PtRu Catalysts Research Articles

Effect of the relationship between particle size, inter-particle distance, and metal loading of carbon supported fuel cell catalysts on their catalytic activity

The effect of the relationship between particle size (d), inter-particle distance (x i ), and metal loading (y) of carbon supported fuel cell Pt or PtRu catalysts on their catalytic activity, based on the optimum d (2.5–3 nm) and x i /d (>5) values, was evaluated. It was found that for y < 30 wt%, the optimum values of both d and x i /d can be always obtained. For y ≥ 30 wt%, instead, the positive effect of a thinner catalyst layer of the fuel cell electrode than that using catalysts with y < 30 wt% is concomitant to a decrease of the effective catalyst surface area due to an increase of d and/or a decrease of x i /d compared to their optimum values, with in turns gives rise to a decrease in the catalytic activity. The effect of the x i /d ratio has been successfully verified by experimental results on ethanol oxidation on PtRu/C catalysts with same particle size and same degree of alloying but different metal loading. Tests in direct ethanol fuel cells showed that, compared to 20 wt% PtRu/C, the negative effect of the lower x i /d on the catalytic activity of 30 and 40 wt% PtRu/C catalysts was superior to the positive effect of the thinner catalyst layer.

Low-defect multi-walled carbon nanotubes supported PtCo alloy nanoparticles with remarkable performance for electrooxidation of methanol

PtCo alloy nanoparticles have been deposited on multi-walled carbon nanotubes (MWNTs) without damaging their intrinsic structures by a soft chemical method. X-ray diffraction depicts a good crystallinity of the supported Pt nanoparticles in the composites and reveals the formation of PtCo alloy. Transmission electron microscope (TEM) images show that the PtCo particles are as small as 1–6nm and uniformly deposited on the MWNT surface. Raman spectroscopy confirms there is a very low defect density on the MWNT surface. Compared with acid-treated MWNT–PtCo, low-defect MWNT–Pt and commercial PtRu catalysts, this low-defect MWNT–PtCo catalyst exhibits excellent electrochemical activity and high poison tolerance toward methanol oxidation reaction. The significantly enhanced performances can be attributed to the good preservation of electronic conductivity of MWNTs, the synergistic effect of the bimetallic active components and high dispersion of PtCo alloy nanoparticles on the MWNT surface.

Optimization of the Electrodepositon Process of PtRu Catalysts for Methanol Electro-Oxidation by Orthogonal Test

Orthogonal test was used to optimize the electrodeposition process of PtRu catalysts for methanol electro-oxidation. The morphology, composition and catalytic activities of the prepared catalysts were measured by scanning electron microscope (SEM), energy dispersive X-Ray spectroscopy (EDS) and cyclic voltammetry (CV). The results show that the optimum electrodeposition conditions are: the concentrations of H2PtCl6 and RuCl3 of 2.5 mM, the concentration of H2SO4 of 0.1 M, the electrodeposition potential of -0.25 V vs SCE, and the electrodeposition time of 10 min. Under these electrodeposition conditions, the prepared PtRu catalyst demonstrates excellent catalytic activity for methanol electro-oxidation.

Effect of a nitrogen-doped PtRu/carbon anode catalyst on the durability of a direct methanol fuel cell

Electrochemical performance and durability of PtRu supported on N-doped Vulcan is evaluated as an anode in membrane electrode assembly (MEA) single-cell direct methanol fuel cell (DMFC) studies. This material is compared to two reference materials, an in-house PtRu catalyst supported on undoped Vulcan, prepared under the same conditions as the N-doped material besides doping, and a commercial PtRu/C (JM5000). Durability was tested out to 645 h, with periodic interruption for electrochemical testing. After durability, the MEA with N-doped PtRu/C retained more electrochemically active metal on the anode than the MEAs with commercial PtRu/C and undoped PtRu/C (124 compared to 106 and 82 cm2 anode active area per cm2 geometric surface area, respectively). From cathode CO stripping experiments and SEM-EDS studies, it was determined that the MEA with the undoped PtRu/C anode has twice as much ruthenium crossover as the MEA with the N-doped PtRu/C anode. Overall, the MEA with N-doped PtRu/C demonstrates significantly better methanol:air polarization performance compared to the MEA with undoped PtRu/C, and performs comparably to the MEA made with the commercial PtRu/C. The increase in durability for the MEA with the N-doped anode is attributed to nitrogen doping mitigating both anode metal dissolution and Ru crossover.

