Browsing by Author "Chen, Rongrong"

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    AQUEOUS LIQUID SOLUTIONS FOR LI-LIQUID BATTERY
    (Office of the Vice Chancellor for Research, 2012-04-13) Salim, Jason; Cheah, Seong Shen; Lee, Wen Chao; Mahootcheian Asl, Nina; Chen, Rongrong; Kim, Youngsik
    The evolvement of Lithium-ion battery industries has begun to carry the industries to step in a new revolution. Consequently, high demand in high energy density batteries in many electronic and electrical appliances, espe-cially energy storage industries been emerged. This new type of batteries has been in extensive research, such as lithium-water battery. Lithium-water battery is a newly developed battery with lithium as the anode and water as the cathode. Lithium is known as one of the most reac-tive metals in periodic table. Therefore, rigorous reaction will be observed when lithium is reacted with water and hence potentially providing an ex-tremely high energy density. This rigorous reaction can be converted into electrical energy and can be stored in a cell. Lithium-water battery is novel and hence, there is no standardized design. In this presentation, lithium anode is separated from water by liquid electrolyte and a ceramic solid electrolyte. The glass-ceramic solid electro-lyte which has Li1.3Ti1.7Al0.3(PO4)3 composition plays an important role of the design of this lithium–water battery. The main purpose of the solid electro-lyte is to separate water from lithium, avoiding a dangerous exothermic re-action. Also, the presence of the super-ionic conductor ceramic can provide very high lithium ion conductivity. The different sizes of solid electrolytes were used in designing Li-liquid battery cell. The effect of the electrolyte size on the voltage of the cell was studied to optimize the cell design. Then, the aqueous solutions containing different chemicals were tested as the liquid cathodes, and their electro-chemical performance were compared to those of the pure DI water. Further results will be presented in the poster presentation.
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    COMPUTATIONAL STUDY OF SURFACE-SEGREGATED PT ALLOY CATALYSTS FOR OXYGEN REDUCTION REACTION
    (2010-07-27T19:21:50Z) Xiao, Chan; Chen, Rongrong; EI-Mounayri, Hazim; Wang, Guofeng
    In this thesis two research objectives have been accomplished using computational simulation techniques. (1) The surface segregation phenomena in the surfaces of (111), unreconstructed (110) and reconstructed (1x2) missing row (110) surfaces of Pt-Ni and Pt-Co disordered alloys have been accurately predicted using Monte Carlo (MC) simulation method, and (2) the configuration and energy of the adsorption of O, O2, OH, and H2O molecules which are presented in oxygen reduction reaction (ORR) on the surface of pure Pt and surface-segregated Pt-binary alloys (i.e., Pt-Ni, Pt-Co and Pt-Fe) have been determined using density functional theory (DFT) calculations. This thesis yields some guiding principles for designing novel catalysts for proton exchange membrane fuel cells. The Pt concentration profiles of the surfaces of Pt-Ni and Pt-Co alloys were attained from the MC simulations in which the system energy was evaluated through the developed modified embedded atom method (MEAM) for Pt-Ni and Pt-Co alloys. It was found from our simulations that the Pt atoms strongly segregate to the outermost layer and the Ni atoms segregate to the second sub-layer in the (111) surface of both Pt-Ni and Pt-Co alloys. When Pt concentration is higher than 75 at.%, pure Pt top layer could be formed in the outermost layer (111) surface of both alloys. Moreover, segregation reversal phenomenon (Ni atoms segregating to the outermost layer while Pt atoms to the second sub-layer) was observed in our MC simulations of unreconstructed (110) surface of Pt-Ni alloys. In contrast, a Pt enriched outermost surface layer was found in a Pt-Ni reconstructed (1x2) missing row (110) surface. Our MC simulation results agree well with published experimental observations. In addition, adsorption of atomic and molecular oxygen, water and hydroxyl on the (111) and (100) surfaces of pure Pt and Pt-based alloys (Pt-Ni, Pt-Co and Pt-Fe) were studied using spin DFT method and assuming a coverage of 0.25 monolayer. Both the optimized configurations and the corresponding adsorption energies for each species were obtained in this study. In particular, we elucidated the influence of the adsorption energies of atomic oxygen and OH on the activity for ORR on Pt binary alloy catalysts in acidic environment. The calculated adsorption energies of atomic oxygen on the (111) surfaces of pure Pt, Pt-Ni, Pt-Co and Pt-Fe are -3.967 eV, -3.502 eV, -3.378 eV and -3.191 eV, respectively. The calculated adsorption energies of hydroxyl on the (111) surfaces of pure Pt, Pt-Ni, Pt-Co and Pt-Fe are -2.384 eV, -2.153 eV, -2.217 eV and -2.098 eV, respectively. The interaction between the adsorbed atomic and hydroxyl and the corresponding (111) surface becomes weaker for the surface-segregated alloys compared to pure Pt catalyst. The same results were obtained for the (100) surfaces.
