Download or read book Study of a Platinum graphene Nanoflakes Catalyst for Oxygen Reduction Reaction of Polymer Electrolyte Membrane Fuel Cells written by Md Mahdi Feroze and published by . This book was released on 2019 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: "This master's thesis investigates the electrocatalytic performance of graphene nanoflakes (GNF) as the support of a noble catalyst towards oxygen reduction reaction (ORR) in acidic medium for application in polymer electrolyte membrane fuel cells (PEMFC). The graphene nanoflakes support is synthesized using methods developed by Pristavita et al. in 2011. Introducing platinum onto the support using thermal plasma is shown not possible in part due to limitations arising from the high boiling point of platinum. A wet chemistry technique developed by Jaoun et al. in 2003 is used to successfully introduce platinum onto the GNF support. The synthesized catalyst shows superior electrocatalytic activity towards ORR compared to a noble commercial catalyst having carbon black as supports, these tests being performed at high rotation speeds of rotating disk electrode (RDE) tests." --

Download or read book Synthesis Characterization and Performance of Graphene Nanoflakes as a Non noble Metal Catalyst in Polymer Electrolyte Membrane Fuel Cells written by Pierre Pascone and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: "One of the goals in catalyst research for proton exchange membrane fuel cells (PEMFCs) is to find a cost-efficient alternative to platinum. Due to sluggish kinetics, the major requirement of the platinum comes from the catalyst layer used for the oxygen reduction reaction (ORR). Functionalized carbon nanomaterials present themselves as good candidates for the replacement of platinum due to their low cost, excellent electrical conductivity, and chemical resistance to acidic and basic environments. In this work, graphene nanoflakes (GNFs), which are nanopowders consisting of stacked graphene sheets, were used to support atomic iron as a non-noble metal catalyst. In the first stage of the study the iron-based catalyst was synthesized. Synthesis steps include the production of GNFs in methane plasma, adsorption of ferric acetate, and pyrolysis in ammonia-rich atmosphere. The catalyst structure was characterized at various stages throughout the synthesis steps and it was found that 0.28 atomic percent of iron could successfully be incorporated onto the surface. However, the synthesis method employed caused a general decrease to all calculated crystallinity parameters: purity decreased by 28%, crystallite size decreased by a factor of 2, and the average length of graphene plane decreased by a factor of 4. Characterization was also performed on the catalyst layer after it had been exposed to the PEMFC environment, revealing that the crystallinity parameters actually improved with respect to exposure time: after 100 hours purity increased by 32%, crystallite size increased by 25%, and the average length of graphene plane increased by 107%. Exposure to the PEMFC environment repairs the damage done to the original GNFs during the synthesis steps. The synthesized catalyst was used in the catalyst layer for the ORR of a PEMFC with a 1 cm2 active surface. A current of 150 mA/cm2 was observed at an applied voltage of 0.5 Volts with a catalyst loading of 1 mg. When the current is normalized with respect to the amount of metal present, the result of 11.8 A/mg of metal catalyst from the present catalyst out-performs most platinum-based catalysts being used in industry; current platinum catalyst have values ranging from 3 to 14 A/mg of platinum. In stability experiments, no losses were observed at the end of 100-hours long experiments performed at an applied voltage of 0.5 Volts. This represents a great improvement over comparable iron-based catalysts, which show a 45% loss under identical test conditions. The increased stability of the catalyst support structure demonstrates the advantage of the high crystallinity and large crystalline lengths of the GNFs in comparison to other commercial carbon blacks." --

