bluuebunny/crossref_metadata_2025 huggingface dataset:
FlhF and Its GTPase Activity Are Required for Distinct Processes in Flagellar Gene Regulation and Biosynthesis in
Campylobacter jejuni
Authors: Balaban Murat , Joslin Stephanie N. , Hendrixson David R.
Published: August 2009

FlhF proteins are putative GTPases that are often necessary for one or more steps in flagellar organelle development in polarly flagellated bacteria. In
Campylobacter jejuni
, FlhF is required for σ
54
-dependent flagellar gene expression and flagellar biosynthesis, but how FlhF influences these processes is unknown. Furthermore, the GTPase activity of any FlhF protein and the requirement of this speculated activity for steps in flagellar biosynthesis remain uncharacterized. We show here that
C. jejuni
FlhF hydrolyzes GTP, indicating that these proteins are GTPases.
C. jejuni
mutants producing FlhF proteins with reduced GTPase activity were not severely defective for σ
54
-dependent flagellar gene expression, unlike a mutant lacking FlhF. Instead, these mutants had a propensity to lack flagella or produce flagella in improper numbers or at nonpolar locations, indicating that GTP hydrolysis by FlhF is required for proper flagellar biosynthesis. Additional studies focused on elucidating a possible role for FlhF in σ
54
-dependent flagellar gene expression were conducted. These studies revealed that FlhF does not influence production of or signaling between the flagellar export apparatus and the FlgSR two-component regulatory system to activate σ
54
. Instead, our data suggest that FlhF functions in an independent pathway that converges with or works downstream of the flagellar export apparatus-FlgSR pathway to influence σ
54
-dependent gene expression. This study provides corroborative biochemical and genetic analyses suggesting that different activities of the
C. jejuni
FlhF GTPase are required for distinct steps in flagellar gene expression and biosynthesis. Our findings are likely applicable to many polarly flagellated bacteria that utilize FlhF in flagellar biosynthesis processes.
Mechanism of Transcriptional Activation by
Pseudomonas aeruginosa
ExsA
Authors: Vakulskas Christopher A. , Brady Keith M. , Yahr Timothy L.
Published: August 2009

ExsA is a transcriptional activator of the
Pseudomonas aeruginosa
type III secretion system (T3SS). The T3SS consists of >40 genes organized within 10 transcriptional units, each of which is controlled by the transcriptional activator ExsA. ExsA-dependent promoters contain two adjacent ExsA binding sites that when occupied protect the −30 to −70 region from DNase I cleavage. The promoters also possess regions bearing strong resemblance to the consensus −10 and −35 regions of σ
70
-dependent promoters. The spacing distance between the putative −10 and −35 regions of ExsA-dependent promoters, however, is increased by 4 to 5 bp compared to that in typical σ
70
-dependent promoters. In the present study, we demonstrate that ExsA-dependent transcriptional activation requires a 21- or 22-bp spacer length between the −10 and −35 regions. Despite the atypical spacing in this region, in vitro transcription assays using σ
70
-saturated RNA polymerase holoenzyme (RNAP-σ
70
) confirm that ExsA-dependent promoters are indeed σ
70
dependent. Potassium permanganate footprinting experiments indicate that ExsA facilitates an early step in transcriptional initiation. Although RNAP-σ
70
binds to the promoters with low affinity in the absence of ExsA, the activator stimulates transcription by enhancing recruitment of RNAP-σ
70
to the P

exsC

and P

exsD

promoters. Abortive initiation assays confirm that ExsA enhances the equilibrium binding constant for RNAP while having only a modest effect on the isomerization rate constant.
The PqrR Transcriptional Repressor of
Pseudomonas aeruginosa
Transduces Redox Signals via an Iron-Containing Prosthetic Group
Authors: Rungrassamee Wanilada , Ryan Kelly C. , Maroney Michael J. , Pomposiello Pablo J.
Published: August 2009

Inducible defenses against oxidative stress are coordinated by redox-sensitive transcription factors that transduce oxidative damage into differential gene expression. The opportunistic human pathogen
Pseudomonas aeruginosa
has evolved under physiological and host-derived sources of oxidative stress. Previous work showed that the
pqrABC
and
pqrR
genes of
P. aeruginosa
, all lacking known functions, were induced by treatment of three different isolates of
P. aeruginosa
with paraquat (PQ), a superoxide-producing agent. Insertional mutation of the
pqrABCR
genes resulted in hypersensitive phenotypes to a variety of oxidants, although the hypersensitivity to PQ was marginal. Mutation of
pqrR
and complementation assays showed that PqrR regulated the
pqrABC
genes in response to PQ. PqrR, a member of the MarR family of transcriptional regulators, contains a C-terminal region with four conserved cysteines, which suggested redox-regulated transcriptional activity. Purified PqrR bound to two discrete sites at the
pqrA
and
pqrR
regulatory regions. The in vitro DNA binding activity of PqrR was decreased by exposure to air and reconstituted by treatment with
dl
-dithiothreitol. Elemental analysis and preliminary electron paramagnetic resonance experiments showed that PqrR contains iron. Interestingly, site-directed mutagenesis of C-terminal cysteines demonstrated that the four conserved cysteine residues are essential for in vivo redox sensing by PqrR.
Single-Residue Changes in the C-Terminal Disulfide-Bonded Loop of thePseudomonas aeruginosaType IV Pilin Influence Pilus Assembly and Twitching Motility
Authors: Harvey Hanjeong , Habash Marc , Aidoo Francisca , Burrows Lori L.
Published: August 2009