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    Depositing Catalyst Layers in Polymer Electrolyte Membrane Fuel Cells: A Review
    (ASME, 2015-12) Strong, Austin; Thornberry, Courtney; Beattie, Shane; Chen, Rongrong; Coles, Stuart R.; Department of Engineering Technology, School of Engineering and Technology
    Fuel cell technology continues to advance and offers to be a potentially promising solution to many energy needs. Of particular interest are manufacturing techniques to improve performance and decrease overall cost. For catalyst deposition on the membrane electrode assembly (MEA), there are a number of techniques that have been used in the past decades. This paper aims to review many of these main techniques that have been published to show the wide variety of catalyst deposition methods.
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    ECSTM Studies of the Electrocatalyst Stability for the AAEM Fuel Cell
    (Office of the Vice Chancellor for Research, 2010-04-09) Xu, Qingmin; Cheng, Ruihua; Thornberry, Courtney; Chen, Rongrong
    Alkaline fuel cells (AFC) have come to the forefront of fuel cell research due to the friendlier environment they provide to the cell’s components in comparison to acid-based Proton Exchange Membrane (PEM) fuel cells. The AFC shows real world application of 60% efficiency, but suffers from long term degradation due to the formation of carbonate precipitates formed from carbon dioxide. A solid-state form of the AFC, the alkaline anion exchange membrane (AAEM) fuel cell, is under development to overcome the degradation, due to the usage of liquid potassium hydroxide (KOH) or sodium hydroxide (NaOH) electrolytes in the AFC. Also, the AFC are known to have a higher rate of contamination and therefore need higher purity fuel than their acidic counterparts. This problem is eliminated by the AAEM fuel cell. The cathode, which consists of the catalyst, ionomer and current supports in the AAEM fuel cell or the AFC, is the key component that determines the cell’s performance and stability. The material found to work best for the AAEM fuel cell is platinum (Pt). The issue with Pt as a catalyst material for these fuel cells is that is it very cost prohibitive for mass production. Therefore, other metals are being investigated to find a material with less cost, but perform as well as the Pt in AAEM fuel cells. Several theories have been proposed as to the cause of cathode degradation. It was found that an increase in current density, temperature and ligand (OH-) concentration accelerated corrosion of catalysts and carbon supports. Studies have been done on the catalyst material of Pt, as well as the highly oriented pytolytic graphite (HOPG). HOPG is a carbon-based material that Pt is deposited upon. So far, most of these studies were done in acid media. The objective of this work is to develop an in situ electrochemical scanning tunneling microcopy (ECSTM) method for characterizing stability of nano-Pt and HOPG substrate under operation conditions of an AFC. Future research will characterize the stability of other metal nanostructure in an attempt to find cheaper and effective alternatives to Platinum.
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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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    LITHIUM-AQUEOUS BATTERY
    (Office of the Vice Chancellor for Research, 2012-04-13) Cavazos, Ana; Mosier, Luke; Chen, Rongrong; Kim, Youngsik
    Due to the exceptionally high energy density Lithium-water batteries have very high storage efficiency. Being able to store more energy is im-portant to many industries including electronics and electric vehicles. This is the reason that much research is being done to optimize and explore new techniques of development for these batteries. The Li-water battery has been designed in this project to test water and other aqueous solutions as the cathode. The lithium in a non-aqueous elec-trolyte acts as the anode of the battery. The solid electrolyte used in the lith-ium water batteries is a glass/ceramic (LISICON). The solid electrolyte acts as a separator allowing the Lithium ions to pass through it without allowing the liquid cathode come into direct contact the Lithium. This paper describes the creation and testing of a Lithium-water battery which uses water and Copper (II) Nitrate as the cathode electrolyte. The purpose of this paper is to compare and contrast the difference in voltage of distilled water and distilled water with Copper (II) Nitrate additives as cath-ode. When the tests were conducted, it was found that Copper (II) Nitrate does in fact increase the voltage of the Lithium-water batteries significantly when compared to the distilled water. These results were expected because of Copper (II) Nitrate’s strong electrolyte properties.
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    Lugar Center for Renewable Energy, Alkaline Anion Exchange Membrane Fuel Cells
    (Office of the Vice Chancellor for Research, 2011-04-08) Chen, Rongrong
    The U.S. Army needs new reliable, long lasting, and lightweight power sources suitable for its future soldiers. A new technology, alkaline anion exchange membrane fuel cells (AAEMFCs) developed by the researchers at the Richard G. Lugar Center for Renewable Energy, has the potential to be an advanced power source for combat applications. AAEMFCs have several advantages over current existing proton exchange membrane (PEM) fuel cells, e.g. non-Pt catalysts with good methanol/ethanol tolerance can be used in the cathodes of the AAEMFCs. Concentrated liquid fuels, such as methanol, ethanol, or ethylene glycol, can be used in the AAEMFCs and have the potential of producing higher power capacity and better durability than the direct alcohol fuel cells based on PEMs. However, several technical barriers need to be overcome for applying this technology for future soldiers. The objective of our research effort is to investigate solutions to these technical challenges, which include developing novel AAEMs with ionic conductivity comparable to the PEMs; novel non-Pt catalysts for anode and cathode and ionomers for elctrochemcial interfaces of electrodes.
