Development Of Highly Active And Stable Compressive Pt Cathode Catalysts For Polymer Electrolyte Membrane Fuel Cells

With the limited fossil fuel reserve and increased power demand, polymer electrolyte membrane fuel cells (PEMFC) have been considered to be a promising alternative to the current energy consumption mode due to its high energy conversion, high efficiency, and zero emissions. However, high cost, poor stability, and sluggish kinetic for oxygen reduction reaction (ORR) of Pt/C cathode catalysts are obstacles for the commercialization of PEMFC for automotive application. The observed poor stability is attributed to a corrosion of carbon supports due to low pH, high temperature, and high anodic potentials (1.0-1.5 V) at the cathode interface during start-up/shutdown conditions. Electrochemical oxidation of carbon results in carbon loss leading to Pt detachment/sintering and subsequent loss of electrochemical surface area (ECSA). Another contributing factor is Pt and/or alloying element dissolution and particle sintering in operating conditions (0.6-1.0 V). In this study, a support material, a Pt catalyst and a compressive Pt lattice catalyst were optimized to develop an active and stable cathode catalyst for PEMFC. A carbon composite catalyst (CCC) was developed from high surface area carbon black (HSACB), which has unique ORR activity and stability compared to those of HSACB. By using CCC support for Pt/C catalysts, the support stability was improved significantly. Also, transition metals embedded in CCC structure were used to synthesize the compressive Pt catalyst by using USC’s novel method. The catalyst indicated improved activity when compared with pristine Pt catalyst. To further enhance activity and stability, a novel activated carbon composite support (ACCS) was developed by optimizing surface area, pore-size distribution, as well as the degree of graphitization and the hydrophobicity. Pt deposition on the ACCS was optimized using a modified polyol process developed in our laboratory in order to control Pt particle size and Pt particle distribution. Fuel cell performance and stability of Pt/ACCS were evaluated using accelerated stress test (AST) protocols recommended by the US Fuel Cell Tech Team for both the catalyst and the support. The Pt/ACCS catalyst showed improved activity and excellent support stability at 1.0-1.5 V over those of commercial catalysts due to the controlled Pt particles and optimized properties of ACCS. Also, a compressive Pt catalyst (Pt*/ACCS) was developed to further increase activity and stability at 0.6-1.0 V. Pt*/ACCS was prepared using the in-house developed procedure in which Co diffuses into the Pt/ACCS catalyst followed by controlled heattreatment. The pyrolysis temperature and Pt/Co ratio were optimized to initiate formation of compressive Pt catalyst. A protective coating method was used to inhibit particle growth during heat treatment which maintains the catalyst particle size in the range between 3 and 5 nm. Pt*/ACCS showed enhanced catalyst stability at 0.6-1.0 V over that of Pt/ACCS while keeping good performance and good support stability. The good stability of Pt*/ACCS is attributed to a potential shift of Pt oxide formation to a more positive direction which results in less Pt dissolution due to less reduction of Pt oxide when the catalyst is cycled in cathode direction from 1.0 to 0.6 V

The amount of astrocytic GABA positively correlates with the degree of tonic inhibition in hippocampal CA1 and cerebellum

A tonic form of synaptic inhibition occurs in discrete regions of the central nervous system and has an important role in controlling neuronal excitability. Recently, we reported that GABA present in astrocyte is the major source of tonic inhibition in cerebellum and that GABA is released through Bestrophin-1 channel by direct permeation. In this study, we screened for the presence of astrocytic GABA in various brain regions such as hippocampus, thalamus, hypothalamus and cerebellum using immunohistochemistry. We found that astrocytic GABA was present in the regions that were reported to show tonic inhibition. Because the existence of tonic inhibition in hippocampal CA1 is somewhat controversial, we compared the amount of astrocytic GABA and tonic inhibition between the hippocampal CA1 pyramidal cell layer and the cerebellar granule cell layer. Unlike cerebellar glial cells, hippocampal astrocytes did not contain GABA. The tonic inhibition was also much lower in the pyramidal neurons of hippocampal CA1 compared to the granule cells of cerebellum. Nevertheless, most of the hippocampal astrocytes expressed Bestrophin-1 channel. These data indicate that the absence of astrocytic GABA results in a low level of tonic inhibition in hippocampal CA1 region

