Polymer electrolyte membrane fuel cell (PEMFC) electrodes with a 0.07 mgPt cm–2 Pt/Vulcan electrocatalyst loading, containing only a sulfonated poly(ionic liquid) block copolymer (SPILBCP) ionomer, ...were fabricated and achieved a ca. 2× enhancement of kinetic performance through the suppression of Pt surface oxidation. However, SPILBCP electrodes lost over 70% of their electrochemical active area at 30% RH because of poor ionomer network connectivity. To combat these effects, electrodes made with a mix of Nafion/SPILBCP ionomers were developed. Mixed Nafion/SPILBCP electrodes resulted in a substantial improvement in MEA performance across the kinetic and mass transport-limited regions. Notably, this is the first time that specific activity values determined from an MEA were observed to be on par with prior half-cell results for Nafion-free Pt/Vulcan systems. These findings present a prospective strategy to improve the overall performance of MEAs fabricated with surface accessible electrocatalysts, providing a pathway to tailor the local electrocatalyst/ionomer interface.
The Kepler mission was designed to determine the frequency of Earth-sized planets in and near the habitable zone of Sun-like stars. The habitable zone is the region where planetary temperatures are ...suitable for water to exist on a planet's surface. During the first 6 weeks of observations, Kepler monitored 156,000 stars, and five new exoplanets with sizes between 0.37 and 1.6 Jupiter radii and orbital periods from 3.2 to 4.9 days were discovered. The density of the Neptune-sized Kepler-4b is similar to that of Neptune and GJ 436b, even though the irradiation level is 800,000 times higher. Kepler-7b is one of the lowest-density planets (approximately 0.17 gram per cubic centimeter) yet detected. Kepler-5b, -6b, and -8b confirm the existence of planets with densities lower than those predicted for gas giant planets.
Berkelium is positioned at a crucial location in the actinide series between the inherently stable half-filled 5f(7) configuration of curium and the abrupt transition in chemical behavior created by ...the onset of a metastable divalent state that starts at californium. However, the mere 320-day half-life of berkelium's only available isotope, (249)Bk, has hindered in-depth studies of the element's coordination chemistry. Herein, we report the synthesis and detailed solid-state and solution-phase characterization of a berkelium coordination complex, Bk(III)tris(dipicolinate), as well as a chemically distinct Bk(III) borate material for comparison. We demonstrate that berkelium's complexation is analogous to that of californium. However, from a range of spectroscopic techniques and quantum mechanical calculations, it is clear that spin-orbit coupling contributes significantly to berkelium's multiconfigurational ground state.
The state-factor approach was used to review the controls on ecosystem processes on the Tanana River floodplain. The approach holds that vegetation and soil development are believed to be strongly ...linked with flooding. This implies that flooding is a state factor that controls the floodplain ecosystem processes in the area.
K2's Campaign 9 (K2C9) will conduct a ∼3.7 deg2 survey toward the Galactic bulge from 2016 April 22 through July 2 that will leverage the spatial separation between K2 and the Earth to facilitate ...measurement of the microlens parallax π E for 170 microlensing events. These will include several that are planetary in nature as well as many short-timescale microlensing events, which are potentially indicative of free-floating planets (FFPs). These satellite parallax measurements will in turn allow for the direct measurement of the masses of and distances to the lensing systems. In this article we provide an overview of the K2C9 space- and ground-based microlensing survey. Specifically, we detail the demographic questions that can be addressed by this program, including the frequency of FFPs and the Galactic distribution of exoplanets, the observational parameters of K2C9, and the array of resources dedicated to concurrent observations. Finally, we outline the avenues through which the larger community can become involved, and generally encourage participation in K2C9, which constitutes an important pathfinding mission and community exercise in anticipation of WFIRST.