Download or read book Synthesis and Performance Evaluation of a Carbon based Catalyst for Use in Polymer Electrolyte Membrane Fuel Cells written by Jasmin De Campos and published by . This book was released on 2018 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: "Polymer electrolyte membrane fuel cells (PEMFCs) are a green technology that can convert chemical energy into electrical energy by reacting oxygen and hydrogen to form water. One major limitation to their large-scale production is the cost of the platinum catalyst, an expensive precious metal. This project looks into altering the catalyst support structure to reduce the platinum required for a certain performance level and thus ultimately decreasing the high PEMFC catalyst costs.Carbon nanotubes (CNTs) are promising as an alternate catalyst support structure due to their high electrical conductivity, large surface areas, and stability under PEMFC operating conditions. In this project, CNTs were first grown onto stainless steel mesh substrates with chemical vapor deposition (CVD) using a "direct-growth" approach. They were then functionalized with oxygen (fCNTs) by plasma enhanced CVD (PECVD) to improve their hydrophilicity to achieve stable catalyst ink dispersions. Lastly, platinum was deposited (Pt-fCNTs) using pulsed laser ablation (PLA), which has been shown to provide homogeneous dispersions of platinum particles with an average size of 3.6 nm and no agglomeration. This final Pt-fCNT material was then prepared for electrochemical testing in rotating disk electrode (RDE) and PEMFC studies. It was also compared to an industry standard catalyst of platinum on carbon black. An additional study was done wherein various quantities of graphene nanoflakes with oxygen functionalization (GNFs) were added to the Pt-fCNT catalyst inks, dubbed GNF-Pt-fCNT samples, to see if their stability could improve overall performance.Pt-CNT samples with different platinum deposition times underwent thermogravimetric analysis (TGA) to find their weight percent content of platinum. Samples with 5, 10, and 30 minutes of platinum deposition contained 3.1 % of residue and 3.6 %, 4.0 %, and 16 % of platinum respectively.RDE studies were performed focusing on the oxygen reduction reaction, the rate-limiting cathodic PEMFC reaction. Four main conclusions were made: i) samples without platinum showed effectively no activity, ii) all GNF-Pt-fCNT samples made with varying ratios of the carbon materials underperformed compared to the commercial or 5-minute Pt-fCNT sample, iii) Pt-fCNT performance did not correlate with platinum weight content, and iv) 5-minute Pt-fCNTs out-performed the commercial catalyst by approximately a factor of 2.Due to the high mass requirements for PEMFC testing, less samples were tested: 30-minute Pt-fCNTs, GNFs mixed with 30-minute Pt-fCNTs in a 1:1 mass ratio, a commercial catalyst, and plain CNTs. The four main conclusions made were i) the plain CNTs once again showed no activity due to a lack of platinum, ii) GNF-Pt-fCNTs underperformed compared to other platinum containing samples, likely due to GNFs hindering the catalyst layer's conductivity and access to catalytic sites, iii) the Pt-fCNTs behaved similarly to the commercial catalyst at higher potentials suggesting similar reaction kinetics at play, and iv) Pt-fCNTs underperformed compared to the commercial catalyst at potentials lower than 0.8 V, suggesting higher ohmic resistances and mass transport limitations of the support material.A mass study was performed on the synthesis and powder collection processes to understand the yields and practicality of the methodologies used. On average, sonication was able to collect only 31 % of the sample synthesized on the mesh. Additionally, the powder collection method for the various samples had a relatively high yield of 82 % with extremely large standard deviations despite identical preparation conditions for the powders. " --

Download or read book Study of an Iron nitrogen graphene Catalyst for Polymer Electrolyte Membrane Fuel Cells written by Pierre Pascone and published by . This book was released on 2018 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: "The work of this thesis is in the field of non-noble metal catalysts for the oxygen reduction reaction (ORR) of a polymer electrolyte membrane fuel cell (PEMFC). The ORR requires a catalyst, platinum providing presently the highest level of catalytic activity and being used in essentially all PEMFC applications. Platinum is however a very expensive metal that has hindered the large scale production of PEMFCs in everyday products, generating a desire to develop a low-cost alternative. In this thesis, the proposed catalyst is composed of iron coming from a salt and a carbon nanomaterial with nitrogen functionalities, with one important goal being to improve the time stability of such iron-based catalyst materials. The carbon nanomaterial used is stacked graphene structures having 5 - 20 atomic layers, referred to as graphene nanoflakes (GNFs). The GNFs were produced in-house through gas phase homogeneous nucleation following the plasma decomposition of a carbon-containing feedstock in an inductively coupled plasma torch reactor. By introducing nitrogen gas, either directly during GNF structural growth or in a second treatment step following growth, nitrogen functional groups are bonded to the surface and edges of graphene in different amounts. Iron acetate was used as the source of iron and added to the GNF structures before being heat-treated to generate the final ORR catalysts. Another recipe for producing the catalyst included phenanthroline as an added nitrogen source. An electrochemical study performed in neutral media was used as a screening technique to determine the effect of nitrogen functionalization on the GNF support system and its interaction with phenanthroline in producing an active catalyst. The best candidate proved to be the catalyst derived from using GNFs with high levels (15 - 20 atomic percent on the surface) of nitrogen, further referred to as high-nitrogen GNFs (HN-GNFs), and without phenanthroline added. This modified synthesis recipe was used for the duration of the thesis. The catalyst`s surface was also characterized with x-ray photoelectron spectroscopy and imaged with electron microscopy. Catalysts with three different iron concentrations were then synthesized and put through another electrochemical study to investigate the effect of the iron weight percent on the catalyst in different media (acidic, neutral, basic). The catalysts performed well in acidic media, which is vital for a PEMFC catalyst; this result indicated that PEMFC testing should proceed. Additionally, having more iron present allowed a characterization study to be carried out to explore what the shape, location, and bonding of the iron nanoparticles were. It was seen that the majority of the iron is in the form of nanoparticles and are not found on the surface, but encapsulated by the graphene sheets of the HN-GNFs.The best materials produced throughout the thesis and evaluated through the electrochemical study were tested in a single-cell PEMFC as the ORR catalyst. Although the current density being drawn from the cell was low when compared to other iron-containing catalysts being developed in other research groups around the world, the catalyst developed effectively showed good stability over the 200 hours of testing." --

