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Xiao X.,General Motors | Lu P.,Trison Business Solutions Inc. | Ahn D.,University of Kentucky
Advanced Materials | Year: 2011

Ultrathin oxide coatings are demonstrated to offer multiple functions for improving the cycling performance of lithium ion batteries. The coatings can serve as an artificial solid electrolyte interphase layer, which significantly suppresses electrolyte decomposition as well as mitigates mechanical degradation. Structure modification is critical for increasing the ion conductivity, and therefore leads to improved current efficiency. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Yu Z.,General Motors | Zhang J.,General Motors | Zhang J.,Lawrence Berkeley National Laboratory | Liu Z.,General Motors | And 8 more authors.
Journal of Physical Chemistry C | Year: 2012

Dealloyed PtCo 3 and PtCu 3 catalysts supported on high surface area carbon (HSC), which were synthesized under different conditions, were tested as cathode electrodes in proton exchange membrane fuel cells. The dealloyed PtCu 3/HSC gave higher initial oxygen reduction reaction (ORR) kinetic activity but much worse durability in a voltage cycling test. Detailed characterization was undertaken to develop insights toward the development of catalysts with both high activity and good durability. In situ X-ray absorption spectroscopy (XAS) analysis showed that dealloyed PtCu 3/HSC exhibited stronger bulk Pt-Pt compressive strains and higher bulk d-band vacancies (attributed in part to a greater ligand effect induced by Pt-Cu bonding) than dealloyed PtCo 3/HSC, factors which can be expected to correlate with the higher initial activity of dealloyed PtCu 3/HSC. Annular dark field (ADF) imaging and electron energy loss spectroscopy (EELS) mapping demonstrated that a strong majority of metal nanoparticles in both dealloyed PtCu 3/HSC and PtCo 3/HSC have variants of core-shell structures. However, the most prevalent structure in the dealloyed PtCo 3/HSC gave multiple dark spots in ADF images, approximately half of which were due to Co-rich alloy cores and half of which arose from voids or surface divots. In contrast, the ADF and EELS data for dealloyed PtCu 3/HSC suggested the predominance of Pt shells surrounding single Cu-rich cores. Further work is needed to determine whether the contrast in durability between these catalysts arises from this observed structural difference, from the differences between the corrosion chemistry of Cu and Co, or from other factors not addressed in this initial comparison between two specific catalysts. © 2012 American Chemical Society.

Kongkanand A.,General Motors | Owejan J.E.,General Motors | Moose S.,General Motors | Dioguardi M.,Trison Business Solutions Inc. | And 2 more authors.
Journal of the Electrochemical Society | Year: 2012

Ultrathin electrodes, such as the 3MNanostructured Thin Film (NSTF) electrode, provide a plausible pathway to reduce platinum cost in low temperature fuel cells. However, several operational shortcomings, involving relatively poor electrode proton conduction and tendencies to collect water in the cathode, were observed in our fuel cell tests. This can be greatly mitigated when a few-micron thick dispersed-catalyst layer is placed adjacent to the NSTF layer, forming a dispersed-catalyst/NSTF hybrid electrode. This dispersedcatalyst layer is also called the "interlayer" because it is located between the NSTF layer and the microporous layer of the cathode diffusion medium. In this study, development of the hybrid electrode was pursued. Emphasis on developing lab-scale fabrication methods that can easily translate to roll-to-roll manufacturing process was a key element of the hybrid electrode development. The fuel cell performance of the electrode showed high sensitivity to fabrication methods. When the dispersed-catalyst layer was coated directly on the NSTF electrode, voltage at high current density dropped significantly. The voltage loss was surmised to be caused by ionomer seepage into the NSTF layer during the coating process. This voltage loss could be eliminated by placing the dispersedcatalyst layer on the gas-diffusion layer and then located adjacent to the NSTF cathode. Interaction between the dispersed-catalyst and NSTF layers and how it affects the fuel cell performance is discussed. Copyright © 2012 The Electrochemical Society.

Kongkanand A.,General Motors | Liu Z.,General Motors | Liu Z.,Corning Inc. | Dutta I.,Trison Business Solutions Inc. | Wagner F.T.,General Motors
Journal of the Electrochemical Society | Year: 2011

3Ms Nanostructured Thin Film (NSTF) electrode offers an alternative path to reduce Pt cost in a polymer electrolyte membrane fuel cell, owing to its unique extended surface structure. To understand the fuel cell performance and the durability of the electrode, it is necessary to know its microstructure. In this report, electrochemical and microstructural evaluations of the NSTF electrodes were done after different stages of ageing in a fuel cell. Changes over time of surface roughness, dealloying, and microstructure were observed. Correlations between NSTF electrode structure and fuel cell performance are discussed. © 2011 The Electrochemical Society.

Shi S.,Brown University | Shi S.,Zhejiang Sci-Tech University | Lu P.,Trison Business Solutions Inc. | Liu Z.,General Motors | And 4 more authors.
Journal of the American Chemical Society | Year: 2012

The mechanism of Li + transport through the solid electrolyte interphase (SEI), a passivating film on electrode surfaces, has never been clearly elucidated despite its overwhelming importance to Li-ion battery operation and lifetime. The present paper develops a multiscale theoretical methodology to reveal the mechanism of Li + transport in a SEI film. The methodology incorporates the boundary conditions of the first direct diffusion measurements on a model SEI consisting of porous (outer) organic and dense (inner) inorganic layers (similar to typical SEI films). New experimental evidence confirms that the inner layer in the ∼20 nm thick model SEI is primarily crystalline Li 2CO 3. Using density functional theory, we first determined that the dominant diffusion carrier in Li 2CO 3 below the voltage range of SEI formation is excess interstitial Li +. This diffuses via a knock-off mechanism to maintain higher O-coordination, rather than direct-hopping through empty spaces in the Li 2CO 3 lattice. Mesoscale diffusion equations were then formulated upon a new two-layer/two-mechanism model: pore diffusion in the outer layer and knock-off diffusion in the inner layer. This diffusion model predicted the unusual isotope ratio 6Li +/ 7Li + profile measured by TOF-SIMS, which increases from the SEI/electrolyte surface and peaks at a depth of 5 nm, and then gradually decreases within the dense layer. With no fitting parameters, our approach is applicable to model general transport properties, such as ionic conductivity, for SEI films on the surface of other electrodes, from the atomic scale to the mesoscale, as well as aging phenomenon. © 2012 American Chemical Society.

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