Dispersion Of Pt Nanoparticles Research Articles

Metal-Support Interactions of Platinum Nanoparticles Decorated N-Doped Carbon Nanofibers for the Oxygen Reduction Reaction.

N-doped carbon materials are discussed as catalyst supports for the electrochemical oxygen reduction reaction (ORR) in fuel cells. This work deals with the preparation of Pt nanoparticles (NPs) supported on N-doped carbon nanofibers (N-CNF) from a polyaniline nanofiber (PANI NF) precursor, and investigates the ORR activity of the produced materials. Initially, Pt NPs are deposited on PANI NFs. The PANI NF precursors are characterized by near-edge X-ray absorption fine structure (NEXAFS) and transmission electron microscopy (TEM) measurements. It is shown, that in the PANI NF precursor materials electrons from the Pt are being transferred toward the π-conjugated systems of the aromatic ring. This strong interaction of Pt atoms with PANI explains the high dispersion of Pt NPs on the PANI NF. Subsequently, the PANI NF precursors are carbonized at different heat-treatment conditions resulting in structurally different N-CNFs which are characterized by NEXAFS, X-ray photoelectron spectroscopy (XPS) ,and TEM measurements. It is shown that an interaction between N-groups and Pt NPs exists in all investigated N-CNFs. However, the N-CNFs differ in the composition of the N-species and the dispersion of the Pt NPs. A small mean Pt NP size with a narrow size distribution is attributed to the presence of pyrdinic N-groups in the N-CNFs, whereas, for the N-CNFs with mainly graphitic and pyrrolic N-groups, an increase in the average Pt NP size with a broad size distribution is found. The ORR activity in alkaline media investigated by Koutecky-Levich analysis of rotating disk electrode measurements showed a largely enhanced ORR activity in comparison to a conventional Pt/C catalyst.

Super-paramagnetic core-shell material with tunable magnetic behavior by regulating electron transfer efficiency and structure stability of the shell

In this work, a spherical nano core-shell material was constructed by encapsulating Fe3O4 microsphere into conductive polymer-metal composite shell. The Fe3O4 microspheres were fabricated by assembling large amounts of Fe3O4 nano-crystals, which endowed the microspheres with super-paramagnetic property and high saturation magnetization. The polymer-metal composite shell was constructed by inserting Pt nano-particles (NPs) into the conductive polymer polypyrrole (PPy). As size and dispersion of the Pt NPs has an important influence on their surface area and surface energy, it was effective to enlarge the interface area between PPy and Pt NPs, enhance the electron transfer efficiency of PPy/Pt composite shell, and reinforced the shell’s structural stability just by tuning the size and dispersion of Pt NPs. Moreover, core-shell structure of the materials made it convenient to investigate the PPy/Pt shell’s shielding effect on the Fe3O4 core’s magnetic response to external magnetic fields. It was found that the saturation magnetization of Fe3O4/PPy/Pt core-shell material could be reduced by 20.5% by regulating the conductivity of the PPy/Pt shell.

Nitrogen-doped carbon with mesoporous structure as high surface area catalyst support for methanol oxidation reaction

Mesoporous nitrogen-doped carbon (MNC) with a high surface area has been synthesized via carbonizing polyaniline using silica nanoparticles as template. The more silica nanoparticles, the smaller the micropore surface area is and the larger the mesoporous surface area is. Moreover, with an increase in the amount of silica nanoparticles, the electrocatalytic activity of Pt/MNC catalysts shows a downward trend after an intimal increase, and the Pt/MNC-1/6 (with the weight ratio of aniline monomer to silica nanoparticles of 1/6) catalyst has the highest activity, ascribed to the optimal Pt nanoparticles size, which is closely related to the pore structure of the support. In addition, the electrocatalytic activity and stability of Pt/MNC-1/6 catalyst are significantly superior to that of Pt/nitrogen-doped carbon (Pt/CNx) catalyst. For the same electrocatalytic activity, the Pt loading of Pt/MNC-1/6 catalyst is reduced by 33.3% compared to the Pt/CNx catalyst. The high electrocatalytic activity originates from the introduction of mesoporous structures that can facilitate mass transfer and improve the dispersion of Pt nanoparticles. Furthermore, the Ostwald ripening behavior of Pt nanoparticles is limited in the mesoporous structure of MNC-1/6, which weakens the aggregation effect of Pt nanoparticles during the electrocatalytic processes, thus enhancing the electrocatalytic stability of the catalyst.

