Carbon Nanotube-supported Platinum Catalysts Research Articles

Diminishing Performance of Pt/CNT in Ethanol Oxidation after High-Potential Scanning

Regenerative fuel cells and the phenomenon of cell reversal (CR) necessitate creating robust catalyst layers for consistent performance in fuel cells. This research used in situ Raman spectroscopy to observe molecular alterations on carbon nanotube-supported platinum catalysts (Pt/CNT) during ethanol oxidation. Following a CR event simulation, the ethanol oxidation efficiency on Pt/CNT was amplified 2.8 times after high-potential scanning but reverted to its initial efficiency after 100 cycles. The adsorbed *CO2− species on Pt/CNT was pivotal for initiating ethanol oxidation, with the rate assessed through Raman analysis. In addition to water electrolysis, the carbon substrate was degraded. This study sheds light on the mechanisms behind catalyst degradation, steering the creation of more advanced catalysts.

Hydrogen generation from sodium borohydride hydrolysis by multi-walled carbon nanotube supported platinum catalyst: A kinetic study

In this study, it is aimed to investigate hydrogen (H2) generation from sodium borohydride (NaBH4) hydrolysis by multi-walled carbon nanotube supported platinum catalyst (Pt/MWCNT) under various conditions (0–0.03 g Pt amount catalyst, 2.58–5.03 wt % NaBH4, and 27–67 °C) in detail. For comparison, carbon supported platinum (Pt/C) commercial catalyst was used for H2 generation experiments under the same conditions. The reaction rate of the experiments was described by a power law model which depends on the temperature of the reaction and concentrations of NaBH4. Kinetic studies of both Pt/MWCNT and Pt/C catalysts were done and activation energies, which is the required minimum energy to overcome the energy barrier, were found as 27 kJ/mol and 36 kJ/mol, respectively. Pt/MWCNT catalyst is accelerated the reaction less than Pt/C catalyst while Pt/MWCNT is more efficient than Pt/C catalyst, they are approximately 98% and 95%, respectively. According to the results of experiments and the kinetic study, the reaction system based on NaBH4 in the presence of Pt/MWCNT catalyst can be a potential hydrogen generation system for portable applications of proton exchange membrane fuel cell (PEMFC).

Facile Route for Bio-Phenol Siloxane Synthesis via Heterogeneous Catalytic Method and its Autonomic Antibacterial Property.

Eugenol, used as bio-phenol, was designed to replace the hydrogen atom of hydrogenterminated siloxane by hydrosilylation reaction under the presence of alumina-supported platinum catalyst (Pt-Al2O3), silica-supported platinum catalyst (Pt-SiO2) and carbon nanotube-supported platinum catalyst (Pt-CNT), respectively. The catalytic activities of these three platinum catalysts were measured by nuclear magnetic resonance hydrogen spectrometer (1H NMR). The properties of bio-phenol siloxane were characterized by Fourier transform infrared spectrometer (FT–IR), UV-visible spectrophotometer (UV) and thermogravimeter (TGA), and its antibacterial property against Escherichia coli was also studied. The results showed that the catalytic activity of the catalyst Pt-CNT was preferable. When the catalyst concentration was 100 ppm, the reaction temperature was 80 °C and reaction time was 6 h, the reactant conversion rate reached 97%. After modification with bio-phenol, the thermal stability of the obtained bio-phenol siloxane was improved. For bio-phenol siloxane, when the ratio of weight loss reached 98%, the pyrolysis temperature was raised to 663 °C which was 60 °C higher than hydrogenterminated siloxane. Meanwhile, its autonomic antibacterial property against Escherichia coli was improved significantly.

Electrochemical CO2 Reduction to Fuels Using Pt/CNT Catalysts Synthesized in Supercritical Medium

The electrochemical reduction of CO2 in the gas phase has been carried out in a solid polymer electrolyte type cell (25 cm2 geometric area) in continuous operation mode using carbon nanotube-supported platinum catalysts (Pt/CNT). The main novelty of this work relies on the use of supercritical media (supercritical CO2) for Pt deposition on CNT. Supercritical synthesis has allowed obtaining small Pt nanoparticles divided into two modal distributions (for 3–4 nm and 8–9 nm, respectively) with a high deposition efficiency (about 80%). The main reaction products of the electrocatalytic conversion of CO2 have been formic acid (59–89%), methane (2–33%), CO (3–11%), methanol (0–1.9%), and small amounts of acetone, isopropanol, and methyl acetate. The CO2 conversion rate multiplies almost by four when increasing current density, although selectivity barely changes. Lower temperature promotes further reduction of CO2 to methane (33% of selectivity) to the detriment of formic acid and CO. However, increases of temp...