Download or read book Plasma Functionalization of Graphene Nanoflakes for Non noble Catalyst in Fuel Cells written by Dustin Binny and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: "Two major obstacles currently limit the commercial viability of proton exchange membrane fuel cells (PEMFCs): cost and operating life. The most important contribution to the high cost of these systems is the use of platinum (Pt) as a catalyst, especially on the cathode where the oxygen reduction reaction (ORR) takes place. This thesis is part of the intensive international research efforts to find an alternative substitute for platinum. Doped carbon nanomaterials have been identified as a potential replacement for platinum ORR-electrocatalyst due to their excellent electrical conductivity and chemical resistance in acidic and basic environments. By doping the carbon nanomaterials with nitrogen, in the preferred pyridinic and quaternary forms, iron can be coordinated to complete the catalytic sites on an atomic scale. Nanocrystalline powder has recently been developed in the Plasma Processing Laboratory (PPL) at McGill University. The particles constituting the powder, in the form of graphene nanoflakes (GNFs), are formed by the superposition of ten graphene layers on average and have a spatial extension on the order of hundreds of nanometers. These planes have many terminating edges upon which nitrogen can be incorporated due to their high reactivity. The crystallinity also leads to a highly stable material paving the way for a promising catalyst replacement in the PEMFC.The objective of this thesis is to take these crystalline GNFs and dope them with nitrogen in high quantities on the edges of the graphene planes in pyridinic and quaternary forms to create the catalytic sites necessary for ORR. An inductively-coupled thermal plasma (ICP) is used to dissociate methane at very high temperatures, with homogeneous GNF nucleation commencing shortly after by way of rapid quenching. Nitrogen doping occurs in a second treatment phase by manipulating plasma conditions in order to create excited and dissociated nitrogen species that react at the edges of the GNFs.Nitrogen doping up to 33.4 at.%Ntotal has been demonstrated, which bests any other nitrogen-doped graphene by at least a factor of 2.6 and even the best nitrogen-doped carbonaceous material by 67%. Pyridinic and quaternary nitrogen constitute 8.2 at.%Npyrid and 4.9 at.%Nquat, respectively. This has been done whilst maintaining the crystalline structure and without introducing defects or impurities that would otherwise affect crystallinity and durability of these materials in future potential applications. Sequential in-situ GNF synthesis and deposition/dispersion onto a carbon cloth, which functions as the gas diffusion layer (GDL) in fuel cells, has also been demonstrated. Solid anchoring of the deposited GNFs on the individual carbon fibers is observed, and columnar growth with open film porosity reveals GNF films of micrometer-scale thicknesses. These films also exhibit desirable properties required for the ORR: porosity, homogeneity over a large area, good contact to the electrical transport throughout the network of particles and accessibility to the catalytic sites. The obtained properties seem in fact unmatched by catalytic particle ink applications commonly used in the manufacture of the catalyst layer. This in-situ work is promising and original, establishing a potential new method of producing membrane electrode assemblies (MEAs) in PEM fuel cell manufacturing.This new graphene nanomaterial could also pave the way for its potential use in supercapacitors, solar cells, biosensors, batteries, fuel storage, field-effect transistors, filtration and electrochemical devices, in addition to the fuel cell catalysis applications under study." --

