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Ionomer adsorption at the surface of a graphite sheet in a solvent-saturated environment was examined using molecular dynamics simulations. The amount of ionomer adsorbed on the graphite surface greatly depended on the equivalent weight (EW) of the ionomer and the alcohol content in the solvent. The maximum ionomer coverage was obtained in water-rich solvent for low EW ionomer, while the addition of alcohol to the solvent was necessary to enhance adsorption of high EW ionomer. The ionomer coverage at the surface with ionized functional groups was lower than that of the bare graphite surface, which indicated a significant effect of the electrostatic repulsive interaction between negatively charged functional groups and sulfonic acid groups on the ionomer adsorption. The effect of the alcohol content and EW of the ionomer on ionomer coverage still remained even in the presence of strong electrostatic interactions between sulfonic acid groups and the functionalized carbon surface. [ABSTRACT FROM AUTHOR]

Abstract: An in situ technique for analyzing ionomer coverage, θion , in catalyst layers was examined. Contributions of Pt and water to electric double layer capacitance, Cdl , were extracted by carbon monoxide (CO) adsorption and the RH dependence of Cdl , respectively. Consequently, θion for Pt (θion , Pt ) and the carbon support (θion , C ) were obtained by comparing Cdl attributed to different interfaces, namely, the interface between the electroconductor and the ionomer or that between the electroconductor and water. The validity of the method was verified by various analyses and experiments, such as water adsorption analysis, analysis of specific capacitance and electrochemical surface area analysis by CO stripping voltammetry. θion of the catalyst layer with two different carbon supports, either ketjen black (KB) or graphitized ketjen black (GKB), was evaluated with this method. In the case of a GKB-based catalyst layer, CO apparently did not cover the entire Pt surface, making the analysis more complicated. In this case, applying Cdl of a pseudo catalyst layer, consisting of the carbon support and the ionomer, was deemed as appropriate. The analysis revealed that θion , Pt and θion , C were ca. 0.39 and ca. 0.25 in the KB system and ca. 0.49 and more than 0.91 in the GKB system. Although the number of primary pores in GKB is very small, θion , Pt seemed small compared with θion , C . From SEM and TEM images, it was found that Pt particles formed clusters on the GKB surface. Presumably, the narrow voids of the Pt clusters contributed to the low θion , Pt . [Copyright &y& Elsevier]

Abstract: The biggest issue that must be addressed in promoting widespread use of fuel cell vehicles (FCVs) is to reduce the cost of the fuel cell system. Especially, it is of vital importance to reduce platinum (Pt) loading of catalyst layers (CLs) in the membrane electrode assembly (MEA) of a proton exchange membrane fuel cell (PEMFC). In order to lower the Pt loading of the MEA, mass transport of reactants related to the performance in high current density should be enhanced significantly as well as kinetics of the catalyst, which can result in the better Pt utilization and effectiveness. In this study, we summarized our analytical approach and methods for reduction of Pt loading in CLs. Microstructure, mass transport properties of the reactants, and their relation in CLs were elucidated by applying experimental analyses and computational methods. A simple CL model for I–V performance prediction was then established, where experimentally elucidated parameters of the microstructure and the properties in CLs were taken into account. Finally, we revealed the impact of lowering the Pt loading on the transport properties, polarization, and the I–V performance. [Copyright &y& Elsevier]

Abstract: The influence of Nafion® film on ORR kinetics and H2O2 formation on a Pt electrode was investigated using RRDE in 0.1M HClO4. It was found that the Nafion®-coated Pt system showed lower apparent ORR activity and more H2O2 production than the bare Pt electrode system. From the temperature sensitivity, it was revealed that the apparent activation energies of ORR in the Nafion®-coated Pt system were lower than the bare Pt electrode system, and the H2O2 formation was suppressed with the increase of the temperature. In order to analyze the results furthermore, other systems (0.1/1.0M, HClO4/CF3SO3H) with the bare Pt electrodes were also examined as references. It was exhibited that the ORR kinetic current, the H2O2 formation, and the apparent activation energies of 1.0M CF3SO3H system were close to those of the Nafion®-coated Pt system. We concluded that the orientation of anion species of Nafion® and CF3SO3H to the Pt surface via water molecules, as well as a fluorocarbon polymer network of Nafion®, might block O2 adsorption, resulting in the smaller effective surface area of the Pt electrode for ORR, the smaller ORR kinetic current, and the more H2O2 production. [Copyright &y& Elsevier]

