Darlene K. Slattery

Semiempirical MO and voltammetric estimation of ionization potentials of organic pigments. Comparison to gas phase ultraviolet photoelectron spectroscopy

Abstract A number of organic pigments were identified by semiempirical molecular orbital calculations, using the PM3 method, as having ionization potential (IP) values of 7.0–9.5 eV. Based on photostability, solubility and commercial availability twelve (quinacridone, isoviolanthrone, indanthrone, indigo, 3,4,9,10 perylenetetracarboxylic dianhydride, bis( p -chlorophenyl)1,4-diketopyrrolo (3,4-C) pyrrole, pyranthrone, indanthrene yellow GCN, 16,17-dimethoxyviolanthrone, indanthrene gold orange, 4,4′-diamino-9,9′,10,10′-tetrone [1,1′ bianthracene], and N,N ′ ditridecyl-3,4,9,10-perlenetetracarboxylic diimide) were chosen for further study. The accuracy of the MO calculations was confirmed by experimental measurement of the ionization potentials for eight of the pigments, using gas phase ultraviolet photoelectron spectroscopy. For compounds having at least three fused rings and containing oxygen, nitrogen, or both, the theoretical and experimental IPs have a linear relationship defined by the equation IP exp =0.694IP Calc +1.9049. Lewis acid pigment solubilization (LAPS) was shown to be a viable approach to preparing electrodes for cyclic voltammetry of pigment solid films. The results of the cyclic voltammetry experiments were utilized to formulate the equation E ox (V vs. NHE)=0.5488 IP Calc −3.042, which relates the experimental oxidation potential to the theoretical IP.

Membrane Degradation Mechanisms and Accelerated Durability Testing of Proton Exchange Membrane Fuel Cells

Proton exchange membrane fuel cells (PEMFCs) have increasingly received worldwide attention as the technology that can lead to substantial energy savings and reductions in imported petroleum and carbon emissions. Cost, durability, performance, reliability, efficiency, and size, are some of the requirements that must be met before PEMFCs can be used commercially. The lifetime requirement for stationary applications is about 40,000 hours and for transportation applications 5,000 (cars) and 20,000 hours (buses) (1). Today, the typical operating temperature for both applications is between 60 – 80°C, but to meet the 2010 and 2015 Department of Energy targets, PEMFCs must operate at temperatures from below the freezing point to higher than 100°C (~120 °C maximum), humidity from ambient to saturated, and half-cell potentials from 0 to >1.5 V. Durability studies of proton exchange membrane fuel cells (PEMFC) show that, along with cost, the long-term stability of PEMFCs is a limiting factor in their commercialization (2-6). Degradation of PEM fuel cells is generally observed as slow, unrecoverable performance decay, followed by sudden failure. The gradual performance loss is typically associated with changes in the electrodes and the membrane. The degradation of electrodes is usually caused by catalyst degradation and carbon corrosion. Membrane chemical and mechanical degradation are related to reactant gas crossover, Pt dissolution and migration, transition metal ion contaminants, and hydroxyl radical formation, and cycling of relative humidity. The chemical decomposition of the side

Complex Hydrides for Hydrogen Storage

Complex hydrides, containing a minimum of 7.5 wt% hydrogen, are being investigated as hydrogen storage compounds for automotive use. As a new project, the work to date has largely involved refurbishment of equipment and acquisition of study materials. Initial experiments have confirmed that the instrumentation is functioning and that the data being obtained agree with that in the literature.

Study of chemically synthesized MgMgH2 for hydrogen storage

Abstract A detailed study was carried out to determine the basis for the improved characteristics of a MgMgH 2 system that was previously reported by Bogdanovic and co-workers in this journal. The hydriding-dehydriding kinetics of this chemically synthesized system were investigated. A scanning electron microscope was used to examine the surface morphology of chemically hydrided samples. The surface of chemically prepared samples appeared to be covered with microspheroidal beads ranging in radius between 0.5 and 0.05 μm formed in a fractal-like configuration. Theoretical analysis indicates that the morphology of the chemically prepared samples could be responsible for rapid hydriding-dehydriding. The kinetic enhancement is believed to be partially due to the substantial increase in the surface area and partially due to the fast diffusion into the smaller particles. The effect of the addition of nickel to the surface was also investigated.

Evaluation of the Durability of Polymer Electrolyte Membranes in Fuel Cells Containing Pt/C and Pt-Co/C Catalysts under Accelerated Testing

One of the main sources of degradation in fuel cells is hydroxyl radical attack of the membrane. Radicals are formed where platinum, hydrogen, and oxygen are present. Radical formation occurs at the electrodes, where reactants diffusing through the membrane can react on the Pt catalyst. Additionally, Pt ions form at the cathode, and can then migrate into the membrane and form a Pt band where there is also significant radical generation. Radical attack of the membrane leads to pinhole and crack formation, resulting in significant hydrogen crossover, large performance losses, and shortened cell life.

Accelerated Durability Testing of Perfluorosulfonic Acid MEAs for PEMFCs Using Different Relative Humidities

Polymer electrolyte membrane fuel cells (PEMFCs) receive worldwide attention as the electricity-generating engine for the hydrogen economy. Cost, durability, performance, reliability, efficiency, and size, are some of the requirements that must be met before PEMFCs can be expanded commercially. The lifetime requirement for onsite, combined heat and power applications is about 40,000 hours and for transportation applications 5,000 (cars) and 20,000 hours (buses). Membrane durability is one of the most important factors limiting the lifetime of PEMFCs.

Accelerated Durability Testing of Perfluorosulfonic Acid MEAs for PEMFCs

There is a strong interest in durability studies of proton exchange membrane fuel cells (PEMFC) because, along with cost, the long-term stability of PEMFC is a limiting factor in their commercialization. Examining the characteristics of a membrane electrode assembly (MEA) over a prescribed amount of time under accelerated degradation conditions can give an indication of the degradation behavior of each MEA. Testing under low humidities and/or high temperatures or by humidity or temperature cycling are techniques that accelerate degradation.

Effect of Equivalent Weight of Phosphotungstic Acid-Incorporated Composite Membranes on the High Temperature Operation of PEM Fuel Cells

Fuel cells have shown great promise for future power sources and there has been substantial advancement in the technology of fuel cells over the past decades. For automobile application, however, there are still challenging issues related to its performance and durability. It is highly desirable to operate fuel cells at high temperature because of a number of benefits, e.g., improved reaction kinetics and carbon monoxide tolerance. Since the conventional polymer electrolytes such as Nafion are not stable at high temperatures, the development of novel membranes that are mechanically, thermally, and electrochemically stable at high temperatures while providing good conductivity under low relative humidity condition is one of the most challenging areas of research for automobile applications of fuel cells. In fact, extensive research efforts have been made to design new proton exchange materials that can overcome the limitations of conventional polymer electrolytes.

Solar Photocatalytic Hydrogen Production from Water Using a Dual Bed Photosystem - Phase I Final Report and Phase II Proposal

In this work we are attempting to perform the highly efficient storage of solar energy in the form of H{sub 2} via photocatalytic decomposition of water. While it has been demonstrated that H{sub 2} and O{sub 2} can be evolved from a single vessel containing a single suspended photocatalyst (Sayama 1994; 1997), we are attempting to perform net water-splitting by using two photocatalysts immobilized in separate containers, or beds. A schematic showing how the device would work is shown.