Download or read book Synthesis and Characterization of Platinum Based Catalysts for Fuel Cells written by Sonam Patel and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Nanostructured Oxygen Reduction Catalyst Designs to Reduce the Platinum Dependency of Polymer Electrolyte Fuel Cells written by Drew Christopher Higgins and published by . This book was released on 2015 with total page 177 pages. Available in PDF, EPUB and Kindle. Book excerpt: Polymer electrolyte fuel cells (PEFCs) are electrochemical devices that efficiently convert hydrogen and oxygen into electricity and water. Their clean point of operation emissions and fast refueling times have resulted in PEFCs being highly touted as integral components of sustainable energy infrastructures, most notably in the transportation sector. The issues associated with hydrogen production and distribution aside, the commercial viability of PEFCs is still hindered by the high cost and inadequate long term operational stability. A main contributor towards both of these issues is the platinum-based electrocatalysts used at the cathode to facilitate the inherently sluggish oxygen reduction reaction (ORR). These expensive precious metal catalysts comprise almost half of the overall PEFC stack cost, and undergo degradation under the cathode environment that is very corrosive due to the acidic and potentiodynamic conditions. There is therefore ample room for cost reduction if reduced platinum ORR catalysts can be developed with sufficient activity and durability to meet the technical targets set for the use of PEFCs in automobiles. In this work, two classes of nanostructured catalysts are investigated. The first is high activity platinum or platinum alloy materials with the objective of surpassing the activity of conventional catalysts on a precious metal basis to achieve cost reductions. The second is non-platinum group metal (non-PGM) catalysts, that while intrinsically less active than platinum, can still provide high power output at moderate operating voltages, such as those encountered during automobile operation. These two catalyst technologies are developed and delivered with the ultimate objective of integrating them together into platinum/non-PGM hybrid electrodes to provide excellent PEFC performance with a reduced platinum dependency. In Chapter 4, titanium nitride - carbon nanotube (TiN-CNT) core-shell nanocomposites developed by a simplistic two step fabrication procedure are reported. These materials are physicochemically characterized by a variety of microscopy and spectroscopy techniques and used as platinum nanoparticle elelectrocatalyst supports (Pt/TiN-CNT) for the ORR. Through half-cell electrochemical testing in acidic electrolyte, improved ORR activity was demonstrated for Pt/TiN-CNTs compared with state of the art commercial Pt/C. The one-dimensional morphology of the TiN-CNT supports is also conducive for integration into highly porous electrode structures with excellent interconnectivity to ensure reactant access and electronic conductivity throughout the catalyst layer, respectively. The long term stability of this catalyst however remains questionable, likely due to oxidation of the titanium nitride surface that results in a thin passivating layer. It is becoming increasingly evident that corrosion of platinum nanoparticle supports is inevitable during fuel cell operation. To overcome this, a focus was then placed on the development of supportless nanostructured platinum catalyst designs. Platinum cobalt nanowires (Pt-Co-NWs) were prepared by simplistic, template free microwave-irradiation process as discussed in Chapter 5. Using cobalt as an alloying element was undertaken owing to the documented ability of this transition metal to modulate the adsorptive properties of platinum and induce increased ORR activity. The one-dimensional anisotropic nanostructure can also provide increased platinum stability owing to the reduced surface energies in comparison to zero dimensional nanoparticles. The Pt-Co-NWs displayed promising ORR activity a through half-cell testing in 0.1 M HClO4. Most notably, using harsh accelerated durability testing (ADT) that consisted of 1,000 electrochemical potential cycles from 0 to 1.5 V vs. RHE at 50 °C, the Pt-Co-NWs maintained the majority of their ORR activity, highlighting exemplary stability. While simple, the drawback of this synthesis approach is that it did not allow for nanowire diameters that were below 40 nm. This resulted in inaccessible platinum atoms within the nanowire cores, highlighting the fact that further improved ORR activity on a platinum mass basis could be achieved with reduced diameters. To accomplish this, the electrospinning approach was used to prepare PtCoNWs (please note the nomenclature distinction). Through investigations in which synthesis parameters were systematically investigated, electrospinning was found to provide a versatile platform for the synthesis of nanowires with tunable diameters and atomic compositions. PtCoNWs with a near unity stoichiometric ratio, excellent atomic distribution and an average diameter of 28 nm were evaluated for ORR activity. Over a four-fold enhancement in Pt mass-based activity at an electrode potential of 0.9 V vs RHE is obtained in comparison to pure platinum nanowires, highlighting the beneficial impact of the alloying structure. A near 7-fold specific activity increase is also observed in comparison to commercial Pt/C catalyst, along with improved electrochemically active surface area retention through repetitive (1,000) potential cycles. Electrospinning is thereby an attractive approach to prepare morphology and composition controlled PtCoNWs that could potentially one day replace conventional nanoparticle catalysts. With the development of PtCoNWs established, developing non-PGM catalysts that can be hybridized with the high activity platinum-based catalysts was required. In Chapter 7, single crystal cobalt disulfide (CoS2) octahedral nanoparticles supported on graphene/carbon nanotube composites were prepared as ORR catalysts. During the simplistic, one-pot solvothermal synthesis, the nanostructured carbon supports were also simultaneously doped with nitrogen and sulfur. Time dependent studies elucidated the growth process of the {111} facet encased octahedra that could only be prepared when carbon support materials were incorporated into the reaction mixture. The impact of carbon support on ORR activity was clear, with the graphene/carbon nanotube composite supported CoS2 octahedra (CoS2-CG) outperforming CoS2 supported on just graphene or carbon nanotubes. Additionally, CoS2-CG provided an on-set potential (0.78 V vs. RHE) and half-wave potential (0.66 V vs. RHE) that was 60 mV and 150 mV higher than the CoS2 particle agglomerates formed when no carbon support was included during catalyst preparation. By combining the synergistic properties of the graphene/carbon nanotube composite and unique shape controlled single crystal CoS2 nanoparticles, CoS2-CG comprises the highest activity non-precious metal transition metal chalcogenide reported to date, and is presented as an emerging catalyst for the ORR in fuel cells. Chapter 8 provides a summary of the conclusions of this body of work, along with strategies that can be employed to capitalize on the scientific advancements made through this thesis. The delivery of PtCoNWs and CoS2-CG that can be reliably prepared by simple techniques provides the crucial first step towards the development of platinum/non-PGM hybrid electrodes. Future projects should focus on the integration of these two catalysts into new electrode arrangements in an attempt to exploit their individual properties. Through this approach, it is hypothesized that synergistic coupling of these two catalysts can lead to PEFC systems with reduced activation losses from the PtCoNWs, along with CoS2-CG providing increased maximum power densities at lower cell voltages, all at reduced platinum contents in comparison to state of the art PEFC cathodes.