Review—Development of Highly Active and Durable Hybrid Compressive Platinum Lattice Catalysts for Polymer Electrolyte Membrane Fuel Cells: Mathematical Modeling and Experimental Work

This review provides a comprehensive overview on the development of highly active and durable platinum catalysts with ultra-low Pt loadings for polymer electrolyte membrane fuel cells (PEMFCs) through a combined mathematical modeling and experimental work. First, simulation techniques were applied to evaluate the validity of the Tafel approximation for the calculation of the mass activity (MA) and specific activity (SA). A one-dimensional agglomeration model was developed and solved to understand the effects of exchange current density, porosity, agglomerate size, Nafion® film thickness, and Pt loading on the MA and SA. High porosity (> 60%) and agglomerations at high Pt loadings cause the loss of the Tafel approximation and consequently the decrease in MA and SA. A new structure parameter was introduced to estimate the real porous structure using the fractal theory. The volumetric catalyst density was corrected by the fractal dimension (measured by Hg porosimetry), which gave a good agreement with the experimental values. The loading-dependent Tafel equation was then derived, which contains both the utilization and the non-linear scaling factor. Second, activated carbon composite support (ACCS) with optimized surface area, porosity, pore size, and pore size distribution was developed. The hydrophilic/hydrophobic ratio, structural properties (amorphous/crystalline ratio), and the number of active sites were optimized through metal-catalyzed pyrolysis. Stability of ACCS and Pt/ACCS were evaluated using an accelerated stress test (AST). The results indicated that Pt/ACCS showed no significant loss of MA and power density after 5,000 cycles at 1.0–1.5 V, while the commercial Pt/C catalysts showed drastic losses of MA and power density. Finally, monolayers of compressed Pt (core–shell-type Pt3Co1) catalysts were structured by diffusing Co atoms (previously embedded in ACCS) into Pt. Compressive Pt lattice (Pt*) catalysts were synthesized through an annealing procedure developed at the University of South Carolina (USC). The Pt*/ACCS catalyst showed high initial power density (rated) of 0.174 gPt kW−1 and high stability (24 mV loss) at 0.8 A cm−2 after 30,000 cycles (0.6–1.0 V). The outstanding performance of Pt*/ACCS is due to the synergistic effect of ACCS and compressive Pt* lattice

The Implication of Substance P in the Development of Tendinopathy: A Case Control Study.

It was reported that substance P had beneficial effects in the healing of acute tendon injury. However, the relationship between substance P and degenerative tendinopathy development remains unclear. The purpose of this study was to determine the role of substance P in the pathogenesis of tendinopathy. Healthy and tendinopathy tendon were harvested from human and tenocytes were cultured individually. The expression levels of genes associated with tendinopathy were compared. Next, substance P was exogenously administered to the healthy tenocyte and the effect was evaluated. The results showed that tendinopathy tenocytes had higher levels of COL3A1, MMP1, COX2, SCX, ACTA2, and substance P gene expression compared to healthy tenocytes. Next, substance P treatment on the healthy tenocyte displayed similar changes to that of the tendinopathy tenocytes. These differences between the two groups were also determined by Western blot. Additionally, cells with substance P had the tendinopathy change morphologically although cellular proliferation was significantly higher compared to that of the control group. In conclusion, substance P enhanced cellular proliferation, but concomitantly increased immature collagen (type 3 collagen). Substance P plays a crucial role in tendinopathy development and could be a future therapeutic target for treatment

Imiquimod enhances excitability of dorsal root ganglion neurons by inhibiting background (K2P) and voltage-gated (Kv1.1 and Kv1.2) potassium channels