PilA, the major pilin subunit ofPseudomonas aeruginosatype IV pili (T4P), is a principal structural component. PilA has a conserved C-terminal disulfide-bonded loop (DSL) that has been implicated as the pilus adhesinotope. Structural studies have suggested that DSL is involved in intersubunit interactions within the pilus fiber. PilA mutants with single-residue substitutions, insertions, or deletions in the DSL were tested for pilin stability, pilus assembly, and T4P function. Mutation of either Cys residue of the DSL resulted in pilins that were unable to assemble into fibers. Ala replacements of the intervening residues had a range of effects on assembly or function, as measured by changes in surface pilus expression and twitching motility. Modification of the C-terminal P-X-X-C type II beta-turn motif, which is one of the few highly conserved features in pilins across various species, caused profound defects in assembly and twitching motility. Expression of pilins with suspected assembly defects in apilA pilTdouble mutant unable to retract T4P allowed us to verify which subunits were physically unable to assemble. Use of two different PilA antibodies showed that the DSL may be an immunodominant epitope in intact pili compared with pilin monomers. Sequence diversity of the type IVa pilins likely reflects an evolutionary compromise between retention of function and antigenic variation. The consequences of DSL sequence changes should be evaluated in the intact protein since it is technically feasible to generate DSL-mimetic peptides with mutations that will not appear in the natural repertoire due to their deleterious effects on assembly.
The
Vibrio cholerae
Flagellar Regulatory Hierarchy Controls Expression of Virulence Factors
Authors: Syed Khalid Ali , Beyhan Sinem , Correa Nidia , Queen Jessica , Liu Jirong , Peng Fen , Satchell Karla J. F. , Yildiz Fitnat , Klose Karl E.
Published: August 2009

Vibrio cholerae
is a motile bacterium responsible for the disease cholera, and motility has been hypothesized to be inversely regulated with virulence. We examined the transcription profiles of
V. cholerae
strains containing mutations in flagellar regulatory genes (
rpoN
,
flrA
,
flrC
, and
fliA
) by utilizing whole-genome microarrays. Results revealed that flagellar transcription is organized into a four-tiered hierarchy. Additionally, genes with proven or putative roles in virulence (e.g.,
ctx
,
tcp
, hemolysin, and type VI secretion genes) were upregulated in flagellar regulatory mutants, which was confirmed by quantitative reverse transcription-PCR. Flagellar regulatory mutants exhibit increased hemolysis of human erythrocytes, which was due to increased transcription of the thermolabile hemolysin (
tlh
). The flagellar regulatory system positively regulates transcription of a diguanylate cyclase, CdgD, which in turn regulates transcription of a novel hemagglutinin (
frhA
) that mediates adherence to chitin and epithelial cells and enhances biofilm formation and intestinal colonization in infant mice. Our results demonstrate that the flagellar regulatory system modulates the expression of nonflagellar genes, with induction of an adhesin that facilitates colonization within the intestine and repression of virulence factors maximally induced following colonization. These results suggest that the flagellar regulatory hierarchy facilitates correct spatiotemporal expression patterns for optimal
V. cholerae
colonization and disease progression.
Two Essential Arginine Residues in the T Components of Energy-Coupling Factor Transporters
Authors: Neubauer Olivia , Alfandega Anja , Schoknecht Janna , Sternberg Ulrich , Pohlmann Anne , Eitinger Thomas
Published: August 2009

Energy-coupling factor (ECF) transporters, a recently discovered class of importers of micronutrients, are composed of a substrate-specific transmembrane component (S component) and a conserved energy-coupling module consisting of a transmembrane protein (T component) and pairs of ABC ATPases (A proteins). Based on utilization of a dedicated (subclass I) or shared (subclass II) energy-coupling module, ECF systems fall into two subclasses. The T components are the least-characterized proteins of ECF importers, and their function is essentially unknown. Using RcBioN and LmEcfT, the T units of the subclass I biotin transporter (RcBioMNY) of a gram-negative bacterium and of the subclass II folate, pantothenate, and riboflavin transporters of a lactic acid bacterium, respectively, we analyzed the role of two strongly conserved short motifs, each containing an arginine residue. Individual replacement of the two Arg residues in RcBioN reduced ATPase activity, an indicator of the transporter function, by two-thirds without affecting the modular assembly of the RcBioMNY complex. A double Arg-to-Glu replacement destroyed the complex and abolished ATPase activity. The corresponding single mutation in motif II of LmEcfT, as well as a double mutation, led to loss of the T unit from the subclass II ECF transporters and inactivated these systems. A single Arg-to-Glu replacement in motif I, however, abolished vitamin uptake activity without affecting assembly of the modules. Our results indicate that the conserved motif I in T components is essential for intramolecular signaling and, in cooperation with motif II, for subunit assembly of modular ECF transporters.
The
Mycoplasma genitalium
MG_454 Gene Product Resists Killing by Organic Hydroperoxides
Authors: Saikolappan Sankaralingam , Sasindran Smitha J. , Yu Hongwei D. , Baseman Joel B. , Dhandayuthapani Subramanian
Published: August 2009

