Gold, as the noblest metal, is an appropriate model electrode to study electrochemical double layers. This study examines the frequency dispersion of the double layer of polished gold electrodes in perchloric acid with impedance spectroscopy under amplitude, electrolyte concentration, and potential variation. The dynamic perturbation of the double layer equilibrium by impedance measurements shows a constant phase (CP) response (phase angle of approximately −75°), which is responsible for a frequency dispersion of the capacitance. The response is almost independent of the excitation amplitude, for which the CP behavior is ascribed to resistive−capacitive (RC) contributions of the electric field-driven ion separation instead of the previously reported diffusionlimited adsorption processes. The RC character of the double layer in combination with the electrolyte resistance is accompanied by a relaxation that can damp the ion movement and the related ion separation. At the relaxation frequency, the capacitance is found to be independent of the electrolyte concentration, which is attributed to a constant ratio of the contributions of damped ion movement and dielectric polarization of water molecules.
Several porous backbone layers of proton conducting BaZr 1-x-y Ce x Y y O 3-δ (BZCY) were prepared by spray-coating or painting on BaZr 0.7 Ce 0.2 Y 0.1 O 2.95 (BZCY72) button cells followed by high temperature firing in air. This step enabled to produce ceramic backbones with various grain and pore sizes. The backbones were further infiltrated with mixed conducting double perovskite Ba 0.5 Gd 0.8 La 0.7 Co 2 O 6-δ (BGLC587) suspensions and annealed in air. The resulting composite layers were tested as oxygen/ steam side electrodes for proton ceramic fuel cells and electrolysers (PCFCs-PCEs). The results confirm that a high performing electrode material such as BGLC587 with partial proton conductivity and high thermal expansion can be applied on a proton conducting electrolyte with low thermal expansion by use of backbone infiltration without losing electrochemical functionality. Indeed, the electrodes display an apparent polarization resistance of only 0.03 cm 2 at 700 • C in oxygen humidified with 2.7% H 2 O. We further extracted and parameterized the impedances associated with the charge and mass transfer reactions in a system where protons are the dominating charge carriers at intermediate to low temperatures and oxide ions dominate the overall transport at high temperature. The fitting revealed to what extent the charge and mass transfer reactions are short-circuited by electronic leak current across the sample at high temperatures and pO 2 's. The acquired activation energies and pre-exponential values were used to explain materials-specific and micro-structural differences between the different electrode architectures.
In this report, we describe fabrication and electrochemical‐performance testing of tubular, anode‐supported fuel cells based on the protonic ceramic BaCe0.2Zr0.7Y0.1O3–δ (BCZY27). These devices are comprised of a 20‐μm‐thick BCZY27 electrolyte spray‐coated and co‐fired onto an extruded, tubular 9.8‐mm‐diameter, 1.25‐mm‐thick 65 wt.% NiO/35 wt.% BCZY27 anode support. Reactive sintering with NiO forms the BCZY27 material from parent oxides. An La0.6Sr0.4 Co0.2Fe0.8O3–δ (LSCF) cathode is applied following co‐sintering. While anode supports can be extruded to 3‐m lengths, the active area of the cells tested here is 7.5 cm2. Performance is quantified through polarization measurements across a range of temperatures with hydrogen‐air reactants. Peak power ranges from 78 to 189 mW cm–2 over the 700–850 °C temperature range. Open‐circuit voltage decreases with increasing operating temperature due to the co‐diffusion of the multiple charge carriers present. The ionic transference number is determined over a range operating temperatures and anode‐gas compositions, and is found to range from 0.77 to 0.88. Finally, an external power supply is used to drive hydrogen across the BCZY27 membrane. At an applied current density of 1 A cm–2 and 700 °C operating temperature, hydrogen flux is measured at 7.5 smL min–1 cm–2 active area.
We describe an experiment, located in south-east Colorado, USA, that measured aerosol optical depth profiles using two L techniques. Two independent detectors measured scattered light from a vertical UV laser beam. One detector, located at the laser site, measured light via the inelastic Raman backscattering process. This is a common method used in atmospheric science for measuring aerosol optical depth profiles. The other detector, located approximately 40 km distant, viewed the laser beam from the side. This detector featured a 3.5 m 2 mirror and measured elastically scattered light in a bistatic L configuration following the method used at the Pierre Auger cosmic ray observatory. The goal of this experiment was to assess and improve methods to measure atmospheric clarity, specifically aerosol optical depth profiles, for cosmic ray UV fluorescence detectors that use the atmosphere as a giant calorimeter. The experiment collected data from September 2010 to July 2011 under varying conditions of aerosol loading. We describe the instruments and techniques and compare the aerosol optical depth profiles measured by the Raman and bistatic L detectors.
Abstract. The Pierre Auger Research and Development Array (RDA) was originally designed to be the precursor of the northern Auger observatory, a hybrid array of 4400 surface detector stations and 39 fluorescence telescopes deployed over 20,000 square kilometers. It is conceived as a test bed aiming at validating an improved and more cost-effective 1-PMT surface detector design and a new peer-to-peer communication system. The array of ten surface detector stations and ten communication-only stations is currently being deployed in southeastern Colorado and will be operated at least until late 2013. It is configured in such a way that it allows testing of a new peer-to-peer communication protocol, as well as a new surface detector electronics design with a larger dynamic range aiming at reducing the distance from the shower core where saturation is observed. All these developments are expected in the short term to improve the performance of the Pierre Auger Observatory and enable future enhancements. In the longer term, it is hoped that some of these new developments may contribute to the design of a next-generation giant ground array.
Metrics & MoreArticle Recommendations S urprisingly, sometimes the most obvious errors are overlooked over and over again. Here we unfortunately have to report one of those cases. The schematic illustrations of the graphical abstract and Figure 6 illustrate the anion as HClO 4− instead of ClO 4 − . These sketches were made during the submission as a reply to a reviewer suggestion. Even though these figures were initially not planned, we have no excuse that this error made it to the final print, and we are sorry for anyone that is interested in this work. The interpretation of the data and mechanisms is not affected by the wrong declaration of this copy and paste error. The corrected graphics are shown as follows.
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