Eco-friendly use of eggshell powder as a bio-filler and flux material to enhance technological properties of fired clay bricks

In this work, an experimental investigation on the use of eggshell powder from waste eggshells as an alternative source of bio-filler and flux to enhance the technological properties of fired clay bricks were carried out. Four different batch compositions were formed with eggshell powder as a bio-filler and flux replacing clay-soil up to 15 wt.%. The clay bricks were prepared by the casting method and were fired at 800, 900, and 1000 °C at the heating rate of 8 °C/min for 120 minutes. The raw materials and produced fired clay bricks were characterized by SEM/EDS, XRF, and XRD, respectively. Besides, technological properties of fired clay bricks (eg. water absorption, apparent porosity, bulk density, and compressive strength) were also determined. The results showed that adding 15 wt.% of eggshell powder as a bio-filler and flux yielded a compressive strength of 4.8 MPa, the bulk density of 2.1 g/cm3, and a lower water absorption value of 11.1% at the firing temperature of 1000 °C. Consequently, the use of eggshell as a bio-filler and flux to enhance the technological properties of fired clay bricks is promising and can be considered as an effective alternative method to reduce environmental concerns caused by inappropriate discarding and landfill construction to dispose of eggshell waste

Recent trends in Carbon support for improved performance of Alkaline Fuel cells

Alkaline Fuel cells (AFCs) are one of the emerging energy future energy sources and energy conversion systems. The use of the anion exchange membrane in alkaline fuel cells (AEMFCs) has made AFCs more versatile. It has also introduced the use of an abundance of catalysts, mostly non-Platinum group metals (PGMs), especially for its more favorable cathodic oxygen reduction (ORR). The benefits and importance of the presence of efficient porous carbon supports to enhance the electroactivity of these catalysts were highlighted. Apart from the well-known carbon allotropes used as catalyst supports, some new and innovative forms of porous carbon and their composites are discussed. Their performance as stand-alone catalysts or as support for non PGMs for ORR in operating conditions of AEMFCs has given a further boost to the future availability of low-cost AFC driven devices

Raman spectroscopy and imaging of Bernal-stacked bilayer graphene synthesized on copper foil by chemical vapour deposition : growth dependence on temperature

We report on the effect of temperature on the growth of bilayer graphene on a copper foil under atmospheric pressure chemical vapour deposition (AP-CVD). Before characterization of the AP-CVD bilayer graphene, a high-quality graphene flake was obtained from the Kish bulk graphite by micro-mechanical exfoliation and characterized by using Raman spectroscopy and imaging. The Raman data of the exfoliated, high-quality graphene flake show monolayer and bilayer graphenes and were compared with the Raman data of AP-CVD graphene. Raman spectroscopy of AP-CVD graphene shows bilayer films that exhibit predominantly Bernal stacking with an I-2D/I-G ratio of similar to 1. At low growth temperature (similar to 780 degrees C), Raman disorder-related peak intensity in the AP-CVD graphene is high and decreases with an increase in growth temperature to the lowest disorder intensity at similar to 973 degrees C. The selected area electron diffraction and atomic force microscopy average step height analysis showed the thickness of the bilayer graphene. The AP-CVD graphene is uniform at low growth temperatures (similar to 780 degrees C) with a high disorder and becomes non-uniform at high growth temperatures (similar to 867-973 degrees C) with a very low disorder as bilayer graphene evolves to form islands with an average lateral size of <10m. Competition between carbon adatoms supply through dehydrogenation of the CHx species, mobility and desorption rate of the carbon-adatom species for nucleation of the bilayer graphene as a function of temperature is elucidated. This study provides further insight into the growth mechanisms of bilayer graphene by AP-CVD on Cu.The South African Research Chairs Initiative of the South Africa Department of Science and Technology and the National Research Foundation (NRF) (grant no. 97994). MF thanks the University of Pretoria and the NRF for financial support during his PhD studies.http://onlinelibrary.wiley.com/journal/10.1002/(ISSN)1097-45552018-05-30hj2017Physic

Three dimensional modelling of the components in supercapacitors for proper understanding of the contribution of each parameter to the final electrochemical performance

Three dimensional (3D) modelling of supercapacitors (SCs) has been investigated for the first time to have a better understanding of and study the effect of each parameter on the final electrochemical results. Based on this model, the resistance of the electrolyte, membrane, current collectors and active materials have effects on the first intersection points on the real axis (x-axis) of the Nyquist plots (equivalent series resistance (ESR)). These results indicate inward shrinking of the cyclic voltammograms (CV) due to a small change in the leakage resistance and resistance of the faradic component of materials, and they also explain the parameters that lead to the deformation of the CV from ideal behaviour. The 3D model was verified with experiments using activated carbon-based SC devices. The experimental results confirmed the 3D model results and suggested that the proposed 3D model is reliable and can be used for the proper design of SC devices.http://www.rsc.org/journals-books-databases/about-journals/journal-of-materials-chemistry-a2019-09-28hj2018Electrical, Electronic and Computer EngineeringPhysic

Asymmetric supercapacitor based on activated expanded graphite and pinecone tree activated carbon with excellent stability