Mycoplasma genitalium
is the smallest self-replicating organism and a successful human pathogen associated with a range of genitourinary maladies. As a consequence of its restricted genome size, genes that are highly conserved in other bacteria are absent in
M. genitalium
. Significantly, genes that encode antioxidants like superoxide dismutase and catalase-peroxidase are lacking. Nevertheless, comparative genomics has revealed that MG_454 of
M. genitalium
encodes a protein with putative function as an organic hydroperoxide reductase (Ohr). In this study, we found that an
M. genitalium
transposon mutant that lacks expression of MG_454 was sensitive to killing by
t
-butyl hydroperoxide and cumene hydroperoxide. To understand whether this sensitivity to hydroperoxides was linked to MG_454, we cloned this gene behind an arabinose-inducible
PBAD
promoter in plasmid pHERD20T and transformed this construct (pHERDMG454) into a
Pseudomonas aeruginosa
strain having deletion in its
ohr
gene (
ohr
mutant) and showing sensitivity to organic hydroperoxides. The
P. aeruginosa ohr
mutant harboring pHERDMG454, when induced with arabinose, was able to reverse its sensitivity to organic hydroperoxides, thus supporting the notion that the product of MG_454 resists organic hydroperoxides in
M. genitalium
. Surprisingly, real-time reverse transcription-PCR showed that expression of MG_454 in
M. genitalium
was not elevated in response to oxidative stress but was elevated in response to physical stresses, like salt (NaCl) and heat. Although failure of MG_454 to respond to oxidative stress in
M. genitalium
implies the absence of a known oxidative stress response regulator in the genome of
M. genitalium
, elevated expression of MG_454 due to physical stress suggests its control by an unidentified regulator.
Degradation of Solid Polymer Membrane in PEFC by Hydrogen Peroxide
Authors: Kato Shinji , Masahira Yuya , Noda Kazuhiko , Imai Hatiro
Published: August 2009

Solid polymer electrolyte membrane has been used as electrolyte in polymer electrolyte fuel cells (PEFC) has high electrical conductivity. The hydrogen peroxide made by the reaction in a fuel cell may degrade the conductivity in PEFC. It is necessary to investigate the degradation behavior of the membrane in the environment where the hydrogen peroxide exists. The membrane that was immersed in hydrogen peroxide was used as a sample of each measurement. The measurement of the proton diffusion rate in the membrane was performed for the measurement of a proton conductivity. The current-voltage curve measurement was performed for the investigation of a fuel cell performance. The measurement of a proton diffusion rate applied to the degradation process in the membrane was effective to evaluate the conductivity in the fuel cell.
End Corrosion of Galvanized Steels under Atmospheric Corrosion Environment
Authors: Sekita Kazuhiro , Hirano Tomiharu , Noda Kazuhiko
Published: August 2009

The corrosion prevention mechanism and edge corrosion of the galvanized steels have been investigated. The atmospheric exposure tests were carried out for the observation of corrosion process on the specimen surface under the seashore environment for one and half years. The wet and dry corrosion cycle tests controlled at 33%RH and 84%RH after dropping 0.5M NaCl solution were carried out for the investigation of corrosion morphology on the galvanized steel. From the results of the exposure tests and the wet/dry cycle tests, it was indicated that the galvanized steel was protected by the corrosion product of Zn under the atmospheric environment. The anodic polarization curve measurements were carried out for the exploration of the anodic polarization behavior under the neutral solution. According to the results in the anodic polarization curves of the galvanized steels, the anodic current density of the edge part was larger than that of the surface part.
Corrosion Behavior of Type 304 and 316 Stainless Steels under Stress Loading Environment
Authors: Suzuki Keita , Noda Kazuhiko
Published: August 2009

Although one of the main reasons why stainless steels are used is corrosion resistance, they do in fact suffer from certain types of corrosion in seashore environments. Stress Corrosion Cracking (SCC) which occurs when stress was applied is one of them. And it is important to evaluate the passivation behavior of the stainless steels that has high corrosion resistance by a passive film under the stress loading environment, because it is assumed that the stress have a effect in the passivation, breakdown of the passive film and repassivation. In this present work, the corrosion behavior of type 304 and 316 stainless steels in sodium chloride solutions using a constant strain is measured by the electrochemical measurement. On the basis of the results that the polarization curve measurement and the potentiostatic polarization curve measurement obtained, the localized corrosion sensitivity was increased in stress loading environment.
Electrochemical Properties and Contact Resistance of Titanium in PEFC Bipolar Plate Environment
Authors: Souma Yasutaka , Muto Izumi , Hara Nobuyoshi
Published: August 2009

In order to assess the applicability of titanium as a separator material for polymer electrolyte fuel cells (PEFCs), the electrochemical surface characteristics of commercially available pure titanium were examined in a simulated PEFC environment. The results of the electrochemical tests showed that the anode and cathode operating potentials of PEFC, -0.36V and 0.64V (vs.Ag/AgCl(3.33M KCl)), lay in the cathodic and anodic polarization regions for Ti, respectively. Under the PEFC cathode condition, a barrier-type film with high charge transfer resistance and high interfacial contact resistance grew on the specimen. Under the PEFC anode condition, an air-formed oxide film dissolved and an oxidation film with low charge transfer resistance and low interfacial contact resistance grew.
Initiation and Propagation of Atmospheric Corrosion on Aluminum Alloys under a Cyclic Wet-dry Condition with a Constant Dew Point
Authors: Dan Zhenhua , Takigawa Shunsuke , Muto Izumi , Hara Nobuyoshi
Published: August 2009

To clarify the mechanism of atmospheric corrosion of aluminum alloys in practical environments, a cyclic wet-dry corrosion test, in which the dew point of the circulating air was maintained at a constant level, has been conducted. The atmospheric corrosion of AA1100-O and AA6061-T6 aluminum alloys was randomly initiated around dispersed intermetallics due to the galvanic coupling between the aluminum matrix and intermetallics. The corrosion rate of aluminum alloys in the first cycle was higher than in the subsequent cycles due to the initiation of localized corrosion. As the number of wet-dry cycles increased, the increase of the amount of corrosion loss on aluminum alloys gradually tapered off, which was mainly attributed to the propagation of localized corrosion initiated in the first cycle. In the wet-dry conditions employed in our test, once localized corrosion was initiated in the first wetting period, no new sites of corrosion occurred in the subsequent cycles.
A Salt Layer Model for the Active Anodic Dissolution to Passive Transition of Nickel in Presence of Chloride
Authors: Agrisuelas Jerónimo , García-Jareño José Juan , Giménez-Romero David , Gregori Joan , Keddam Michel , Vicente Francisco
Published: August 2009

