The proton conductance of Nafion 117 was measured as a function of water content and temperature and compared to changes in the phase state of water. Conductance was measured using a direct current four-point probe technique, while the water phase was determined from differential scanning calorimetry of the melting transitions. Arrhenius plots of conductance show a crossover in the activation energy for proton transport for temperatures coinciding with the melting and freezing of water. This crossover temperature depends on the membrane's water content per acid group, , and displays hysteresis between heating and cooling. Using calorimetry to estimate the fraction of the frozen water phase, both the crossover temperature and the hysteresis are found to correlate with the phase state of the water. For membranes starting with water contents above ϳ 8, the calorimetry and conductivity curves merge at low temperature, suggesting the formation of a common acid hydrate with similar network connectivity; for lower starting water contents, the low-temperature conductivity drops rapidly with . Based on Poisson-Boltzmann models, differences between the conductivity and calorimetry are attributed to gradients in the proton concentration that result in a proton-depleted core in the hydrated pores, which freezes first and contributes minimally to conductivity.

3M's Nano Structured Thin Film (NSTF) electrode, being a core-shell catalyst, offers a novel mean to enhance the performance and lower Pt cost in a polymer electrolyte fuel cell (PEFC). In the present work, fuel cell performance of NSTF is reported and the underlying physics dictating NSTF behavior is probed. It was found that NSTF with 0.15 mg Pt /cm 2 Pt loading shows comparable performance to that of a conventional Pt/C electrode with 0.4 mg Pt /cm 2 loading in a highly humidified condition at 80 C. However, the NSTF performs poorly under dry conditions. A single-phase model was developed to elucidate the underlying phenomenon governing NSTF performance under partially-humidified conditions. NSTF proton conductivity as a function of relative humidity (RH) was determined and the model predictions were compared against a range of experimental data. Detailed results suggest that poor NSTF performance under dry operation is due to low proton conductivity over Pt surface, which reduces catalyst utilization. The importance of water management is highlighted to improve NSTF performance. The high cost of Pt in a fuel cell stack is one of the key barriers to the commercialization of fuel cell vehicle technology. Current state-of-the-art fuel cell vehicles use approximately 72-94 grams of Pt, but it has been estimated that a Pt loading of less than 15 g is required to achieve cost-competiveness with internal combustion engine technology.

An experimental procedure using isothermal galvanostatic operation was developed to quantify the charge ͑water͒ accumulation in proton exchange membrane ͑PEM͒ fuel cells at subfreezing conditions prior to voltage failure ͑i.e., zero cell voltage͒. The charge passed until voltage failure was compared to charge ͑water͒ storage estimates in the membrane phase and the cathode electrode void volume. Cryo-scanning electron microscope images of electrodes following voltage failure were used to assess ice filling of the cathode electrode void volume. At very low current densities, the membrane absorbs a maximum of Ϸ14 to Ϸ15 water molecules/per sulfonate group ͑ max Ϸ 14-15͒ and cathode electrode voids are completely ice filled. It is shown that the maximum charge storage of a membrane electrode assembly increases with electrode void volume and the difference between max and initial . With increasing current densities, decreasing fractions of the maximum charge storage can be utilized, which is shown to be related both to water transport resistances in the membrane phase and to reduced ice filling of the electrode void volume. Experimental results show that the charge storage utilization is mainly controlled by the current density and is less dependant on initial water content or electrode thickness.Proton exchange membrane ͑PEM͒ fuel cells are presently being investigated as an alternative power source for vehicles that require cold climate operation. At low temperatures, PEM fuel cell ͑PEMFC͒ performance suffers from the same irreversibilities that occur during operation at normal temperatures, namely, ohmic, kinetic, and mass transport losses. Our previous studies investigated the ohmic losses due to membrane conductivity 1 and oxygen reduction reaction ͑ORR͒ kinetic losses 2 at temperatures below 0°C. During operation at subfreezing temperatures, the amount of product water that can be produced prior to voltage failure ͑i.e., zero cell voltage͒ is essentially limited by the maximum water uptake of the membrane and the cathode electrode void volume, because the loss of water vapor into the reactant gases is negligible significantly below 0°C. This maximum water uptake can also be expressed in terms of a maximum charge storage ͑in coulombs͒. The latter is a more convenient measure because it corresponds to the maximum time integral of the current by which a frozen fuel cell must reach 0°C before voltage failure occurs as a result of reactant blockage by ice. This concept of maximum charge storage and its relation to mass transport of product water into the membrane as well as into the cathode electrode void volume is the focus of this study. Please note that the concept of charge storage in this study is synonymous with the quantity of water produced electrochemically; it is not to be confused with the platinum and double-layer charge capacity of the electrode, which is negligibly small 3 compared to the charge quantities discussed in this paper.During subfreezing operation, ice formation from product water in electrod...

A study was conducted to understand the physical and chemical changes in fuel cell membranes that result from Freeze/Thaw (F/T) cycling which might occur in electric vehicles. Nafion™ membranes and membrane electrode assemblies (MEA) were subjected to 385 temperature cycles between +80 °C and –40 °C over a period of three months to examine the effects on key properties. These studies were done on both compressed and uncompressed materials in the un‐humidified state. Although no catastrophic failures were seen, the analytical results shed some light on the relationship of temperature cycling to membrane structure, water management, ionic conductivity, gas permeability and mechanical strength. Changes in water swelling behavior and dry densities were noted and the effect on ionic conductivity and cell performance was examined. The impact on catalyst activity and structural integrity of MEAs was evaluated electrochemically.