Microwave assisted polyol method for the preparation of Pt/C, Ru/C and PtRu/C nanoparticles and its application in electrooxidation of methanol

A polyol process activated by microwave irradiation was implemented to prepare efficient Pt/C, Ru/C and Pt1Ru1/C electrocatalysts for methanol oxidation with reducing synthesis cost and time. Study of the post-synthesis mixture by UV–visible spectroscopy led to determine the minimum batch temperature and synthesis time necessary for the complete reduction of metal salts. It was shown that disappearance of metal salts and colloid formation took place after 5min at 100°C for Pt, 5min at 130°C for Ru and 5min at 160°C for Pt1Ru1. The PtRu catalyst characterizations by TGA, TEM and XRD indicated that the nominal loading and nominal composition were achieved, and that the structure of this material consisted of a mixture of Pt0.8Ru0.2 monocrystalline particles of ca. 2.5–3.0nm, RuO2 nanoclusters and probably Ru nanoclusters. Pt1Ru1/C catalyst displayed a high activity towards CO and methanol electrooxidation, with onset potentials of ca. 0.2V lower than those obtained on Pt/C catalysts, and a low surface poisoning at 0.6V vs. as demonstrated by chronoamperometry measurement RHE and in situ infrared reflectance spectroscopy.

Synthesis and electrocatalytic performance of high loading active PtRu multiwalled carbon nanotube catalyst for methanol oxidation

Multiwalled carbon nanotube (MWCNT) supported PtRu catalyst was prepared by improved aqueous impregnation method. The catalyst nanoparticles were characterized by using high resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) measurements. According to the results of physicochemical characterization, PtRu alloy nanoparticles with low content of surface oxidation states were successfully synthesized on the outer surface of MWCNT supporting materials. Electrocatalytic activity of catalyst materials was investigated by using electrochemical half cell and CO stripping analyses. Results of electrochemical measurements indicate that the prepared PtRu/MWCNT catalyst shows an enhanced electrochemical activity toward methanol oxidation and a high electrocatalytic activity for CO oxidation. It is believed that superior performance of the PtRu/MWCNT catalyst is mostly attributed to the high degree of alloy formation and low contents of oxidized species of Pt and Ru.

A linear molecule functionalized multi-walled carbon nanotubes with well dispersed PtRu nanoparticles for ethanol electro-oxidation

The performance-enhanced PtRu electrocatalysts derived from polyoxyethylene bis(amine) functionalized multi-walled carbon nanotubes (POB-MWCNTs) were fabricated by electrostatic self-assembly technology, in which Pt and Ru precursors were first uniformly distributed on the POB-functionalized MWCNT surface via the electrostatic interaction and then reduced in situ to PtRu nanoparticles in ethylene glycol-water solution. In this process, POB as the wrapping molecule not only preserves the integrity and well dispersion of MWCNTs, but also facilitates the even distribution of PtRu nanoparticles on the surface of MWCNTs. The structure and catalytic properties of the PtRu catalysts were characterized by various spectroscopic techniques such as FT-IR, Raman, TGA, XPS, TEM and XRD spectrometry, and the electrocatalytic properties for ethanol oxidation were investigated by cyclic voltammetry and chronoamperometry. It was revealed that the as-prepared PtRu catalysts possess a high electrocatalytic activity and stability for the electro-oxidation of ethanol, and it provides a facile and eco-friend approach to large-scale production of high performance fuel cell eletrocatalysts.

Nitrogen-doping templated nanoporous graphitic nanocage and its supported catalyst towards efficient methanol oxidation

A unique hollow graphitic nanocage material made up of a few graphitic layers is prepared by using a nitrogen (N)-doping template. The removal of N atoms creates a high density of nanopores on the shells of hollow graphitic nanocages. The prepared N-templated nanocages have a higher specific surface area (595 vs. 530m2g−1) and a much larger mesopore volume (0.72 vs. 0.42cm3g−1) in comparison to the material prepared without the N-doping template. The nanopores on the shell of a N-templated nanocage significantly increase the utilization of its hollow structure for loading catalysts to provide more reaction electro-active sites while promoting molecule diffusion across the shell, making it an excellent material to support PtRu catalysts towards efficient methanol oxidation, which is superior to regular graphitic nanocage supported PtRu and the commercial PtRu/C with the same amount of PtRu loading.