<p>Abstract</p> <p>Background</p> <p>Imiquimod (IQ) is known as an agonist of Toll-like receptor 7 (TLR7) and is widely used to treat various infectious skin diseases. However, it causes severe itching sensation as its side effect. The precise mechanism of how IQ causes itching sensation is unknown. A recent report suggested a molecular target of IQ as TLR7 expressed in dorsal root ganglion (DRG) neurons. However, we recently proposed a TLR7-independent mechanism, in which the activation of TLR7 is not required for the action of IQ in DRG neurons. To resolve this controversy regarding the involvement of TLR7 and to address the exact molecular identity of itching sensation by IQ, we investigated the possible molecular target of IQ in DRG neurons.</p> <p>Findings</p> <p>When IQ was applied to DRG neurons, we observed an increase in action potential (AP) duration and membrane resistance both in wild type and TLR7-deficient mice. Based on these results, we tested whether the treatment of IQ has an effect on the activity of K⁺channels, K_v1.1 and K_v1.2 (voltage-gated K⁺channels) and TREK1 and TRAAK (K_2Pchannels). IQ effectively reduced the currents mediated by both K⁺channels in a dose-dependent manner, acting as an antagonist at TREK1 and TRAAK and as a partial antagonist at K_v1.1 and K_v1.2.</p> <p>Conclusions</p> <p>Our results demonstrate that IQ blocks the voltage-gated K⁺channels to increase AP duration and K_2Pchannels to increase membrane resistance, which are critical for the membrane excitability of DRG neurons. Therefore, we propose that IQ enhances the excitability of DRG neurons by blocking multiple potassium channels and causing pruritus.</p

Opposing Somatic and Dendritic Expression of Stimulus-Selective Response Plasticity in Mouse Primary Visual Cortex

Daily exposure of awake mice to a phase-reversing visual grating stimulus leads to enhancement of the visual-evoked potential (VEP) in layer 4 of the primary visual cortex (V1). This stimulus-selective response potentiation (SRP) resembles and shares mechanistic requirements with canonical long-term synaptic potentiation (LTP). However, it remains to be determined how this augmentation of a population response translates into altered neuronal activity of individual V1 neurons. To address this question, we performed longitudinal calcium imaging of layer 4 excitatory neurons in V1 and tracked changes associated with the induction and expression of SRP. We found no evidence for a net change in the fraction of visually responsive neurons as the stimulus became familiar. However, endoscopic calcium imaging of layer 4 principal neurons revealed that somatic calcium transients in response to phase-reversals of the familiar visual stimulus are reduced and undergo strong within-session adaptation. Conversely, neuropil calcium responses and VEPs are enhanced during familiar stimulus viewing, and the VEPs show reduced within-session adaptation. Consistent with the exquisite selectivity of SRP, the plasticity of cellular responses to phase-reversing gratings did not translate into altered orientation selectivity to drifting gratings. Our findings suggest a model in which augmentation of fast, short-latency synaptic (dendritic) responses, manifested as enhanced layer 4 VEPs, recruits inhibition to suppress cellular activity. Reduced cellular activity to the familiar stimulus may account for the behavioral correlate of SRP, orientation-selective long-term habituation.National Institutes of Health (U.S.) (R01EY023037

Review – Development of highly active and durable hybrid compressive platinum lattice catalysts for polymer electrolyte membrane fuel cells: mathematical modeling and experimental work

This review provides a comprehensive overview on the development of highly active and durable platinum catalysts with ultra-low Pt loadings for polymer electrolyte membrane fuel cells (PEMFCs) through a combined mathematical modeling and experimental work. First, simulation techniques were applied to evaluate the validity of the Tafel approximation for the calculation of the mass activity (MA) and specific activity (SA). A one-dimensional agglomeration model was developed and solved to understand the effects of exchange current density, porosity, agglomerate size, Nafion® film thickness, and Pt loading on the MA and SA. High porosity (> 60%) and agglomerations at high Pt loadings cause the loss of the Tafel approximation and consequently the decrease in MA and SA. A new structure parameter was introduced to estimate the real porous structure using the fractal theory. The volumetric catalyst density was corrected by the fractal dimension (measured by Hg porosimetry), which gave a good agreement with the experimental values. The loading-dependent Tafel equation was then derived, which contains both the utilization and the non-linear scaling factor. Second, activated carbon composite support (ACCS) with optimized surface area, porosity, pore size, and pore size distribution was developed. The hydrophilic/hydrophobic ratio, structural properties (amorphous/crystalline ratio), and the number of active sites were optimized through metal-catalyzed pyrolysis. Stability of ACCS and Pt/ACCS were evaluated using an accelerated stress test (AST). The results indicated that Pt/ACCS showed no significant loss of MA and power density after 5,000 cycles at 1.0–1.5 V, while the commercial Pt/C catalysts showed drastic losses of MA and power density. Finally, monolayers of compressed Pt (core–shell-type Pt3Co1) catalysts were structured by diffusing Co atoms (previously embedded in ACCS) into Pt. Compressive Pt lattice (Pt*) catalysts were synthesized through an annealing procedure developed at the University of South Carolina (USC). The Pt*/ACCS catalyst showed high initial power density (rated) of 0.174 gPt kW−1 and high stability (24 mV loss) at 0.8 A cm−2 after 30,000 cycles (0.6–1.0 V). The outstanding performance of Pt*/ACCS is due to the synergistic effect of ACCS and compressive Pt* lattice.JRC.C.4-Sustainable Transpor

