Browsing by Author "Wu, Min"

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    A Graphite-Polysulfide Full Cell with DME-Based Electrolyte
    (ECS, 2016) Bhargav, Amruth; Wu, Min; Fu, Yongzhu; Department of Mechanical Engineering, School of Engineering and Technology
    Over the last decade, vast improvements have been made in the field of lithium-sulfur batteries bringing it a step closer to reality. In this field of research, deep understanding of the polysulfide shuttle phenomenon and their affinity with carbons, polymers and other hosts have enabled the design of superior cathodes with prolonged life. However, the anode side has undergone comparatively less transformation. In this work, we have developed a new electrolyte based on 1,2-dimethoxyethane (DME) solvent that enables reversible intercalation of lithium ions in graphite. A novel method to introduce solid lithium polysulfide into a carbon current collector as the cathode has been demonstrated and the electrode shows stable cycling with the new electrolyte. A full cell consisting of a lithiated graphitic anode and lithium polysulfide cathode is constructed, which exhibits an initial capacity as high as 1,500 mAh g−1 (based on the sulfur in the cathode) and a reversible capacity of 700 mAh g−1 for 100 cycles. This full cell is capable of delivering over 460 mAh g−1 at rates as high as 2C. The cell degradation over prolonged cycles could be due to the polysulfide shuttle which results in instability of the SEI layer on the graphitic anode.
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    Mutation-induced remodeling of the BfmRS two-component system in Pseudomonas aeruginosa clinical isolates
    (AAAS, 2020-11) Cao, Qiao; Yang, Nana; Wang, Yanhui; Xu, Chenchen; Zhang, Xue; Fan, Ke; Chen, Feifei; Liang, Haihua; Zhang, Yingchao; Deng, Xin; Feng, Youjun; Yang, Cai-Guang; Wu, Min; Bae, Taeok; Lan, Lefu; Microbiology and Immunology, School of Medicine
    Genetic mutations are a primary driving force behind the adaptive evolution of bacterial pathogens. Multiple clinical isolates of Pseudomonas aeruginosa, an important human pathogen, have naturally evolved one or more missense mutations in bfmS, which encodes the sensor histidine kinase of the BfmRS two-component system (TCS). A mutant BfmS protein containing both the L181P and E376Q substitutions increased the phosphorylation and thus the transcriptional regulatory activity of its cognate downstream response regulator, BfmR. This reduced acute virulence and enhanced biofilm formation, both of which are phenotypic changes associated with a chronic infection state. The increased phosphorylation of BfmR was due, at least in part, to the cross-phosphorylation of BfmR by GtrS, a noncognate sensor kinase. Other spontaneous missense mutations in bfmS, such as A42E/G347D, T242R, and R393H, also caused a similar remodeling of the BfmRS TCS in P. aeruginosa. This study highlights the plasticity of TCSs mediated by spontaneous mutations and suggests that mutation-induced activation of BfmRS may contribute to host adaptation by P. aeruginosa during chronic infections.
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    Protection of Human Lung Cells against Hyperoxia Using the DNA Base Excision Repair Genes hOgg1 and Fpg
    (2002-07) Wu, Min; He, Ying-Hui; Kobune, Masayoshi; Xu, Yi; Kelley, Mark R.; Martin II, William J.
    Hyperoxia causes pulmonary toxicity in part by injuring alveolar epithelial cells. Previous studies have shown that toxic oxygen-derived species damage DNA and this damage is recognized and repaired by either human enzyme 8-oxoguanine DNA glycosylase (hOgg1) or Escherichia coli enzyme formamidopyrimidine DNA glycosylase (Fpg). To determine whether these DNA repair proteins can reduce O2-mediated DNA damage in lung cells, A549 lung epithelial cells were transduced with either hOgg1 or Fpg using a retroviral vector containing enhanced green fluorescent protein. Expression of each gene in the transduced cells was confirmed by fluorescent microscopy, Northern blotting, Western blotting, and an enzymatic oligonucleotide cleavage assay. A549 cells expressing either hOgg1 or Fpg were protected from hyperoxia as evidenced by a decrease in DNA damage and a corresponding increase in cell survival. Further, we determined that overexpression of hOgg1 or Fpg partially mitigated the toxic effects of hydrogen peroxide in lung cells. Our data suggest that increased expression of DNA base excision repair genes might represent a new approach for protecting critical lung cells from the toxic effects of hyperoxia.
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    Studies of Sulfur-based Cathode Materials for Rechargeable Lithium Batteries
    (2016) Wu, Min; Fu, Yongzhu; Xie, Jian; Zhu, Likun; Anwar, Sohel
    Developing alternative cathodes with high capacity is critical for the next generation rechargeable batteries to meet the ever-increasing desires of global energy storage market. This thesis is focused on two sulfur-based cathode materials ranging from inorganic lithium sulfide to organotrisulfide. For lithium sulfide cathode, we developed a nano-Li2S/MWCNT paper electrode through solution filtration method, which involved a low temperature of 100 °C. The Li2S nanocrystals with a size less than 10 nm were formed uniformly in the pores of carbon paper network. These electrodes show an unprecedented low overpotential (0.1 V) in the first charges, also show high discharge capacities, good rate capability, and excellent cycling performance. This superior electrochemical performance makes them promising for use with lithium metal-free anodes in rechargeable Li–S batteries for practical applications. For organotrisulfide cathode, we use a small organotrisulfide compound, e.g. dimethyl trisulfide, to be a high capacity and high specific energy organosulfide cathode material for rechargeable lithium batteries. Based on XRD, XPS, SEM, and GC-MS analysis, we investigated the cell reaction mechanism. The redox reaction of DMTS is a 4e- process and the major discharge products are LiSCH3 and Li2S. The following cell reaction becomes quite complicated, apart from the major product DMTS, the high order organic polysulfide dimethyl tetrasulfide (DMTtS) and low order organic polysulfide dimethyl disulfide (DMDS) are also formed and charged/discharged in the following cycles. With a LiNO3 containing ether-based electrolyte, DMTS cell delivers an initial discharge capacity of 720 mAh g-1 and retains 74% of the initial capacity over 70 cycles with high DMTS loading of 6.7 mg cm-2 at C/10 rate. When the DMTS loading is increased to 11.3 mg cm-2, the specific energy is 1025 Wh kg-1 for the active materials (DMTS and lithium) and the specific energy is 229 Wh kg-1 for the cell including electrolyte. Adjusting on the organic group R in the organotrisulfide can achieve a group of high capacity cathode materials for rechargeable lithium batteries.