Promoting role of bismuth on carbon nanotube supported platinum catalysts in aqueous phase aerobic oxidation of benzyl alcohol

PtBi/CNT catalyst was synthesized by a one-step polyol reduction method assisted by microwave radiation, and its catalytic performance was investigated in aerobic oxidation of benzyl alcohol in the aqueous phase. Pt and BiOx species uniformly dispersed on the CNT surfaces and strong synergic interaction between them occurred, which confirmed by the comprehensive analysis of TEM, XRD, XPS and electrochemical characterizations. Further investigations revealed that the synergic effect effectively promoted the activation of both molecular oxygen and benzyl alcohol substrate; also protected Pt active sites from over-oxidization. The advantage of such synergic effect was reflected in the increased yield for the desired product benzaldehyde: PtBi/CNT catalyst exhibited about 3.5 times higher yield toward benzaldehyde compared to Pt/CNT catalyst. Furthermore, owing to the positive effect of Bi avoiding Pt from oxidizing, the deactivation of PtBi/CNT (with 2% selectivity and 9% conversion decrease) is much slower than that of Pt/CNT (with 8% selectivity and 39% conversion decrease) after six reaction cycles. PtBi/CNT catalyst was proved as a remarkably effective catalyst with high stability for the aerobic oxidation of benzyl alcohol.

Synthesis of multiwall carbon nanotube-supported platinum catalysts by solution plasma processing for oxygen reduction in polymer electrolyte fuel cells

Two preparation methods with solution plasma (SP) processing were carried out to produce Pt nanoparticles (PtNPs) on multi-wall carbon nanotubes (MWCNTs). One is the method that PtNPs were attached on MWCNTs using a SP irradiation after PtNPs were solely produced by a SP irradiation. The other is that the formation of PtNPs on MWCNTs was performed using a SP irradiation after a Pt precursor was adsorbed on MWCNTs. PtNPs were well anchored and uniformly dispersed on the MWCNTs prepared by using the latter method. The average sizes of PtNPs estimated by transmittance electron microscopy (TEM) images were about 5 to 9nm with the former method and about 2 to 3nm with the latter method, respectively. It was revealed that the bulk of PtNPs produced by a solution plasma irradiation is in metal state analyzed on the basis of X-ray diffraction (XRD) measurements. An accelerated durability test was performed using a saw-tooth potential wave. Apparent degradation rates of Pt/MWCNTs prepared by the methods toward oxygen reduction activity were smaller than that of 20% Pt-XC72R.

Processing of pristine carbon nanotube supported platinum as catalyst for PEM fuel cell

Pristine multiwalled carbon nanotube supported platinum catalyst (Pt/CNT) has been developed by reduction of Pt salt on CNTs in ethylene glycol solution. The reactions were carried out under different pH conditions followed by detailed physical and electrochemical characterizations. The I–V performance of unit Polymer electrolyte membrane fuel cell shows a peak Power density of 325 mWcm−2 with catalyst prepared in alkaline medium, an increase of >250 % as compared to 87 mWcm−2 obtained, while employing catalyst prepared in acidic medium and tested under similar conditions. This is attributed not only to the uniform distribution of Pt nanoparticles with small particle size in range of 2–3 nm, but also to the metallic or zero oxidation state in which most of the Pt is present when reduction is carried out in alkaline medium.

Activation of carbon-supported platinum catalysts by sodium for the low-temperature water-gas shift reaction

The activation of multi-walled carbon nanotube-supported platinum catalysts for the low-temperature water-gas shift reaction is demonstrated by the addition of sodium. Nitric acid oxidation of the carbon nanotubes allows for the addition of sodium through ion-exchange and creates anchoring sites for platinum. We show that an oxidized platinum state is stabilized by the presence of sodium. Evidence for a sodium-promoted Pt-(OH)x active site is given through XPS analysis of the catalysts before and after reaction and confirmed by CO-TPR. Removal of the oxygen groups and partial removal of sodium by annealing the Na-modified carbon nanotubes to 800°C in inert atmosphere creates a surface on which Pt is initially very active, but of lower stability due to the absence of a sufficient number of surface sodium anchoring sites.

Catalytic performance of acid-treated multi-walled carbon nanotube-supported platinum catalyst for PEM fuel cells

Effects of the surface functional groups of multi-walled carbon nanotubes (MWCNTs) as catalyst support for the durability of polymer electrolyte membrane fuel cells (PEMFCs) were examined at high Pt loading conditions. The amount of oxygen functional groups on the MWCNTs surface was increased as the acid treatment time and temperature increased. We found that more functional groups in MWCNTs improved initial Pt dispersion but deteriorated durability due to the reduced carbon corrosion resistance. The experimental results also showed that despite the surface oxidation, Pt/MWCNT catalysts showed highly improved durability than Pt/C catalysts due to the graphitic nature of MWCNTs. Membrane electrode assembly (MEA) fabricated by 4h acid treated MWCNTs at 25°C showed 4 times better durability than commercial Pt/C based MEA at the reverse potential operation generated by fuel starvation conditions. We believe that MWCNTs can be effectively used for PEMFCs even at high loading due to their excellent anti-corrosion properties.