Understanding experience-dependent plasticity of cellular and network activity in the mouse primary visual cortex

Thesis: Ph. D. in Neuroscience, Massachusetts Institute of Technology, Department of Brain and Cognitive Sciences, June, 2019Cataloged from the PDF version of thesis. Vita.Includes bibliographical references (pages 143-153).Sensory experiences in daily life modulates corresponding primary sensory cortices and eventually alter our behavior in a befitting manner. One of the most impactful sensory modules is vision. Primary visual cortex (V1) in mammals is particularly malleable during a juvenile critical period, but this plasticity lasts even in adulthood. A representative form of visual cortical plasticity is ocular dominance (OD) plasticity following temporary monocular deprivation (MD). Here, we used a mouse model of amblyopia and revealed that juvenile OD plasticity, which manifests as depression of response to the deprived eye, requires expression of an immediate early gene, Arc. Also, the juvenile OD shift requires the activity of N-methyl-D-aspartate (NMDA) receptors in layer 4 excitatory principal neurons in V1. Another simple but powerful phenomenon of an adult form of visual cortical plasticity is stimulus-selective response potentiation (SRP). SRP is induced simply through experience to the same gratings visual stimulus over days, resulting in potentiation of visually-evoked potentials (VEPs) in layer 4 of V1. Due to the lack of studies regarding the cellular and network activity changes coincident with the induction of SRP, we have used calcium indicator expressing mice to visualize cellular activity across days of SRP training. Using two-photon calcium imaging, we found that there is indeed no significant net change in the population of active neurons during presentation of the familiar (trained) visual stimulus. Follow-up endoscopic calcium imaging revealed that rather, there is a significant reduction of somatic calcium responses selectively for the familiar visual stimulus on the test day following 5 days of SRP induction. Interestingly, the cellular calcium response to the first presentation of the familiar visual stimulus in each block was substantially similar to the response to those of a novel, yet unseen visual stimulus. However, calcium responses to the familiar visual stimulus dramatically decreased as stimulation was repeated in each presentation block within, and across days of SRP training, whereas the response to the novel visual stimulus on the test day was maintained. The findings that short-latency VEP responses are potentiated, while the slower responses revealed by calcium imaging are depressed suggest that feedback inhibition in V1 is strongly recruited by visual recognition of familiar stimulus. A number of previous studies have suggested that deficits in experience-dependent sensory cortical plasticity and perceptual learning are associated with neuropsychiatric disorders such as autism spectrum disorder (ASD), Rett syndrome and schizophrenia. Our results, therefore, may contribute to our understanding of the underlying mechanisms of these disorders and may help inform ways of intervention and treatments.by Taekeun Kim.Ph. D. in NeurosciencePh.D.inNeuroscience Massachusetts Institute of Technology, Department of Brain and Cognitive Science

Effect of Cylinder Size on the Modulus of Elasticity and Compressive Strength of Concrete from Static and Dynamic Tests

The primary objective of this study is to investigate the effects of cylinder size (150 by 300 mm and 100 by 200 mm) on empirical equations that relate static elastic moduli and compressive strength and static and dynamic elastic moduli of concrete. For the purposes, two sets of one hundred and twenty concrete cylinders, 150 by 300 mm and 100 by 200 mm, were prepared from three different mixtures with target compressive strengths of 30, 35, and 40 MPa. Static and dynamic tests were performed at 4, 7, 14, and 28 days to evaluate compressive strength and static and dynamic moduli of cylinders. The effects of the two different cylinder sizes were investigated through experiments in this study and database collected from the literature. For normal strength concrete (≤40 MPa), the two different cylinder sizes do not result in significant differences in test results including experimental variability, compressive strength, and static and dynamic elastic moduli. However, it was observed that the size effect became substantial in high strength concrete greater than 40 MPa. Therefore, special care is still needed to compare the static and dynamic properties of high strength concrete from the two different cylinder sizes