Synthesis and Characterization of Platinum-based Multi-component Catalysts for Direct Methanol Fuel Cells PDF Download

Author: Li Ren
Publisher:
ISBN:
Category : Fuel cells
Languages : en
Pages : 154

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"In the thesis work, Pt-based binary, ternary, quaternary alloy anode catalysts supported on sonochemically treated multi-walled carbon nanotubes (CNTs) were synthesized with ethylene glycol reduction of corresponding metal chloride salts. Inductively coupled plasma-mass spectroscopy (ICP-MS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM) were used for catalyst characterization. Cyclic voltammetry for methanol oxidation and CO stripping were used to evaluate the performance of the catalysts. PtRu nanoparticles supported on CNTs (PtRu/CNT) were prepared under a series of pHs. It was found that the PtRu particle size, composition, and catalytic activity were all sensitive to the deposition pHs. CO stripping results provided the peak potential and active surface area for each catalyst. The atomic ratios tended to approach the predetermined ratio 1:1 with the increase of pH, which is favored by bi-functional catalytic mechanism. PtRu catalysts prepared at higher pHs presented better electrochemical activity toward methanol oxidation. Humidified oxygen treatment of the PtRu/CNT led to improved activity of the catalysts toward methanol electro-oxidation, implying that Ru hydroxide is better than Ru as a co-catalyst. PtRu, PtOs, PtRuOs, and PtRuOsIr nanoparticles supported on CNTs with atomic ratios of Pt:Ru (tr:46), Pt:Os (80:20), Pt:Ru:Os (54:36:10), and Pt:Ru:Os:Ir (44:36:10:5) were prepared. Cyclic voltammetry for the methanol oxidation and CO stripping at the catalysts showed that PtRu/CNT and PtRuOsIr/CNT have the best performance toward methanol oxidation, PtRuOs/CNT has the lowest activity, but PtOs/CNT exhibits better catalytic activity only at potential or 0.73 V"--Abstract, leaf iii.

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Category :
Languages : en
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Languages : en
Pages : 1

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Methanol electrochemical oxidation reaction (MOR) catalysts are receiving great interest especially for the application in direct methanol fuel cells (DMFCs). Much interest in DMFCs development is focused on portable power applications, because DMFCs can be better miniaturised than other fuel cells. [partial abstract].

Author: Kingshuk Dutta
Publisher: Elsevier
ISBN: 0128191597
Category : Technology & Engineering
Languages : en
Pages : 565

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Direct Methanol Fuel Cell Technology presents the overall progress witnessed in the field of DMFC over the past decade, highlighting the components, materials, functions, properties and features, designs and configurations, operations, modelling, applications, pros and cons, social, political and market penetration, economics and future directions. The book discusses every single aspect of DMFC device technology, the associated advantages and drawbacks of state-of-the-art materials and design, market opportunities and commercialization aspects, and possible future directions of research and development. This book, containing critical analyses and opinions from experts around the world, will garner considerable interest among actual users/scientists/experts. Analyzes developments of membrane electrolytes, electrodes, catalysts, catalyst supports, bipolar plates, gas diffusion layers and flow channels as critical components of direct methanol fuel cells Includes modeling of direct methanol fuel cells to understand their scaling up potentials Discusses commercial aspects of direct methanol fuel cells in terms of market penetration, end application, cost, viability, reliability, social and commercial perception, drawbacks and prospects

Author: Sonam Patel
Publisher:
ISBN:
Category :
Languages : en
Pages :

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Platinum (Pt) and platinum alloys have attracted wide attention as catalysts to attain high performance to increase the power density and reduce the component cost of polymer electrolyte membrane fuel cells (PEMFCs). Extensive research has been conducted in the areas of new alloy development and understanding of mechanisms of electrochemical oxygen reduction reaction (ORR). The durability of PEMFCs is also a major barrier to the commercialization of these fuel cells. Recent studies have suggested that potential cycling can gradually lead to loss of active surface area due to Pt dissolution and nanoparticle grain growth [1]. In this thesis we report a one-step synthesis of highly-dispersed Pt nanoparticles and Pt- Cobalt supported on Ketjen carbon black (20% Pt/C & 20% Pt3Co/C) as electro-catalysts for PEMFCs. Pt particles with size in the range of ~ 2.6nm (Pt/C) and 3.9 nm (Pt3Co/C) were obtained through adsorption on carbon supports and subsequently thermal decomposition of platinum acetylacetonate (Pt(acac)2). A comparative characterization analysis, including X-ray diffraction (XRD), high resolution transmission electron microscope (HR-TEM), FT-iR, EDAX, cyclic voltammetry (CV), and oxygen reduction reaction (ORR) activity, was performed on the synthesized and commercial (46.5wt% TKK) catalysts. The analysis was to reveal the Pt dispersion on the carbon support, particle size and distribution, electrochemical surface area (ECA), and ORR activities of these catalysts. It was found that the synthesized Pt/C showed similar particle size to that of the TKK catalysts (2.6nm and 2.7nm, respectively), but narrower particle size distribution; while the particle size for Pt3Co/C was found to be ~3.9 nm. Accelerated durability tests (ADT) under potential cycles were also performed for Pt/C and TKK to study the electrochemical degradation of the catalysts in corrosive environments. The ADTs revealed that the two catalysts (Pt/C & TKK) were comparable with respect to degradation in ECA and ORR activities. Initial electrochemical evaluation of Pt3Co/C was conducted, but durability studies were not attempted in this thesis due to its worse ORR kinetics than those of the Pt/C catalyst. From the experimental data, it was found that particle size impacted negatively the ECA and ORR activity of the catalysts.

