High Performance, High Durability Non-precious Metal Fuel Cell Catalysts PDF Download

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Languages : en
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This invention relates to non-precious metal fuel cell cathode catalysts, fuel cells that contain these catalysts, and methods of making the same. The fuel cell cathode catalysts are highly nitrogenated carbon materials that can contain a transition metal. The highly nitrogenated carbon materials can be supported on a nanoparticle substrate.

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Languages : en
Pages : 307

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This project was directed at reducing the dependence of PEM fuel cells catalysts on precious metals. The primary motivation was to reduce the cost of the fuel cell stack as well as the overall system cost without loss of performance or durability. Platinum is currently the catalyst of choice for both the anode & the cathode. However, the oxygen reduction reaction (ORR) which takes place on the cathode is an inherently slower reaction compared to the hydrogen oxidation reaction (HOR) which takes place on the anode. Therefore, more platinum is needed on the cathode than on the anode to achieve suitable fuel cell performance. As a result, developing a replacement for platinum on the cathode side will have a larger impact on overall stack cost. Thus, the specific objectives of the project, as stated in the solicitation, were to produce non-precious metal (NPM) cathode catalysts which reduce dependence on precious metals (especially Pt), perform as well as conventional precious metal catalysts currently in use in MEAs, cost 50% less compared to a target of 0.2 g Pt/peak kW, & demonstrate durability of greater than 2000 hours with less than 10% power degradation. During the term of the project, DOE refined its targets for NPM catalyst activity to encompass volumetric current density. The DOE Multi-Year RD & D Plan (2005) volumetric current density targets for 2010 & 2015 are greater than 130 A/cm3 & 300 A/cm3 at 800 mV (IR-free) respectively. The initial approach to achieve these targets was to use vacuum deposition techniques to deposit transition metal, carbon and nitrogen moieties onto 3M's nanostructured thin film (NSTF) catalyst support. While this approach yielded compounds with similar physicochemical characteristics as catalysts reported by others as active for ORR, the activity of these vacuum deposited catalysts was not satisfactory. In order to enhance catalytic activity additional process steps were introduced, the most successful of which was a thermal treatment. To withstand the high temperatures (~900 ðC), alternative supports to NSTF were introduced. A variety of carbon fabrics were tested for this purpose. Vacuum deposited materials were used as precursors & physicochemically transformed via thermal treatment to produce substantially better catalytic activity. This activity was further amplified by increasing the surface area of the carbon fabrics which lead to significant gains in fuel cell performance. The second synthetic approach is based on 3M nanotechnology & involves depositing precursor catalytic materials on high surface area supports, initially carbon. These materials were subsequently thermally treated in a nitrogen-containing gas atmosphere. While this approach is similar to others reported in the literature, we exploited 3M's nanotechnology platform & our expertise in the areas of synthesis & application of the precursor on the substrate. ORR activity proved higher for the materials produced via this approach. In fact, to our knowledge, the performance achieved on this effort exceeded the best previously reported for any NPM catalyst. With 4-nitroaniline as a precursor, the volumetric current density of our material achieved 19 A/cm3 at 800 mV, exceeding the value reported by DOE as the 2005 status (8 A/cm3) by a factor of more than two. We emphasize a unique feature of this project is that all measurements were done in real PEM fuel cells using 50-cm2 MEAs, therefore rendering credibility to the data for practical projection to a fuel cell stack application. In addition, with the price of the precursor nitroaniline only $1.5 kg on the commodity market enabling the DOE requirement of reducing the cost of the catalyst by a factor of two. A drawback of high-performing catalysts on carbon supports is their poor durability. Therefore, in the last stage of this project the focus of shifted toward improving the stability of the NPM catalyst. For that purpose alternative supports to carbon were introduced, The best catalyst synthesis methods remained practically the same for the new supports. Consequently, catalysts were made that were stable up to 1.4 V & one such material ran for over 1000 hours in a 50-cm2 fuel cell with no significant performance loss. In conclusion, by using precursor materials that are commodity items this project achieved the best performing & the most durable NPM catalyst reported thus far in PEM fuel cells. The knowledge base in the area of NPMC has been substantially increased & a solid platform for reaching the 2010 and 2015 targets of the DOE Multi-Year RD & D Plan has been established.