Nitrogen-doped porous carbons supported Pt nanoparticles for methanol oxidation in alkaline medium

Honeycomb-like nitrogen-doped porous carbons (NPCs) have been prepared using ionic liquids 1-butyl-3-methylimidazolium dicyanamide (BMIMdca) as the carbon precursor, and silica spheres as the templates. The obtained NPCs were employed as supports of Pt nanoparticles for methanol oxidation in alkaline medium. The high surface area and the porous structure are beneficial to the uniform dispersion of Pt nanoparticles to increase their utilization. The electrocatalytic activity of methanol oxidation on Pt nanoparticles supported on NPCs (Pt/NPCs) is higher than that of Pt on commercial Vulcan XC-72R carbon (Pt/C). The results showed that NPCs are a potential candidate for application as electrocatalyst supports in alkaline direct methanol fuel cells.

Catalytic Activity and Thermal Stability of Arc Plasma Deposited Pt Nano-Particles on CeO2-Al2O3.

In this study, catalytic activity and thermal stability of the arc plasma deposited (APD) Pt nano-particles on A12O3 and CeO2-Al2O3 were compared with that of the conventionally prepared Pt/Al2O3. All the catalysts were characterized by BET-surface area, transmission electron microscopy, X-ray photoelectron spectroscopy, CO-pulse chemisorption, H2-temperarture programmed reduction and X-ray absorption near edge spectroscopy. Through the quantum chemical calculations of different metal oxide support, CeO2 was identified as a suitable anchoring material with high energy level between the Pt species (Pt(0) and PtO(x)) on ceria. Subsequently, the results of XPS and XANES revealed the presence of abundant Pt(0) metal species in APD catalysts. The addition of ceria to Al2O3 support enhanced the dispersion of Pt nano-particles. The H2-TPR of Pt/CeO2-Al2O3 (APD) catalyst showed high-temperature reduction peaks corresponding to the interaction of Pt with ceria on alumina by Pt-O-Ce. Consequently, the Pt nano-particles deposited on CeO2-Al2O3 by APD attained strong thermal resistance at high temperatures. In addition, superior catalytic activities for CO and C3H6 oxidation and NO(x) reduction were obtained for the Pt/CeO2- Al2O3 (APD) catalyst.

Catalytic activity and controllable deposition of platinum nanoparticles on ionic polymer-functionalized graphene as catalysts for direct methanol fuel cells