Carbide Derived Carbons Supported Pt and Pt-Ru Catalysts for PEMFC

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Diamond Nanoparticles as a Support for Pt and PtRu Catalysts for Direct Methanol Fuel Cells

Diamond in nanoparticle form is a promising material that can be used as a robust and chemically stable catalyst support in fuel cells. It has been studied and characterized physically and electrochemically, in its thin film and powder forms, as reported in the literature. In the present work, the electrochemical properties of undoped and boron-doped diamond nanoparticle electrodes, fabricated using the ink-paste method, were investigated. Methanol oxidation experiments were carried out in both half-cell and full fuel cell modes. Platinum and ruthenium nanoparticles were chemically deposited on undoped and boron doped diamond nanoparticles through the use of NaBH(4) as reducing agent and sodium dodecyl benzene sulfonate (SDBS) as a surfactant. Before and after the reduction process, samples were characterized by electron microscopy and spectroscopic techniques. The ink-paste method was also used to prepare the membrane electrode assembly with Pt and Pt-Ru modified undoped and boron-doped diamond nanoparticle catalytic systems, to perform the electrochemical experiments in a direct methanol fuel cell system. The results obtained demonstrate that diamond supported catalyst nanomaterials are promising for methanol fuel cells.

Electrochemical Characterization of PtRu Nanoparticles Supported on Mesoporous Carbon for Methanol Electrooxidation

Nanoparticles of PtRu supported on mesoporous carbon were obtained by the impregnation and reduction method with NaBH4. The high-surface-area mesoporous carbon was obtained by carbonization of a resorcinol-formaldehyde polymer with a cationic polyelectrolyte as a soft template. Surface characterization performed by transmission electron microscopy and powder X-ray diffraction showed a homogeneous distribution and high dispersion of metal particles. The PtRu catalyst shows an electrochemical active surface area, determined by CO stripping, 45% higher than PtRu catalyst synthesized by the same method on Vulcan. This translated in a 25% increase in the methanol oxidation current as well as a lower poisoning rate and higher turnover frequency, as was assessed by cyclic voltammetry and chronoamperometry. Differential electrochemical mass spectroscopy indicated an 8% higher conversion efficiency of methanol to CO2, demonstrating the benefits of using a mesoporous carbon as catalyst support.

Effect of Plasma Treatments to Graphite Nanofibers Supports on Electrochemical Behaviors of Metal Catalyst Electrodes

In the present work, we had studied the graphite nanofibers as catalyst supports after a plasma treatment for studying the effect of surface modification. By controlling the plasma intensity, a surface functional group concentration was changed. The nanoparticle size, loading efficiency, and catalytic activity were studied, after Pt-Ru deposition by a chemical reduction. Pt-Ru catalysts deposited on the plasma-treated GNFs showed the smaller size, 3.58 nm than the pristine GNFs. The catalyst loading contents were enhanced with plasma power and duration time increase, meaning an enhanced catalyst deposition efficiency. Accordingly, cyclic voltammetry result showed that the specific current density was increased proportionally till 200 W and then the value was decreased. Enhanced activity of 40 (mA mg(-1)-catalyst) was accomplished at 200 W and 180 sec duration time. Consequently, it was found that the improved electroactivity was originated from the change of size or morphology of catalysts by controlling the plasma intensity.

CO electrooxidation on Pt–Ru catalysts supported on carbon nanotubes

CO electrooxidation studies can be done in relation to either the poisoning effect in methanol fuel cells or to be applied as basis for the development of electrochemical CO sensors. In the present work, Pt and PtRu catalysts supported on multiwalled carbon nanotubes, CNTs, are probed with regard to their ability to detect changes in the CO concentration in acidic solutions. Pt and PtRu particles were dispersed onto pretreated CNTs by a modified polyol process using RuCl3 and H2PtCl6 as their metallic precursors. The physical characterization and dispersion of the catalytic particles were obtained through SEM and TEM images, and EDX analysis provided the chemical composition. CO oxidation was studied applying electrochemical techniques. For both catalysts, linear relationships were obtained when relating chronoamperometric current densities to different CO concentrations, indicating their possible application as CO sensors’devices materials.