The active/passive transition of nickel in an acid medium which contains chloride ions is analyzed by means of a theoretical model which considers a nickel chloride salt layer precipitation coupled with a nickel ion diffusion process away from the electrode surface. There is obtained a good agreement between experimental and calculated impedance spectra. From this simulation procedure it is observed that the polarization curves shape is a consequence of the surface fraction blocked by salt layer (θb) that depends on the applied potential. Moreover, variations in salt properties with the stabilization potential cannot be neglected since it is necessary to consider a continuous decrease in diffusion layer thickness (δ).
Characterization of Amorphous Anodic Nb2O5 Nanofilm for Gas Sensing
Authors: Kowalski Damian , Aoki Yoshitaka , Habazaki Hiroki
Published: August 2009

Amorphous Nb2O5 film of 167 nm thickness was fabricated by anodic oxidation of sputter deposited niobium and characterized by TEM, GD-OES and AFM. The electric properties of the anodic films with sputter-deposited circular gold electrodes were studied by AC impedance spectroscopy in ambient gas atmospheres of air, argon, oxygen or hydrogen in the temperature range of 25 - 200OC. The amorphous Nb2O5 showed the character of n-type semiconductor. The conductivity of the film, following the Arrhenius behaviour, was independent of the oxygen partial pressure, but was largely dependent on hydrogen partial pressure. The conductivity of the Nb2O5 film at room temperature in dry hydrogen was 2.2 orders of magnitude as high as that in air. The enhanced conductivity could be associated with partial reduction of Nb5+ in dry hydrogen atmosphere. The addition of water vapor to hydrogen atmosphere reduced conductivity probably due to suppressing the reduction of Nb2O5.
The Mechanism of Oxide Film Formation on AISI 316 Stainless Steel in Sulphate Solutions
Authors: Sequeira Cesar A. , Santos Diogo M. , Sousa Jose Rodrigues , Brito Paulo
Published: August 2009

Oxide film formation on AISI 316 stainless steel (a material often used for building nuclear reprocessing plants) in acidic and neutral sodium sulphate solutions is investigated using electrochemical and surface analysis techniques. It is found that the corrosion potential varies with pH in the amount of -55 mV / pH unit and critical currents increase with decreasing pH and increasing temperature in neutral solutions. The activation energy for the reaction in the active region is 45.6 kJ mol-1. Potentiostatic experiments indicate that three different film building processes are involved in film formation: the initial active-passive transition, the logarithmic growth of the film and the parabolic growth of the film. AES shows chromium enrichment at the surface, and ESCA gives little difference for the relative amount of Fe2+ and Fe3+ for 0.2 and 0.6 V. A theoretical model is being developed to account for the observed kinetics.
Renewable Highest Capacity Boride/Air Energy Storage
Authors: Licht Stuart , Wu Huiming , Yu Xingwen , Wang Yufei
Published: August 2009

Electric vehicles are attractive from an environmental perspective. However, the capacity of electrochemically stored, compared to fossil fuel, energy is very low. This severely limits their transportation range, and has been a major impediment to their implementation. The first renewable electrochemical energy system which stores more energy than gasoline is presented, and with an order of magnitude higher capacity than lithium-ion batteries, VB2 opens a pathway towards electric vehicles with a viable driving range. Our recently demonstrated zirconia hydroxide-shuttle overlayer, stabilizes alkaline charge transfer chemistry and prevents corrosion of the boride anode, and is applied to form a functional, highest energy capacity vanadium boride/air fuel cell.
Ni - based Electrodes for Hydrogen and Oxygen Generation
Authors: Villa Marco , Milanese Chiara , Nelli Paolo , Salvi Paolo , Verardi Erwin , Marini Amedeo , Zangari G.
Published: August 2009

We discuss the effects of treatments (cathodic/anodic conditioning, red ox cycles) upon the electrochemical properties of Ni-based electrodes in concentrated alkaline solutions. We find that day-long treatments greatly enhance the red ox reactions of the Ni-electrodes which occur between hydrogen evolution (HER) and oxygen evolution reactions (OER). The effects upon HER and OER are also discussed.
Improvement of LiNi1/3Co1/3Mn1/3O2 by a Cationic Substitution and Effect of Over-lithiation
Authors: Ligneel Eric , Nazri Gholam-Abbas
Published: August 2009

The transition metal layered oxides offer a good discharge capacity at high voltage a suitable cathode material for hybrid and/or full electric vehicles applications. The LiNi1/3Co1/3Mn1/3O2 provides discharge capacity in excess of 200mAh/g when charged to 4.5V. However, its capacity retention suffers when charged to high voltages. In this work, we study the impact of cationic substitutions and excess lithium on electrochemical performance of the Li[Ni1/3Co1/3Mn1/3]O2. The XRD and electrochemical tests have shown has shown a strong structural stability and capacity modification of the new materials Li1+x(Ni1/3Co1/3Mn1/3)1-xO2 (0.04<x<0.12).
The Study on the Electrochemical Behavior of Electrolysis Manganese Dioxide in Magnesium Sulfate Solution by Microelectrode CV and XRD
Authors: Si Yujun , Chen Changguo , Xiong Zhongping
Published: August 2009