Abstract: Theoretical analysis of ORR on Pt (111) was carried out with the combined technique of DFT calculation and the UBI-QEP method in order to understand the overall ORR pathways, behavior of H2O2 formation, and the impact of trifluoromethane sulfonic acid (CF3SO3H and TfOH) coverage, the alternative material of Nafion®, on the reactivity on the Pt surface. The ORR scheme consisting of elementary reactions was then modeled to determine the dominant path and the limiting step based on their activation energies. The results showed that the dominant ORR path included the H2O2 formation step and OOH formation step was limiting. When TfOH covered the Pt surface, it was revealed that the adsorption energy of an O2 molecule on Pt (111) was decreased due to the lower Fermi level and the d-band center, resulting in decreasing the activation energy of the limiting step. TfOH, however, could suppress the O2 adsorption on the Pt surface. In addition, with the TfOH coverage, it was indicated that the limiting step of ORR was shifted to H2O-production step which was after the H2O2 production, resulting in the enhancement of the H2O2 formation. [Copyright &y& Elsevier]

This paper deals with brush wear and current distribution of carbon brushes on steel slip rings. Measurements of brush wear and brush current have been carried out both in generators in service and in a laboratory test rig. Wear rates increase with increasing brush current only for positive brushes on-site, whereas an evident correlation between brush current and brush wear was found for both polarities in the laboratory. The magnetizing current is, in general, unevenly distributed between the brushes operating in parallel, and the current shifts between different brushes during operation. The current distribution becomes more uneven with increasing mean current density and with increasing circumferential velocity of the slip ring. [ABSTRACT FROM AUTHOR]

Abstract: A detailed analysis is made of the relation between the degradation behavior of a membrane electrode assembly (MEA) and deposited Pt (Pt band) in the membrane during an open-circuit voltage (OCV) hold test. Molecular-structural changes in the membrane are investigated by micro-Raman spectroscopy. When the Pt band was not significantly observed in the membrane after the test, the membrane is relatively stable. In contrast, when the Pt band was clearly formed, the membrane around it was intensively degraded. The magnitude of the fluoride ion emission rate (FER) of the effluent water from the anode and the cathode was also consistent with the location of the Pt band. It was verified that the Pt band is one of the factors accelerating membrane degradation, and the catalyst materials strongly affects the degradation. Besides, not the cation transport which enhances the degradation but the kinetics of either the H2O2 and/or hydroxyl radical production might be the rate determining step. [Copyright &y& Elsevier]

Nonlinear Rayleigh waves propagating in a substrate coated with a thin elastic film are studied numerically. The evolution model consists of the nonlinear spectral equations of Zabolotskaya [J. Acoust. Soc. Am. 91, 2569-2575 (1992)] augmented ad hoc to include film dispersion. The dispersion relation is obtained from linear theory but is otherwise exact. Both loading and stiffening films are considered. Computations are performed for nonlinear evolution of an initially sinusoidal Rayleigh wave under three distinct dispersion regimes corresponding to different film thicknesses. The validity of the evolution model is also examined [ABSTRACT FROM AUTHOR]

It has been reported that multiple injections of 1-hydroxyethylidene-1,1-bisphosphonate (HEBP) to rats prevent mineralization of incisor dentin, thereby revealing high concentrations of calcium in the non-mineralized matrix of circumpulpal dentin. To identify the molecules responsible for calcium accumulation in circumpulpal dentin matrix, rats were injected daily with HEBP (8 mg P/kg) for 7 d, and the incisors processed for various histochemical and immunohistochemical staining of non-collagenous matrices of dentin. Cuprolinic blue reactions for proteoglycans (PGs) were equally distributed in non-mineralized matrix of mantle and circumpulpal dentin layers. Dentin sialoprotein (DSP) and osteopontin (OPN) immunoreactions were found in non-mineralized circumpulpal dentin matrix, but not in mantle dentin. In normal incisors, however, predentin matrix showing significant DSP immunoreactivity was negative for Ca-GBHA reactions. HEBP-affected, non-mineralized OPN immunopositive bone matrix was also non-reactive for calcium. From these observations, neither PGs, OPNnor DSP appear to be responsible for calcium accumulation in HEBP-affected circumpulpal dentin. Stains-all reactive component, possibly dentin phosphoprotein (DPP), only showed the same distribution as that of Ca-GBHA in both HEBP-affected and normal dentin matrix, implicating a possible contribution of DPP to calcium accumulation in circumpulpal dentin and, hence, to appositional mineralization of dentin. [ABSTRACT FROM AUTHOR]

