Growth of graphene underlayers by chemical vapor deposition

We present a simple and very convincing approach to visualizing that subsequent layers of graphene grow between the existing monolayer graphene and the copper catalyst in chemical vapor deposition (CVD). Graphene samples were grown by CVD and then transferred onto glass substrates by the bubbling method in two ways, either direct-transfer (DT) to yield poly (methyl methacrylate) (PMMA)/graphene/glass or (2) inverted transfer (IT) to yield graphene/PMMA/glass. Field emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM) were used to reveal surface features for both the DT and IT samples. The results from FE-SEM and AFM topographic analyses of the surfaces revealed the underlayer growth of subsequent layers. The subsequent layers in the IT samples are visualized as 3D structures, where the smaller graphene layers lie above the larger layers stacked in a concentric manner. The results support the formation of the so-called “inverted wedding cake” stacking in multilayer graphene growth.MF thanks the Government of Lesotho, the University of Pretoria and the NRF for financial support for his study. A.T.C.J acknowledges support from the LRSM, through the U.S. National Science Foundation MRSEC, Grant No. DMR-1120901.http://scitation.aip.org/content/aip/journal/advahb2014ai201

Solvothermal synthesis of NiAl double hydroxide microspheres on a nickel foam-graphene as an electrode material for pseudo-capacitors

In this paper, we demonstrate excellent pseudo-capacitance behavior of nickelaluminum double hydroxide microspheres (NiAl DHM) synthesized by a facile solvothermal technique using tertbutanol as a structure-directing agent on nickel foam-graphene (NF-G) current collector as compared to use of nickel foam current collector alone. The structure and surface morphology were studied by X-ray diffraction analysis, Raman spectroscopy and scanning and transmission electron microscopies respectively. NF-G current collector was fabricated by chemical vapor deposition followed by an ex situ coatingmethod of NiAlDHMactivematerial which forms a composite electrode. The pseudocapacitive performance of the composite electrode was investigated by cyclic voltammetry, constant charge–discharge and electrochemical impedance spectroscopy measurements. The composite electrode with the NF-G current collector exhibits an enhanced electrochemical performance due to the presence of the conductive graphene layer on the nickel foam and gives a specific capacitance of 1252 F g−1 at a current density of 1 A g−1 and a capacitive retention of about 97% after 1000 charge–discharge cycles. This shows that these composites are promising electrode materials for energy storage devices.A.T.C.J acknowledges support from the LRSM, through the U.S. National Science Foundation MRSEC, Grant No. DMR-1120901. D M acknowledges the financial support from the University of Pretoria and the NRF Doctorate Innovation Fund for his study.http://scitation.aip.org/content/aip/journal/advaam201

Pyrolysed almond shells used as electrodes in microbial electrolysis cell

9 p.The large cost of components used in microbial electrolysis cell (MEC) reactors represents an important limitation that is delaying the commercial implementation of this technology. In this work, we explore the feasibility of using pyrolysed almond shells (PAS) as a material for producing low-cost anodes for use in MEC systems. This was done by comparing the microbial populations that developed on the surface of PAS bioanodes with those present on the carbon felt (CF) bioanodes traditionally used in MECs. Raw almond shells were pyrolysed at three different temperatures, obtaining the best conductive material at the highest temperature (1000 °C). The behaviour of this material was then verified using a single-chamber cell. Subsequently, the main test was carried out using two-chamber cells and the microbial populations extant on each of the bioanodes were analysed. High-throughput sequencing of the 16S rRNA gene for eubacterial populations was carried out in order to compare the microbial communities attached to each type of electrode. The microbial populations on each electrode were also quantified by real-time polymerase chain reaction (realtime PCR) to determine the amount of bacteria capable of growing on the electrodes’surface. The results indicated that the newly developed PAS bioanodes possess a biofilm similar to those found on the surface of traditional CF electrodes. This research was possible thanks to the financial support of the Junta de Castilla y León, and was financed by European Regional Development Funds (LE320P18). C. B. thanks the Spanish Ministerio de Educación, Cultura y Deporte for support in the form of an FPI fellowship grant (Ref #: BES-2016-078329)

Adhesion and degradation of organic and hybrid organic-inorganic light-emitting devices

