Browsing by Subject "Fuel cells"

Now showing 1 - 6 of 6
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    Atomically dispersed iron sites with a nitrogen–carbon coating as highly active and durable oxygen reduction catalysts for fuel cells
    (Springer Nature, 2022) Liu, Shengwen; Li, Chenzhao; Zachman, Michael J.; Zeng, Yachao; Yu, Haoran; Li, Boyang; Wang, Maoyu; Braaten, Jonathan; Liu, Jiawei; Meyer, Harry M., III; Lucero, Marcos; Kropf, A. Jeremy; Alp, Esen E.; Gong, Qing; Shi, Qiurong; Feng, Zhenxing; Xu, Hui; Wang, Guofeng; Myers, Deborah J.; Xie, Jian; Cullen, David A.; Litster, Shawn; Wu, Gang; Mechanical and Energy Engineering, Purdue School of Engineering and Technology
    Nitrogen-coordinated single atom iron sites (FeN4) embedded in carbon (Fe–N–C) are the most active platinum group metal-free oxygen reduction catalysts for proton-exchange membrane fuel cells. However, current Fe–N–C catalysts lack sufficient long-term durability and are not yet viable for practical applications. Here we report a highly durable and active Fe–N–C catalyst synthesized using heat treatment with ammonia chloride followed by high-temperature deposition of a thin layer of nitrogen-doped carbon on the catalyst surface. We propose that catalyst stability is improved by converting defect-rich pyrrolic N-coordinated FeN4 sites into highly stable pyridinic N-coordinated FeN4 sites. The stability enhancement is demonstrated in membrane electrode assemblies using accelerated stress testing and a long-term steady-state test (>300 h at 0.67 V), approaching a typical Pt/C cathode (0.1 mgPt cm−2). The encouraging stability improvement represents a critical step in developing viable Fe–N–C catalysts to overcome the cost barriers of hydrogen fuel cells for numerous applications.
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    Integrated micro PEM fuel cell with self-regulated hydrogen generation from ammonia borane
    (2015-08) Zamani Farahani, Mahmoud Reza; Zhu, Likun
    An integrated micro PEM fuel cell system with self-regulated hydrogen generation from ammonia borane is reported to power portable electronics. Hydrogen is generated via catalytic hydrolysis reaction of ammonia borane solution in microchannels with nanoporous platinum catalyst electroplated inside the microchannels. The self-regulation of the ammonia borane solution is achieved by using directional growth and selective venting of hydrogen bubbles in microchannels, which leads to agitation and addition of fresh solution without power consumption. The device is fabricated on combination of polystyrene sheets cut by graphic cutter, a stainless steel layer cut using wire electrical discharge machining and bonding layers with double-sided polyimide tape. Due to the seamless bonding between the hydrogen generator and the micro fuel cell, the dead volume in the gas connection loops can be significantly reduced and the response time of self-regulation is reduced.
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    Lithium Ion Battery Failure Detection Using Temperature Difference Between Internal Point and Surface
    (2011-12) Wang, Renxiang; Chen, Yaobin; Chen, Rongrong; Rizkalla, Maher
    Lithium-ion batteries are widely used for portable electronics due to high energy density, mature processing technology and reduced cost. However, their applications are somewhat limited by safety concerns. The lithium-ion battery users will take risks in burn or explosion which results from some internal components failure. So, a practical method is required urgently to find out the failures in early time. In this thesis, a new method based on temperature difference between internal point and surface (TDIS) of the battery is developed to detect the thermal failure especially the thermal runaway in early time. A lumped simple thermal model of a lithium-ion battery is developed based on TDIS. Heat transfer coefficients and heat capacity are determined from simultaneous measurements of the surface temperature and the internal temperature in cyclic constant current charging/discharging test. A look-up table of heating power in lithium ion battery is developed based on the lumped model and cyclic charging/discharging experimental results in normal operating condition. A failure detector is also built based on TDIS and reference heating power curve from the look-up table to detect aberrant heating power and bad parameters in transfer function of the lumped model. The TDIS method and TDIS detector is validated to be effective in thermal runaway detection in a thermal runway experiment. In the validation of thermal runway test, the system can find the abnormal heat generation before thermal runaway happens by detecting both abnormal heating power generation and parameter change in transfer function of thermal model of lithium ion batteries. The result of validation is compatible with the expectation of detector design. A simple and applicable detector is developed for lithium ion battery catastrophic failure detection.