Ground magnetic field variations have been used to investigate ionospheric dynamics for more than a century. They are usually explained in terms of an electric circuit in the ionosphere driven by an electric field, but this is insufficient to explain how magnetic field disturbances are dynamically established. Here we explain and simulate how the ionosphere dynamically responds to magnetospheric forcing and how it leads to magnetic field deformation via Faraday's law. Our approach underscores the causal relationships, treating the magnetic field and velocity as primary variables (the B, v paradigm), whereas the electric field and current are derived, in contrast to the E, j paradigm commonly used in ionospheric physics. The simulation approach presented here could be used as an alternative to existing circuit‐based numerical models of magnetosphere‐ionosphere coupling. Plain Language Summary: Ground magnetic field variations have been used to investigate ionospheric dynamics for more than a century. They are usually explained in terms of an electric circuit in the ionosphere driven by an electric field; similar to how we would explain the magnetic field of a current‐carrying wire. However, this approach oversimplifies the complex reality in space plasmas. Here, the relationship between currents and magnetic fields is reversed: currents should be understood as a consequence of the magnetic field, and not the other way around. In this paper we explain and simulate how the ionosphere dynamically responds to forcing from above, and how it leads to magnetic field deformation that corresponds to an electrical current. Key Points: We present a model and simulation of how the magnetic field in the ionosphere dynamically changes in response to external forcingOur model emphasizes the causal relationships, treating B and v as primary instead of E and j, as is commonly done in ionospheric physicsSimulation results highlighting the self‐consistent ionospheric response in the B, v paradigm are presented [ABSTRACT FROM AUTHOR]

The ionospheric convection electric field is often assumed to be a potential field. This assumption is not always valid, especially when the ionosphere changes on short time scales T≲5 $T\lesssim 5$ min. We present a technique for estimating the induction electric field using ground magnetometer measurements. The technique is demonstrated on real and simulated data for sudden increases in solar wind dynamic pressure of ∼ ${\sim} $1 and 10 nPa, respectively. For the real data, the ionospheric induction electric field is 0.15 ± $\pm $ 0.015 mV/m, and the corresponding compressional flow is 2.5 ± $\pm $ 0.3 m/s. For the simulated data, the induction electric field and compressional flow reach 3 mV/m and 50 m/s, respectively. The induction electric field can locally constitute tens of percent of the total electric field. Inclusion of the induction electric field increased the total Joule heating by 2.4%. Locally the Joule heating changed by tens of percent. This corresponds to energy dissipation that is not accounted for in existing models. Plain Language Summary: In the study of ionospheric dynamics, it is often assumed that the ionospheric electric field is a potential field. This means the contribution from induction is neglected. The induction electric field is described by Faraday's law and relates to temporal changes in the magnetic field. This assumption only holds when the ionospheric dynamics change slowly. In this study, we present a technique for calculating the ionospheric induction electric field using measurements of the magnetic field on the ground. We demonstrate the technique on real and simulated data of a dynamic event, that is, a sudden commencement. We find that the induction electric field, on a global scale, is small compared to the potential electric field. Inclusion of the induction electric field increased the total energy dissipation, that is, Joule heating, by only a couple of percent but resulted in local variations of tens of percent. Furthermore, we quantified and visualized the compression flow which is the compression and expansion of the magnetic field related to the temporal evolution of a dynamic ionospheric event. Key Points: A method for estimating the induction electric field using ground magnetometer measurements is presentedLocally, the estimated induction electric field can constitute tens of percent of the total electric fieldThe spatial pattern of ionospheric Joule heating is shown to be highly affected by the induction electric field, even during weak induction [ABSTRACT FROM AUTHOR]