The rechargeability of electrolysis manganese dioxide (EMD) and its structural change during discharge/charge cycling in neutral MgSO4 solution are investigated using powder microelectrode cyclic voltammetry, galvanostatic charge/ discharge and X-ray diffraction analysis. The cyclic voltammogram reveales that two kinds of material generated after the first reduction process. One of them is electrochemically active, while another is inactive. The rechargeability of EMD in the neutral MgSO4 solution is partially determined by the inactive material. X-ray diffractions of EMD electrodes before discharge, after discharge and recharge give the same result of the cyclic voltammogram. The irreversible structural change of EMD is confirmed during the discharge/charge cycles. The results from cyclic voltammetric tests and galvanostatic discharge investigations are also consistent. The processes of reduction and oxidation are controlled by the diffusion of protons in EMD electrode. The microelectrode cyclic voltammetry technique is a prompt method for detecting the electrochemical performance of powder cathode material EMD.
Microstructure and Performance of Anode Supported Cell by Pore Size of Anode
Authors: Choi Jin H. , Lee Taehee , Park Tae-Sung , Yoo Keun-Bae , Yoo Young-Sung
Published: August 2009

The anode substrate is prepared with nickel oxide, YSZ (yttria-stabilized zirconia) and graphite. Five anode substrates and single cells are respectively prepared using graphite powders with an average particle size of 44m, 75m and 150m at a graphite volume ratio of 24%, and with a graphite volume ratio of 18%, 24% and 30% at an average particle size of 75m. The microstructures of anode substrates are observed by optical micrograph and scanning electron micrograph. The electrical conductivity of anode substrate is measured in hydrogen using AC impedance spectroscopy and the performance of single cell is also analyzed by AC impedance spectroscopy and current-voltage test. The anode substrate (NY 1) with the smallest pore size shows the highest conductivity and the single cell prepared with this substrate shows the better performance. It is likely that there are good percolations of nickel and large populations of three phase boundary (TPB) in NY 1 due to its small pore size. In order to increase TPB sites, the catalytic active layer composed of the fine-grained nickel and YSZ is inserted between anode substrate and electrolyte and the performance of this multi-layered single cell increases by 20%.
Polyaniline-Modified Electrodes for the Anode of the Direct Ascorbic Acid Fuel Cell
Authors: Yano Jun , Hirayama Hisashi , Kitani Akira
Published: August 2009

A conductive polymer, polyaniline (PANI), was electrodeposited on a glassy carbon electrode. Using this PANI-modified electrode, L-ascorbic acid was electro-oxidized, and the electrocatalytic activity of PANI was evaluated for 1) the effect of preparation conditions of PANI, 2) the durability of catalytic action and 3) the effect of metal deposition. The highest electrocatalytic activity was obtained with SO42--doped PANI. The durability of the catalytic action was significantly improved by the PANI modification. The metal deposition deactivated rather than activated the PANI-modified electrode. The PANI-modified electrode was regarded as a promising anode for the direct ascorbic acid fuel cell because it was known to be a highly active toward the electro-oxidation of L-ascorbic acid for a long time and was entirely free from harmful heavy metals and expensive Pt.
The Effect of Non-Stoichiometric Lithium use on a Novel Cathode Material-Li2MnO3•LiMO2 (M=Mn1/4Ni1/4Co1/2)
Authors: Xiaoguang Hao , Wei Zhu , Lingling Zeng
Published: August 2009

In this study, one series of lithium ion battery cathode materials were synthesized by sol-gel method. The main difference to discriminate them is the lithium amount. The galvanostatic charge/discharge test was used to analyze the effect of non-stoichiometric lithium use on the electrochemical characteristics of this kind of cathodes. The additional lithium content does affect the capacity and voltage plateau features of these materials.
Microstructure Control of Ni-ScSZ Anode Support for LT-SOFC
Authors: Miyazaki Masato , Sasaki Kazuya , Suzuki Akihiro , Terai Takayuki
Published: August 2009

A microstructure control method of the Ni-scandia-stabilized zirconia (ScSZ) cermet anode support, which is used for a low temperature solid oxide fuel cells prepared by low temperature processes for fabrications of electrolyte film and cathode electrode, was studied. In this study, addition of Polymethyl methacrylate (PMMA) powder as a pore-former and changing the sintering temperature were conducted to change the microstructure of the Ni-ScSZ cermet anode support. Effects of the size and the amount of the PMMA powder particle and the sintering temperature on the sizes of Ni particle, ScSZ particle and pore were investigated. The pores were classified into three kinds depending on the origin. Effects of the amount and size of the PMMA powder particle and the sintering temperature on the size and volume of the three kinds of pores were also examined.
Cathode Supported Honeycomb SOFCs for Intermediate Temperature Operation
Authors: Shimizu Sota , Yamaguchi Toshiaki , Fujishiro Yoshinobu , Awano Masanobu
Published: August 2009

Cathode supported honeycomb SOFCs have developed recently for intermediate temperature operation, space saving, and quick start and stop. In this study, the effect of anode length, thickness, and conductivity on the performance of cathode supported honeycomb SOFCs by electrical simulation. In the case of 10mm anode length, to suppress the deviation from the ideal current (current loss) under 10%, the anode thickness needs to be 20 µm. And, honeycomb SOFCs with different anode thickness could be prepared by lowering the heat treatment temperature before forming anode layer. Electrochemical evaluations for honeycomb SOFCs with the anode thickness of 4.6 or 10.2 µm were conducted. The performance of honeycomb with 10.2 µm thick anode was twice as good as that with 4.6 µm thick anode. The activation and gas diffusion polarization were decreased.
Silver Metal Oxyfluoride Perovskite for High Volumetric Energy Storage
Authors: Tong Wei , Yoon Won-Sub , Cosandey Frederic , Amatucci G.
Published: August 2009

