Archives—September 2010

Evaluation of Water Transport Characteristics of PEM Fuel Cell Diffusion Media

Thursday September 30, 2010 4:00 – 5:00 p.m.
ME-EM Building, Room 112

Michael W. Ellis
Virginia Tech

Polymer electrolyte membrane (PEM) fuel cells are under development for a wide range ofportable power, transportation, and stationary applications. Proper water management in theelectrodes of PEM fuel cells is essential to achieving efficient operation. Detailed multi-physicsmodels of transport processes within the electrodes have been developed over the last decade.However, in several areas, the development of experimental techniques for characterizing theelectrode transport properties has not kept pace with modeling advances. Recently developedtechniques provide approaches for measuring critical gas diffusion media transport propertiesincluding the dependence of capillary pressure on liquid saturation and the dependence of liquidrelative permeability on saturation.We have demonstrated experimental techniques relevant to gas diffusion media that allow us tomeasure the relationship between liquid saturation and capillary pressure and to measure therelative permeability of the media to both liquid and gas phases. These techniques provide anexperimental basis for relating diffusion media characteristics to factors such as compression andwet-proofing, thus providing guidance for diffusion media design and for overall improvementof PEM fuel cell performance.

Basic Science Research in Solid Oxide Fuel Cells

Thursday September 16, 2010 4:00 – 5:00 p.m.
ME-EM Building, Room 112

Xiao-Dong Zhou
University of South Carolina

I will describe material physics and electrochemistry of the cathode for solid oxide fuel cells(SOFC). focusing on the relationship between the electrochemical performance of a macroscaleSOFC system and physical properties of its micro/atomic scale components. The emphasis willbe on research at atomic scale, with a particular emphasis on experimental and theoreticalapproaches to investigate a conjugated phenomenon for the cathode: the dichotomy betweenperformance and performance stability. I will illustrate these approaches by using the concept ofdisorder in materials (e.g. lattice defects) to study charge exchange and transport in thecomponents and across the interfaces in an SOFC. Moreover, the role of defects on enhancedtransport properties of oxide conductors at nanoscale will be discussed, which offersopportunities for technological innovations. In addition, I will discuss cross-validation of fuelcell measurements from dc 1-V sweep and ac electrochemical impedance spectroscopy.

Nanostructured Metals and Metal Oxides for High Capacity Li-Ion Batteries

Thursday September 9, 2010 4:00 – 5:00 p.m.
ME-EM Building, Room 112

Ming Au
Savannah River National Laboratory

Currently, carbon base anodes are being used for Li-ion rechargeable batteries through Li ion intercalationprocess. The theoretic capacity is limited at 372 mAh/g. The volume expansion and breakdown of solidelectrochemical interface (SEI) of carbon anodes during overcharging is one of the reasons of thermal runawayand fire ignition. Searching for new anode materials that possesses higher energy storage capacity andinherent fire safety is not only scientist’s passion, but the mandate of industries and customers, particularlyfor plug-in hybrid vehicles and portable power sources.It is found that metals and metal oxides can host Li ions through conversion process that changes latticestructure of metal oxides or forms metal alloys. The theoretic capacity of metal oxides and metals is in therange of 500 4000 mAh/g. The volume of some metal oxides will shrink down during conversion with lessmechanical stress. The metal oxides do not react with polymer electrolyte and generate exceed heat. Thealigned nanostructure, such as nanorods, creates large inter-rods space that is capable to store the chargesand accommodates the volume expansion caused by conversion. It is expected the aligned nanorods of metaloxides will offer high energy and power density and inherent safety. Growing free standing nanostructuredanode materials on current collectors directly without additives and binders represent a new trend of anodefabrication with simplified process and low cost.This presentation will introduce several approaches for synthesis of the aligned nanorods and hollownanoporous spheres, show their structural features and discuss their applications in Li-ion battery.