Fluorescence Recovery After Photobleaching Techniques to Measure Translational Mobility in Microscopic Samples

The scope of photobleaching applications and the method itself are briefly reviewed. Two current applications in this laboratory are then outlined. First, the use of spatial Fourier transforms to analyze video photobleaching measurements is presented. This method extracts diffusion coefficients using all the image data and it does not require that the initial condition created by photobleaching be known. Second, the use of genetic engineering methods coupled with photobleaching analysis is discussed as means to uncover the structural determinants of membrane protein lateral mobility

Drying colloidal systems: laboratory models for a wide range of applications

The drying of complex fluids provides a powerful insight into phenomena that take place on time and length scales not normally accessible. An important feature of complex fluids, colloidal dispersions and polymer solutions is their high sensitivity to weak external actions. Thus, the drying of complex fluids involves a large number of physical and chemical processes. The scope of this review is the capacity to tune such systems to reproduce and explore specific properties in a physics laboratory. A wide variety of systems are presented, ranging from functional coatings, food science, cosmetology, medical diagnostics and forensics to geophysics and art

Charging and discharging electrochemical supercapacitors in the presence of both parallel leakage process and electrochemical decomposition of solvent

Simple models for electrochemical supercapacitors are developed to describe the charge-discharge behaviors in the presence of both voltage-independent parallel leakage process and electrochemical decomposition of solvent. The models are validated by experimental data collected using a symmetric two-electrode test cell with carbon powder as the electrode layer material and stainless steel as the current collector.Peer reviewed: YesNRC publication: Ye

PEM fuel cell cathode contamination in the presence of cobalt ion (Co2+)

This paper reports the effects of Co\ub2\u207a contamination on PEM fuel cell performance as a function of Co\ub2\u207a concentration and operating temperature. A significant drop in fuel cell voltage occurred when Co\ub2\u207a was injected into the cathode air stream, and Co\ub2\u207a contamination became more severe with decreasing temperature. To investigate in detail the mechanism of Co\ub2\u207a poisoning, AC impedance was monitored before and during Co\ub2\u207a injection, revealing that both charge transfer and mass transport related processes deteriorated significantly in the presence of Co\ub2\u207a, whereas membrane conductivity decreased to a lesser extent. Surface cyclic voltammetry and contact angle measurements further revealed changes in physical properties, such as active Pt surface area and hydrophilicity, furthering our understanding of the contamination process.Cet article signale les effets de la contamination par le Co2+ sur le rendement de piles MEP en fonction de la concentration et de la temp\ue9rature du Co2+. Une baisse importante de la tension d\u2019une pile \ue0 combustible s\u2019est produite lorsque du Co2+ a \ue9t\ue9 inject\ue9 dans le flux d\u2019air de la cathode et la contamination par le Co2+ s\u2019est aggrav\ue9e lorsqu\u2019on a abaiss\ue9 la temp\ue9rature. Afin d\u2019\ue9tudier en d\ue9tail le m\ue9canisme d\u2019empoisonnement au Co2+, on a suivi l\u2019imp\ue9dance c.a. avant et pendant l\u2019injection de Co2+, ce qui a r\ue9v\ue9l\ue9 que les m\ue9canismes li\ue9s au transfert des charges et au transport de masse se d\ue9t\ue9rioraient consid\ue9rablement en pr\ue9sence de Co2+, alors que la conductivit\ue9 de la membrane subissait une moindre diminution. Des mesures de voltamp\ue9rom\ue9trie cyclique de surface et des angles de contact ont en outre r\ue9v\ue9l\ue9 des modifications des propri\ue9t\ue9s physiques, comme la taille de la surface active du Pt et le caract\ue8re hydrophile, ce qui am\ue9liore notre connaissance du processus de contamination.Peer reviewed: YesNRC publication: Ye

Durability of PEM fuel cell cathode in the presence of Fe3+ and Al3+

The contamination effects of Fe\ub3\u207a and Al\ub3\u207a on the performance of polymer electrolyte membrane fuel cells were investigated by continuously injecting Fe\ub3\u207a or Al\ub3\u207a salt solution into the air stream of an operating fuel cell. Both metal ions individually caused significant cell performance degradation at a level of only 5ppmmol in air. In addition, elevated temperature accelerated fuel cell performance degradation in the presence of Fe\ub3\u207a. Moreover, the presence of Fe\ub3\u207a in an operating fuel cell resulted in the cell\u2019s sudden death, due to the formation of membrane pinholes that may have been promoted by the enhanced production of peroxy radicals catalyzed by Fe species. Half-cell tests in liquid electrolyte revealed that the presence of Al\ub3\u207a in the electrolyte changed the kinetics and mechanisms of the oxygen reduction reaction by reducing the kinetic current densities and the electron transfer number.Peer reviewed: YesNRC publication: Ye

Effect of Co2+ on oxygen reduction reaction catalyzed by Pt catalyst, and its implications for fuel cell contamination

The oxygen reduction reaction (ORR) catalyzed by Pt was studied in the presence of Co2+ using cyclic voltammetry (CV), rotating disk electrode (RDE), and rotating ring-disk electrode (RRDE) techniques in an effort to understand fuel cell cathode contamination caused by Co2+. Findings indicated that Co2+ could weakly adsorb on the Pt surface, resulting in a slight change in ORR exchange current densities. However, this weak adsorption had no significant effect on the nature of the ORR rate determining steps. The results from both RDE and RRDE indicated that the overall electron transfer number of the ORR in the presence of Co2+ was reduced, with ~9% more H2O2 being produced. We speculate that the weakly adsorbed Co2+ on Pt could react with the H2O2 intermediate and form a Co2+\u2013H2O2 intermediate, inhibiting the further reduction of H2O2 and thus resulting in more H2O2 production. The fuel cell performance drop observed in the presence of Co2+ could be attributed to the reduction in overall electron transfer number and the increase in H2O2 production. Higher production could intensify the attack by H2O2 and its radicals on membrane electrode assembly components, including the ionomer, carbon support, Pt particles, and membrane, leading to fuel cell degradation.Peer reviewed: YesNRC publication: Ye