Download or read book Graphene Science Handbook written by Mahmood Aliofkhazraei and published by CRC Press. This book was released on 2016-04-27 with total page 480 pages. Available in PDF, EPUB and Kindle. Book excerpt: Explore the Practical Applications and Promising Developments of GrapheneThe Graphene Science Handbook is a six-volume set that describes graphene's special structural, electrical, and chemical properties. The book considers how these properties can be used in different applications (including the development of batteries, fuel cells, photovoltaic

Download or read book Improving the Durability of Nanostructured Thin Film Supported Platinum Fuel Cell Catalysts with the Addition of Iridium and Ruthenium written by Timothy Crowtz and published by . This book was released on 2017 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: One of the remaining challenges driving polymer electrolyte membrane hydrogen fuel cell research is the durability of the Pt oxygen reduction reaction (ORR) catalyst. Pt is inherently unstable; minute amounts (in the order of ng/cm2 are dissolved every time the fuel cell is started, goes from idle to load, or shut-down. In addition, corrosion of carbon-based materials (ubiquitous inside fuel cells) occurs during the start-up and shut-down and also contributes to the steady decline of fuel cell performance. Adding oxygen evolution reaction (OER) catalysts, of which only Ru and Ir are stable in the acidic conditions of the fuel cell, can decrease Pt loss and carbon corrosion by mitigating the degradation mechanism which occurs during the start-up and shut-down phases. There are two challenges in developing this materials solution (there are other solutions, based on hardware systems) to the fuel cell durability problem: 1) finding the right mixture of Ru and Ir, (Ru is cheaper, more active, but less stable than Ir), and 2) balancing an increase of OER activity with a loss of ORR activity due to Pt coverage by the Ru and Ir. A spread of compositions containing various amounts of Ir or Ru on 85 ug/cm2 of Pt were sputter deposited on a nanostructured thin film state-of-the art catalyst support made by 3M. The nanostructured thin film was grown by 3M on glassy carbon disks designed for a rotating disk electrode, which was used to simulate what happens to a fuel cell cathode during repeated start-up, operation, and shut-down. Experimental difficulties of glassy carbon disk corrosion were overcome with the application of high vacuum silicone grease (silicone oil and fumed silica) to the glassy carbon disk. The silicone grease did not affect the ORR activity. Ir was found to be better at protecting the ORR activity than Ru, and an Ir on Pt sputter deposition scheme was found to be better than a Ir intermixed with Pt scheme. The second study looked for ways to visualize the OER and ORR durability of about 50 of ternary (Ir on Ru on Pt) compositions. Increasing Ir loading improved the durability of both ORR and OER activity. Various Ru loadings provided little benefit except when combined with 10 ug/cm2 Ir. There was a large amount of scatter in the data. In particular some of the experiments attained a stable ORR activity, something which should not be possible given the nature of electrochemical Pt dissolution. Further work on identifying the source of these problems is needed before another catalyst screening study is done.

