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Author: Chandrani Roy Chowdhury
Publisher:
ISBN:
Category :
Languages : en
Pages : 832
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Book Description
Author: Chandrani Roy Chowdhury
Publisher:
ISBN:
Category :
Languages : en
Pages : 832
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Author: Tanushree Ghosh
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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In the search of better catalysts for fuel cells, synthesis of several intermetallic compounds and alloys as nanoparticles has been investigated. In order to obtain these materials as catalysts for fuel cells, chemical co-reduction of precursors in the absence of surfactants with suitable reducing agents has been chosen as the method of synthesis. This work was done in collaboration with combinatorial groups and electrochemists for identifying potential catalysts and electrochemically evaluating them. Starting with PtPb, the scope of this method has been extended to obtain Pt intermetallic compounds and alloys with metals across the periodic table with sodium naphthalide as the reducing agent. The sodium napthalide method has been compared side by side with the sodium borohydride method for metals which can be reduced by both. Other reducing agents have also been explored. PtPb synthesis using sodium naphthalide has been investigated in detail as a case study. Factors affecting room temperature crystallization of PtPb and contributing to low activity observed previously have been identified and addressed by changing the Pt precursor and post reduction work-up. Extending to Pt-Ti, additional factors, which need to be considered for highly reactive metals have been identified. Each of the parameters involved (metal precursor, reducing agent, reducing agent and precursor concentrations, reaction solvent, stirring time, reaction temperature, post reaction washed and annealing) have been analyzed in depth for co-reduction of Pb, Ti and the elements lying in between in reactivity. The observations and inferences in each case have been discussed. Alloy and intermetallic phases of Pt with Ni, Mn, Cr, V, Cd and Hg have been synthesized as nanoparticles. Powder X-ray diffraction, SEM and TEM (scanning and transmission electron microscopy respectively) imaging, surface area measurements (using BET isotherm) and energy dispersive X-ray analysis (EDX) have been performed on all phases mentioned above. In some cases, IR, TGA (thermogravimetric analysis) and MS (mass spectroscopy) studies have also done on these phases in-order to identify contaminants. Several of these phases have shown significant activity for oxidation of formic acid. The electrochemical evaluations have been discussed. Challenges encountered in obtaining these materials clean with the sodium napthalide method have been discussed and are being addressed with other reducing agents like nBuLi. Lastly, in collaboration with the Adzic group in the Brookhaven National Laboratories, activity of PtPb for the oxygen reduction reaction in both nascent and modified form (with monolayer of Pt deposited by underpotential deposition) has been studied. Pd alloys and intermetallic compounds with Pb and Fe have also been synthesized, characterized and similarly evaluated. All these materials were found to active and stable catalysts for the oxygen reduction reaction. Initial experiments were done with Pt3Cr and PtNi.
Author: Shaojun Guo
Publisher: Elsevier Inc. Chapters
ISBN: 0128081635
Category : Science
Languages : en
Pages : 29
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Author: Minh Thai Nguyen
Publisher:
ISBN:
Category :
Languages : en
Pages : 180
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Polymer Electrolyte Membrane Fuel cells are electrochemical devices that convert energy stored in chemical bonds of fuel (hydrogen gas, methanol, etc.) directly into electrical energy with high theoretical efficiency. The major challenges are the slow oxygen reduction reaction kinetics, requiring a significant amount of Pt catalyst to achieve significant current densities. Finding catalysts, which are more active and cheaper than Pt, as well as being stable under cathodic conditions will be key to making this technology more economically attractive. First, a method was developed to synthesize ordered intermetallic nanoparticles in the 4-6 nm size range. The synthetic method used was a modified solution phase coreduction method, which is able to synthesize ordered intermetallic nanoparticles in the 4-6 nm size range. This method was used to form carbon supported, ordered tetragonal Pt2MM' (M and M' are = Fe, Co, or Ni) nanoparticles. After extensive characterization and electrochemical measurements, it was found that ordered tetragonal Pt2FeNi/C catalyst showed the highest activity roughly four times as efficient as pure platinum, with a half-wave potential roughly 30 mV more positive than the Pt/C standard. The ordered tetragonal material also showed high stability under cathodic conditions, losing roughly 10% of the 3d element after 2000 cycles (from 0.05 - 1.10 V at 50 mV/s).