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Momodu, D. Y., T. Tong, M. G. Zebaze Kana, A. V. Chioh, and W. O. Soboyejo. "Adhesion and degradation of organic and hybrid organic-inorganic light-emitting devices." Journal of Applied Physics 115, no. 8 (2014): 084504. and may be found at http://dx.doi.org/10.1063/1.4867051This paper presents the results of a combined analytical, computational, and experimental study of adhesion and degradation of Organic Light Emitting Devices (OLEDs). The adhesion between layers that are relevant to OLEDs is studied using an atomic force microscopy technique. The interfacial failure mechanisms associated with blister formation in OLEDs and those due to the addition of TiO2 nanoparticles into the active regions are then elucidated using a combination of fracture mechanics, finite element modeling and experiments. The blisters observed in the models are shown to be consistent with the results from adhesion, interfacial fracture mechanics models, and prior reports of diffusion-assisted phenomena. The implications of the work are then discussed for the design of OLED structures with improved lifetimes and robustness

Fixed-Wing Micro Air Vehicle for the 2020 WPI UAV Competition

A Fixed Micro Air Vehicle was designed and constructed in order to compete in the 2020 WPI UAV Competition, for which the scoring was based on weight fraction, flight time, payload target accuracy, autonomy, and originality. Some key features of the aircraft were its carbon fiber design, its 6.02 foot wingspan, and unloaded weight of 3.92 pounds. The one flight test performed revealed issues with stability and handling, which could not be resolved due to the Coronavirus pandemic

Growth of graphene underlayers by chemical vapor deposition

We present a simple and very convincing approach to visualizing that subsequent layers of graphene grow between the existing monolayer graphene and the copper catalyst in chemical vapor deposition (CVD). Graphene samples were grown by CVD and then transferred onto glass substrates by the bubbling method in two ways, either direct-transfer (DT) to yield poly (methyl methacrylate) (PMMA)/graphene/glass or (2) inverted transfer (IT) to yield graphene/PMMA/glass. Field emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM) were used to reveal surface features for both the DT and IT samples. The results from FE-SEM and AFM topographic analyses of the surfaces revealed the underlayer growth of subsequent layers. The subsequent layers in the IT samples are visualized as 3D structures, where the smaller graphene layers lie above the larger layers stacked in a concentric manner. The results support the formation of the so-called “inverted wedding cake” stacking in multilayer graphene growth

Effect of conductive additives to gel electrolytes on activated carbon-based supercapacitors

This article is focused on polymer based gel electrolyte due to the fact that polymers are cheap and can be used to achieve extended potential window for improved energy density of the supercapacitor devices when compared to aqueous electrolytes. Electrochemical characterization of a symmetric supercapacitor devices based on activated carbon in different polyvinyl alcohol (PVA) based gel electrolytes was carried out. The device exhibited a maximum energy density of 24 Wh kg−1 when carbon black was added to the gel electrolyte as conductive additive. The good energy density was correlated with the improved conductivity of the electrolyte medium which is favorable for fast ion transport in this relatively viscous environment. Most importantly, the device remained stable with no capacitance lost after 10,000 cycles

Effect of conductive additives to gel electrolytes on activated carbon-based supercapacitors

This article is focused on polymer based gel electrolyte due to the fact that polymers are cheap and can be used to achieve extended potential window for improved energy density of the supercapacitor devices when compared to aqueous electrolytes. Electrochemical characterization of a symmetric supercapacitor devices based on activated carbon in different polyvinyl alcohol (PVA) based gel electrolyteswas carried out. The device exhibited a maximum energy density of 24 Wh kg−1 when carbon black was added to the gel electrolyte as conductive additive. The good energy densitywas correlated with the improved conductivity of the electrolyte medium which is favorable for fast ion transport in this relatively viscous environment. Most importantly, the device remained stable with no capacitance lost after 10,000 cycles.The South African Research Chair Initiative (SARChi) in Carbon Technology and Materials of the Department of Science and Technology (DST) and the National Research Foundation (NRF). F. Barzegar and D. Y. Momodu acknowledge financial support from the University of Pretoria and the NRF for their PhD bursaries, while A. Bello acknowledges NRF through SARChI in Carbon Technology and Materials and University of Pretoria for his Postdoctoral financial support. A.T. C. Johnson acknowledges support from the Laboratory for Research on the Structure of Matter, National Science Foundation MRSEC, grant number DMR-1120901.http://scitation.aip.orgcontent/aip/journal/advaam201