Billyde Brown

Graphenated carbon nanotubes for enhanced electrochemical double layer capacitor performance

This letter reports on nucleation and growth of graphene foliates protruding from the sidewalls of aligned carbon nanotubes (CNTs) and their impact on the electrochemical double-layer capacitance. Arrays of CNTs were grown for different time intervals, resulting in an increasing density of graphene foliates with deposition time. The samples were characterized using electrochemical impedance spectroscopy, scanning electron microscopy, and transmission electron microscopy. Both low and high frequency capacitance increased with increasing foliate density. A microstructural classification is proposed to explain the role of graphene edges, three-dimensional organization, and other features of hybrid carbon systems on their electrochemical properties.

Alloying Effects of Cosputtered Gold-Platinum Thin Films on the Oxygen Reduction Reaction in Acidic Electrolyte

A better understanding of the effects of alloying Pt with Au on the oxygen reduction reaction (ORR) was achieved in this study. Recent investigations of carbon-supported Au-Pt nanoparticle catalysts have shown enhanced response for the ORR with respect to pure Pt nanoparticles. These results were reported to be due to homogeneous mixing of Au and Pt atoms that was accomplished in nanoscale particles, effectively removing the miscibility gap inherent in the equilibrium phase diagram. In this study, cosputtering of Au and Pt is used to form 350 nm thick films to achieve homogeneous mixing without nanoparticle geometries, thereby isolating the effects of alloying from nanoparticle effects. ORR activity and stability at these electrodes are investigated via cyclic voltammetry in O 2 -saturated 0.5 M H 2 SO 4 under oxidizing potentials. Cosputtering yielded solid solution alloys throughout the entire composition range as shown by X-ray diffraction results. Furthermore, as-deposited near-surface compositions determined by X-ray photoelectron spectroscopy indicated that extensive Au surface segregation was avoided by room-temperature deposition. Metastable compositions within the miscibility gap, explicitly Pt 21 Au 79 , Pt 43 Au 57 , and Pt 59 Au 41 , were found to be significantly more electrocatalytic for O 2 reduction than the pure Pt film, although Pt 43 Au 57 and Pt 59 Au 41 rapidly lost catalytic activity with subsequent potential sweeps.

Perspectives on the Growth of High Edge Density Carbon Nanostructures: Transitions from Vertically Oriented Graphene Nanosheets to Graphenated Carbon Nanotubes

Insights into the growth of high edge density carbon nanostructures were achieved by a systematic parametric study of plasma-enhanced chemical vapor deposition (PECVD). Such structures are important for electrode performance in a variety of applications such as supercapacitors, neural stimulation, and electrocatalysis. A morphological trend was observed as a function of temperature whereby graphenated carbon nanotubes (g-CNTs) emerged as an intermediate structure between carbon nanotubes (CNTs) at lower temperatures and vertically oriented carbon nanosheets (CNS), composed of few-layered graphene, at higher temperatures. This is the first time that three distinct morphologies and dimensionalities of carbon nanostructures (i.e., 1D CNTs, 2D CNSs, and 3D g-CNTs) have been synthesized in the same reaction chamber by varying only a single parameter (temperature). A design of experiments (DOE) approach was utilized to understand the range of growth permitted in a microwave PECVD reactor, with a focus on identifying graphenated carbon nanotube growth within the process space. Factors studied in the experimental design included temperature, gas ratio, catalyst thickness, pretreatment time, and deposition time. This procedure facilitates predicting and modeling high edge density carbon nanostructure characteristics under a complete range of growth conditions that yields various morphologies of nanoscale carbon. Aside from the morphological trends influenced by temperature, a relationship between deposition temperature and specific capacitance emerged from the DOE study. Transmission electron microscopy was also used to understand the morphology and microstructure of the various high edge density structures. From these results, a new graphene foliate formation mechanism is proposed for synthesis of g-CNTs in a single deposition process.

A novel array chip to monitor in situ composite degradation using electrochemical impedance spectroscopy.

OBJECTIVES This paper presents a novel array-chip technology used to monitor the physical properties of dental composites in situ. The DECAY chip (Degradation via Electrochemical Array) leverages microfabrication techniques to construct a uniform array of recessed wells that may be filled with dental restorative materials (e.g. composite or amalgam) and analyzed electrochemically in solution. METHODS The array enables the uniform preparation of multiple specimens and reference controls on a common substrate, all of which may be simultaneously evaluated. The DECAY-chip presented here consists of a 3 × 3 array of 100 μm deep wells, and is used to monitor the degradation of a common dental composite as a function of time. RESULTS The data correlate changes in the measured dielectric properties to surface and bulk changes as the composite is exposed to an ethanol:DI mixture (75% ethanol). A model for the system is presented, as are future plans to simplify the methodology for rapid materials screening and in vitro analyses. SIGNIFICANCE This in situdiagnostic chip will enable evaluation of composite specimens, tested under a wide range of simulated oral environments. It may also serve as a screening platform for new composite formulations and aid in the study of materials degradation and failure mechanisms.