Author: Zhongwei Chen
Publisher: John Wiley & Sons
ISBN: 3527664920
Category : Technology & Engineering
Languages : en
Pages : 448

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Written and edited by top fuel cell catalyst scientists and engineers from both industry and academia, this is the first book to provide a complete overview of this hot topic. It covers the synthesis, characterization, activity validation and modeling of different non-noble metal electrocatalysts, as well as their integration into fuel cells and their performance validation, while also discussing those factors that will drive fuel cell commercialization. With its well-structured approach, this is a must-have for researchers working on the topic, and an equally valuable companion for newcomers to the field.

Author: Gaopeng Jiang
Publisher:
ISBN:
Category : Electrochemistry
Languages : en
Pages : 148

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To address the global energy and environmental challenges, the polymer electrolyte membrane fuel cell (PEMFC) is proposed and developed as one of the most promising power source candidates for various applications including electric vehicles, stationary power stations and portable devices due to its high efficiency and low emissions. However, the intrinsically sluggish reaction at the cathode, namely the oxygen reduction reaction (ORR), hinders the large-scale commercialization of the PEMFC as expensive and scarce platinum-based catalysts are used to accelerate this reaction. In order to reduce the cost of PEMFC, non-precious metal catalyst (NPMC) towards ORR has been developed and already brought itself from a pure scientific curiosity to a practically viable option for some commercial applications. In this work, two classes of low-cost NPMCs are investigated. One class is composed of high temperature treated transition metal-nitrogen-carbon M-N-C (M=Fe, Co) complex catalyst, especially iron-nitrogen-carbon complex (Fe-N-C) catalyst. These materials can demonstrate decent ORR activity and durability and provide high power output at moderate operating voltages. The other class with an even lower cost is the metal-free catalyst, which omits the metal content from M-N-C catalysts completely. This type of catalyst demonstrates excellent durability, especially in the presence of species that can cause contamination (e.g. carbon monoxide) or species that can cross-over (e.g. methanol). These two classes of NPMCs are developed and delivered with the ultimate objective of achieving a significant cost reduction in PEMFC while maintaining excellent PEMFC performance and durability. Herein, the research in this thesis starts with novel N, S-co-doped Fe-N-C catalysts to meet the objective of obtaining a highly economical and efficient NPMC. The catalyst is fabricated via pyrolyzing the composite of in-situ polymerized novel N, S-co-containing precursor, polyrhodanine (PRh) onto the acid-treated carbon black via the initiation of FeCl3. The N, S-co-doped Fe-N-C catalyst is obtained after two heat-treatment steps with one acid-leaching step in between. The catalyst demonstrates excellent ORR activity, bearing a half-wave potential of 0.77 V vs RHE in the acidic electrolyte. It also shows an excellent H2-air PEMFC performance, ranking the obtained peak power density (386 mW cm-2 at 0.46 V) among the best reported NMPC catalyst in H2-air PEMFC in the world. The N, S-co-doped Fe-N-C catalyst tends to catalyze the oxygen reduction via four electron pathway according to its number of transferred electrons (>3.94) and low peroxide yield (

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Languages : en
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The objective of this project is to develop novel non-precious metal electrocatalysts for oxygen reduction reaction (ORR), and demonstrate the potential of the catalysts to perform at least as good as conventional Pt catalysts currently in use in polymer electrolyte membrane fuel cell (PEMFC) with a cost at least 50 % less than a target of 0.2 g (Pt loading)/peak kW and with durability> 2,000 h operation with less than 10 % power degradation. A novel nitrogen-modified carbon-based catalyst was obtained by modifying carbon black with nitrogen-containing organic precursor in the absence of transition metal precursor. The catalyst shows the onset potential of approximately 0.76 V (NHE) for ORR and the amount of H2O2 of approximately 3% at 0.5 V (NHE). Furthermore, a carbon composite catalyst was achieved through the high-temperature pyrolysis of the precursors of transition metal (Co and Fe) and nitrogen supported on the nitrogen-modified carbon-based catalyst, followed by chemical post-treatment. This catalyst showed an onset potential for ORR as high as 0.87 V (NHE), and generated less than 1 % of H2O2. The PEM fuel cell exhibited a current density of 2.3 A cm-2 at 0.2 V for a catalyst loading of 6.0 mg cm-2. No significant performance degradation was observed for 480 h continuous operation. The characterization studies indicated that the metal-nitrogen chelate complexes decompose at the temperatures above 800 oC. During the pyrolysis, the transition metals facilitate the incorporation of pyridinic and graphitic nitrogen groups into the carbon matrix, and the carbon surface modified with nitrogen is active for ORR. In order to elucidate the role of transition metal precursor played in the formation of active sites in the non-precious metal catalysts, a novel ruthenium-based chelate (RuNx) catalyst was synthesized by using RuCl3 and propylene diammine as the Ru and N precursors, respectively, followed by high-temperature pyrolysis. This catalyst exhibited comparable catalytic activity and selectivity for ORR as the Pt catalyst. A theoretical analysis is made of the four-electron reduction reaction of oxygen to water over the mixed anion and cation (202) surface of pentlandite structure Co9Se8, one of several selenide phases. Reversible potentials for forming adsorbed reaction intermediates in acid are predicted using adsorption energies calculated with the Vienna ab initio simulation program (VASP) and the known bulk solution values together in a linear Gibbs energy relationship. The effect of hydrophobic and structural properties of a single/dual-layer cathode gas diffusion layer on mass transport in PEM fuel cells was studied using an analytical expression. The simulations indicated that liquid water transport at the cathode is controlled by the fraction of hydrophilic surface and the average pore diameter in the cathode gas diffusion layer. The optimized hydrophobicity and pore geometry in a dual-layer cathode GDL leads to an effective water management, and enhances the oxygen diffusion kinetics.