A graphene mesosponge (GMS), which has a sponge-like mesoporous framework, was applied to a catalyst support for polymer electrolyte fuel cell. Platinum loaded GMS (Pt/GMS) was prepared as electrocatalyst for oxygen reduction reaction (ORR) measurement and compared with platinum loaded Ketjen black (Pt/KB). ORR activity was evaluated by rotating ring disk electrode (RRDE) method to analyze hydrogen peroxide (H 2 O 2) evolution behavior as an indicator of ionomer coverage on Pt. It was found that the ORR area specific activity of Pt/GMS was 1.2 times higher than that of Pt/KB with less H 2 O 2 yield, mainly attributed to the lower ionomer coverage at Pt/GMS. It was also observed by transmission electron microtomography (3D-TEM) that Pt/GMS has a lot of pores between the sponge-like mesoporous framework with Pt nanoparticles therein. On the other hand, Pt/KB showed smoother agglomerate shapes with Pt nanoparticles inside the KB agglomerates mainly. Considering the frame-like mesoporous carbon network having hydrophobic basal nanosurface of the graphene of GMS and the aqueous electrolyte in this system, it is concluded that the ionomer can form self-aggregation with its hydrophobic domain inside, resulting in ineffective coverage of the ionomer on the nanostructure of GMS and the Pt nanoparticles in the GMS agglomerates. [ABSTRACT FROM AUTHOR]

In this study we use high quality convection data from the Electron Drift Instrument (EDI) on board Cluster to investigate how tail reconnection affects the average convection pattern in the magnetotail lobes when the interplanetary magnetic field (IMF) has a dominating east-west ($B_y$) component.We find that the convection chances from a convection dominantly the $Y_\textrm{GSM}$-direction, but opposite in the two hemispheres, to a flow oriented more towards the plasma sheet when reconnection enhances in the near Earth tail.This result is consistent with recent observations of the convection in the ionosphere, which suggest that the nightside convection pattern becomes more north-south symmetric when tail reconnection increases.This is also supported by simultaneous auroral observations from the two hemispheres, which shows that conjugate auroral features become more symmetric during substorm expansion phase when tail reconnection maximizes.The return to a more symmetric state can be interpreted as the result of reduced asymmetric lobe pressure during periods with strong tail reconnection, and is therefore consistent with asymmetric lobe pressure being the cause of the initial asymmetry in the magnetosphere. [ABSTRACT FROM AUTHOR]

Platinum in the form of nanoparticles is the key and most expensive component of polymer electrolyte membrane fuel cells, while trifluoromethanesulfonic acid (CF3SO3H) is the smallest fluorinated sulfonic acid. Nafion, which acts as both electrolyte and separator in fuel cells, contains -CF2SO3H groups. Consequently, research on the electrochemical behaviour of Pt in aqueous CF3SO3H solutions creates important background knowledge that can benefit fuel cell development. In this contribution, Pt electro-oxidation is studied in 0.1 M aqueous CF3SO3H as a function of the polarization potential (Ep, 1.10 ≤ Ep ≤ 1.50 V), polarization time (tp, 100 ≤ tp ≤ 104 s), and temperature (T, 278 ≤ T ≤ 333 K). The critical thicknesses (X1), which determines the applicability of oxide growth theories, is determined and related to the oxide thickness (dox). Because X1 > dox for the entire range of Ep, tp, and T values, the formation of Pt surface oxide follows the interfacial place-exchange or the metal cation escape mechanism. The mechanism of Pt electro-oxidation is revised and expanded by taking into account possible interactions of cations, anions, and water molecules with Pt. A modified kinetic equation for the interfacial place exchange is proposed. The application of the interfacial place-exchange and metal cation escape mechanisms leads to an estimation of the Ptδ+-Oδ- surface dipole (μPtO), and the potential drop (Vox) and electric field (Eox) within the oxide. The Pt-anion interactions affect the oxidation kinetics by indirectly influencing the electric field within the double layer and the surface oxide. [ABSTRACT FROM AUTHOR]

