References using NanoLab nanotubes as sensors, catalysts & battery electrodes|
1. S M Vemuru, R Wahi, S Nagarajaiah, P M Ajayan. Strain sensing using a multiwalled carbon nanotube film. The journal of strain analysis for engineering design.
Abstract: The effectiveness of multiwalled carbon nanotubes (MWCNTs) as strain sensors is investigated. The key contribution of this paper is the study of real-time strain response at the macroscale of MWCNT film under tensile load. In addition, real-time voltage change as a function of temperature is examined. MWCNT films attached to a brass specimen by epoxy using vacuum bonding have been studied. The brass specimen is subjected to tensile loading, and voltage output from the MWCNT film is obtained using a four-point probe and a sensitive voltage measurement device. Experimental results show that there is a linear change in voltage across the film when subjected to tension, and the MWCNT film fully recovers to its unstressed state upon unloading and exhibits stable electromechanical properties. The effect of temperature on the voltage output of the nanotube film under no load condition is investigated. From the results obtained it is evident that MWCNT films exhibit a stable and predictable voltage response as a function of temperature. An increase in temperature leads to an increase in conductivity of the nanotube film. The study of MWCNT film for real-time strain sensing at the macroscale is very promising, and the effect of temperature on MWCNT film (with no load) can be reliably predicted.
2. Xiang-Rong Ye, Yuehe Lin, Chongming Wang, Mark H. Engelhard, Yong Wang and Chien M. Wai. (2004). Supercritical fluid synthesis and characterization of catalytic metal nanoparticles on carbon nanotubes. J. Mater. Chem. 14, 908 - 913, DOI: 10.1039/b308124a
Abstract: A rapid, convenient and environmentally benign method has been developed for the fabrication of metal nanoparticle–multiwall carbon nanotube (MWCNT) composites. Nanoparticles of palladium, rhodium and ruthenium are deposited onto functionalized MWCNTs through a simple hydrogen reduction of metal– -diketone precursors in supercritical carbon dioxide, and are characterized by transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) analyses. These highly dispersed nanoparticles, with a narrow range of size distribution and good adhesion on MWCNT surfaces, are expected to exhibit promising catalytic properties for a variety of chemical reactions. Preliminary experiments demonstrate that Pd nanoparticles supported on MWCNTs are effective catalysts for hydrogenation of olefins in carbon dioxide. The Pd nanoparticle–MWCNT composite also shows a high electrocatalytic activity in oxygen reduction for potential fuel cell application
3. Ren, Li and Yangchuan Xing. (2008, July). Effect of pH on PtRu electrocatalysts prepared via a polyol process on carbon nanotubes. Electrochimica acta, Volume 53, Issue 17,: 5563-5568.
Abstract: This paper reports a study on the pH effects on the PtRu nanoparticles synthesized in a polyol process that were deposited on carbon nanotubes (CNTs) by reducing metal salts using ethylene glycol at various pHs. It was found that the nanoparticle size, composition, and catalytic activity all were sensitive to pH. The nanoparticles decreased in size as the preparation pH increased from 1.6 to 10.0, with the largest size at 2.47 nm and the smallest at 1.13 nm. An exception was found for pH at 0.7, which resulted in an average size of only 1.01 nm. Preparation pH was found to affect polyol reaction mechanisms, which are believed to be dominated by direct metal reduction at low pH and by both direct metal reduction and hydroxide reduction at high pH. However, at high pH the reactions were limited by hydroxide reductions, and longer reaction durations were needed to fully deposit the metals. To study the pH effect on the electrochemical activity of the catalysts, CO stripping techniques were used to determine peak potentials and active surface areas. Together with cyclic voltammetry in the electro-oxidation of methanol, it was found that the catalyst prepared at pH 8.4 has the best performance.
4. Li, Liang., and Xing, Yangchuan. (2008). Electrochemical durability of carbon nanotubes at 80°C. Journal of power sources, Vol. 178, no. 1.
Abstract: Carbon nanotubes (CNTs) have been studied as an alternative catalyst support in polymer electrolyte membrane (PEM) fuel cells. Recent studies showed that CNTs appear to be more resistant to electrochemical corrosion than carbon black (CB). In a previous study, we have demonstrated the room temperature durability of multiwalled CNTs in both non-catalyzed and catalyzed electrochemical oxidations. This paper is to report results conducted at 80°C—an operational temperature of PEM fuel cells. It was found that multiwalled CNTs are still more resistant than CB at the elevated temperature. However, the electrochemical oxidation rate is more rapid than that at the room temperature. As a result, a decrease in oxidation currents was observed with cyclic voltammetry, attributed to that the initial surface oxides were quickly converted to more stable oxides or carbon dioxide due to the high temperature. For CNTs, extended oxidation could not occur, in contrast to CB, because it requires attacking on the intact graphite planes which are corrosion resistant under the experimental conditions. It was found that the kinetics followed different power laws in time for different carbons.