Download or read book Nanostructured Materials Supported Oxygen Reduction Catalysts in Polymer Electrolyte Membrane Fuel Cells written by Ja-Yeon Choi and published by . This book was released on 2013 with total page 95 pages. Available in PDF, EPUB and Kindle. Book excerpt: Polymer electrolyte membrane (PEM) fuel cells have been viewed as promising power source candidates for transport, stationary, and portable applications due to their high efficiency and low emissions. The platinum is the most commonly used catalyst material for the oxygen reduction reaction (ORR) at the cathode of PEM fuel cells; however, the limited abundance and high cost of platinum hinder the large-scale commercialization of fuel cells. To overcome this limitation, it is necessary to enhance the catalyst utilization in order to improve the catalytic activity while decreasing or eliminating the use of platinum. The material on which the catalyst is supported is important for the high dispersion and narrow distribution of Pt nanoparticles as well as other non-precious metal active sites, and these characteristics are closely related to electrocatalytic activity of the catalysts. The support materials can influence the catalytic activity by interplaying with catalytic metals, and the durability of the catalyst is also greatly dependent on its support. A variety of support materials like carbons, oxides, carbides, and nitrides have been employed as supports materials for fuel cell catalysts, and much effort has been devoted to the synthesis of the novel carbon supports with large surface area and/or pore volume, including nanostructured carbons such as carbon nanotubes (CNTs), carbon nanofibers, and mesoporous carbon. These novel nanostructured carbon materials have achieved promising performance in terms of catalytic activity and durability. However, there is still enormous demand and potential for the catalysts to improve.

Download or read book Improving Oxygen Reduction Reaction Catalysts for Polymer Electrolyte Membrane Fuel Cells written by Jarrid A. Wittkopf and published by . This book was released on 2017 with total page 106 pages. Available in PDF, EPUB and Kindle. Book excerpt: Polymer electrolyte membrane fuel cells include proton exchange membrane fuel cells (PEMFCs) and hydroxide exchange membrane fuel cells (HEMFCs). PEMFCs use a proton conducting electrolyte, generating an acidic environment, while HEMFCs employ a hydroxide conducting electrolyte, providing a basic environment. For both types of fuel cells, the oxygen reduction reaction (ORR) at the cathode is sluggish and controls the fuel cell performance. Therefore, this thesis focuses on improving ORR catalyst activity and durability. ☐ PEMFCs, the more mature technology, have been commercially implemented in fuel cell cars like the Toyota Mirai and Honda Clarity. However, PEMFCs are expensive because they require a large amount of platinum (Pt) catalyst to overcome the ORR overpotential and the rapid catalyst degradation caused by the acidic operating environment. Current PEMFCs use Pt nanoparticles supported on amorphous carbon black as ORR catalysts. These catalysts have activity and durability concerns resulting from both the Pt nanoparticles and the amorphous carbon support. Strategies to improve catalyst activity and durability include generating a support-less catalyst, increasing the durability of the catalyst support, and switching to a basic environment. ☐ A transition to unsupported catalysts with an extended surface structure improves specific activity and durability and in turn, the cost-effectiveness of the entire fuel cell. Pt-coated copper nanowires (Pt/CuNW) exemplify these desirable catalytic traits. Improving this platform, post-synthetic processing is used to further enhance the ORR performance of the Pt/CuNW catalyst. Specifically, annealing followed by electrochemical dealloying increases activity by introducing geometric lattice tuning through Cu alloying. The resultant bimetallic PtCu-coated copper nanowire (PtCu/CuNW) catalyst yields ORR specific and mass activities of 2.65 mA cmPt-2 and 1.24 A mgPt-1, surpassing the respective DOE targets (SA and MA) of 0.72 mA cmPt-2 and 0.44 A mgPt-1. PtCu/CuNWs demonstrate enhanced durability over Pt nanoparticle catalysts by maintaining 64.1 % of its active surface area after undergoing 30,000 cycles of a potential cycling accelerated durability test (0.6 - 1.1 vs RHE). Post durability PtCu/CuNWs outperformed the DOE targets with a SA and MA of 1.50 mA cmPt-2 and 0.477 A mgPt-1 ☐ Alternately, increasing catalyst support durability through the introduction of a more durable carbon support has also been accomplished. Highly graphitic and cost-effective Cup-stacked carbon nanofiber supports have the potential to address the support durability concerns. Pt supported on carbon black (Vulcan XC-72) and cup-stacked carbon nanofibers as well as each carbon support alone underwent a high potential (1.4 V vs RHE) accelerated durability test in acidic and basic environments using rotating disk electrode techniques. It was shown that in all environments the cup-stacked carbon nanofiber support demonstrated higher durability and the catalysts tested in the basic environment had better overall stability compared to their acidic counterpart. ☐ HEMFCs have the potential for incorporating a wide variety of non-precious metal catalysts and promise to dramatically lower the fuel cell cost. One commercially available non-precious metal catalyst is Acta 4020. This carbon-based catalyst, containing 3.5 wt. % transition metals, when compared to state-of-the-art Pt/C catalysts shows comparable ORR performance and superior durability while exposed to a potential cycling (0.6 – 1.1 V vs RHE) accelerated durability test. Fuel cell testing also demonstrated the feasibility of incorporating this catalyst into the cathode electrode of a HEMFC.