Ionospheric dayside dynamics is strongly controlled by the interaction between the Interplanetary Magnetic Field (IMF) and the Earth's magnetic field near the dayside magnetopause, while nightside ionospheric dynamics depends mainly on magnetotail activity. However, we know little about the influence of magnetotail activity on the dayside ionospheric dynamics. We investigate this by performing superposed epoch analyses of ground magnetic field data for substorms occurring during northward IMF. In such substorms, dayside reconnection is minimized, allowing us to separate the effects of the magnetotail activity on the dayside current system. We find that as nightside activity elevates, the dayside ionospheric current elevates. Our analyses indicate that the lobe cells are less distinct before onset than during non‐substorm northward IMF conditions. They become more pronounced after onset, possibly due to magnetospheric reconfiguration or a remote effect of the nightside current. We discuss possible mechanisms that may explain our observations. Plain Language Summary: Aurora in the high latitude upper atmosphere is a major observable illustration of events occurring in the nightside of the Earth's magnetosphere called substorms. Substorms increase the electric current of the upper atmosphere at high latitudes. The increment lasts for tens of minutes before it decays. The impact of substorms on the dayside current system is not known. We study substorms during certain conditions, and we find that the dayside currents also tend to increase with substorms. We discuss potential explanations of that influence on the dayside. Our findings help us understand the origins of the dynamics of the upper atmosphere. Key Points: Analyses of ground magnetometer data from substorms during northward Interplanetary Magnetic Field (IMF) show that substorms impact the NBZ dayside ionospheric currentsDuring substorms under northward IMF conditions, lobe cells are unusually weak before onset and become more distinct afterWe suggest possible mechanisms by which magnetotail dynamics can influence dayside ionospheric currents [ABSTRACT FROM AUTHOR]

A mathematical model focusing on local gas transport in a single carbon primary particle was developed by combining the classical agglomerate model with local gas transport in the vicinity of a Pt particle. Two local gas transport processes—gas transport through an ionomer thin film at Pt particles deposited on the surface of the carbon primary particle and gas transport through water at Pt particles deposited inside the carbon primary particle—were newly introduced. The model showed qualitative agreement with the experimentally measured gas transport resistance of catalyst layers with different effective Pt surface areas, which had not been captured by the classical agglomerate approach. The experimental data were fitted by significantly reducing the gas permeability for the local gas transport processes in the vicinity of the Pt surface, which was 1/4–1/20 of the permeability measured in the bulk materials. The corrections of gas permeability were all related to the local gas transport in the vicinity of the Pt surface, which implied the presence of a high energy barrier for reactant gas transport at ionomer/Pt and water/Pt interfaces. The influence of structural parameters of catalyst layers on the gas transport resistance was presented to provide a guideline toward the reduction of the gas transport resistance at low Pt loading. [ABSTRACT FROM AUTHOR]

Water sorption isotherm of catalyst layers in polymer electrolyte fuel cells is analyzed by a mathematical model. The model takes into account multi-layer water adsorption on adsorption sites and capillary condensation in hydrophilic pores. The detailed structures of CLs including the pore size distribution, volume fraction of hydrophilic pores, and ionomer coverage over carbon supports and Pt surface are thoroughly considered. Quantitative estimation of water uptake at different locations in CLs as a function of vapor activity is successfully achieved. The model reveals that water adsorption in CLs firstly takes place on the adsorption sites such as side chains in Nafion ® ionomer, Pt surface, and surface groups on carbon supports at low vapor activity. The primary pores are filled with capillary condensed water at activity of 0.4. The condensation of water in the secondary pores is observed at activity from 0.9 to 1. The wetting property of the primary pores strongly depends on carbon materials, while surface of the secondary pores is found to show the hydrophobic nature irrespective of carbon materials. The amount and location of water in CLs are correlated with electrochemical double layer and effective proton conductivity. [ABSTRACT FROM AUTHOR]

Highlights: [•] A method of evaluating gas transport resistance inside carbon supports was developed. [•] Gas transport resistance was higher inside than outside the carbon support. [•] Pt was less effective inside the carbon support than on the outer surface. [ABSTRACT FROM AUTHOR]

Theoretical analysis of oxygen reduction reaction (ORR) on cathode Pt(111), Pt3Cu(111), and PtCu(111) surfaces in a polymer electrolyte fuel cell (PEFC) is performed to investigate the ORR mechanisms on Pt(111) and the effect of alloying. From density functional theory (DFT) calculations, we found that the difference in adsorption energy of O2 molecules on the surface has a strong relation with the number of d-electrons and the position of the d-band center of the surface Pt atoms. From the results of the activation energy calculations using the unity bond index-quadratic exponential potential (UBI-QEP) method, we show that the oxygen atom coverage on Pt(111) surface has a strong influence on the ORR activity. In addition, it was found that Pt3Cu(111) and PtCu(111) surfaces have lower coverage compared with that of Pt(111) surface, which results in the enhancement of ORR activity. [ABSTRACT FROM AUTHOR]