Direct methanol fuel cells (DMFCs) are considered promising candidates for mobile and -erating temperature [1]. Moreover, platinum (Pt) is an excellent catalyst and one of the best electrode materials for DMFCs [2-4]. However, the high cost, low electrocatalytic activity and stability of common Pt catalyst inhibit their broad application for DMFCs [3]. It is well known that the electrocatalytic performance of a fuel cell greatly depends on the composi-tion, shape, size, and dispersion of the catalyst nanoparticles (NPs). The materials supporting catalyst play an important role in controlling these properties [5]. However, during fuel-cell operation, a gradual oxidation of the carbon support leads to detachment of Pt NPs from the carbon support, allowing their agglomeration, which can reach an unacceptable level [6]. In the past few years, graphene has emerged as the ideal material for a variety of dif-ferent energy applications including fuel cells, Li-ion batteries, supercapacitors, and solar cells. This is because of its large thermal conductivity, high surface area, high mechanical stability, and excellent electrical conductivity [7]. Chemical modification of the inert surface of graphene sheets is necessary for the uniform dispersion of Pt NPs. Currently, chemical modification is achieved by methods including acid oxidation, ionic liquid [8], and conduc-tive polymer [9]. Recently, we developed a facile and efficient route to decorate Pt NPs onto reduced gra-phene oxide (RGO) functionalized with poly(diallyldimethyl ammonium chloride) ( PDDA), as acationic polymer. In this work, we investigated the synergistic effect of a poly(sodium 4-styrenesulfonate) (PSS)-functionalized graphene support and PDDA polymer for obtain-ing better electrocatalytic performance for DMFCs. These results demonstrated that, with high electronic conductivity and easier charge transfer, Pt/PDDA- PSS-functionalized RGO (PRGO) exhibited higher activity and stability than did Pt-decorated PDDA-RGO (Pt/PDDA-RGO), and Pt-decorated RGO (Pt/RGO).PSS (MW = 70,000) and PDDA (20 wt% in water) was purchased from Sigma-Aldrich (St. Louis, MO, USA). Graphite (99.9%) was purchased from Bay Carbon Inc. (Bay City, MI, USA) and H2PtCl66H2O was purchased from Sigma-Aldrich. Ethanol (99.8%), methanol (99.8%), and ethylene glycol (EG, 99.0%) were purchased from DAE JUNG Company and used without further purification. Distilled water was used in all preparation experiments.Graphene oxide (GO) was synthesized from graphite powders using a modified Hummer’s method [10]. Briefly, graphite powders were first oxidized by sulfuric acid (H

Promotion effect of manganese oxide on the electrocatalytic activity of Pt/C for methanol oxidation in acid medium

The modification of Pt/C by incorporating metal oxides for electrocatalytic oxidation of methanol has gained major attention because of the efficiency loss during the course of long-time operation. This work describes the preparation of Pt–MnO2/C electrocatalysts through a chemical route using ethylene glycol or a mixture of ethylene glycol and sodium borohydride as a reducing agent. The crystallite structure and particle size of synthesized electrocatalysts are determined using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The addition of MnO2 improves the dispersion of Pt nanoparticles. The electrocatalytic activity of Pt–MnO2/C towards methanol oxidation in H2SO4 solution is investigated using cyclic voltammetry and electrochemical impedance spectroscopy. The onset potential value of methanol oxidation peak is negatively shifted by 169mV when MnO2 is introduced to Pt/C. Moreover, the charge transfer resistance value at Pt–MnO2/C is about 10 times as low as that at Pt/C. Chronoamperometry and chronopotentiometry show that CO tolerance is greatly improved at Pt–MnO2/C. The increased electrocatalytic activity and enhanced ability to clean platinum surface elect manganese oxide as a suitable promoter for the anode performance in direct methanol fuel cells (DMFCs).

Effect of hybridization of Pt supported mesoporous-CMK-3 into Pt-CB as cathode catalyst on cell performance and durability in proton exchange membrane fuel cell

Mesoporous carbon molecular sieve, CMK-3 is successfully prepared through the carbonization of hexagonally arrayed mesoporous SBA-15 as a template and Pt nanoparticles are then deposited onto CMK-3. Mesoporous Pt-CB(1 − x)/Pt-CMK-3x hybrid catalysts (x = 0.0, 0.4, 0.5, 0.7 and 1.0) are adopted as a cathode catalyst in polymer electrolyte membrane fuel cell for the purpose of enhancing mass transfer and durability. Transmission electron micrograph and X-ray diffraction micrograph analyses show the uniform dispersion of Pt nanoparticles without any distinct agglomeration through the mesopores of CMK-3 with particle size of ∼2.3 nm. X-ray photoelectron spectroscopy analysis confirms the oxidation state of Pt species deposited onto CMK-3. The electrochemical active surface areas (ECSA) obtained by cyclic voltammetry analysis for various Pt-CB(1 − x)/Pt-CMK-3x are estimated to be 27.4 m2 g−1, 38.9 m2 g−1, 44.7 m2 g−1, 36.9 m2 g−1 and 30.8 m2 g−1 for x = 0.0, 0.4, 0.5, 0.7 and 1.0, respectively. The single cell test shows that the cell performance is highly consistent with ECSA: that is, the cell performance of Pt-CB(0.5)/Pt-CMK-3(0.5) is drastically enhanced by 62% and 322% compared with those of Pt-CMK-3 and Pt-CB alone, respectively. The drastic enhancement in cell performance is attributed to synergistic effect of enhanced mass transfer and fairly good Pt utilization. Accelerated durability test shows a drastic enhancement in durability of Pt-CMK-3 and various Pt-CB/Pt-CMK-3 hybrid catalysts compared to that of Pt-CB. The start-up/shut-down cycling test shows that mesoporous CMK-3 could be an excellent candidate for alternative supporting materials to commercial Pt-CB.