Author: Ja-Yeon Choi
Publisher:
ISBN:
Category : Catalysts
Languages : en
Pages : 118

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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. Two approaches being widely accepted to overcome this limitation are 1) to improve Pt utilization to boost the activity while reducing the loading, or 2) to develop non-precious metal catalysts (NPMCs) with sufficient activity and stability to be used in the PEM fuel cells. Despite the ample amount of research and improvements, the activity and stability of these NPMCs must be further improved to be practical in PEMFC applications. The activity can be further enhanced by several different approaches including but not limited to: 1) use of different dopants (nitrogen, boron, sulfur, etc.) precursors, 2) use of different non-platinum group metals (Fe, Co, Mn), 3) utilizing high surface area support materials and 4) applying heat treatment in various conditions. The combination of these approaches affect the active site density and distribution, electronic structure of the active site thus affecting its kinetics and turn over frequency, electrical conductivity and stability of the catalyst in various ways. Herein, two chapters are included exploring with the above mentioned combinations to synthesize highly active and stable catalysts, followed by another chapter investigating its fuel cell performance and discussing possible causes of stability loss with a method to verify the issue with flooding of the microporous active sites. In the first study, non-precious metal oxygen reduction reaction (ORR) catalysts were prepared by pyrolyzing a carbon supported complex consisting of iron acetate coordinated with 1,2,4,5-tetracyanobenzene (TCNB) in an iron phtalocyanine-like polymer arrangement. By employing these small precusursor molecules, it is expected that more uniform and complete coverage of the carbon support material can be obtained, and by using the in situ formation and polymerization of FePc, effective iron-center segregation can be achieved. The results suggest that this type of catalyst has great potential used as a non-precious PEM fuel cell catalyst. In the second study, Co-N decorated porous graphene aerogel catalyst was synthesized as an efficient catalyst for ORR. In the preparation process, polyaniline (PANI) is introduced as a pore-forming agent to aid in the self-assemble of graphene species into a porous aerogel networks, and a nitrogen precursor to induce in situ nitrogen doping. Such highly desired structures can not only expose sufficient active sites for the ORR but also guarantee the fast mass transfer in the catalytic process, which provides significant catalytic activity with positive onset and half wave potentials, low hydrogen peroxide yield and remarkable stability in acid medium. In the last chapter, with a highly microporous catalyst made with dual nitrogen precursors (phenanthroline and polyaniline), a systematic study is performed to investigate micropore flooding in-situ before and after stability testing. The results do not support micropore flooding as being a large contributor to instability, at least for the family of NPMCs evaluated in this work. The protocol outlined here can be used by other researchers in the NPMC community to diagnose micropore flooding in their own respective catalysts. Several recommendations for future work were suggested in the last section of this work to further apply the knowledge to design a highly active, durable, and low-cost NPMCs.

Author: Jarrid A. Wittkopf
Publisher:
ISBN: 9780355251920
Category :
Languages : en
Pages : 106

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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.