All-solid-state batteries with Li metal anode can address the safety issues surrounding traditional Li-ion batteries as well as the demand for higher energy densities. However, the development of solid electrolytes and protective anode coatings possessing high ionic conductivity and good stability with Li metal has proven to be a challenge. Here, we present our informatics approach to explore the Li compound space for promising electrolytes and anode coatings using high-throughput multi-property screening and interpretable machine learning. To do this, we generate a database of battery-related materials properties by computing Li + migration barriers and stability windows for over 15,000 Li-containing compounds from Materials Project. We screen through the database for candidates with good thermodynamic and electrochemical stabilities, and low Li + migration barriers, identifying promising new candidates such as Li 9 S 3 N, LiAlB 2 O 5 , LiYO 2 , LiSbF 4 , and Sr 4 Li (BN 2) 3 , among others. We train machine learning models, using ensemble methods, to predict migration barriers and oxidation and reduction potentials of these compounds by engineering input features that ensure accuracy and interpretability. Using only a small number of features, our gradient boosting regression models achieve R 2 values of 0.95 and 0.92 on the oxidation and reduction potential prediction tasks, respectively, and 0.86 on the migration barrier prediction task. Finally, we use Shapley additive explanations and permutation feature importance analyses to interpret our machine learning predictions and identify materials properties with the largest impact on predictions in our models. We show that our approach has the potential to enable rapid discovery and design of novel solid electrolytes and anode coatings. [ABSTRACT FROM AUTHOR]

Presently, all empirical coupling functions quantifying the solar wind—magnetosphere energy—or magnetic flux conversion assume that the coupling is independent of the sign of the dawn‐dusk component (B y) of the Interplanetary Magnetic Field (IMF). In this paper we present observations strongly suggesting an explicit IMF B y effect on the solar wind‐magnetosphere coupling. When the Earth's dipole is tilted in the direction corresponding to northern winter, positive IMF B y is found to on average lead to a larger polar cap than when IMF B y is negative during otherwise similar conditions. This explicit IMF B y effect is found to reverse when the Earth's dipole is inclined in the opposite direction (northern summer) and is consistently observed from both hemispheres. We interpret the different responses of the polar cap size due to the sign of IMF B y to likely be a result of differences in the dayside reconnection rate. Key Points: The sign of IMF B y likely affects the rate of opening of magnetic flux on the dayside magnetosphereThis explicit IMF B y effect depends on the orientation of the magnetic dipole axis of the EarthThe underlying mechanism(s) explaining the observed dependence is poorly understood [ABSTRACT FROM AUTHOR]

We have developed a new technique that enable us to identify, separate, and quantify the sources of high latitude ionospheric convection. Usually, the ionospheric convection is examined by the electrostatic potential, as the convection will follow contours of equipotentials. We will show that in order to identify, separate, and quantify the underlying processes responsible for the observed convection pattern, it can be more beneficial to look at a quantity we show is proportional to the divergence of the convection electric field. We here use the Spherical Elementary Convection Systems (SECS) technique to describe the ionospheric convection electric field as the sum of the fields from a distribution of artificial nodes on a spherical surface, each having their own curl-free elementary field. We show that such a representation is highly suitable for the identification and quantification of the sources of ionospheric convection as the strength of the elementary fields are proportional to the divergence of the convection electric field. We use this method to study the ionospheric convection using SuperDARN during northward IMF, and demonstrate its ability to separate the sources of ionospheric convection related to lobe reconnection and tail reconnection. Utilizing this ability, we isolate the effect from lobe reconnection and study how different orientations of the Earth's magnetic dipole axis affect the lobe convection strength inside the dayside polar cap, in which we relate to the lobe reconnection rate assuming a strong coupling between the two regions. We find that the inferred lobe reconnection rate increase linearly with increasing dipole tilt angle. Our findings indicate that the summer hemisphere can typically have twice the lobe reconnection rate compared to the opposite hemisphere. [ABSTRACT FROM AUTHOR]

