Richard E. Rocheleau

Operational Performance Recovery of SO2-Contaminated Proton Exchange Membrane Fuel Cells

Airborne sulfur contaminants (SO 2 , H 2 S, and COS) cause the performance of proton exchange membrane fuel cells (PEMFCs) to degrade because they adsorb to the Pt catalysts and modify reaction sites for oxygen reduction. Electrochemical methods can be used for PEMFC performance recovery by oxidizing adsorbed sulfur species (SO x ) on the Pt catalysts to sulfate (SO 2- 4 ) at high potentials and then removing them as water-soluble anions at low potentials. We examine the effectiveness of five distinct methods for PEMFC performance recovery after 3 h of exposure to 1 ppm SO 2 in air at 60°C and 48.3 kPa g (7 psi) and relative humidity of 100 | 50% (anode | cathode). The methods are tested when the Pt surface is partially covered but not completely saturated with sulfur species. The methods include variations in the cathode potential and gas environment (N 2 or air). In the optimum method, the cells are switched from normal H 2 | air operation to H 2 | N 2 by electrochemically consuming O 2 in the air. The potential is then cycled between 0.09 and 1.1 V. vs the potential at the anode to restore 97% of the platinum catalyst electrochemical surface area. This in situ N 2 cycling method returns the polarization curves of contaminated PEMFCs to their original performance in less than 3 min.

Drive cycle generation for stochastic optimization of energy management controller for hybrid vehicles

A methodology to generate drive cycles based on probabilistic driving profiles is presented in this paper. The described approach can be utilized for the stochastic optimization of an energy management controller (EMC) for hybrid electric vehicles (HEVs). It enables for an optimal design towards a probabilistic driving portfolio such as individual driving characteristics of the vehicle operator, location, traffic conditions, topography and environment. Hence, maximum fuel efficiency for the individual driver can be achieved. The introduced method is implemented in a drive cycle generation tool. The approach is validated using a model of a parallel HEV powered by fuel cells. Simulation results are presented and the advantage of the proposed method over conventional approaches is proven.

Thin-film yttria-stabilized tetragonal zirconia

Abstract Yttria-stabilized zirconia thin films deposited by radio-frequency sputtering from a 3 mol% Y 2 O 3 ZrO 2 target show primarily tetragonal orientation. Annealing in air further reduces the fraction of monoclinic phase and enhances the crystallinity of the tetragonal phase. Films annealed at 700 °C for 2 h showed a phase composition which was greater than 95% tetragonal.

Semiconductor processing and manufacturing

The viability of semiconductor deposition and treatment processes for manufacturing are assessed and critical issues identified for CdTe, Cu(InGa)Se2, thin film silicon and amorphous silicon technologies. The focus is on increasing throughput and decreasing costs. Specific issues include deposition rate, materials utilization, adhesion, uniformity, equipment and process scale-up, compatibility with subsequent processing, module performance and environmental concerns.

Copper gallium diselenide photocathodes for solar photoelectrolysis

Copper chalcopyrite films exhibit properties suitable for solar energy conversion processes such as direct bandgap, and excellent carrier transport. To explore the possibilities of solar-powered hydrogen production by photoelectrolysis using these materials, we have synthesized p-type polycrystalline CuGaSe2 films by vacuum co-evaporation of the elemental constituents, and performed physical and electrochemical characterizations of the resulting films and electrodes. Based on CuGaSe2 material with 1.65 eV bandgap, a 2.2 micron thick electrode exhibited an outdoor 1-sun photocurrent of 16 mA/cm2, while a 0.9 micron thin device still produced 12.6 mA/cm2 in conjunction with vigorous gas evolution. Flatband potential measurements and bias voltage requirements for saturation photocurrents indicate a valence band position to high for practical device implementation. Future photoelectrolysis devices may be based on copper chalcopyrites with lower valence band maximum in conjunction with a suitable auxiliary junction.

THERMODYNAMIC CHARACTERIZATION OF HYDROGEN INTERACTION WITH IRIDIUM POLYHYDRIDE COMPLEXES

Hydrogen interaction with solid iridium complexes IrXH{sub 2}(PPr3{sup i}){sub 2} (X=Cl, I) was investigated. Gaseous hydrogen was found to react reversibly with solid chloro-iridium complex IrClH{sub 2}(PPr3{sup i}){sub 2} forming IrClH{sub 2}(PPr3{sup i}){sub 2}H{sub 2}. The relative partial molal enthalpy and entropy were obtained from equilibrium isotherms at different hydrogen concentrations. The decrease in entropy with increasing hydrogen concentration and the absence of plateaus in the equilibrium isotherms were consistent with a single phase solid solution with two chemical components. Hydrogen release from solid iodo-iridium complex IrIH{sub 2}(PPr3{sup i}){sub 2}H{sub 2} was not observed at temperatures up to 350 K, indicating stronger hydrogen bonding. {copyright} {ital 1999 Materials Research Society.}