Author: Sivapregasen Naidoo
Publisher:
ISBN:
Category : Direct methanol fuel cell
Languages : en
Pages : 530

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The direct methanol fuel cell or DMFC is emerging as a promising alternative energy source for many applications. Developed and developing countries, through research, are fast seeking a cheap and stable supply of energy for an ever-increasing number of energy-consuming portable devices. The research focus is to have DMFCs meeet this need at an affordable cost is problematic. There are means and ways of making this a reality as the DMFC is found to be complementary to secondary batteries when used as a trickle charger, full charger, or in some other hybrid fuel cell combination. the core functioning component is a catalyst containing MEA, where when pure platinum is used, carbon monoxide is the thermodynamic sink and poisons by preventing further reactions at catalytic sites decreasing the life span of the catalyst if the CO is not removed. research has shown that the bi-functional mechanism of a platinum-ruthenium catalyst is best because methanol dehydrogenates best on platinumand water dehydrogenation is best facilitated on ruthenium. It is also evident that the addition of other metals to that of PtRu/C can make the catalyst more effective and effective and increase the life span even further. In addition to this, my research has attempted to reduce catalyst cost for DMFCs by developing a low-cost manufacturing technique for catalysts, identify potential non-noblel, less expensive metallic systems to formbinary, ternary and quarternary catalysts.

Author: Jonathan R. Mann
Publisher:
ISBN: 9780542789816
Category :
Languages : en
Pages : 146

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Platinum-based particles are synthesized via the polyol process in an effort to include various metal oxides in a multi-phase catalyst for the direct ethanol fuel cell anode. Among Eu, In, La and Nb, no single metal oxide with platinum yields open circuit potentials or maximum current densities as high as tin oxide with platinum. For this reason, particles with platinum, tin oxide and the oxide of a third metal were developed. Platinum tin/indium oxide slightly outperforms platinum tin oxide. The particles are characterized by TEM, EDX, XRD and ICP. The metal oxides and the platinum are located together in one particle, uniformly 5.3 nm in diameter. ICP analysis indicates that the catalysts are 20% platinum on carbon and the metals of the oxides are on the order of 1-2% by mass. The catalytic abilities of the particles were evaluated in a single cell direct ethanol fuel cell where polarization curves were taken up to 130°C, and oxidation products were analyzed by gas chromatography. Open circuit voltages of as high as 0.82 V were obtained for platinum tin/indium oxide catalysts and current densities as high as 0.4 A cm-2 were seen. The cells produced large amounts of acetaldehyde and acetic acid, as well as small amounts of methanol and carbon dioxide. A spillover mechanism is proposed for the oxidation of ethanol to CO2 on these platinum/metal oxide catalysts.

Author:
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ISBN:
Category :
Languages : en
Pages :

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Author: Liufeng Xiong
Publisher:
ISBN:
Category :
Languages : en
Pages : 344