A novel electroactive nanostructured silver niobium oxyfluoride (SNOF) has been successfully synthesized through the mechanochemical reaction by utilizing AgFx and Nb2O5 precursors. A combination of XRD and Raman studies revealed the structure to be perovskite. Preliminary electrochemical evaluation indicated that this new electrode material exhibited very good electrochemical activity with high volumetric energy density.
Double-Walled Carbon Nanotubes as an Electrode for Direct Methanol Fuel Cell Applications
Authors: Tang Shuihua , Sun Gongquan , Sun Shiguo , Qi Jing , Xin Qin , Haarberg Geir Martin
Published: August 2009

Double-walled carbon nanotubes (DWNTs) supported platinum catalyst exhibited good activity and stability for oxygen reduction reaction (ORR). This can be attributed to its high specific surface area, relatively high crystallization and special network which can facilitate electron transfer, water removal and oxygen or air access to the catalyst active sites. The pore size distribution profile of DWNTs showed it had large part of mesopores which is favorable for mass transportation, X-ray diffraction patterns indicated that DWNTs is better in crystallization than the most used commercial carbon black XC72R. Platinum particles were uniformly distributed on the surface of DWNTs and its average size was 2~3 nm even for the nominal 60 wt% Pt/DWNTs catalyst. The actual Pt loading was 54.9 wt% calculated by scanning electron microscopy coupled with element dispersive spectroscopy (SEM-EDS) result for this 60 wt% Pt/DWNTs catalyst. Pt/DWNTs catalyst demonstrated better oxygen reduction activity and single-cell performance than commercial Pt/XC72R catalyst (from Johnson Matthey company) under identical conditions, and the single-cell performance was quite stable when it was discharged at constant current of 100 mA/cm2 for 20 hours.
Zinc Negative Electrode for Direct Borohydride Fuel Cells
Authors: Santos Diogo M. , Sequeira Cesar A.
Published: August 2009

Zinc is evaluated as negative electrode for the direct electrochemical oxidation of sodium borohydride. Open-circuit potential measurements, cyclic voltammetry, chronoamperometry, and chronopotentiometry are used to characterise the electrode behaviour, namely the oxidation reaction at the Zn/BH4- interface. Two consecutive oxidation steps are identified and a possible working mechanism is proposed. A relatively low electrocatalytic activity of Zn for borohydride oxidation is indicated. A laboratory direct sodium borohydride/hydrogen peroxide fuel cell using a Zn anode is studied at room temperature. Cell voltages of 2.14 V and short-circuit currents of 1050 mA cm-2 are reported but cell stability is limited to 6 hours operation. Specific energies and maximum capacities (based on total H2O2 weight) of 2553 mWh kg-1 and 1438 mAh kg-1, respectively, are obtained. A maximum power density of about 470 mW cm-2 at a cell voltage of 1.1 V and current density of 426 mA cm-2 is reported.
Modeling Nafion: Water Diffusion and Polymer Relaxation
Authors: Onishi Lisa , Prausnitz John , Newman John
Published: August 2009

Transient water sorption was measured using gravisorption at 50 degrees C. The water diffusion coefficient is 3{plus minus}1x(10)^-8 cm2/s, a hundred times smaller than the steady-state diffusion coefficients reported in the literature. A water-diffusion polymer-relaxation model was developed and provides a semiquantitative fit of the experimental data. In this model, the polymer relaxation rate constant is 100,000 s.
Hydrogen and Nanostructured Carbon by Plasma Decomposition of Natural Gas
Authors: Boutot Tobie , Bullerwell Josephine , Liu Zhuomin , Niu WenWen , Whidden Tom K. , Yang Yun
Published: August 2009

This report describes a commercial plasma reactor system for the GHG-free production of hydrogen enriched natural gas (HENG) using natural gas as a feedstock. The process demonstrated stable operation for the production of 20 vol% HENG fuel. The specific energy requirements of the process were found to be competitive with other GHG-free hydrogen production processes. The HENG fuel produced in the process was used as a fuel for a commercial hot water heater and demonstrated reductions of ca. 22% in the NOx emissions of the system boiler. The solid carbon by-product of the process was found to consist of a mixture of amorphous and nanostructured carbons. The nanostructured material was composed of stacked graphene layers of up ca. 7-10 layers thickness and 100 nm diameter.
Study of the Electrochemical Oxidation of H2 on Ni/YSZ
Authors: Cimenti Massimiliano , Hill Josephine
Published: August 2009

The results of an experimental investigation of the electrochemical oxidation of H2 on Ni/YSZ interfaces based on electrochemical impedance spectroscopy (EIS) are presented. An optimized single atmosphere 3-electrode configuration was used to avoid EIS distortions. Charge-transfer coefficients and exchange currents were determined as a function of the electrode overpotential, partial pressures, and temperature (700 to 800{degree sign}C). Both current-overpotential curves and EIS results indicate that the overall oxidation rate is possibly limited by a chemical and an electrochemical process. The electrochemical process is a second electron-donation step, while the chemical step could be related to the formation of a NiO layer or, more likely, to adsorption of charged intermediates with surface coverages that vary with the overpotential. The results were compared to postulated reaction mechanisms.
Improving the Sulphur Tolerance of Nickel Catalysts for Running Solid Oxide Fuel Cells on Waste Biogas
Authors: Laycock Christian J. , Staniforth John , Ormerod Mark
Published: August 2009

To explore the possibility of running Solid Oxide Fuel Cells (SOFC) on biogas, reactions of 2/1 CH4/CO2 gas mixtures over Ni/YSZ (yttria-stabilised zirconia) SOFC anode materials have been investigated using on-line quadrupole mass spectrometry in the temperature range 750-1000{degree sign}C. Carbon deposition has been analysed by post-reaction temperature programmed oxidation (TPO). Hydrogen sulphide (H2S) added to the reactant stream established the effect of sulphur containing gases on the reforming characteristics, carbon deposition and durability of nickel-based anodes. In addition to investigating the behaviour of a conventional Ni/YSZ anode, the performance of gold-, hafnia- and ceria-doped Ni/YSZ anodes were also studied in terms of their influence on the reforming activity, carbon deposition and sulphur tolerance.
Direct Utilization of Methanol on Ceria-based Anodes for SOFC
Authors: Cimenti Massimiliano , Hill Josephine
Published: August 2009