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    Multiple Metal-Nitrogen Bonds Synergistically Boosting the Activity and Durability of High-Entropy Alloy Electrocatalysts
    (American Chemical Society, 2024) Zhao, Xueru; Cheng, Hao; Chen, Xiaobo; Zhang, Qi; Li, Chenzhao; Xie, Jian; Marinkovic, Nebojsa; Ma, Lu; Zheng, Jin-Cheng; Sasaki, Kotaro; Mechanical and Energy Engineering, Purdue School of Engineering and Technology
    The development of Pt-based catalysts for use in fuel cells that meet performance targets of high activity, maximized stability, and low cost remains a huge challenge. Herein, we report a nitrogen (N)-doped high-entropy alloy (HEA) electrocatalyst that consists of a Pt-rich shell and a N-doped PtCoFeNiCu core on a carbon support (denoted as N-Pt/HEA/C). The N-Pt/HEA/C catalyst showed a high mass activity of 1.34 A mgPt-1 at 0.9 V for the oxygen reduction reaction (ORR) in rotating disk electrode (RDE) testing, which substantially outperformed commercial Pt/C and most of the other binary/ternary Pt-based catalysts. The N-Pt/HEA/C catalyst also demonstrated excellent stability in both RDE and membrane electrode assembly (MEA) testing. Using operando X-ray absorption spectroscopy (XAS) measurements and theoretical calculations, we revealed that the enhanced ORR activity of N-Pt/HEA/C originated from the optimized adsorption energy of intermediates, resulting in the tailored electronic structure formed upon N-doping. Furthermore, we showed that the multiple metal-nitrogen bonds formed synergistically improved the corrosion resistance of the 3d transition metals and enhanced the ORR durability.
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    STUDY OF CATALYST LAYER FOR POLYMER ELECTROLYTE FUEL CELL
    (2010-07-27T18:58:35Z) Xu, Fan; Xie, Jian; Chen, Jie; Petrache, Horia
    There are three parts in this work centered on the catalyst layer of Polymer Electrolyte Fuel Cell (PEFC) in this thesis. The first part is for making best MEA structure. One of the major aims of this investigation is to understand the micro-structural organization of ionomer particles and Pt/C aggregates dispersed in a catalyst ink. The dispersion of Nafion® ionomer particles and Pt/C catalyst aggregates in liquid media was studied using ultra small angle x-ray scattering (USAXS) and cryogenic TEM technologies. A systematic approach was taken to study the dispersion of each component (i.e. ionomer particles and Pt/C aggregates) first, then the combination, last the catalyst ink. A multiple curve fitting was used to extract the particle size, size distribution and geometry from scattering data. The results suggests that the particle size, size distribution and geometry of each system are not uniform, rather, vary significantly. The results also indicate that interaction among components (i.e. ionomer particles and Pt/C aggregates) exists. The cryogenic TEM, by which the size and geometry of particles in a liquid can be directly observed, was used to validate the scattering results, which shows the excellent agreement. Based on this study, a methodology of analyzing dispersion of Pt/C particles, Nafion® particles in a catalyst ink has been developed and can serve as a powerful tool for making a desired catalyst ink which is a critical step for making rational designed MEA. The carbon corrosion process is the second part of the thesis. The carbon corrosion process of low–surface-area Pt/XC72 and high-surface-area Pt/BP2000 was investigated xi using an developed accelerated durability testing (ADT) method under simulated fuel cell conditions (a Rotating Disk Electrode (RDE) approach). Compared with the complex MEA system, this innovated approach using RDE can simply focus on carbon corrosion process and avoid the use of MEA in which many degradation/corrosion processes simultaneously occur. It was observed that different carbon corrosion processes resulted in different performance (electrochemical active surface area, mass activity and double layer capacity) decay of catalysts. The corrosion process was studied using TEM. It was found that in the case of Pt/XC72, major corrosion occurred at the center of the Pt/XC72 particle, with some minor corrosion on the surface of the carbon particle removing some amorphous carbon black filaments, while in the case of Pt/BP2000, the corrosion started on the surface. The understanding of carbon corrosion process provides the guidance for making high corrosion resistance catalysts to increase the durability performance of PEFC. Based on the second work, XC72 carbon blacks were etched using steam under different time and used as a new high corrosion resistance catalysts support for the oxygen reduction reaction. TEM results show that the center part of the XC72 particle was more easily etched away. XRD results show that the 002 and 10 peaks of the XC72 based samples are initially sharp, but then broaden during the corrosion process. TEM results of Pt particles show that the steam etching can improve dispersion uniformity of Pt nanoparticles on the surface of carbon support and reduce the Pt particles size. Electrochemical characterization results show that the mass activity of etched carbon black for 1 hour was 1.3 and 34 times greater than that of the carbon blacks etched for 3h and that of carbon blacks non-ecthed. ECSA of the carbon blacks was also significantly increased after etching. MEA test showed after 45 hours testing, the performance MEA with steam etching 1 hour XC72 based catalyst decreases much less than the MEA with commercial catalyst. Clearly, steam etching is a simple and efficient method to increase the performance and durability of the fuel cells catalysts.
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    Study of catalysts with high stability for proton exchange membrane fuel cells
    (2015-08) Yang, Fan; Xie, Jian
    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.