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Hewage N.,University of Connecticut | Yang B.,University of Connecticut | Yang B.,Center for Clean Energy Engineering | Agrios A.G.,University of Connecticut | And 2 more authors.
Dyes and Pigments | Year: 2015

Alkyl- or aryl-carboxylic acid-functionalized porphyrinic dyes are sought after because of their propensity to adhere strongly to many metal oxide surfaces as required for their application as, for instance, sensitizers in dye-sensitized solar cells (DSSCs), in air purification, or chemosensing systems. The SNAr reaction of the pentafluorophenyl group is a versatile method to introduce functionality into meso-pentafluorophenyl-substituted porphyrins. The conditions to introduce one through four alkyl- or aryl-carboxyl functionalities using mercaptopropionate or 3,4-dihydroxybenzoate esters, respectively, are explored, and the regioisomeric products are spectroscopically characterized. Their saponification to the corresponding carboxylic acids was studied. By experimental determination of their optical properties (absorption and emission spectroscopy) and their frontier orbital positions by cyclic voltammetry, we demonstrate the minimal electronic influence this derivatization method has on the chromophore. © 2015 Elsevier Ltd. All rights reserved. Source

Uddin Md.A.,Center for Clean Energy Engineering | Wang X.,Center for Clean Energy Engineering | Wang X.,University of Connecticut | Qi J.,Center for Clean Energy Engineering | And 5 more authors.
ECS Transactions | Year: 2013

The performance and durability of PEFCs were investigated by introducing HCl and five different chloride salts into the air stream of an operating fuel cell. Under the same operating conditions and at a constant 28.5 mM chloride (Cl-) concentration, cell performance degradation can be ranked as HCl> AlCl3 > FeCl3 > CrCl3 > NiCl2, MgCl2. Water evaporation in the flow field surface was found to be causing precipitation of chloride salts. At lower RH, water content decreased and salt deposits completely blocked some of flow channels and caused death of the fuel cell. Moreover, contaminants crossed the GDL, reached the CCM surface, and caused significant performance drop. © The Electrochemical Society. Source

Koehle M.,University of Connecticut | Koehle M.,Center for Clean Energy Engineering | Moreno A.M.,University of Connecticut | Moreno A.M.,Center for Clean Energy Engineering | And 2 more authors.
ACS National Meeting Book of Abstracts | Year: 2011

Processing of biomass-derived oxygenates, such as ethanol, glycerol, and bio-oil, has tremendous potential to generate H 2 fuel with no net CO 2 emissions, providing a clean, renewable, and sustainable fuel source. While extensive experimental research has been carried out on oxygenates reforming, there still lacks a comprehensive understanding of the underlying surface kinetics on an elementary reaction level due to the complexity of reforming chemistry for such large molecular systems. In this work, we will discuss the development of a comprehensive and predictive microkinetic model for catalytic reforming of ethanol, utilizing a combination of semi-empirical and first-principles methods as well as experiments to estimate the kinetic parameters for species and elementary reactions. Validation of the microkinetic model against experimental data and analysis of reaction pathways will be presented, along with the approaches for extension of this work to model larger oxygenates, such as glycerol and bio-oil. Source

Sharma H.,University of Connecticut | Sharma H.,Center for Clean Energy Engineering | Moreno A.M.,University of Connecticut | Moreno A.M.,Center for Clean Energy Engineering | And 2 more authors.
ACS National Meeting Book of Abstracts | Year: 2011

The precious metal-based Diesel oxidation catalyst (DOC) plays a fundamental role in reducing diesel fuel particulate matter and other harmful emissions such as hydrocarbons (HC), carbon monoxide (CO) and nitric oxides (NO x), which have adverse impact on human health and environment. Despite the extensive research on these catalysts, comprehensive and predictive kinetic models for simultaneous prediction of multiple emissions oxidation are lacking. In this work, a detailed elementary step microkinetic model for oxidation of CO, NO, other nitrogen containing emissions (NH3 and HCN) as well as toxic aldehydes (CH 2O) is developed. The detailed mechanism development is carried out using several parameter estimation techniques: semi-empirical Unity Bond Index-Quadratic Exponential Potential (UBI-QEP), Transition State Theory (TST), quantum mechanical Density Functional Theory (DFT), and temperature programmed experiments. Model predictions for catalytic oxidation of various emission components will be discussed as a function of operating conditions (see Figure for HCN oxidation). Source

Kim S.,University of Connecticut | Kim S.,Center for Clean Energy Engineering | Myles T.D.,Center for Clean Energy Engineering | Kunz H.R.,University of Connecticut | And 7 more authors.
Electrochimica Acta | Year: 2015

The effects of polytetrafluoroethylene (PTFE) binder content in the catalyst layer of high temperature polymer electrolyte membrane fuel cells (HT-PEMFCs) utilizing phosphoric acid doped Advent TPS® polymer electrolyte membranes (pyridine bearing aromatic polyethers, TPS) has been investigated in terms of both hydrogen/oxygen and hydrogen/air performance. The anode and cathode gas diffusion electrodes (GDE) were fabricated with different PTFE/carbon weight ratios by a flame based process known as the Reactive Spray Deposition Technology (RSDT) method in order to increase the active platinum (Pt) surface area, with a goal of decreasing overall Pt levels to a total loading of 0.1 mg cm-2. The electrodes, prepared with different amounts of PTFE binder, have been tested in a single cell, with a 25 cm2 geometric area, under an operating temperature range of 160-200 °C. Tests measuring the Pt nanoparticle dispersion on the carbon supports, the pore size distribution, and the electrochemical surface area of the catalyst layer were also performed. The best cell performance was achieved with PTFE/carbon weight ratio of 0.9 over the entire range of operating temperatures. This optimal PTFE binder content resulted in well-developed Pt dispersion on the carbon support and small, uniformly sized pores which develop ideal capillary forces for distributing the phosphoric acid electrolyte evenly throughout the catalyst layer. This led to a high number of triple phase boundaries and maximized Pt utilization. © 2015 Elsevier Ltd. Source

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