Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session Q16: Focus Session: Polymers and Energy: Fuel Cells and Batteries |
Hide Abstracts |
Sponsoring Units: DPOLY GERA DMP Chair: Karim Alamgir, The University of Akron Room: B115 |
Wednesday, March 17, 2010 11:15AM - 11:51AM |
Q16.00001: Water Retention and Proton Conductivity of Block Copolymers in Contact with Humid Air Invited Speaker: Membranes composed of diblock copolymers with a hydrophilic and a hydrophobic block were contacted with humid air. We are particularly interested in the properties of membranes with hydrophilic phases with characteristic sizes in the 2-5 nm range. These membranes get wetter as the surrounding air gets hotter at constant relative humidity. Changes in the proton conductivity of the membrane and partitioning of water between and the air and the membrane were recorded after step changes in the air temperature at constant relative humidity. We find surprising differences between symmetric and asymmetric block copolymers. In particular, the conductivity of asymmetric block copolymers evolves mush more slowly than water concentration. \textit{In-situ} small angle neutron scattering measurements were used to understand the origin of this behavior. [Preview Abstract] |
Wednesday, March 17, 2010 11:51AM - 12:03PM |
Q16.00002: Theoretical and simulation study of charge distribution and transport in ionomers Philip Taylor, Elshad Allahyarov, Kaytlin Brinker, Zachary Tobin We have used a combination of analytical theory and simulation to investigate the effect of various material parameters on the proton conductivity of Nafion-like polyelectrolyte membranes. We make use of a cylindrical geometry to model both a hydrophilic channel of small diameter and an ionomer-filled cylindrical pore of larger size. For the water-filled channel we find the proton density distribution as a function of distance from the electrode and from the cylinder axis by means of a combination of a modified Butler-Volmer-Frumkin theory and a lattice-based simulation. For the ionomer-filled pore we study by coarse-grained simulation the proton conductance as a function of sidechain length, with particular attention to the regime where the radius of the cylinder approximates the sidechain length. [Preview Abstract] |
Wednesday, March 17, 2010 12:03PM - 12:15PM |
Q16.00003: Simulation study of proton transport in a cylindrically confined ionomer channel Elshad Allahyarov, Philip Taylor, Hartmut L\"owen Coarse-grained simulation methods have been used to investigate confinement-induced morphological changes in Nafion-like ionomers and their effect on proton conductivity. The system we study models a cylindrical pore in a matrix of supporting material that can be hydrophilic or hydrophobic, with pore diameters that vary from 2 to 7 nm. We report results that indicate the dependence of the equilibrium structure on the matrix material and pore diameter, and on the humidity of the ionomer as defined by the ratio, $\lambda$, of the number of water molecules to the number of sulfonate groups. In particular, we report the relationship between cylinder diameter and the existence of continuous pathways for proton conductance at low levels of humidity. These suggest an optimum diameter and hydrophobicity for fuel-cell membranes composed of an impervious matrix penetrated by cylindrical ionomer-filled pores. [Preview Abstract] |
Wednesday, March 17, 2010 12:15PM - 12:27PM |
Q16.00004: A complete set of ion transport properties in a microstructured electrolyte Scott Mullin, Ashoutosh Panday, Greg Stone, Nitash Balsara The microstructured block copolymer electrolyte poly(styrene)-\textit{block}-poly(ethylene oxide) (PS-PEO) doped with lithium bis(trifluoromethanesulfonimide) (LiTFSI) is of interest for battery applications because LiTFSI segregates to the PEO phase to form ion-conductive channels, while the PS phase provides mechanical strength. Ionic conductivity in this system follows an unpredicted increase with molecular weight. In order to better understand this increase, the salt diffusion coefficient and lithium ion transference number have been measured for lamellar PS-PEO samples as a function of molecular weight. Together, these parameters fully describe ion transport in this system, thus providing fresh insight into the effects of block copolymer microstructure. [Preview Abstract] |
Wednesday, March 17, 2010 12:27PM - 12:39PM |
Q16.00005: Retarding Dendrite Formation in Rechargeable Lithium Metal Batteries with Block Copolymer Electrolytes Greg Stone, Scott Mullin, Nitash Balsara The block copolymer electrolyte polystyrene-block-poly(ethylene oxide) (PS-PEO) is designed to extend the lifetime and cyclability of rechargeable lithium metal batteries. The PEO phase conducts lithium ions, while the PS phase provides mechanical strength to prevent short circuit due to dendrite growth -- a primary failure mechanism in this battery chemistry. The duration an electrolyte can be cycled before short circuit is reported for both PEO and PS-PEO electrolytes. For all current densities tested, the PS-PEO electrolyte resisted short circuiting at least two orders of magnitude longer than the PEO electrolyte. SEM imaging showed lithium metal protrusions into the PS-PEO electrolyte were an order of magnitude larger than the domain size of the block copolymer structure. These results along with theoretical results from literature indicate that slowed dendrite growth is due to enhanced bulk modulus in the PS-PEO electrolytes. [Preview Abstract] |
Wednesday, March 17, 2010 12:39PM - 12:51PM |
Q16.00006: Synthesis of nanoporous materials using block copolymers and applications as battery separators David Wong, Scott Mullin, Greg Stone, Nitash Balsara A method for synthesizing nanoporous battery separators using poly(styrene-b-ethylene-b-polystyrene) (SES) is presented. The polyethylene block serves as a structural component, while the polystyrene block promotes wetting of the electrolyte. The ionic conductivity of these systems swollen with 1M LiPF6/Ethylene Carbonate/Diethyl Carbonate (EC/DEC) electrolyte was measured by AC impedance. Other groups have shown that radiation induced grafting of gel polymer electrolytes can increase the conductivity of a porous PE/LiPF6/EC/DEC system by as much as an order of magnitude. Data showing the ionic conductivity as a function of void fraction of the separator are presented. [Preview Abstract] |