Download or read book Impact of Polymer Electrolyte Membrane Degradation Products on Oxygen Reduction Reaction Activity for Platinum Electrocatalysts written by and published by . This book was released on 2014 with total page 8 pages. Available in PDF, EPUB and Kindle. Book excerpt: The impact of model membrane degradation compounds on the relevant electrochemical parameters for the oxygen reduction reaction (i.e. electrochemical surface area and catalytic activity), was studied for both polycrystalline Pt and carbon supported Pt electrocatalysts. Model compounds, representing previously published, experimentally determined polymer electrolyte membrane degradation products, were in the form of perfluorinated organic acids that contained combinations of carboxylic and/or sulfonic acid functionality. Perfluorinated carboxylic acids of carbon chain length C1 - C6 were found to have an impact on electrochemical surface area (ECA). The longest chain length acid also hindered the observed oxygen reduction reaction (ORR) performance, resulting in a 17% loss in kinetic current (determined at 0.9 V). Model compounds containing sulfonic acid functional groups alone did not show an effect on Pt ECA or ORR activity. Lastly, greater than a 44% loss in ORR activity at 0.9V was observed for diacid model compounds DA-Naf (perfluoro(2-methyl-3-oxa-5-sulfonic pentanoic) acid) and DA-3M (perfluoro(4-sulfonic butanoic) acid), which contained both sulfonic and carboxylic acid functionalities.

Download or read book Concentration Effects of Polymer Electrolyte Membrane Degradation Products on Oxygen Reduction Activity for Three Platinum Catalysts written by and published by . This book was released on 2014 with total page 6 pages. Available in PDF, EPUB and Kindle. Book excerpt: A rotating disk electrode (RDE) along with cyclic voltammetry (CV) and linear sweep voltammetry (LSV), were used to investigate the impact of two model compounds representing degradation products of Nafion and 3M perfluorinated sulfonic acid membranes on the electrochemical surface area (ECA) and oxygen reduction reaction (ORR) activity of polycrystalline Pt, nano-structured thin film (NSTF) Pt (3M), and Pt/Vulcan carbon (Pt/Vu) (TKK) electrodes. ORR kinetic currents (measured at 0.9 V and transport corrected) were found to decrease linearly with the log of concentration for both model compounds on all Pt surfaces studied. Ultimately, model compound adsorption effects on ECA were more abstruse due to competitive organic anion adsorption on Pt surfaces superimposing with the hydrogen underpotential deposition (HUPD) region.

Download or read book Electrocatalysts for Fuel Cells and Hydrogen Evolution written by Abhijit Ray and published by BoD – Books on Demand. This book was released on 2018-12-05 with total page 130 pages. Available in PDF, EPUB and Kindle. Book excerpt: The book starts with a theoretical understanding of electrocatalysis in the framework of density functional theory followed by a vivid review of oxygen reduction reactions. A special emphasis has been placed on electrocatalysts for a proton-exchange membrane-based fuel cell where graphene with noble metal dispersion plays a significant role in electron transfer at thermodynamically favourable conditions. The latter part of the book deals with two 2D materials with high economic viability and process ability and MoS2 and WS2 for their prospects in water-splitting from renewable energy.

