsorption analyses were utilized to evaluate the structure and morphology of all samples in this study. The major aim of integrating carbon-based nanomaterials (graphene foam, graphene oxide and activated carbon) into Ni-based oxides and hydroxides in this study is to take advantage of their outstanding characteristics. These include good electrical conductivity, high corrosion resistance, large SSA, low-cost, good cyclic and temperature stability, as well as the capability to serve as a substrate for growth of other materials to form a suitable composite. The electrochemical evaluation as a potential supercapacitor electrode was employed in a three (3)-electrode configuration for the as-prepared Ni(OH)2/carbon based electrodes (NiOH)2/graphene foam and Ni(OH)2/graphene oxide electrodes) while the gas sensing characteristics of NiO/carbon-based electrodes were investigated using NCSM-CSIR gas sensing station controlled by a KEITHLEY pico-ammeter system. The electrochemical results of Ni(OH)2/carbon-based electrodes have demonstrated a superior electrochemical performance as compared to the pristine Ni(OH)2 electrodes with the results comparable and even better than some earlier related studies available in the literature. Similarly, NiO/carbonbased electrodes in the form of NiO/graphene foam and NiO/activated carbon electrodes both exhibited enhanced gas sensing properties in comparison to the pristine NiO electrode due to the increased specific surface area and electrical conductivity that are linked to its sensing response, response time and recovery time. Thus, the results obtained from these studies have clearly established the viability of these carbon-based nanomaterial composites as promising candidates for electrochemical supercapacitor and gas sensing applications.Thesis (PhD)--University of Pretoria, 2017.CSIR-National Centre for Nano-Structured MaterialsSouth African national research foundation (NRF)PhysicsPhDUnrestricte