Wednesday, March 17, 2010 12:51PM - 1:03PM |
Q16.00007: First Principles Study of Phase Transformations in Polyvinylidene Fluoride V. Ranjan, Marco Buongiorno Nardelli, J. Bernholc Polyvinylidene fluoride (PVDF) with a small concentration of chlorotrifluoroethylene (CTFE) has been observed to store very high energy [1] as compared to currently used polymers. Chain rotations within the PVDF crystal have been proposed as the reason behind the high energy storage. However, in a recent work, we suggested [2] that the ultra-high energy storage in P(VDF-CTFE) is due to an electric-field induced phase transition from the non-polar $\alpha$ to the polar $\beta$-PVDF. We have now determined a low-energy relaxation path from $\alpha$- to $\beta$-PVDF which confirms this suggestion. Our first-principles calculations reveal an intricate relationship between the kinetics of the chain rotation and the phase transformatio \\[4pt] [1] B. Chun, Science \textbf{313}, 334 (2006).\\[0pt] [2] V. Ranjan, Phys. Rev. Lett. \textbf{99}, 047801 (2007). [Preview Abstract] |
Wednesday, March 17, 2010 1:03PM - 1:15PM |
Q16.00008: Experimental studies of charge transport and storage in microbial biofilms Nikhil Malvankar, Kelly Nevin, Ashley Franks, Madeline Vargas, Kengo Inoue, Mark Tuominen, Derek Lovley We discuss results of ac impedance spectroscopy and dc I-V measurements applied to microbial biofilms and demonstrate that the biofilms of \textit{Geobacter sulfurreducens }that grow on the anodes of microbial fuel cells are electronically conductive, with conductivities comparable to conjugated polymers. To investigate the components conferring the conductivity, we studied novel strains of \textit{G. sulfurreducens} and mutants deficient in various outer surface components. Strains producing more current, produced biofilms with higher conductivity, demonstrating that conduction is the mechanism for long-range electron transfer through the biofilms. There was a direct correspondence between biofilm conductivity and the abundance of pili, referred to as microbial nanowires. Electrochemical gating suggested that in contrast to conventional redox activated hopping, charge transport is polaron-like. Biofilms also exhibited supercapacitor behavior. The results are being incorporated into a physical model of electron transfer and storage through the biofilms. [Preview Abstract] |
Wednesday, March 17, 2010 1:15PM - 1:27PM |
Q16.00009: Anodes for glucose fuel cells made of carbonized nanofibers with embedded carbon nanotubes Sabina Prilutsky, Yachin Cohen, Eyal Zussman, Vadim Makarov, Eugenia Bubis, Pinchas Schechner Electrodes made of carbonized polyacrylonitryle nanofibers, with and without embedded multiwall carbon nanotubes (MWCNT) were fabricated by the electrospinning (ES) process and evaluated as anodes in a glucose fuel cell (FC). The effect of several processing and structural characteristics, such as the presence of MWCNTs, polymer concentration in the ES solution and silver electroless plating, on FC performance were measured The carbon electrodes were successful as anodes showing significant activity even without additional silver catalyst, with noticeable improvement by incorporation of MWCNTs. The orientation of graphitic layers along the fiber axis and the coherence of layer packing were shown to be important for enhanced electrode activity. The maximal values of open circuit voltage (OCV) and peak of power density (PP$_{D})$ of unmetallized electrodes, 0.4 V and 30 $\mu $W/cm$^{2}$, were found for composite carbon nanofiber electrode. Electroless silver metallization leads to enhanced performance. Maximal values of OCV and PP$_{D}$ of silvered electrodes were measured to be about 0.9 V and 400 $\mu $W/cm$^{2}$. Thus, carbonized nanofibers with embedded MWCNTs may form a good basis for glucose FC anodes, but better metallization and cell-configuration allowing proper mixing are required. [Preview Abstract] |
Wednesday, March 17, 2010 1:27PM - 1:39PM |
Q16.00010: Performance of direct methanol fuel cells under various conditions Yong Hee Chung, Asad Mehmood Performance of direct methanol fuel cells has been examined in terms of diffusion layer thickness, methanol feed rate and temperature. Thickness of anode diffusion layer showed significant effect on the cell performance, while no noticeable change was observed for different thicknesses of cathode diffusion layers. The cell performance was measured to be improved with the increase in methanol feed rate. The result was interpreted in a mathematical model. [Preview Abstract] |
Wednesday, March 17, 2010 1:39PM - 1:51PM |
Q16.00011: Proton-Conducting Metal-Organic Frameworks Jamie Ford, Jason Simmons, Taner Yildirim Vehicles powered by polymer electrolyte membrane (PEM) fuel cells are an exciting alternative to current fossil fuel technology. The membranes in these cells serve as both charge transporter, ferrying protons from the anode to the cathode, and gas diffusion barrier, preventing the backflow of oxygen to the anode. Currently, hydrated sulfonated polymers are the preferred material for these membranes. The presence of water, however, limits the operating temperature to 100 C, reducing the electrode kinetics and CO tolerance of the entire system. In an effort to increase the efficiency and operating temperature of these fuel cells, we are investigating the proton conductivity of new host/guest materials based on metal-organic frameworks (MOFs) loaded with imidazole. These thermally stable frameworks provide well-defined pores that accommodate imidazole networks and form proton-conducting pathways. Here, we will present the structure and proton dynamics of these materials as elucidated by elastic and inelastic neutron scattering measurements. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700