Fabrication of Nonenzymatic Glucose Sensors Based on Multiwalled Carbon Nanotubes with Bimetallic Pt-M (M = Ru and Sn) Catalysts by Radiolytic Deposition

Nonenzymatic glucose sensors employing multiwalled carbon nanotubes (MWNTs) with highly dispersed Pt-M (M = Ru and Sn) nanoparticles (Pt-M@PVP-MWNTs) were fabricated by radiolytic deposition. The Pt-M nanoparticles on the MWNTs were characterized by transmittance electron microscopy, elemental analysis, and X-ray diffraction. They were found to be well dispersed and to exhibit alloy properties on the MWNT support. Electrochemical testing showed that these nonenzymatic sensors had larger currents (mA) than that of a bare glassy carbon (GC) electrode and one modified with MWNTs. The sensitivity (A mM−1), linear range (mM), and detection limit (mM) (S/N = 3) of the glucose sensor with the Pt-Ru catalyst in NaOH electrolyte were determined as 18.0, 1.0–2.5, 0.7, respectively. The corresponding data of the sensor with Pt-Sn catalyst were 889.0, 1.00–3.00, and 0.3, respectively. In addition, these non-enzymatic sensors can effectively avoid interference arising from the oxidation of the common interfering species ascorbic acid and uric acid in NaOH electrolyte. The experimental results show that such sensors can be applied in the detection of glucose in commercial red wine samples.

The electrocatalytic properties of carbon supported PtRu/C nanoalloys in oxidation of small organic molecules: Comparison with Pt/C catalyst

The electrocatalytic activity of carbon supported PtRu/C catalysts, with different composition, toward the electrooxidation of methanol, CO and formic acid were examined in acid and alkaline solution at ambient temperature using thin-film rotating disk electrode (RDE) method and compared with activity of Pt/C. The catalysts were characterized by XRD, AFM and STM techniques. XRD pattern revealed that PtRu-1/C catalyst is consisted of two structures e.g. Pt-Ru-fcc and Ru-hcp (the solid solution of Ru in Pt and the small amount of Ru or solid solution of Pt in Ru), as opposed to PtRu-2/C catalyst which is consisted of one structure mostly, Pt-Ru-fcc. According to STM images, PtRu as well as Pt, particles size were between 2 and 6 nm, which is in a good agreement with the mean particles size determined by XRD. To establish the activity and stability of the catalysts potentiodynamic and quasi steady-state measurements were performed. It was found that the activity of Pt and PtRu for CO and methanol oxidation is a strong function of pH of solution. The kinetics are much higher in alkaline than in acid solution and the difference between Pt/C and PtRu/C is much less pronounced in alkaline media. Results presented in this work indicate that activity of PtRu catalysts depends on catalyst composition, e.g. on Pt/Ru atomic ratio, as well as on alloying degree of catalysts. Comparison of CO, methanol and formic acid oxidation on PtRu-2/C, PtRu-1/C and Pt/C catalysts revealed that PtRu-2/C is the most active one. It was shown that the PtRu-2/C catalyst, due to fact that it is consisted of only one phase, with high alloying degree, through the bifunctional mechanism improved by electronic effect, achieve the activity two times higher related to PtRu-1/C in the oxidation of all organic molecules investigated, and about three times higher compared to Pt/C in the oxidation of methanol and CO, and five times higher in formic acid oxidation.

Exploring the Fuel Limits of Direct Oxidation Proton Exchange Membrane Fuel Cells with Platinum Based Electrocatalysts

This paper reports data on a number of more challenging potential direct proton exchange membrane (PEM) fuel cell fuels using standard membrane electrode assemblies. We have demonstrated that methane, and also molecules that can be conventionally catalytically dehydrogenated, can produce activity in PEM fuel cells. Methane and cyclohexane can be electrochemically oxidized but poorly. For the first time we have demonstrated that hydrogen storage compounds, N-ethyl-dodecahydrocarbazole, and dodecahydrofluorene -as the neat liquids, can be oxidized in fuel cells. The high OCV shows that the thermodynamics are very favorable for using the compounds in a direct PEM fuel cell setup. However, it is clear from this work that considerably more research is needed for devising adequate electrooxidation catalysts for these hydrogen-regenerable fuels. Direct hydroquinone fuel cells using a PtRu catalyst system where hydroquinone is oxidized to benzoquinone are demonstrated. The effects of temperature, pressure and feed concentration on the fuel cell performance were evaluated. At a 20 psi back pressure, 80°C cell temperature and 0.5 M feed concentration with a PtRu oxidation catalyst an open circuit potential of 297 mV was observed with a maximum current density of 15 mA/cm2 at 100 mV.