Ceria-based anodes containing nickel, copper, or copper-cobalt were tested for the direct utilization of pure methanol in solid oxide fuel cells at 1073 K. Cell performance and stability was determined at conditions favorable to carbon deposition to verify whether carbon deposits caused irreversible damage to the anodic microstructure. Results indicated that both pyrolysis and catalytic decomposition of methanol are important processes for direct utilization operation. Cell performance with methanol was similar or higher than with humidified hydrogen. Better performance with alcohol was a consequence of the improved electronic conductivity in the presence of carbon deposits. No significant micro-structural changes were detected on the anodes despite the formation of carbon.
Tentative Determination of the Acidity Level in Room Temperature Ionic Liquids by Electrochemical Methods
Authors: Malherbe Cedric , Robert Thierry , Magna Lionel , Olivier-Bourbigou Hélène , Gilbert Bernard
Published: August 2009

In our attempt to evaluate the acidity levels reached by acidified ionic liquids (BMImBF4, BMImNTf2 and BMImOTf + HOTf or HNTf2), the uncertainty on the pKas of the indicators needed for the Hammett spectrophotometric procedure was pointed out. As consequence another method is proposed, based on the H+/H2 couple potential measurement. In this purpose, if dynamic methods failed mainly for lack of sufficient reversibility, potentiometry with a hydrogen electrode gave meaningful results. The R0(H+) Strehlow function, could be calculated, using the Fc+-Fc couple as reference assumed as solvent independent. The obtained results show that i) the acidities are much higher than those in water; ii) the acidities measured by the hydrogen electrode are higher than those measured by the Hammett method; iii) the sequence of acidities for solutions of similar content of added acid is still BF4- > NTf2- > OTf- as previously measured with the Hammett method.
Influence of Anion Structure on Transport Properties of Perfluorosulfonylamide Ionic Liquids
Authors: Umecky Tatsuya , Saito Yuria , Tsuzuki Seiji , Matsumoto Hajime
Published: August 2009

We studied transport properties, i.e., viscosity (η), conductivity (σ), and cation and anion self-diffusion coefficients (Dcation, Danion), for C2mim-ILs, N122.1O2-ILs, and N1224-ILs, where C2mim+ is 1-ethyl-3-methylimidazolium, N122.1O2+ is N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium, and N1224+ is N-butyl-N,N-diethyl-N-methylammonium, composed of perfluorosulfonylamide anions. Ten perfluorosulfonylamide anions, i.e., C0C0 (FSA, FSI), C0C1 (FTA), C1C1 (TFSA, TFSI), C1C2, C2C2 (BETA, BETI), C1C4, C4C4, CTFSA, C3FSA, and TSAC, were used in this work. Walden product and "ionicity" quantity were determined from the transport property data. It became apparent that there was high correlation between the Walden product and the "ionicity" quantity for the ILs. The results of the Walden product and the "ionicity" quantity indicated that by comparison with the N122.1O2-ILs and the N1224-ILs the ion dissociation of the C2mim-ILs was large and hardly changed with the amide anion structures.
An XAFS Study of Niobium Chloride in the Ionic Liquid 1-Ethyl-3-Methyl Imidazolium Chloride/Aluminum Chloride
Authors: Roeper Donald , Pandya Kumi , Cheek Graham T. , O'Grady William
Published: August 2009

Niobium chloride was studied with extended X-ray absorption fine structure spectroscopy (EXAFS) in acidic and basic aluminum chloride/1-ethyl-3-methyl imidazolium chloride (EMIC) ionic liquids. Although anhydrous Nb2Cl10 is more soluble in the basic melt than in the acidic melt, the EXAFS data shows that the coordination shell around the niobium does not change in the different ionic liquids. Both the acidic and basic melts show a coordination of five chlorides in the first shell. This indicates that in this series of ionic liquids, the Nb2Cl10 breaks up into two NbCl5 entities in both the acidic and the basic melts.
Liquid Ordering Structure in Binary Room Temperature Ionic Liquids Based on Aliphatic Quaternary Ammonium Ions
Authors: Mizuhata Minoru , Minowa Takeshi , Maekawa Masanori , Deki Shigehito
Published: August 2009

The effects of hetero-species on the local ordering structure composed of AQA cation are discussed with alkali metal- and alkali earth metal cations (Li+, Na+, K+, Rb+, Cs+, Mg2+, Ca2+, Sr2+, and Ba2+) as hetero-species, taking into account the difference of ionic potential of metal cations. The effects of secondary cationic species on the ordering structure in ILs are discussed. Binary ILs refer to mixture of N111,8[TFSI] and M[TFSI]z (M = Li+, Na+, K+, Rb+, Cs+, Mg2+, Ca2+, Sr2+, Ba2+) in an appropriate molar ratio (x = 0.1, 0.2, 0.3, 0.5, z = 1, 2), denoted as MxN111,81-x[TFSI]{1+(z-1)x}. From the results of SAXS and WAXS measurement of MxN111,81-x[TFSI]{1+(z-1)x}, the intensity assigned to ordering structure increases with addition of M[TFSI]z and, is higher in mixed with alkali earth metal cation than alkali metal cation. Cationic structural ordering is enhanced by the effects of added metal cation.
Wind to Ammonia: Electrochemical Processes in Room Temperature Ionic Liquids
Authors: Pappenfus Ted M. , Lee Kyung-mee , Thoma Laura M. , Dukart Carly R.
Published: August 2009