Download or read book Study of Catalysts with High Stability for Proton Exchange Membrane Fuel Cells written by Fan Yang and published by . This book was released on 2015 with total page 84 pages. Available in PDF, EPUB and Kindle. Book excerpt: The innovation and investigation of catalysts in proton exchange membrane fuel cells are included in this thesis. In the first part of this work, stability of the catalyst support of PEMFC catalyst is investigated. Nanoscale platinum particles were loaded on two different kinds of carbon supports, nano graphene sheets and functionalized carbon black/graphene hybrid were developed by the liquid phase reaction. The crystal structure of two kinds of catalysts was characterized by X-ray diffractometer (XRD). The morphology and particle size were characterized by scanning electron microscope (SEM) and transmission electron microscope (TEM). Pt loading was measured by thermal gravimetric analysis (TGA). The Brunauer, Emmett and Teller (BET) method was applied to test the surface area of the catalysts. The electrochemical surface area (ECSA) and mass activity during oxygen reduction reaction (ORR) process for two kinds of catalyst were tested by cyclic voltammetry method under different conditions. The stability of the catalysts were tested by accelerated durability test (ADT). The results show that although the mass activity of Pt/graphene is much lower, the stability of it is much better than that of the commercial catalyst. After adding functionalized carbon black (FCB) as spacer, the stability of the catalyst is preserved and at the meantime, the mass activity becomes higher than 20% Pt/XC72 catalyst. The lower mass activity of both catalysts are due to the limitation of the electrolyte diffusion into the carbon support because of the aggregation nature of graphene nano-sheets. After introducing functional carbon black as spacer, the mass activity and ECSA increased dramatically which proved that FCB can be applied to prevent the restacking of graphene and hence solved the diffusion problem. In the meantime, the durability was still keeping the same as Pt/graphene catalyst. In the second part of the work, the restacking problem was solved by introducing FCB as spacers between functionalized graphene nanosheets. The same measurement was applied to test the electrochemical performance of Pt/FCB/FG catalyst. The new catalyst showed a higher mass activity compared to Pt/graphene catalyst which meant the restacking problem was partially solved. The durability of the Pt/FCB/FG catalyst was still excellent.

Download or read book Platinum Electrocatalysis written by Mohammad Javad Eslamibidgoli and published by . This book was released on 2016 with total page 110 pages. Available in PDF, EPUB and Kindle. Book excerpt: Formation of hydrogen peroxide and oxygenated radical species are the leading cause of chemical degradation observed in polymer electrolyte membranes (PEM) in polymer electrolyte fuel cells. Recent experimental studies have shown that Pt nano-deposits in the PEM, which originate from Pt dissolution in the catalyst layer, play an important role in radical-initiated membrane degradation. Surface reactions at Pt particles facilitate the formation of reactive oxygen species. The net effect of Pt surface processes on membrane degradation depends on the local equilibrium conditions around the Pt nano-deposits, specifically, their equivalent local electrode potential. In this thesis, we first present a multi-step theoretical approach, validated by a collaborative experimental study, to understand the impact of environmental conditions around the Pt nanodeposits on membrane chemical degradation. In the first step, we developed a physical analytical model for the potential distribution at Pt nanodeposits in the PEM. Given the local potential, we identify the surface adsorption state of Pt. Thereafter, density functional theory (DFT) was used to investigate the influence of the Pt adsorption state on the mechanism of oxygen reduction reaction (ORR), particularly the formation of hydrogen peroxide and hydroxyl radical as the two important reactive oxygen species for membrane degradation. In a separate work, we employed DFT to study the atomistic mechanism for interfacial place-exchange between surface Pt atom and chemisorbed oxygen at oxidized Pt (111)-water interfaces. Understanding the criteria for Pt oxide growth is a crucial step to comprehend the mechanisms of Pt dissolution during electrochemical processes.

Download or read book Advanced Electrode Materials written by Ashutosh Tiwari and published by John Wiley & Sons. This book was released on 2016-11-04 with total page 563 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book covers the recent advances in electrode materials and their novel applications at the cross-section of advanced materials. The book is divided into two sections: State-of-the-art electrode materials; and engineering of applied electrode materials. The chapters deal with electrocatalysis for energy conversion in view of bionanotechnology; surfactant-free materials and polyoxometalates through the concepts of biosensors to renewable energy applications; mesoporous carbon, diamond, conducting polymers and tungsten oxide/conducting polymer-based electrodes and hybrid systems. Numerous approaches are reviewed for lithium batteries, fuel cells, the design and construction of anode for microbial fuel cells including phosphate polyanion electrodes, electrocatalytic materials, fuel cell reactions, conducting polymer based hybrid nanocomposites and advanced nanomaterials.