Author: Julia Müller-Hülstede
Publisher:
ISBN:
Category :
Languages : en
Pages : 0

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Author: Foroughazam Afsahi
Publisher:
ISBN:
Category :
Languages : en
Pages : 249

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Fuel cells have great potential for use as alternative energy conversion devices for a wide variety of applications. Proton exchange membrane fuel cells (PEMFCs) are considered to be potential replacements for internal combustion engines in automobiles, owing to their reduced emissions and better efficiency. A platinum (Pt)-based catalyst is required to facilitate both hydrogen oxidation reaction (HOR) and oxygen reduction reaction (ORR) which occur at the anode and cathode of PEMFCs, respectively. The ORR kinetic is inherently very sluggish and is considered the limiting factor facing the performance of PEMFCs. In order to generate power at an acceptable rate for real world applications, a significant amount of Pt catalyst is required. This is traditionally in the form of Pt nanoparticles evenly distributed on a porous carbon support material (Pt/C). Pt is an extremely expensive noble metal with very limited natural abundance. Thus, large-scale commercialization of PEMFCs requires significant advances in catalyst development in order both to reduce the amount of Pt metal and to enhance catalyst durability. In this research work, we employed Metal-Organic Frameworks (MOFs) as a sole precursor for preparing PEMFC electrocatalysts. Owing to their crystalline, porous, hybrid structure, these materials have potential to be applied as PEMFCs electrocatalyst precursor. The clearly-defined three-dimensional structure of these materials can produce a high density of metal active sites evenly distributed through their regularly arranged structure. They can therefore enhance catalyst utilization. The organic linkers of the MOF-based precursor would be converted to carbon during thermal activation while maintaining the porous framework, leading to catalysts with high surface area and uniformly distributed active sites without the need for a carbon support. Pt and Fe containing MOF precursors were synthesized and used as the sole precursor to develop both Pt and non-precious (Fe)-based electrocatalysts for PEMFCs. A Pt-based electrocatalyst was the first reported on implementation of precious metal containing MOFs for developing PEMFC electrocatalyst. The Pt-based electrocatalyst derived from this Pt-containing MOF precursor demonstrated catalytic performance comparable to the commercially available Pt/C especially for HOR at the anode side. To prepare a non-precious electrocatalyst, Fe containing MOF belonging to a different class of MOF materials other than ZIFs was synthesized and used as the sole electrocatalyst precursor. This was the first report on using non-ZIF MOF precursor for ORR electrocatalyst development. This Fe-based electrocatalyst revealed promising ORR activity and PEM fuel cell performance when applied at the cathodic catalytic layer of the corresponding membrane electrode assembly (MEA). In addition, the effect of catalyst ink composition prepared from the MOF derived Pt-based electrocatalyst, in terms of Nafion ionomer content, on the overall performance of PEMFC was investigated via a macroscopic CFD model. The trend predicted from the model calculations was then surveyed experimentally in search for the optimum Nafion ionomer content. Furthermore, the products of thermal transformation of Pt-based MOF into carbon-black based electrocatalyst were studied using a.c. impedance spectroscopy. Along with the electrocatalyst precursor, thermolysis products of parent MOF-253 (Al-containing) were considered in these studies. The materials subjected to thermolysis at increasing temperatures were found to pass through different conduction states starting from insulator and ending up with a particular metal-like conductance with positive temperature dependence and high ambient conductivity.

Author: Bosi Peng
Publisher:
ISBN:
Category :
Languages : en
Pages : 0

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Proton exchange membrane fuel cells (PEMFCs) offer an attractive zero-emission power generation technology to realize a carbon-neutral future. However, the competitiveness of PEMFCs is severely constrained by the costly precious metal catalysts needed for the cathode oxygen reduction reaction (ORR). This thesis aims to address two critical challenges in ORR catalysts, activity and durability. To this end, we first developed a facile molecular surface modification approach using dimethylformamide to improve the microkinetics of the physisorption/desorption process in ORR, to achieve an unprecedented specific activity of 21.8 mA/cm2 in modified model PtCuNi catalyst. Next, by exploiting a unique design of jagged Pt nanowire catalysts, we developed a high-performance PEMFC using PtCo nanowire catalysts to realize an unprecedented mass activity of 1.06 A/mgPt, far surpassing the Department of Energy target. Lastly, exploiting a strong-metal-oxide binding effect, we further designed a unique ultrafine Pt nanocatalysts with embedded cobalt oxide to achieve superior power performance and life durability. These studies offer new perspectives on fuel cell catalyst design and hold significant promise to substantially reduce the lifetime adjusted cost for widespread adoption of PEMFCs in practical technologies.