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Nilles J.M.,EXCET INC. | Connell T.R.,EXCET INC. | Durst H.D.,Edgewood Chemical Biological Center
Analyst | Year: 2010

We explore a thermal separation technique for use with Direct Analysis in Real Time (DART). By applying gas temperature ramping, we are able to disburse a mixture of compounds in time. The three components were selected to create a challenging mixture that would not likely be discerned solely using exact mass capabilities. While the thermal separation technique is of low resolution, it preserves the inherent rapid, non-contact, ambient characteristics of the ion source. © 2010 The Royal Society of Chemistry.

O'Grady W.E.,U.S. Navy | Roeper D.F.,EXCET INC. | Natishan P.M.,U.S. Navy
Journal of Physical Chemistry C | Year: 2011

We generated molecular simulations of Cl - interacting at different sites in aluminum oxide models and carried out FEFF8 calculations to obtain the local l-projected density of states (LDOS) spectra. These are compared to our earlier experimental X-ray absorption near-edge structure (XANES) data in order to study the interactions of chloride ions with the passive oxide film on aluminum as a function of electrochemical potential at the Cl K edge. This led to a number of new insights in the mechanism of the breakdown of the passive film in chloride solutions. Importantly, we show the chloride first attacks the hydroxyl components of the aluminum oxide, penetrates the oxide film, and finally attacks the metal surface. © 2011 American Chemical Society.

Garsany Y.,EXCET INC. | Singer I.L.,U.S. Navy | Swider-Lyons K.E.,U.S. Navy
Journal of Electroanalytical Chemistry | Year: 2011

Evaluation of Pt/Vulcan carbon (Pt/VC) electrocatalysts for the oxygen reduction reaction (ORR) is dependent on the quality of the electrocatalyst- coated thin film electrode used for rotating disk electrode (RDE) methodology. Traditionally, films are made by dropping a catalyst ink on an inverted, stationary glassy-carbon electrode, and then air-drying it, but the resulting films are irreproducible and often have poor quality. We present a drying procedure for making reproducible, smooth thin electrocatalyst films, by rotating the electrocatalyst ink on the glassy-carbon electrode substrate at 700 rpm while it is drying. The differences between the morphologies of films made with the rotational versus the stationary drying methods are illustrated with 3D optical profilometry and scanning electron microscopy. Film thickness and uniformity was determined by optical interferometric profilometry for films prepared with both drying methods. The stationary drying method leads to a non-uniform film with thicknesses varying from 0.042 μm in the center of the disk electrode to 4.5 μm towards the edge of the electrode. The rotational drying method yields a uniform film thickness of about 0.8 μm over the entire electrode surface. The difference in these film morphologies is quantified for the ORR electrocatalytic activity of a 19.7% and 40% Pt/VC electrocatalyst. The platinum mass and area-specific activities for the ORR are on average 72% and 56% higher for electrocatalyst made by this rotational drying method, compared to those made from the stationary drying method. © 2011 Elsevier B.V. All rights reserved.

Baturina O.A.,U.S. Navy | Gould B.D.,U.S. Navy | Garsany Y.,U.S. Navy | Garsany Y.,EXCET INC. | Swider-Lyons K.E.,U.S. Navy
Electrochimica Acta | Year: 2010

SO2 poisoning of carbon-supported Pt3Co (Pt 3Co/VC) catalyst is performed at the cathode of proton exchange membrane fuel cells (PEMFCs) in order to link previously reported results at the electrode/solution interface to the FC environment. First, the surface area of Pt3Co/VC catalyst is rigorously characterized by hydrogen adsorption, CO stripping voltammetry and underpotential deposition (upd) of copper adatoms. Then the performance of PEMFC cathodes employing 30 wt.% Pt3Co/VC and 50 wt.% Pt/VC catalysts is compared after exposure to 1 ppm SO2 in air for 3 h at constant cell voltage of 0.6 V. In agreement with results reported for the electrode/solution interface, the Pt3Co/VC is more susceptive to SO2 poisoning than Pt/VC at a given platinum loading. Both catalysts can be recovered from adsorbed sulfur species by running successive polarization curves in air or cyclic voltammetry (CV) in inert atmosphere. However, the activity of Pt3Co/VC having ∼3 times higher sulfur coverage is recovered more easily than Pt/VC. To understand the difference between the two catalysts in terms of activity recovery, platinum-sulfur interaction is probed by thermal programmed desorption at the catalyst/inert gas interface and CV at the electrode/solution interface and in the FC environment.

Garsany Y.,EXCET INC. | Baturina O.A.,U.S. Navy | Swider-Lyons K.E.,U.S. Navy | Kocha S.S.,Nissan Technical Center North America Inc.
Analytical Chemistry | Year: 2010

A tutorial is provided for methods to accurately and reproducibly determine the activity of Pt-based electrocatalysts for the oxygen reduction reaction in proton exchange membrane fuel cells and other applications.The impact of various experimental parameters on electrocatalyst activity is demonstrated, and explicit experimental procedures and measurement protocols are given for comparison of electrocatalyst activity to fuel cell standards. (To listen to a podcast about this article, please go to the Analytical Chemistry multimedia page at pubs.acs.org/page/ancham/audio/index.html.). © 2010 American Chemical Society.

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