This work presents results obtained from the production of low-cost carbons from expanded graphite (EG) and pinecone (PC) biomass, activated in potassium hydroxide (KOH) and finally carbonized in argon and hydrogen atmosphere. A specific surface area of 808 m2 g−1 and 457 m2 g−1 were measured for activated pinecone carbon (APC) and activated expanded graphite (AEG), respectively. The electrochemical characterization of the novel materials in a 2-electrode configuration as supercapacitor electrode shows a specific capacitance of 69 F g−1 at 0.5 A g−1, high energy density of 24.6 W h kg−1 at a power density of 400 W kg−1. This asymmetric supercapacitor also exhibits outstanding stability after voltage holding at the maximum voltage for 110 h, suggesting that the asymmetric device based on different carbon materials has a huge capacity for a high-performance electrode in electrochemical applications.The National Research Foundation of South Africa (Grant Number: 61056).http://www.elsevier.com/locate/apenergy2018-12-01hj2018Electrical, Electronic and Computer Engineerin

Hydrothermal synthesis of simonkolleite microplatelets on nickel foam-graphene for electrochemical supercapacitors

Nickel foam-graphene (NF-G) was synthesized by chemical vapour deposition followed by facial in situ aqueous chemical growth of simonkolleite (Zn5(OH)8Cl2·H2O) under hydrothermal conditions to form NF-G/simonkolleite composite. X-ray diffraction and Raman spectroscopy show the presence of simonkolleite on the NF-G, while scanning and transmission electron microscopies show simonkolleite micro-plates like structure evenly distributed on the NF-G. Electrochemical measurements of the composite electrode give a specific capacitance of 350 Fg−1 at current density of 0.7 Ag−1 for our device measured in three-electrode configuration. The composite also shows a rate capability of ~87% capacitance retention at a high current density of 5Ag−1,which makes it a promising candidate as an electrode material for supercapacitor applications.The University of Pretoria and the National Research Foundation (NRF) of South Africa.http://www.springer.com/chemistry/physical/journal/10008hb2013ai201

Surfactant assisted synthesis of copper oxide (CuO) leaf-like nanostructures for electrochemical applications

Three different copper oxide (CuO) leaf-like nanostructures have been synthesised by micelles micro emulsion method using a surfactant of copper dodecyl sulphate (Cu(DS)2) by varying the concentration of sodium hydroxide (NaOH). This study was carried out to investigate the effect of NaOH concentration on the stability, crystalline domain and pseudocapacitance behaviour of the leaf-like nanostructures. The samples were characterized by X-ray diffraction (XRD), thermogravimetry analysis (TGA), Raman spectroscopy, Fourier-Transform Infrared (FTIR), scanning electron microscopy (SEM) and Transmission electron microscopy (TEM). It was observed that the crystalline domain size (12 nm-18 nm) and size distribution of the as-synthesized nanocrystals decreases with increasing concentration of NaOH. The interactions mechanism and formation of the leaf-like structure have been elucidated and correlated with various analytical techniques. The domain size and NaOH concentration tend to influence the charge transfer resistance.South African Research Chairs Initiative of the Department of Science and Technology (DST) and the National Research Foundation (NRF). University of Pretoria and NRF.http://journal.sapub.org/materialshb201

Silver nanoparticles decorated on a three-dimensional graphene scaffold for electrochemical applications

Silver metal nanoparticles were decorated by electron beam evaporation on graphene foam (GF) grown by chemical vapour deposition. X-ray diffraction, Raman spectroscopy, scanning and transmission electron microscopy, and atomic force microscopy were used to investigate the structure and morphology of the graphene foam/silver nanoparticles (GF/Ag). Both samples were tested as electrodes for supercapacitors. The GF/Ag exhibited a significantly higher capacitive performance, including a specific capacitance value of (~110 Fg-1) and excellent cyclability in a three-electrode electrochemical cell. These results demonstrate that graphene foam could be an excellent platform for metal particles for investigating improved electrochemical performance.The South African Research Chairs Initiative (SARCHi) of the Department of Science and Technology (DST) and the National Research Foundation (NRF).http://www.elsevier.com/locate/jpcshb2013ai201

Morphological characterization and impedance spectroscopy study of porous 3D carbons based on graphene foam-PVA/phenol-formaldehyde resin composite as an electrode material for supercapacitors

The design and fabrication of porous electrode materials is highly desirable for improving the performance of electrochemical supercapacitors (ECs) and thus, it is important to produce such porous materials in large quantities. In this study, we used a microwave method to produce porous carbonaceous materials designated as graphene foam/polyvinyl alcohol/formaldehyde (GF/PVA/F) and graphene foam-polyvinyl alcohol/phenol-formaldehyde (GF/PVA/PF) from graphene foam, phenol formaldehyde and polyvinyl alcohol (PVA). Scanning electron microscopy (SEM), Raman spectroscopy and Fourier-Transform Infrared Spectroscopy (FTIR) were used to characterize the surface morphology, structural defects and functional groups of the materials respectively. Based on these porous materials, the two symmetrical ECs fabricated exhibited a specific capacitance in the range of 0.62–1.92 F cm 2, phase angles of 81 and 84 and resistor–capacitor (RC) relaxation time constants of 4 and 14 seconds. The physicochemical properties of the electrolyte ion (diffusion) and its influence on the capacitive behavior of the porous materials were elucidated. These encouraging results demonstrate the versatile potential of these porous materials (GF/PVA/F and GF/PVA/PF) in developing high energy storage devices.South African Research Chairs Initiative of the South African Department of Science and Technology (SARCHi-DST), the National Research Foundation (NRF) and the University of Pretoria.http://www.rsc.org/advanceshb201

Hydrothermal synthesis of manganese phosphate/graphene foam composite for electrochemical supercapacitor applications

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 (Grant No. 61056).https://www.elsevier.com/locate/jcis2018-05-31hb2017Physic