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Proton exchange membrane fuel cells (PEMFC) and direct methanol fuel cells (DMFC) are attractive power sources as they offer high conversion efficiencies with low or no pollution. However, the most commonly used platinum electrocatalyst is expensive and the world supply of Pt is limited. In addition, the slow oxygen reduction and methanol oxidation kinetics as well as the poisoning of the Pt catalyst at the cathode resulting from methanol permeation from the anode through the Nafion membrane to the cathode lead to significant performance loss. Also, the electrocatalyst utilization in the electrodes also needs to be improved to reduce the overall cost of the electrocatalysts and improve the fuel cell performance. This dissertation explores nanostructured Pt alloys with lower cost and higher catalytic activity than Pt for oxygen reduction in PEMFC to understand the effect of synthesis and structure on the catalytic activity, methanol tolerant Pt/TiOx nanocomposites for oxygen reduction in DMFC, nanostructured Pt-Ru alloys for methanol oxidation in DMFC, and improvement in the utilization of Pt by optimizing the membrane-electrode assembly (MEA) fabrication. From a systematic investigation of a series of Pt-M alloys (M = Fe, Co, Ni, and Cu), the catalytic activity of Pt-M alloys is correlated with the extent of atomic ordering. More ordered Pt alloys exhibit higher catalytic activity than disordered Pt alloys. The higher activity of the ordered Pt alloys is found to relate to various factors including the Pt-Pt distance, Pt: 5d orbital vacancy, {100} planar density and surface atomic configuration. The catalytic activity of the Pt alloys is also influenced by the synthesis method. Low temperature solution methods usually result in smaller particle size and higher surface area, while high temperature routes result in larger particle size and lower surface area but with a greater extent of alloying. Pt/TiOx/C nanocomposites exhibit higher performance than Pt for oxygen reduction in DMFC. The nanocomposites show higher electrchochemical surface area, lower charge transfer resistance, and higher methanol tolerance than Pt. Pt-Ru alloy synthesized by a reverse microemulsion method exhibits higher catalytic surface area than the commercial Pt-Ru. The higher catalytic activity is attributed to a better control of the particle size, crystallinity, and microstructure. Membrane-electrode assemblies (MEAs) fabricated by a modified thin film method exhibit much higher electrocatalyst utilization efficiency and performance than the conventional MEAs in PEMFC. Power densities of 715 and 610 mW/cm2 are obtained at a Pt loading of, respectively, 0.1 and 0.05 mg/cm2 and 90 oC. The higher electrocatalyst utilization is attributed to the thin catalyst layer and a better continuity of the membrane/catalysts layer interface compared to that in the conventional MEAs.

Author: Christopher Odetola
Publisher:
ISBN:
Category :
Languages : en
Pages : 0

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Catalysts in the electrodes of polymer exchange membrane fuel cells (PEMFCs) serve a critical function in reactions which can be used to generate electrical energy from chemical fuels. Pt nanoparticles are commonly dispersed on a conductive support and used as electrode materials in these devices because of their exceptional catalytic activity and electrochemical active surface area. The performance and stability of these electrodes strongly depend on the characteristics of the support. Catalysts supported on high surface area carbon black are widely used in low-temperature fuel cells. In PEMFCs, these catalyst materials can be exposed to high potential and low pH values, resulting in irreversible loss of activity that will limit the useful lifetime of the cell, ultimately leading to its failure. Pt is a noble metal which has good intrinsic stability, but carbon is not thermodynamically stable resulting in the corrosion of the catalyst support under these conditions. The design of more resilient platinum catalyst supports to carry out the successful reaction in a fuel cell's catalyst layer is required to extend the lifetime of PEMFCs degradation. In this thesis, two approaches were used to synthesize robust catalyst support materials for fuel cell applications. In the first case, carbon surfaces were functionalised to enhance their interactions with the catalyst and secondly, stable metal oxide was combined with modified carbon substrates, to maximise contacts within the composite electrocatalysts and to prevent carbon corrosion of a single phase carbon support catalyst. TiO2 NPs, were first chemically bonded to the surfaces of Vulcan carbon to help anchor the Pt catalyst nanoparticles through strong metal-support interactions. Validation of a dual phase catalyst support is an important goal of this research. Each material phase offers a unique advantage that can only be recognized by the preparation of a composite electrocatalyst. Pristine Vulcan (PV) was functionalised with glucose hydroxyl functional groups that react with the base titanium metal alkoxide in a sol-gel reaction and then calcined to form a more chemically crystalline surface. This is followed by impregnation reduction process to deposit the nanostructured Pt catalyst. Material characterization data of synthesized materials were used to correlate the effects of support structure and composition on resilient performance. Advantages from the TiO2/C supports toward performance and durability were contrasted against a set of control samples and demonstrated ex situ. The prepared composite catalysts showed substantial enhancements toward oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR) as well as improved stability of the Pt-TiO2 heterogeneous interface formed between catalyst and support. The enhanced performance and durability of these composite catalysts is improved by applying the science of materials and interfaces to the synthesis of composite supports, thus serving as an example for further progress and optimization. Irradiation of these composite catalysts with UV-visible light also showed ~ 171 % photo enhanced activity for MOR, which clearly demonstrates a synergistic effect between the photo- and electrocatalysts. The comparison between the prepared catalysts indicates that there is an appropriate ratio of carbon and TiO2 to obtain the best performance of these photoelectroactive materials. These results demonstrate that methanol oxidation is achieved by electro- and photoelectrocatalysis using a simple and affordable method. This procedure can be conveniently exploited to enhance the response of direct methanol fuel cell electrodes.