Ultra-low mass loading of platinum nanoparticles on bacterial cellulose derived carbon nanofibers for efficient hydrogen evolution

The ultra-low loading amount of Pt nanoparticles on three-dimensional bacterial cellulose derived carbon nanofibers (BCF) was achieved by using a modified atomic layer deposition (ALD) process for hydrogen evolution reaction (HER). The only 5 cycles of ALD led to a high dispersion of Pt nanoparticles on BCF surfaces with an average size of 2nm, possessing an as low as 0.87wt% of mass loading. The HER catalytic performance revealed that the as-prepared Pt/BCF have good catalytic activity and stability. The present work provides a general strategy for minimizing the demand of precious-metal catalysts while maintaining their high catalytic efficiency.

Deoxyribonucleic acid directed metallization of platinum nanoparticles on graphite nanofibers as a durable oxygen reduction catalyst for polymer electrolyte fuel cells

Effective surface functionalization to the hydrophobic graphite nanofibers (GNF) is performed with the biomolecule, namely deoxy-ribo-nucleic-acid (DNA) via π–π interactions. Pt nanoparticles are impregnated on GNF–DNA composite by ethylene glycol reduction method (Pt/GNF–DNA) and its effect on electro catalytic activity for oxygen reduction reaction (ORR) is systemically studied. Excellent dispersion of Pt nanoparticles over GNF–DNA surfaces with no evidence on particle aggregation is a remarkable achievement in this study. This result in higher electro chemical surface area of the catalyst, enhanced ORR behavior with significant enhancement in mass activity. The catalyst is validated in H2–O2 polymer electrolyte fuel cell (PEFC) and a peak power density of 675 mW cm−2 is achieved at a load current density of 1320 mA cm−2 with a minimal catalyst loading of 0.1 mg cm−2 at a cell temperature of 70 °C and 2 bar absolute pressure. Repeated potential cycling up to 10000 cycles in acidic media is also performed for this catalyst and found excellent stability with only 60 mV drop in the ORR half wave potential. The superior behavior of Pt/GNF–DNA catalyst is credited to the robust fibrous structure of GNF and its effective surface functionalization process via π–π interaction.

Effect of LiCl content on pore structure of catalyst layer and cell performance in high temperature polymer electrolyte membrane fuel cell

GDEs (gas diffusion electrodes) fabricated with catalyst layer, supporting layer and GDL (gas diffusion layer) are prepared for high temperature polymer electrolyte membrane fuel cell. A supporting layer consisting of different amount of PTFE (polytetrafluorethylene)-bonded carbon black from 0.0 g to 0.2 g is coated onto GDL to prevent Pt loss into GDL and to enhance the intimate contact between catalyst layer and GDL. Various catalyst layers are prepared by different LiCl content in PBI (polybenzimidazole) solution and coated directly on the top of optimized supporting layer. After preparing GDE, LiCl is leached out of the catalyst layer and the pore structure of GDE left behind the leaching is investigated with LiCl content. The N2 adsorption isotherm indicates that leaching of LiCl from catalyst layer leaves the pores behind and the BET surface area is increased with LiCl content. It is seen that the LiCl content significantly affects the dispersion of Pt nanoparticles in PBI: that is, too low LiCl content leads to non-uniform dispersion of Pt nanoparticles, resulting in poor cell performance. An appropriate amount of LiCl would lead to better cell performance.