5. Li, Liang., and Xing, Yangchuan. (2007). Pt-Ru nanoparticles supported on carbon nanotubes as methanol fuel cell catalysts. Journal of physical chemistry, vol. 111, no. 6.
Abstract: Bimetallic Pt-Ru alloy catalysts have been demonstrated to be more active than pure Pt catalysts in the electrooxidation of methanol. We report here a study on Pt-Ru nanoparticle catalysts supported on sonochemically functionalized carbon nanotubes. The catalysts were prepared by directly reducing the corresponding salts, K2PtCl4 and K2RuCl5, in an ethylene glycol aqueous solution containing dispersed carbon nanotubes. Three catalysts of different Pt to Ru atomic ratios, namely, Pt53Ru47, Pt69Ru31, and Pt77Ru23, were prepared for investigation of the compositional effects. It was shown that highly dispersed bimetallic Pt-Ru alloy nanoparticles with no agglomeration can be synthesized on the carbon nanotubes with average particle sizes of less than 3.0 nm in diameter. The Pt-Ru nanoparticles are uniform and cover only the outside of the carbon nanotubes. It was found that the polyol process produced alloy compositions that are not consistent with the metal ratios in the precursors. It was also found that the lattice spacings of these catalysts are different due to the different compositions of the catalysts. Cyclic voltammetry showed that the catalysts were electrocatalytically active in the electrooxidation of methanol. Among the three catalysts, the Pt53Ru47 catalyst produced the best performance. This catalyst was found to be the most stable, while the other two deactivated faster in the oxidation of methanol. All three Pt-Ru catalysts have higher electrocatalytic activities than a commercial catalyst of Pt50Ru50 supported on carbon black. However, the Pt69Ru31 and Pt77Ru23 catalysts showed poorer stability that can be justified by the bifunctional mechanism of bimetallic Pt-Ru alloys.
6. Ren, Guoqiang., and Xing, Yangchuan. (2006). Deposition of metallic nanoparticles on carbon nanotubes via a fast evaporation process. Nanotechnology, Vol. 17.
Abstract: A new technique was developed for the deposition of colloidal metal nanoparticles on carbon nanotubes. It involves fast evaporation of a suspension containing sonochemically functionalized carbon nanotubes and colloidal nanoparticles. It was demonstrated that metallic nanoparticles with different sizes and concentrations can be deposited on the carbon nanotubes with only a few agglomerates. The technique does not seem to be limited by what the nanoparticles are, and therefore would be applicable to the deposition of other nanoparticles on carbon nanotubes. PtPd and CoPt3 alloy nanoparticles were used to demonstrate the deposition process. It was found that the surfactants used to disperse the nanoparticles can hinder the nanoparticle deposition. When the nanoparticles were washed with ethanol, they could be well deposited on the carbon nanotubes. The obtained carbon nanotube supported metal nanoparticles were characterized by transmission electron microscopy, energy dispersive x-ray spectroscopy, x-ray photoelectron spectroscopy, and cyclic voltammetry.
7. Li, Liang., and Xing, Yangchuan. (2006). Electrochemical durability of carbon nanotubes in non-catalyzed and catalyzed oxidations. Journal of electrochemical society, vol. 153, no. 10.
Abstract: Noncatalyzed and catalyzed electrochemical oxidations of multiwalled carbon nanotubes (CNTs) were studied with the aim to understand their durability as catalyst support in polymer electrolyte membrane (PEM) fuel cells. Bare and Pt-deposited CNTs were investigated in 1.0 M sulfuric acid at a constant potential of 1.2 V. Carbon black (CB, Vulcan XC-72R) was also studied under the same experimental conditions. The carbons were oxidized at room temperature in the form of thin-film electrodes with time durations up to 48 h. Cyclic voltammetry was used to monitor the surface oxide redox reactions as a way to quantify the degree of surface oxidation on the carbons. It was found that the redox current peaks were stabilized after 8 h for CNTs, but they continue to increase for CB, showing that CNTs are more resistant to electrochemical oxidation. Similar trends were observed in the catalyzed oxidation with Pt-deposited carbons. However, much larger currents were observed, demonstrating that catalyzed oxidation had indeed occurred. The observed durability demonstrated that CNTs would be a better catalyst support in PEM fuel cells in which the commonly used CB often undergoes severe electrochemical corrosion.
8. Hull, Robert Victor, Li, Liang, Xing, Yangchuan Chusuei, Charles C. (2006). Pt nanoparticle binding on functionalized multiwalled carbon nanotubes. Chemistry of materials, vol. 18, no. 7.