Polyaniline-Functionalized Carbon Nanotube Supported Platinum Catalysts

Electrocatalytically active platinum (Pt) nanoparticles on a carbon nanotube (CNT) with enhanced nucleation and stability have been demonstrated through introduction of electron-conducting polyaniline (PANI) to bridge the Pt nanoparticles and CNT walls with the presence of platinum-nitride (Pt-N) bonding and π-π bonding. The Pt colloids were prepared through ethanol reduction under the protection of aniline, the CNT was dispersed well with the existence of aniline in the solution, and aniline was polymerized in the presence of a protonic acid (HCl) and an oxidant (NH(4)S(2)O(8)). The synthesized PANI is found to wrap around the CNT as a result of π-π bonding, and highly dispersed Pt nanoparticles are loaded onto the CNT with narrowly distributed particle sizes ranging from 2.0 to 4.0 nm due to the polymer stabilization and existence of Pt-N bonding. The Pt-PANI/CNT catalysts are electroactive and exhibit excellent electrochemical stability and therefore promise potential applications in proton exchange membrane fuel cells.

Carbon nanotube supported platinum catalysts for the ozonation of oxalic acid in aqueous solutions

Ozonation of oxalic acid in the presence of carbon nanotube (CNT) supported platinum (Pt/CNT) catalyst in aqueous solution was studied. The activity and stability of Pt/CNT, the influence of preparation conditions on Pt/CNT activity and the ozonation mechanism of oxalic acid with Pt/CNT were investigated. It was found that Pt/CNT was more active for oxalic acid removal and more resistant to ozonation compared with the case of activated carbon supported Pt catalyst. The Pt loading, reduction temperature and pyrolysis atmosphere significantly influenced the Pt/CNT activity, especially for pyrolysis atmosphere. By means of X-ray diffraction and X-ray photoelectron spectroscopy analysis, the aggregation of Pt and the existence of chemisorbed oxygen with Pt were found when the Pt/CNT catalyst was prepared by calcination, which are unfavorable for its performance. The CNT was oxidized and some acidic groups were generated in calcination, which also cause a decrease of Pt/CNT activity. A free radical mechanism was proposed which involves ozone decomposition and hydrogen peroxide formation for oxalic acid degradation on Pt/CNT. The redox couple of Pt red/Pt ox was suggested to be crucial for the improvement of CNT activity. The Pt/CNT has a good stability after five re-uses without any leaching of Pt.

Sulfonation of carbon-nanotube supported platinum catalysts for polymer electrolyte fuel cells

Sulfonic acid groups were grafted onto the surface of carbon-nanotube supported platinum (Pt/CNT) catalysts to increase platinum utilization in polymer electrolyte fuel cells (PEFCs) by both thermal decomposition of ammonium sulfate and in situ radical polymerization of 4-styrenesulfonate. The resultant sulfonated Pt/CNT catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectrometry, thermal gravimetric analysis (TGA) and electrochemical methods. The electrodes with the Pt/CNT catalysts sulfonated by the in situ radical polymerization of 4-styrenesulfonate exhibited better performance than did those with the unsulfonated counterparts, mainly because of the easier access with protons and well dispersed distribution of the sulfonated Pt/CNT catalysts, indicating that sulfonation is an efficient approach to improve performance and reduce cost for the Pt/CNT-based PEFCs. The electrodes with the Pt/CNT catalysts sulfonated by the thermal decomposition of ammonium sulfate, however, did not yield the expected performance as in the case of carbon black supported platinum (Pt/C) catalysts, probably due to the significant agglomeration of platinum particles on the CNT surface at high temperatures, indicating that the Pt/CNT catalysts are more sensitive to temperature than the Pt/C catalysts.

Nitrobenzene hydrogenation with carbon nanotube-supported platinum catalyst under mild conditions

Abstract Carbon nanotube (CNT)-supported Pt catalysts have been prepared by impregnation and reduction–precipitation method using chloroplatinic acid as metal precursor. The structure of the catalysts has been characterised using TEM, BET and XPS. The catalytic performance for nitrobenzene hydrogenation was evaluated under atmospheric pressure and ambient temperature. The results show that the catalysts, both of low and higher Pt loading, show high activity for nitrobenzene directly hydrogenating to aniline under mild conditions. The highly dispersed Pt and mesoporosity structure of acid-oxidized CNT-supported Pt catalyst are responsible for the extraordinary activity.