Previous studies have shown that conjugate auroral features are displaced in the two hemispheres when the interplanetary magnetic field (IMF) has a transverse (Y) component. It has also been shown that a BY component is induced in the closed magnetosphere due to the asymmetric loading of magnetic flux in the lobes following asymmetric dayside reconnection when the IMF has a Y component. The magnetic field lines with azimuthally displaced footpoints map into a "banana"-shaped convection cell in one hemisphere and an "orange"-shaped cell in the other. Due to the Parker spiral our system is most often exposed to a BY -dominated IMF. The dipole tilt angle, varying between ±34∘ , leads to warping of the plasma sheet and oppositely directed BY components in dawn and dusk in the closed magnetosphere. As a result of the Parker spiral and dipole tilt, geospace is asymmetric most of the time. The magnetic storm on 17 August 2001 offers a unique opportunity to study the dynamics of the asymmetric geospace. IMF BY was 20–30 nT and tilt angle was 23∘. Auroral imaging revealed conjugate features displaced by 3–4 h magnetic local time. The latitudinal width of the dawnside aurora was quite different (up to 6∘) in the two hemispheres. The auroral observations together with convection patterns derived entirely from measurements indicate dayside, lobe and tail reconnection in the north, but most likely only dayside and tail reconnection in the Southern Hemisphere. Increased tail reconnection during the substorm expansion phase reduces the asymmetry. [ABSTRACT FROM AUTHOR]

Infrared spectroscopy of adsorbed hydroxide (OH ad ) has been performed on the high index planes of Pt: n (111)–(100) and n (111)–(111) series. The bending mode of OH ad (δ PtOH ) appears on these surfaces around 1080 cm − 1 , which is similar to the result on the low index planes of Pt. The band intensity of δ PtOH depends on surface structure and electrode potential. At 0.9 V vs RHE, the band intensity of δ PtOH increases with the decrease of the step atom density: the intensity of δ PtOH is higher on the surfaces with lower activity of the oxygen reduction reaction (ORR). These results suggest that the adsorption of OH ad is site specific and the deactivating species of the ORR. [ABSTRACT FROM AUTHOR]

The fuel cell electric vehicle (FCEV) is expected to be one of the promising “ZERO” emission vehicles along with the battery electric vehicle. For the commercialization of the FCEV, it is significantly important to reduce the production cost, especially of the catalyst layer. Generally, the catalyst layer is composed mainly of Pt nano-particles and a carbon support, and their structure greatly affects the performance and durability of the fuel cell. For example, a Pt/C catalyst consisting of highly dispersed Pt nanoparticles loaded on a high-surface area carbon support is preferable to achieve a better initial performance, whereas such a catalyst often suffers from poor durability. In order to construct a well-balanced catalyst layer, the design of the carbon support is of essential importance. This review describes the mechanism of carbon corrosion caused by the drive modes of the vehicle in both cathode and anode catalyst layers, together with methods for analysis and characterization. Since these processes are often a bottleneck in the development of the FCEV, we hope that the present review will be helpful to the development and improvement of the technology related to FCEVs. [TANSO 2015 (No. 266) 21–30.] [ABSTRACT FROM AUTHOR]

In order to improve the electricity generation performance of fuel cell electric vehicles, it is necessary to optimize the microstructure of the catalyst layer of a polymer electrolyte fuel cell. The catalyst layer is formed by a wet coating process using catalyst inks. Therefore, it is very important to observe the microstructure of the catalyst ink. In this study, the morphology of carbon-supported platinum (Pt/C) particles in catalyst inks with a different solvent composition was investigated by cryogenic scanning electron microscopy (cryo- SEM). In addition, the morphology of the ionomer, which presumably influences the formation of agglomerated Pt/C particles in a catalyst ink, was investigated by cryogenic transmission electron microscopy (cryo-TEM). The results of a cryo-SEM observation revealed that the agglomerated Pt/C particles tended to become coarser with a higher 1-propanol (NPA) weight fraction. The results of a cryo-TEM observation indicated that the actual ionomer dispersion in a catalyst ink formed a network structure different from that of the ionomer in the solvent. [ABSTRACT FROM AUTHOR]

Optimizing the catalyst layer structure is one of the key issues for improving performance despite lower platinum loading. The catalyst ink, consisting of platinum-loaded carbon particles and ionomer dispersed in an aqueous solvent, is a key factor for controlling the structure of the catalyst layer because the catalyst layer is prepared in a wet coating process. For that purpose, we visualized the nanostructure of the ionomer in the catalyst ink by cryogenic electron microscopy, especially cryogenic transmission electron microscopy (cryo-TEM). By cryo-TEM, it was revealed that ionomer molecules formed rod-like aggregates macro-homogeneously in the solvent, and a similar morphology was observed in a carbon-particle-containing solvent. In contrast, ionomer aggregates in the catalyst ink containing platinum nanoparticles loaded on carbon particles were denser in the vicinity of the platinum-loaded carbon particles. That can be attributed to strong interaction between platinum nanoparticles and sulfonic acid groups in the ionomer. It also implies that a good understanding of ionomer morphology in the catalyst ink can play an important role in controlling the catalyst layer microstructure for reducing platinum loading. [ABSTRACT FROM AUTHOR]