Nanostructured trimetallic Pt/FeRuC, Pt/NiRuC, and Pt/CoRuC catalysts for methanol electrooxidation

We report the preparation and characterization of metal–carbon nanocomposites (NiRuC, FeRuC, and CoRuC) with bimetallic Ni–Ru, Fe–Ru, and Co–Ru nanoparticles incorporated into the pore walls of ordered mesoporous carbon, which were synthesized via a template strategy. Pt nanoparticles were deposited on the nanocomposites separately, which is different from the traditional alloying method. Nitrogen adsorption, X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, and thermogravimetric analysis techniques were used to characterize the materials. It was found that bimetallic nanoparticles (Ni–Ru, Fe–Ru, and Ru–Co) are homogenously dispersed in the carbon matrix and Pt nanoparticles with a size of less than 5 nm are widely distributed within the nanocomposites. The Pt/CoRuC catalyst shows better catalytic activity for the methanol oxidation reaction (MOR) than Pt on FeRuC or NiRuC, and its performance is also closer to that of the commercial PtRu catalyst with a slightly higher metal loading. A kinetic-based impedance model was used to simulate the electrochemical properties of the catalysts and matches well with the MOR performances of the catalysts. The promotional effect of the bimetallic/carbon nanocomposites on the catalytic activity of Pt was evidenced, and more importantly, the ligand effect was demonstrated by our results to be the major factor in the enhancement. Our investigation not only provides further insight into the roles of Fe, Ni and Co in MOR, but also assists in the design and synthesis of the new types of nanostructured electrocatalyst supports.

Durability of different carbon nanomaterial supports with PtRu catalyst in a direct methanol fuel cell

PtRu catalysts with similar particle size and composition were deposited on three different carbon supports: Vulcan, graphitized carbon nanofibers (GNF) and few-walled carbon nanotubes (FWCNT) and their performance for methanol oxidation was studied in an electrochemical cell and in a single cell DMFC. The electrochemical results indicate that with PtRu/GNF and PtRu/FWCNT higher current densities are obtained and oxidation intermediates deactivate the surface less compared to the same catalyst on Vulcan support. Conversely, PtRu/Vulcan provided the highest open circuit voltage OCV and current densities in DMFC experiments due to a well-optimized electrode layer structure. Because stability is a key requirement for fuel cell commercialization, 6-day-long fuel cell stability tests were carried out, showing that PtRu/Vulcan degraded significantly. This was due to the collapse of the secondary structure of the electrode layer revealed by post characterization of the membrane electrode assembly (MEA) with SEM and TEM. PtRu/GNF exhibited slightly poorer initial performance but better stability because the structure of the anode layer was maintained. PtRu/FWCNT showed the worst initial performance and long-term stability. The good stability of non-optimized PtRu/GNF MEAs shows the potential of these novel nanocarbon supported catalysts as stable fuel cell components after proper MEA optimization.

NaOH 활성화된 탄소나노섬유의 직접 메탄올 연료전지용 연료극 촉매의 담지체로서의 특성 고찰

Porous carbon nanofibers(CNF) were synthesized via NaOH activation at 700~, and the porous CNF-supported PtRu catalysts were evaluated for the anode in direct methanol fuel cells. The change of surface characteristics by NaOH activation was examined by analyses of the specific surface area and pore size distribution. The morphological and structural modification was investigated under scanning electron microscopy. The activity of catalysts supported on porous CNFs was examined by cyclic voltammograms and single cell tests. The pore formation on CNF by the NaOH activation was discussed, concerning the catalyst activity, when they were applied as catalyst supports.

A Comparative Study of Carbon-Supported Pt-Mo and Pt-Ru Catalysts for the Anodic Oxidation of Methanol

Different carbon-supported Pt-Mo and Pt-Ru materials were synthesized and a systematic study was carried out in order to evaluate their catalytic activity towards methanol oxidation. Direct current methods were applied in sulfuric acid and methanol - containing electrolytes, in order to evaluate the electrochemical response of the studied electrodes. Pt-Mo catalysts reveal similar performances and, in some cases, higher than Pt-Ru materials. For both catalysts series, it was found that low loadings of the promoting metal (Ru or Mo) improve the methanol oxidation activity. Characterizations by means of transmission electron microscopy and X-Ray Diffraction allowed to measure mean particle sizes below 10 nm for all phases. The Pt-Ru catalysts consist of metallic Pt and metallic ruthenium, while in the The Pt-Mo materials platinum is present in its metallic state and MoO3 is the predominant molybdenum species.