N-arachidonoyl glycine is an endogenous arachidonoyl amide that activates the orphan G protein-coupled receptor (GPCR) GPR18 in a pertussis toxin (PTX)-sensitive manner and produces antinociceptive and antiinflammatory effects. It is produced by direct conjugation of arachidonic acid to glycine and by oxidative metabolism of the endocannabinoid anandamide. Based on the presence of enzymes that conjugate fatty acids with glycine and the high abundance of palmitic acid in the brain, we hypothesized the endogenous formation of the saturated Nacyl amide N-palmitoyl glycine (PalGly). PalGly was partially purified from rat lipid extracts and identified using nanohigh-performance liquid chromatography/hybrid quadrupole time-of-flight mass spectrometry. Here, we show that PalGly is produced after cellular stimulation and that it occurs in high levels in rat skin and spinal cord. PalGly was up-regulated in fatty acid amide hydrolase knockout mice, suggesting a pathway for enzymatic regulation. PalGly potently inhibited heat-evoked firing of nociceptive neurons in rat dorsal horn. In addition, PalGly induced transient calcium influx in native adult dorsal root ganglion (DRG) cells and a DRG-like cell line (F-11). The effect of PalGly on the latter cells was characterized by strict structural requirements, PTX sensitivity, and dependence on the presence of extracellular calcium. PalGlyinduced calcium influx was blocked by the nonselective calcium channel blockers ruthenium red, 1-(␤-[3-(4-methoxyphenyl)propoxy]-4-methoxyphenethyl)-1H-

Although exposure to ionizing radiation (IR) can produce significant neurotoxicity, the mechanisms mediating this toxicity remain to be determined. Previous studies using neurons isolated from the central nervous system show that IR produces reactive oxygen species and oxidative DNA damage in those cells. Because the base excision DNA repair pathway repairs single-base modifications caused by ROS, we asked whether manipulating this pathway by altering APE1 expression would affect radiation-induced neurotoxicity. In cultures of adult hippocampal and sensory neurons, IR produces DNA damage as measured by phosphorylation of histone H2A.X and results in dose-dependent cell death. In isolated sensory neurons, we demonstrate for the first time that radiation decreases the capsaicin-evoked release of the neuropeptide CGRP. Reducing APE1 expression in cultured cells augments IR-induced neurotoxicity, whereas overexpressing APE1 is neuroprotective. Using lentiviral constructs with a neuronal specific promoter that selectively expresses APE1’s different functions in neurons, we show that selective expression of the DNA repair competent (redox inactive) APE1 constructs in sensory neurons resurrects cell survival and neuronal function, whereas use of DNA-repair deficient (redox active) constructs is not protective. Use of an APE1 redox-specific inhibitor, APX3330, also facilitates neuronal protection against IR-induced toxicity. These results demonstrate for the first time that the repair function of APE1 is required to protect both hippocampal and DRG neuronal cultures—specifically neuronal cells—from IR-induced damage, while the redox activity of APE1 does not appear to be involved.

Ionomer-free ultrathin electrodes, such as the 3M Nanostructured Thin Film (NSTF) electrode, provide plausible pathways to reduce Pt cost in low temperature fuel cells. However, several operational shortcomings involving relatively poor electrode proton conduction under relatively dry conditions and a tendency to collect water in the cathode at low temperature were observed in our fuel cells. In this study, three approaches of material modifications to the NSTF cathode were developed to enhance the operational robustness of these electrodes. The overall strategies were to improve electrode proton conductivity, water removal capability via the cathode, and water storage capacity. In the first approach, an ionomer was coated onto the NSTF surface to improve electrode proton conductivity and water removal capability, the latter by introducing the hydrophobic domains of the PTFE-like ionomer backbone. In the second approach, silica nanoparticles were coated onto the NSTF surface to improve electrode proton conductivity via retention of thin water films under dry conditions. In the last approach, an additional layer of carbon or Pt/C was placed adjacent to the NSTF layer to improve electrode water removal capability and water storage capacity. It was demonstrated that these approaches can decrease the operational shortcomings of the NSTF electrode and enhance its competitiveness from an overall fuel cell system standpoint. These approaches can relax the system operation constraints needed for NSTF cathodes and can thereby expand avenues for NSTF electrode development.

An experimental procedure was developed to measure oxygen reduction reaction kinetics in subfreezing polymer electrolyte membrane (PEM) fuel cells. The procedure was also used to measure kinetics at temperatures above 0°C , and results compared to those collected with a traditional kinetic measurement technique. In general, because of brief time durations in which PEMFCs can be operated below freezing temperatures, short equilibration times were required and thus, enhanced catalyst activity was observed. At progressively lower subfreezing temperatures, suspected mass transport or uncompensated ohmic losses resulted in nonlinear Tafel plots, which at lower decades of current density become linear with a slope close to that predicted by Tafel kinetics, 2.303RT∕αnormalcF . Consistent with results of other researchers at nonfrozen conditions, low water (or ice) content in the fuel cell results in lower catalyst activity and performance at subfreezing temperatures. Cyclic voltammograms indicate that the rate of oxide formation decreases at subfreezing temperatures and low water contents, indicating proton activity as a likely reason for reduced catalytic activity. Arrhenius plots of current density at a constant overpotential are linear (constant activation energy) over the temperature range from 55to−40°C , indicating no fundamental change in reaction mechanism at subfreezing temperatures.