An oxidation-resistant and elastic mesoporous carbon, graphene mesosponge (GMS), is prepared. GMS has a sponge-like mesoporous framework (mean pore size is 5.8 nm) consisting mostly of single-layer graphene walls, which realizes a high electric conductivity and a large surface area (1940 m2 g−1). Moreover, the graphene-based framework includes only a very small amount of edge sites, thereby achieving much higher stability against oxidation than conventional porous carbons such as carbon blacks and activated carbons. Thus, GMS can simultaneously possess seemingly incompatible properties; the advantages of graphitized carbon materials (high conductivity and high oxidation resistance) and porous carbons (large surface area). These unique features allow GMS to exhibit a sufficient capacitance (125 F g−1), wide potential window (4 V), and good rate capability as an electrode material for electric double-layer capacitors utilizing an organic electrolyte. Hence, GMS achieves a high energy density of 59.3 Wh kg−1 (material mass base), which is more than twice that of commercial materials. Moreover, the continuous graphene framework makes GMS mechanically tough and extremely elastic, and its mean pore size (5.8 nm) can be reversibly compressed down to 0.7 nm by simply applying mechanical force. The sponge-like elastic property enables an advanced force-induced adsorption control. [ABSTRACT FROM AUTHOR]

Abstract: A new method was developed for evaluating the gas transport resistance of the catalyst layer, RCL , based on gas crossover through the Nafion® membrane. Using this method, gas transport resistance toward Pt catalyst (per unit of Pt surface area), Rmicro ,Pt, was investigated for both hydrogen and oxygen. This method is applicable to low relative humidity (RH) conditions because of the extremely low limiting current density attributed to crossover gases. It was used to investigate the RH dependence of RCL for hydrogen and oxygen, which has so far been difficult to measure. A comparison of the limiting current density due to the hydrogen oxidation reaction (HOR) with and without inert gas flow suggested that the decrease in the HOR current at a high potential is mainly due to mass transfer loss caused by a loss of effective surface area, Seff , and not by a loss of inherent Pt activity. For hydrogen, it is possible with this method to evaluate the potential dependence of Seff for the electrochemical reactions rather than the electrochemical surface area (ECA) determined by proton adsorption in the low potential region. It was found that Rmicro ,Pt increased for both hydrogen and oxygen with a lower RH. The trend of RH dependence and the impact of RH on Rmicro ,Pt were very similar to the tendencies observed for the Nafion® membrane. However, the gas transport resistance of the ionomer was notably higher for oxygen than for hydrogen, considering its relationship in the membrane. Adsorption of the ionomer onto the Pt/C catalyst might be one of the factors accounting for this difference. [Copyright &y& Elsevier]

Abstract: Potential profile in PEFC electrolyte membrane has been investigated by using microprobe technique in order to help understand membrane degradation mechanism. In particular, potential distribution in the membrane under several operation conditions has been measured by using microprobes inserted in the membrane. A theoretical model has been developed to predict the potential distribution under different cell current density with cells of different rib/channel width. The model showed good agreement with experimental result. [Copyright &y& Elsevier]

The solar wind influence on geospace can be described as the sum of a directly driven component, or dayside reconnection, and an unloading component, associated with the release of magnetic energy via nightside reconnection. The two processes are poorly correlated on short time scales, but exactly equal when averaged over long time windows. Because of this peculiar property, regression models of ionospheric electrodynamics that are based on solar wind data are time scale specific: Models derived from 1 min resolution data will be different from models derived from hourly, daily, or monthly data. We explain and quantify this effect on simple linear regression models of various geomagnetic indices. We also derive a time scale-dependent correction factor that can be used with the Average Magnetic field and Polar current System model. Finally, we show how absolute estimates of the nightside reconnection rate can be calculated from solar wind measurements and geomagnetic indices. [ABSTRACT FROM AUTHOR]