Effect of microwave calcination on catalytic properties of Pt/MgAl(Sn)Ox catalyst in cyclohexane dehydrogenation to cyclohexene

This paper describes an investigation on catalytic properties of Pt nanoparticles supported on MgAl(Sn)Ox mixed oxide for cyclohexane dehydrogenation to cyclohexene. The MgAl(Sn)Ox supports were synthesized by microwave calcined hydrotalcite-derived precursors, and Pt/MgAl(Sn)Ox catalysts were prepared by an incipient wetness impregnation method. The catalysts were characterized by X-ray diffraction (XRD), hydrogen temperature-programmed reduction (H2-TPR), hydrogen temperature-programmed desorption (H2-TPD), X-Ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The results showed that the microwave calcination changed the interfacial character between Pt and support, and strengthened the interaction between tin and support, and facilitated the high dispersion of Pt nanoparticles presented on the support. These effects resulted in higher activity, stability and cyclohexene selectivity in cyclohexane dehydrogenation to cyclohexene.

Hierarchical polybenzimidazole-grafted graphene hybrids as supports for Pt nanoparticle catalysts with excellent PEMFC performance

The inhomogeneous surface of state-of-the-art carbon supports leads to a weak Pt–C interaction and, thereby, the non-uniform dispersion of Pt nanoparticles and is responsible for the poor activity and stability of proton exchange membrane fuel cells (PEMFCs). In order to improve the surface uniformity, polybenzimidazole (PBI) has been covalently grafted onto both carbon black (Vulcan XC-72) and graphene by surface-initiated polymerization. Pt nanoparticles decorated on PBI-grafted carbon black and graphene show much narrower particle size distribution and smaller average particle size than on their pristine counterparts. Oxygen reduction reactions (ORRs) carried out on a rotating disk electrode (RDE) show the higher activity of Pt/PBI-XC72 and Pt/PBI-graphene than Pt/XC72 (ETEK-BASF) and Pt/graphene, respectively. With the insertion of negatively charged SO3H-carbon black (FCB) between positively charged PBI-graphene sheets, the lamellar structure of the graphene becomes more expanded, further enhancing the ORR activity and giving rise to a higher mass activity of 183mA/mgPt at 0.9V vs. RHE on Pt/PBI-graphene+FCB than the 101mA/mgPt of Pt/PBI-graphene and the 149mA/mgPt of commercial Pt/XC72. The accelerated degradation testing (ADT) with transmission electron microscopy (TEM) characterizations demonstrated that the PBI functionalization helps to strongly anchor Pt nanoparticles on the surface of both the carbon black and the graphene, which slows down the dissolution and migration/coalescence of the Pt nanoparticles during the durability tests. Furthermore, Pt/PBI-XC72 and Pt/PBI-graphene+FCB cathode catalysts have been applied in PEMFCs and they show encouraging mass activities in membrane electrode assembly (MEA) configuration. The beginning of life (BOL) MEA performance of the Pt/PBI-graphene+FCB shows a dramatic increase of the limiting current from ca.500mA/cm2 to 2250mA/cm2, which further confirms the effective prevention of graphene restacking because of FCB insertion. In addition, the presence of the highly stable graphitic structure of graphene leads to the significant enhancement of durability during accelerated stress tests (AST) in PEMFCs: where the cell voltage at 1500mA/cm2 after 1000 cycles (1.0–1.5V) can be retained >60% for Pt/PBI-graphene+FCB while for Pt/XC72, it decays more rapidly to 0V. This study suggests the promise of using Pt/PBI-graphene+FCB hybrid cathode catalysts in fuel cells to achieve the DOE targets (i.e.<30mV loss at 1500mA/cm2 after 30K potential cycling from 1.0V to 1.5V).