Abstract: To create new catalyst materials for fuel cell applications, multiwalled carbon nanotubes (CNTs) were functionalized with -C=O, -C-O-C-, -COO-, and -C-OH groups using a sonochemical treatment method under acidic aqueous solution (HNO3/H2SO4) conditions to make them amenable to deposition of highly dispersed, ~4 nm diameter Pt nanoparticles. The Pt-CNT interface was probed with X-ray photoelectron spectroscopy (XPS), extended X-ray absorption fine structure spectroscopy (EXAFS), and Raman and attenuated total reflection infrared (ATR-IR) spectroscopies to elucidate the nature of the Pt cluster-CNT surface binding. The degree of disorder of the sp3-hybridized C from the CNTs, as measured by the Raman D-to-G integrated peak area ratios, increased with the degree of surface oxidation of the CNTs. EXAFS of the Pt LIII edge showed Pt coordination with oxygen (in the form of PtOx) at the outermost perimeter of the Pt clusters while the majority of the bulk, as shown by the XPS Pt 4f core level, was in the metallic form. Infrared measurements showed that the carbonyl C=O stretching at 1700 cm-1 red shifted to ~1550 cm-1 following Pt cluster deposition. In addition, changes in the C-O structural features at ~1030 and 1150 cm-1 were observed, indicative of Pt cluster binding with the ionic form of carboxylate, COO(Pt), or ester-like, C(=O)CO(Pt), O atoms.
9. Xing, Yangchuan., Li, Liang., Chusuei, Charles C., and Hull, Robert Victor. (2005). Sonochemical oxidation of multi-walled carbon nanotubes. Langmuir, vol. 21, no. 9.
Abstract: Functionalization of carbon nanotubes (CNTs) is important for enhancing deposition of metal nanoparticles in the fabrication of supported catalysts. A facile approach for oxidizing CNTs is presented using a sonochemical method to promote the density of surface functional groups. This was successfully employed in a previous study [J. Phys. Chem. B 2004, 108, 19255] to prepare highly dispersed, high-loading Pt nanoparticles on CNTs as fuel cell catalysts. X-ray photoelectron spectroscopy (XPS), transmission electron microscopy, cyclic voltammetry, and settling speeds were used to characterize the degree of surface functionalization and coverage. The sonochemical method effectively functionalized the CNTs. A mixture of -C-O-/-C=O and -COO- was observed along with evidence for weakly bound CO at longer treatment times. The integrated XPS C 1s core level peak area ratios of the oxidized-to-graphitic C oxidation states, as well as the atom % oxygen from the O 1s level, showed an increase in peak intensity (attributed to -COx) with increased sonication times from 1 to 8 h; the increase in C surface oxidation correlated well with the measured atom %. Most of the CNT surface oxidation occurred between 1 and 2 h. The sonochemically treated CNTs were also studied by cyclic voltammetry and settling experiments, and the results were consistent with the XPS observations.
10. Xing, Yangchuan. (2004). Synthesis and electrochemical characterization of uniformly-dispersed high loading Pt nanoparticles on sonochemically-treated carbon nanotubes. Journal of physical chemistry B, vol. 108, no. 50.
Abstract: A sonochemical process was developed to treat carbon nanotubes in nitric and sulfuric acids to create surface functional groups for metal nanoparticle deposition. Carbon nanotubes treated in the sonochemical process are shown to lead to the deposition of uniformly dispersed high loading Pt nanoparticles, which have not been achieved with carbon nanotubes treated in reflux processes. Pt nanoparticles of a size less than 5 nm and loading up to 30 wt % with little aggregation were synthesized on the sonochemically treated carbon nanotubes. Cyclic voltammetry measurements in 1.0 M H2SO4 showed that the Pt nanoparticles on carbon nanotubes are more than 100% active in the electrochemical adsorption and desorption of hydrogen than the Pt nanoparticles supported on carbon black. This enhancement of electrochemical activity is attributed to the unique structures of carbon nanotubes and the interactions between the Pt nanoparticles and the carbon nanotube support. The ability to synthesize high loading Pt on carbon nanotubes using the sonochemical technique makes it possible to prepare high loading catalysts for the cathode of polymer electrolyte membrane (PEM) fuel cells.
11. Evaluation and testing of commercially-available carbon nanotubes as negative electrodes for lithium ion cells.
Abstract: Rechargeable lithium ion (Li-ion) battery technology offers significant performance advantages over the nickel-based technologies used for energy storage for the majority of NASA’s missions. Specifically Li-ion technology offers a threefold to fourfold increase in gravimetric and volumetric energy densities and produces voltages in excess of three times the value of typical nickel-based battery systems. As part of the Advanced Battery Technology program at NASA Glenn Research Center (GRC), a program on the evaluation of anodes for Li-ion cells and batteries was conducted. This study focused on the feasibility of using carbon nanotubes as anodes in Li-Ion cells. Candidate materials from multiple sources were evaluated. Their performance was compared to a standard anode comprised of mesocarbon microbeads.
This page was created on 08/16/2011|