Author: Yi Liu
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Synchrotron based X-ray techniques in combination with electrochemical methods have been employed to characterize the composition and structure of ordered intermetallic materials in bulk polycrystalline, single crystal and nanoscale forms as electrocatalysts for fuel cell applications. The major objective of this research project is to thoroughly understand the structure/composition/property/activity relationships of these materials and obtain valuable information to guide the design of new electrocatalysts. It is of great importance to characterize ordered intermetallic phases as electrocatalysts since they exhibit excellent electrocatalytic activity towards the oxidation of small organic molecules. In addition, intermetallic phases can serve as model system for the electrocatalyst resaerch, complementing alloy materials and modified single crystal surfaces. In-situ gazing incidence diffraction was applied to characterize polycrystalline PtBi and PtPb intermetallic electrodes in the absence or presence of active fuel molecules in supporting electrolyte. While absence of active fuel molecules, the surface composition and structure of these electrodes were significantly altered as a function of applied upper limit potential (Eulp) while cycling to increasingly positive values. Less noble metals (Bi and Pb) leached out from the matrix. The process resulted that Pt nanocrystal domains were formed on the surface. Instead of cycling the potential, the electrochemical pretreatment of holding the potential reproducibly generated bismuth oxide domains with the diameter of ca. 50 nm on PtBi electrodes. It is surprising that the electrocatalytic activities of different terminations of PtBi electrodes after different electrochemical pretreatments were very similar. This suggests that the activity of PtBi comes from the boundary lines of bismuth oxide and PtBi domains. On the other hand, for PtPb electrodes, no oxidized lead species were formed after similar electrochemical pretreatment. PtBi and PtPb single crystal (100) and (001) facets were prepared by orienting the crystals via back Laue reflection method (BRL). Well-defined Pt domains with 6 fold symmetry but offsetting 23 deg to the (001) directions were produced while cycling the potential to +0.80 V. On the other hand, highly oriented polycrystalline Pt domains with no offset angle to the substrates were formed after similar treatment. Anisotropic activity properties were only observed for PtPb (100) and (001) electrodes towards the formic acid oxidation. X-ray fluorescence (XRF) and X-ray absorption spectroscopic (XAS) methods were utilized to characterize intermetallic nanoparticles. A multi-functional general method was developed to simultaneously obtain XRF and EXAFS data in an in-situ measuring fashion. EXAFS data suggest that bismuth atoms had been essentially oxidized for initial modified electrodes, but the nanoparticles still had the intermetallic crystal structure. Quantitative XRF data suggest the leaching out of bismuth occurred at relatively negative potentials when compared to bulk electrodes.
Author: Weitian Zhao
Publisher:
ISBN:
Category :
Languages : en
Pages : 67
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One of the major challenges in fuel cell technologies, particularly for Proton Exchange Membrane Fuel Cells (PEMFCs), is developing effective catalysts for use in both the anode and cathode. Ordered intermetallic compounds have shown considerable potential for fuel cell applications due to their enhanced catalytic activity, better durability and lower cost. In this work, Pd-Sn intermetallic compounds were investigated. PdSn and Pd3Sn nanoparticles were synthesized under air-free conditions and were tested for their electrochemical properties. Both materials showed poor activities in acidic environment for formic acid and methanol oxidation, but enhanced activities under basic conditions. Various electrochemical tests and structural characterization including high-resolution TEM/STEM and EDX were performed to investigate the changes in these materials that might have resulted in such performance. In this thesis, we also focus on developing stable catalyst supports for fuel cell electrodes, another topic in fuel cell research. Motivated by recent studies which revealed the potential of transition metal nitrides as high performance catalyst supports, we developed a facile synthesis of single-phase, nanocrystalline macroporous chromium nitride and chromium titanium (oxy)nitride with an inverse opal morphology. Characterization using XRD, SEM, HR-TEM/STEM, TGA and XPS is reported. Interconversion of macroporous CrN to Cr2O3 and back to CrN while retaining the inverse opal morphology was also demonstrated. iii.
Author: Emerilis Casado Rivera
Publisher:
ISBN:
Category :
Languages : en
Pages : 392
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Author: San Ping Jiang
Publisher: CRC Press
ISBN: 1466512539
Category : Science
Languages : en
Pages : 584
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Book Description
Boasting chapters written by leading international experts, Nanostructured and Advanced Materials for Fuel Cells provides an overview of the progress that has been made so far in the material and catalyst development for fuel cells. The book covers the most recent developments detailing all aspects of synthesis, characterization, and performance.It
Author: Minhua Shao
Publisher: MDPI
ISBN: 3038422347
Category : Science
Languages : en
Pages : 689
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Book Description
This book is a printed edition of the Special Issue "Electrocatalysis in Fuel Cells" that was published in Catalysts
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 11
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Book Description
The research program from 2010 to the end of the grant focused on understanding the factors important to the synthesis of single phase intermetallic nano-particles (NPs), their size, crystalline order, surface properties and electrochemical activity. The synthetic method developed is a co-reduction of mixtures of single metal precursors by strong, soluble reducing agents in a non-protic solvent, tetrahydrofuran (THF). With some exceptions, the particles obtained by room temperature reduction are random alloys that need to be annealed at modest temperatures (200 to 600 °C) in order to develop an ordered structure. To avoid significant particle size growth and agglomeration, the particles must be protected by surface coatings. We developed a novel method of coating the metal nanoparticles with KCl, a by-product of the reduction reaction if the proper reducing agents are employed. In that case, a composite product containing individual metal nanoparticles in a KCl matrix is obtained. The composite can be heated to at least 600 °C without significant agglomeration or growth in particle size. Washing the annealed product in the presence of catalyst supports in ethylene glycol removes the KCl and deposits the particles on the support. Six publications present the method and its application to producing and studying new catalyst/support combinations for fuel cell applications. Three publications concern the use of related methods to explore new lithium-sulfur battery concepts.