MoOx-promoted Pt catalysts for the water gas shift reaction at low temperatures

Pt-Mo/SiO2 catalysts were prepared using impregnation-reduction methods. Mo-promoted Pt catalysts exhibit much higher water gas shift reaction activity at low temperatures than Pt/SiO2 catalysts. Various characterization methods including inductive coupled plasma atomic emission spectrometry, X-ray diffraction, transmission electron microscopy, X-ray absorption near edge spectrum, and X-ray photoelectron spectroscopy were applied to investigate the composition, structure and chemical state of the Pt-Mo/SiO2 catalysts. Our results indicate that the added Mo species effectively improves the dispersion of Pt nanoparticles and the synergistic effect between the Pt nanoparticles and surface MoOx species enhances the catalytic performance for the water gas shift reaction. Pt nanoparticles decorated with highly dispersed MoOx patches are found to be the active architecture.

Non-Carbon Catalyst Support for Polymer Electrolyte Fuel Cells

The most commonly used anode and cathode electrocatalysts in polymer electrolyte fuel cells (PEFCs) are nanosized platinum or platinum alloy (Pt-M1M2) particles dispersed on high surface area, porous, conductive carbon black (e.g., Vulcan XC-72). Carbon has become the state-of-the-art support due to its good electrical conductivity (e.g., 2 S/cm for Vulcan XC-72) and chemical stability in the fuel cell environment. However, during extended PEFC operation, or load cycling, and start-up/shut-down, the carbon undergoes electrochemical oxidation to form surface oxides and CO2, accompanied by catalyst (Pt or Pt-M) oxidation/dissolution.1-3 The presence of Pt or Pt-M nanoparticles also accelerates the carbon corrosion.1 As a result, Pt particles sinter into larger particles, accompanied by weakening of the interaction between Pt and the carbon support which results in the dislodging of Pt from the carbon support.3-5 These processes lead to the loss of electrochemically active surface area (ECSA) of the electrocatalysts, resulting in a decline in fuel cell performance. Carbon corrosion is especially problematic in the automotive application, where the frequent shutdowns result in localized potentials close to 1.0 V at the air/fuel boundary in the Pt/C anode of the PEFC and as high as ~1.5 V at the Pt/C cathode.6,7 To improve the durability of electrocatalysts and PEFCs, more durable catalyst support materials than carbon black have been investigated or developed. They include more stable carbon forms such as graphitized carbon8-9 and carbon nanotubes/nanofibers10-11 and non-carbon supports such as conducting/semiconducting oxides,12-14 transition metal carbides,15 nitrides (mainly TiN),16 and silicides (mainly TiSi2)17-19. In this work, we report on our investigations of alternative transition metal silicides (TMSs) as PEFC cathode catalyst supports. The candidate support materials were identified by studying the chemical and electrochemical stability and oxygen reduction reaction (ORR) catalytic activity of seven TMSs. Various synthetic approaches including colloidal synthesis using different capping agents, strong electrostatic adsorption (SEA), and wet impregnation were explored to make the silicide-supported Pt catalysts (Pt/TMS) with the desired phase, composition, and microstructure. The effect of the support treatment was also studied. The properties of the prepared Pt/TMS catalysts were characterized using transmission electron microscopy (TEM), X-ray diffraction (XRD), temperature-programmed oxidation/temperature-programmed reduction (TPO/TPR), and rotating disk electrode techniques. Select silicides showed the requisite electronic conductivity and promising stability against oxidative degradation. Further work is needed to improve the dispersion of Pt nanoparticles on the silicide supports to translate these materials into viable fuel cell catalysts. Acknowledgements Argonne National Laboratory is managed for the U.S Department of Energy by the University of Chicago Argonne, LLC, under contract DE-AC-02-06CH11357. References Z. Siroma, K. Ishii, K. Yasuda, Y. Miyazaki, M. Inaba, and A. Tasaka, Electrochem. Comm. , 7, 1153 (2005).L. Li and Y. C. Xing, J. Electrochem. Soc. , 153, A1823 (2006).Y. H. Liu, B. L.Yi, Z. G. Shao, D. M. Xing, and H. M. Zhang, Electrochem. Solid State Lett., 9, A356 (2006).G. A. Gruver, R. F. Pascoe, and H. R. Kunz, J. Electrochem. Soc. , 127, 1219 (1980).Y. Y. Shao, G. P. Yin, Z. B. Wang, and Y. Z., Gao, J. Power Sources , 167, 235 (2007).C. A. Reiser, L. Bregoli, T. W. Patterson, et al., Electrochem. Solid State Lett. , 8, A273 (2005).Y. Ishigami, K. Takada, H. Yano, et al., J. Power Sources, 196, 3003(2011).K. Miyazaki, H. Shirakata, T. Abe, et al., Fuel Cells, 10, 960 (2010).S. Zhang, Y. Y. Shao, X. H. Li, et al., J. Power Sources, 195, 457 (2009).J. B Yang, G. Goenaga, A. Call, and D. J. Liu, Electrochem.Solid State Lett. , 13, B55(2010).H. S Oh, K.Kim, Y. J. Ko, and H. Kim, Internat. J. Hydro. Energy, 35, 701 (2009).H. Chhina, S. Campbell, and O. Kesler, J. Electrochem. Soc., 154, B533 (2007).Y. Liu, A. Ishihara, S. Mitsushima, and K.Ota, Electrochimi. Acta, 55, 1239 (2010).H. Chhina, D. Susac, S. Campbell, and O. Kesler, Electrochem. Solid State Lett., 12, B97 (2009).M. Nie, P. K. Shen, M. Wu, Z. D. Wei, and H. Meng, J. Power Sources, 162, 173 (2006).I. C. Halalay, B. Merzougui, M. K. Carpenter, S. Swathirajan, G. C. Garabedian, A. M. Mance, and C. Mei, US Patent No. 7,622,216 (2009).B. Merzougui, I. C. Halalay, M. K. Carpenter, and S. Swathirajan, US Patent No. 7,767,330 (2010).B. Merzougui, I. C. Halalay, J. T. Johnson, G. C. Garabedian, M. P. Balogh, and S. Swathirajan, Pub. No. US/2008/0118818 A1 (2008).J. Wu, F. Xia, M. Pan, andX.-D. Zhou, J. Electrochem. Soc., 159, B654 (2012).