Surface soils on recently deposited alluvium along the Tanana River, Alaska, have an elevated pH and are high in salts such as calcium carbonate and calcium sulfate. With advancing plant succession ...surface soil chemistry changes, and when the alder - balsam poplar stage is reached these salt deposits are absent. To test the hypothesis that soil surface salt (salt crust) accumulates as a result of the combined action of capillary rise of groundwater and surface evaporation, a treated plot experiment was undertaken in the early open willow stage on the floodplain where the soil surface was devoid of litter. Treatments, applied in early summer, were salt crust removed, leaf litter added on the surface (evaporation barrier), and polyethylene sheeting installed at a depth of 30 cm (capillary rise barrier). Surface 5-cm soil samples, collected in September, showed significant reductions from salt crust removal and surface litter application in electrical conductance and amounts of bicarbonate, sulfate, calcium, magnesium, potassium, and sodium. In clearings within dense alder - balsam poplar stands on the first terrace, forest floor removal resulted in significantly increased amounts of surface soil sodium, sulfate, calcium, and magnesium. However, this treatment did not result in re-establishment of the salt crust, probably because of a higher ground surface elevation at this terrace and consequent deeper water table. On lower, early-successional terraces salt crusts may form in a period of only several weeks if precipitation is low. The advent of a complete litter layer has great significance in the successional sequence on these soils not only because of nutrient cycling as a result of decomposition processes but also because of the probable physical effect of severely decreasing rates of evaporation from the mineral soil surface. In the latter case, although we did not directly measure mineral soil surface evaporation rates with and without litter layers, movement of salt solution injected at 25 cm in the soil profile to the surface was restricted by application of a surface litter layer.
A break in periodicity occurs in the actinide series between plutonium and americium as the result of the localization of 5f electrons. The subsequent chemistry of later actinides is thought to ...closely parallel lanthanides in that bonding is expected to be ionic and complexation should not substantially alter the electronic structure of the metal ions. Here we demonstrate that ligation of californium(III) by a pyridine derivative results in significant deviations in the properties of the resultant complex with respect to that predicted for the free ion. We expand on this by characterizing the americium and curium analogues for comparison, and show that these pronounced effects result from a second transition in periodicity in the actinide series that occurs, in part, because of the stabilization of the divalent oxidation state. The metastability of californium(II) is responsible for many of the unusual properties of californium including the green photoluminescence.
Improvements in polymer electrolyte fuel cell (PEFC) electrode performance have primarily focused on catalyst and ionomer developments, marginalizing the importance of catalyst ink formulation. ...Herein, the effect of ink formulation is examined across a series of cathodes comprised of PtCo supported on high surface area carbon (PtCo/HSC) and Nafion ionomer using an array of in situ electrochemical and ex situ characterization techniques. In contrast to prior work on Pt/Vu systems, ink water content had little effect on the electrochemically determined ionomer coverage for the PtCo/HSC electrocatalyst examined here. Characterization using nano-scale resolution X-ray computed tomography (nano-CT) demonstrated that water-rich ink formulations lead to a reduction in aggregate size (ionomer + PtCo/HSC), improving local O2 transport. This understanding, combined with the use of a commercially-available electrocatalyst was used to produced state-of-the-art membrane electrode assemblies with Pt loadings of 0.03/0.08 mgPt/cm2 on the anode and cathode respectively, having; i) > 1 A/mgPt (0.9 ViR-free, 150 kPa, 80 °C, 100% RH, H2/O2), ii) 320 mA/cm2 at 0.8 V, 150 kPa, 80 °C, 100% RH, H2/Air), and iii) > 1 W/cm2elec at rated power (0.67 V, 250 kPa, 94 °C, 65% RH, H2/Air) or < 0.11 gPt/kWrated.
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•Ink water content (nPA:H2O ratio) primarily affects O2 transport.•Ionomer coverage on catalyst has weaker effects for HSC-supported catalysts.•Higher ink water leads to smaller PtCo/HSC aggregate particles and lower RnF.•70 wt% H2O PtCo/HSC MEA exceeds US DOE 2020 performance targets.
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