In this project, an alternative approach to synthesize ammonia electrochemically from wind energy, nitrogen gas, and ethanol is reported. Initial electrolyses have been attempted using room temperature ionic liquids (RTILs) as the electrolyte solvent in the presence of lithium ions. Bis(trifluoromethanesulfonyl)imide salts of 1-Ethyl-3-methylimidizolium (EMI-TFSI) and 1-Butyl-1-methylpyrrolidinium (PYR14-TFSI) were tested in this investigation. These results are compared to the use of tetrahydrofuran as the solvent. The data suggests EMI-TFSI is not an appropriate ionic liquid for the lithium mediated reduction of N2, whereas the increased electrochemical stability of PYR14-TFSI offers greater promise. Current efficiencies (3.8%) for NH3 formation in THF are consistently higher than PYR14-TFSI at atmospheric temperatures and pressures. The amount of ammonia synthesized was quantified by performing the Berthelot reaction.
Waste Water Remediation Using Electrochemically Cycled Extractants in Room Temperature Ionic Liquids
Authors: Carter M. , Bley Richard , Clark Jennifer , Marotta Christopher
Published: August 2009

This project involved preliminary development of an electrochemically activated, regenerable anion-exchange system for nitrate removal from waste water. The goal was to combine desirable features of liquid-liquid extraction, e.g., fast kinetics and process simplicity, with those of anion-exchange processes using resins. At the same time, volatile organic solvents would be eliminated and replaced with a regenerative medium. We developed a liquid-liquid extraction system using a non-volatile, water insoluble room temperature ionic liquid (RTIL) in place of the organic phase. Because RTILs are intrinsic electrolytes, they provide a ready method of in situ electrochemical activation and deactivation of redox-active extractants, such as ferrocenes. The redox-active extractant made nitrate recovery in a small volume possible, while avoiding consumable chemical oxidants and reductants and without generating large secondary waste streams, such as are obtained during regeneration of ion-exchange resins.
Exploring the Influence of Ionic Liquid Ion Structure on Cellulose Solvation
Authors: Brown Kathryn Eva , Geng Xinglian , McDanel William , Henderson Wesley
Published: August 2009

Although ionic liquids (ILs) have been demonstrated to dissolve cellulose, only a limited number of ILs are known, at present, to be effective as solvents and the link between ion structure and cellulose dissolution remains poorly understood. The present study explores two classes of ILs based upon either the acetate anion or the choline cation to examine this link. Some preliminary data on the thermal stability and viscosity of these ILs is reported. Cellulose dissolution data will be reported in a full manuscript.
The Structure and Dynamics of Silk and Cellulose Dissolved in Ionic Liquids
Authors: Trulove Paul C. , Reichert William M. , De Long H. C. , Kline Steve , Rahatekar Sameer , Gilman Jeffrey , Muthukumar Murugappan
Published: August 2009

Small Angle Neutron Scattering (SANS) and Dynamic Light Scattering (DLS) have been used to investigate the structure and dynamics of silk and cellulose in ionic liquids. In the ionic liquid, 1-ethyl-3-methylimidazolium chloride, SANS data indicates a persistence length for both silk and cellulose of ~3 nm and the size of both of these polymers in this IL are on the order of 300-500 nm, indicating significant aggregation. DLS measurements of silk and cellulose in the IL, 1-ethyl-3-methylimidazolium acetate, gave very different results than the SANS in the chloride salt. Both silk and cellulose in the acetate salt are on the order of 14 nm in size indicating minimal aggregation.
Ionic Liquids in the Preparation of Biopolymer Composite Materials
Authors: Haverhals Luke , Isaacs Thelissa A. , Page Eric , Reichert William M. , De Long H. C. , Trulove Paul C.
Published: August 2009

Preliminary data are shown for the mechanical properties of cellulose and silk composite blends with and without nanomodifiers. Composite strength increases with increasing cellulose concentration for samples created with two different coagulation solutions. In general, samples containing > 30% silk are difficult to handle and test because they are extremely brittle. The addition of nanocomposites may increase overall strength of samples, but is dependent on the morphology of the nanomaterial added.
Nonaqueous Solvatochromatic Behavior of Nile Blue A Perchlorate in Imidazolium-Exchanged Clays and its Implication Toward Exfoliation in Polymeric Composites
Authors: Fox Douglas M. , Trulove Paul C. , De Long H. C. , Gilman Jeffrey , Maupin Paul H.
Published: August 2009

Ultraviolet (UV) and visible (VIS) light absorption and emission spectroscopy is a powerful tool for probing solute-solvent interactions. Recently, we have identified the use of Nile Blue as a sensitive fluorescent probe in identifying the local nanoenvironment, such as confinement within clay nanolayers. In this study we examine the solvatochromic behavior of Nile Blue adsorbed montmorillonite in solvents of varying polarity and the influence of an adsorbed imidazolium surfactant. The fluorescence behavior in solvents is compared to its behavior in polymers with similar chemical structures to the solvents.
The Mechanism of Absorption of CO2 in Ionic Liquids: a Computational and Raman Spectroscopy Study
Authors: Reichert William M. , Eucker William , Trulove Paul C. , Urban Joseph J. , De Long H. C.
Published: August 2009

Ionic liquids have the ability to solubilize various gases especially CO2, but the interaction that results in the solubility is unknown. In order to study the mechanism of solubility, a two prong approach, experimental and computational, was undertaken. Raman spectroscopy was performed on various CO2 infused ionic liquids to investigate the shift in the Raman bands which relate to the interactions between the gas and ions. In concert, a computational study was conducted to support the Raman data with possible conformations for the ion-CO2 complexes.