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    Modulation of MRSA virulence gene expression by the wall teichoic acid enzyme TarO
    (Springer Nature, 2023-03-22) Lu, Yunfu; Chen, Feifei; Zhao, Qingmin; Cao, Qiao; Chen, Rongrong; Pan, Huiwen; Wang, Yanhui; Huang, Haixin; Huang, Ruimin; Liu, Qian; Li, Min; Bae, Taeok; Liang, Haihua; Lan, Lefu; Microbiology and Immunology, School of Medicine
    Phenol-soluble modulins (PSMs) and Staphylococcal protein A (SpA) are key virulence determinants for community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA), an important human pathogen that causes a wide range of diseases. Here, using chemical and genetic approaches, we show that inhibition of TarO, the first enzyme in the wall teichoic acid (WTA) biosynthetic pathway, decreases the expression of genes encoding PSMs and SpA in the prototypical CA-MRSA strain USA300 LAC. Mechanistically, these effects are linked to the activation of VraRS two-component system that directly represses the expression of accessory gene regulator (agr) locus and spa. The activation of VraRS was due in part to the loss of the functional integrity of penicillin-binding protein 2 (PBP2) in a PBP2a-dependent manner. TarO inhibition can also activate VraRS in a manner independent of PBP2a. We provide multiple lines of evidence that accumulation of lipid-linked peptidoglycan precursors is a trigger for the activation of VraRS. In sum, our results reveal that WTA biosynthesis plays an important role in the regulation of virulence gene expression in CA-MRSA, underlining TarO as an attractive target for anti-virulence therapy. Our data also suggest that acquisition of PBP2a-encoding mecA gene can impart an additional regulatory layer for the modulation of key signaling pathways in S. aureus.
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    New Understandings of Ethanol Oxidation Reaction Mechanism on Pd/C and Pd2Ru/C Catalysts in Alkaline Direct Ethanol Fuel Cells
    (Elsevier, 2018-05) Guo, Junsong; Chen, Rongrong; Zhu, Fu-Chun; Sun, Shi-Gang; Vilullas, Hebe M.; Engineering Technology, School of Engineering and Technology
    Ethanol oxidation reaction (EOR) on Pd2Ru/C and Pd/C catalysts in alkaline media is studied comprehensively by cyclic voltammetry, chronoamperometry, in situ FTIR, single fuel cell test and electrochemical impedance spectroscopy measurements. The results show that, as compared to Pd/C, Pd2Ru/C favors acetaldehyde formation and hinders its oxidation. Based on X-ray absorption data, which evidence that Ru promotes a larger electronic vacancy of the Pd 4d band, it is expected that the formation of adsorbed ethoxy is favored on Pd2Ru/C and followed by its oxidation to acetaldehyde facilitated by oxygenated species provided by Ru. In contrast, acetaldehyde oxidation is more difficult on Pd2Ru/C than on Pd/C likely because the adsorption energy of the reactive species is increased. We also show that the performance of Pd2Ru/C anode in alkaline direct ethanol fuel cell (ADEFC) is initially better but degrades much more rapidly than that with Pd/C anode under the same test conditions. The degradation is demonstrated to result from the accumulation of large amounts of acetaldehyde, which in alkaline media forms dimers by the aldol condensation reaction. The dimers tend to be responsible for blocking the active sites for further ethanol oxidation. This comprehensive study provides new understandings of the roles of Ru in Pd2Ru/C for EOR in alkaline media, unveils the causes of the performance degradation of fuel cells with Pd2Ru/C and demonstrates that initial good performances are not necessarily a valid criterion for selecting appropriate anode catalysts for ADEFC applications.
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    Nitrogen-doped carbon nanotubes with encapsulated Fe nanoparticles as efficient oxygen reduction catalyst for alkaline membrane direct ethanol fuel cells
    (Elsevier, 2017-12) Rauf, Muhammad; Chen, Rongrong; Wang, Qiang; Wang, Yu-Cheng; Zhou, Zhi-You; Engineering Technology, School of Engineering and Technology
    Exploring low-cost and highly efficient non-precious metal electrocatalysts toward oxygen reduction reaction is crucial for the development of fuel cells. Herein, we report the synthesis of bamboo-like N-doped carbon nanotubes with encapsulated Fe-nanoparticles through high-temperature pyrolysis of multiple nitrogen complex consisting of benzoguanamine, cyanuric acid, and melamine. As-prepared catalyst exhibits high catalytic activity for oxygen reduction with onset potential of 1.10 V and half-wave potential of 0.93 V, as well as low H2O2 yield (<1%) in alkaline medium. The mass activity of the catalyst at 1.0 V (0.58 A g−1) can reach 43% of state-of-the-art commercial Pt/C. This catalyst also exhibits high durability and ethanol tolerance. When it was applied in alkaline membrane direct ethanol fuel cell, the peak power density could reach to 64 mW cm−2, indicating its attractive application prospect in fuel cells.