Efficient electrocatalytic performance of thermally exfoliated reduced graphene oxide-Pt hybrid

High quality thermally exfoliated reduced graphene oxide (RGO) nanosheets decorated with platinum nanocrystals have been synthesized using a simple environmentally benign process. The electrocatalytic behaviour of the Pt–RGO nanohybrid for methanol oxidation was studied using cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy. High resolution transmission electron microscopy shows uniform dispersion of Pt nanoparticles of ∼2–4nm size. X-ray diffraction and selected area diffraction studies reveal (111) orientation of the platinum nanoparticles. The cyclic voltammetry and chronoamperometry results indicate higher catalytic activity and stability for Pt–RGO compared to commercial Pt-C. The electrochemical active surface area of Pt–RGO (52.16m2/g) is found to be 1.5 times that of commercial Pt-C. Impedance spectroscopy shows different impedance behaviour at different potential regions, indicating change in methanol oxidation reaction mechanism with potential. The reversal of impedance pattern to the second quadrant, at potentials higher than ∼0.40V, indicates change in the rate determining reaction.

Graphene nanosheets modified by nitrogen-doped carbon layer to support Pt nanoparticles for direct methanol fuel cell

In this paper, we utilize aniline to form nitrogen-doped carbon layer (NCL) to modify graphene nanosheets, which serve as the support of Pt nanoparticles for direct methanol fuel cell. NCL is expected to prevent the agglomeration between graphene nanosheets, leading to better performances of the catalyst. X-ray diffraction (XRD) and transmission electron microscopy (TEM) tests were performed to characterize physical properties of the prepared catalysts and cyclic voltammetry and chronoamperometry were conducted for the electrochemical activities and stabilities toward methanol electrooxidation. The results show that the aggregation between separated graphene sheets was reduced by the NCL, leading to better dispersion of Pt nanoparticles on the graphene nanosheets. This improvement makes Pt catalyst give better activity and stability toward methanol electrooxidation.

Pt nanoparticles interacting with graphitic nitrogen of N-doped carbon nanotubes: Effect of electronic properties on activity for aerobic oxidation of glycerol and electro-oxidation of CO

Effects of specific nitrogen functionality and oxidative functionalization of the surfaces of nitrogen-doped carbon nanotubes (NCNTs) on the interaction between Pt nanoparticles (NPs) and NCNTs have been systematically investigated. Their catalytic consequences were studied using aerobic oxidation of glycerol and electro-oxidation of CO as probing reactions. By transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and X-ray diffraction (XRD), it was revealed that nitrogen dopant obviously enhanced the dispersion of Pt NPs. Strong interaction between Pt and NCNTs was observed. Graphitic nitrogen preferentially interacted with Pt NPs, evidenced by strong electron transfer from graphitic nitrogen as electron donor to metallic Pt NPs. The oxygen-containing groups introduced by H2O2 oxidation of NCNTs may reduce the donor–acceptor interaction due to the electronegativity of oxygen. By changing the nitrogen amount of NCNTs and introducing oxygen groups, the electron enrichment of Pt NPs can be tuned. Superior catalytic activity was achieved over Pt/NCNTs in the oxidation of glycerol and electro-oxidation of CO, compared with conventional carbon nanotubes as support. Moreover, for both aerobic oxidation of glycerol and electro-oxidation of CO, it was observed that the intrinsic activity depended strongly on the electron enrichment of Pt NPs, ascribed to Pt4f7/2(0) binding energy from XPS, suggesting a promising approach to improving catalytic activity by maximizing the interaction between Pt NPs and graphitic nitrogen sites.

Simultaneous Pt deposition and nitrogen doping of graphene as efficient and durable electrocatalysts for methanol oxidation

Nitrogen doping could effectively enhance the catalytical activity of graphene-supported Pt nano-electrocatalysts for methanol oxidation reaction. Previously, the main strategy to the synthesis of Pt/N-graphene is the two-step reaction while it involves the complicated synthesis. In this work, we describe a facile and simple one-pot reaction including the reduction of graphene oxide, nitrogen doping of graphene, and uniform deposition of Pt nanoparticles on doped graphene. Compared with the Pt/graphene catalyst without nitrogen-doping, Pt/N-graphene exhibits excellent activity and durability towards methanol oxidation reaction, which is mainly ascribed to the contribution of the improved dispersion of Pt nanoparticles and the enhanced interaction between it and nitrogen-doped graphene. It is expected that this facile, green and economic single-step synthesis approach for the Pt/N-graphene electrocatalyst could be widely utilized to the nitrogen-doped graphene catalysts.

The enhanced electrocatalytic activity and stability of supported Pt nanopartciles for methanol electro-oxidation through the optimized oxidation degree of carbon nanotubes

Carbon nanotubes (CNTs) with different oxidation degrees are synthesized by the modified Hummer's method and used as the support materials for platinum (Pt) catalysts. The effect of their oxidation degree on the catalytic activity and stability of the supported Pt catalysts for methanol electrooxidation is investigated for the first time. The electrocatalytic activity for methanol oxidation reaction increases with increasing the oxidation degree due to more oxygen-containing species introduced to CNTs, which improves the dispersion of Pt nanoparticles and also modifies the electronic structure of Pt catalysts. However, under more severe oxidation condition, the stability of Pt catalysts decreases due to the destruction of graphitic structure of CNTs. Therefore, the optimized treatment condition for the CNTs is mild oxidation, which provides the supported Pt catalysts with both excellent catalytic activity and stability.