Probing the reaction pathway in (La_(0.8)Sr_(0.2))_(0.95)MnO_(3+δ) using libraries of thin film microelectrodes

Libraries of (La_(0.8)Sr_(0.2))_(0.95)MnO_(3+δ) (LSM) thin film microelectrodes with systematically varied thickness or growth temperature were prepared by pulsed laser deposition, and a novel robotic instrument was used to characterize these libraries in automated fashion by impedance spectroscopy. The measured impedance spectra are found to be described well by an electrochemical model based on a generalized transmission model for a mixed conducting oxide, and all trends are consistent with a reaction pathway involving oxygen reduction over the LSM surface followed by diffusion through the film and into the electrolyte substrate. The surface activity is found to be correlated with the number of exposed grain boundary sites, which decreases with either increasing film thickness (at constant growth temperature) or increasing film growth temperature (at constant thickness). These findings suggest that exposed grain boundaries in LSM films are more active than exposed grains towards the rate-limiting surface process, and that oxygen ion diffusion through polycrystalline LSM films is faster than many prior studies have concluded

Exceptional power density and stability at intermediate temperatures in protonic ceramic fuel cells

Over the past several years, important strides have been made in demonstrating protonic ceramic fuel cells (PCFCs). Such fuel cells offer the potential of environmentally sustainable and cost-effective electric power generation. However, their power outputs have lagged behind predictions based on their high electrolyte conductivities. Here we overcome PCFC performance and stability challenges by employing a high-activity cathode, PrBa_(0.5)Sr_(0.5)Co_(1.5)Fe_(0.5)O_(5+δ) (PBSCF), in combination with a chemically stable electrolyte, BaZr_(0.4)Ce_(0.4)Y_(0.1)Yb_(0.1)O_3 (BZCYYb4411). We deposit a thin dense interlayer film of the cathode material onto the electrolyte surface to mitigate contact resistance, an approach which is made possible by the proton permeability of PBSCF. The peak power densities of the resulting fuel cells exceed 500 mW cm^(−2) at 500 °C, while also offering exceptional, long-term stability under CO_2

Exceptional power density and stability at intermediate temperatures in protonic ceramic fuel cells

Over the past several years, important strides have been made in demonstrating protonic ceramic fuel cells (PCFCs). Such fuel cells offer the potential of environmentally sustainable and cost-effective electric power generation. However, their power outputs have lagged behind predictions based on their high electrolyte conductivities. Here we overcome PCFC performance and stability challenges by employing a high-activity cathode, PrBa_(0.5)Sr_(0.5)Co_(1.5)Fe_(0.5)O_(5+δ) (PBSCF), in combination with a chemically stable electrolyte, BaZr_(0.4)Ce_(0.4)Y_(0.1)Yb_(0.1)O_3 (BZCYYb4411). We deposit a thin dense interlayer film of the cathode material onto the electrolyte surface to mitigate contact resistance, an approach which is made possible by the proton permeability of PBSCF. The peak power densities of the resulting fuel cells exceed 500 mW cm^(−2) at 500 °C, while also offering exceptional, long-term stability under CO_2

Out-of-Plane Ionic Conductivity Measurement Configuration for High-Throughput Experiments

An approach for measuring conductivity of thin-film electrolytes in an out-of-plane configuration, amenable to high-throughput experimentation, is presented. A comprehensive analysis of the geometric requirements for success is performed. Using samaria-doped ceria (Ce_(0.8)Sm_(0.2)O_(1.9), SDC) excellent agreement between bulk samples and thin films with continuous and patterned electrodes, 100–500 μm in diameter, is demonstrated. Films were deposited on conductive Nb-doped SrTiO_3, and conductivity was measured by AC impedance spectroscopy over the temperature range from ∼200 to ∼500 °C. The patterned electrode geometry, which encompassed an array of microdot metal electrodes for making top contact, enabled measurements at hundreds of positions on the film, implying the potential for measuring hundreds of composition in a single library

Out-of-Plane Ionic Conductivity Measurement Configuration for High-Throughput Experiments

An approach for measuring conductivity of thin-film electrolytes in an out-of-plane configuration, amenable to high-throughput experimentation, is presented. A comprehensive analysis of the geometric requirements for success is performed. Using samaria-doped ceria (Ce_(0.8)Sm_(0.2)O_(1.9), SDC) excellent agreement between bulk samples and thin films with continuous and patterned electrodes, 100–500 μm in diameter, is demonstrated. Films were deposited on conductive Nb-doped SrTiO_3, and conductivity was measured by AC impedance spectroscopy over the temperature range from ∼200 to ∼500 °C. The patterned electrode geometry, which encompassed an array of microdot metal electrodes for making top contact, enabled measurements at hundreds of positions on the film, implying the potential for measuring hundreds of composition in a single library

Scanning impedance probe for high-​throughput electrochemical characterization of solid state electrodes

We have developed a robotic instrument that can measure the electrochem. impedance of hundreds of thin-film microelectrodes in automated fashion. By measuring electrodes with systematically varied area, thickness, surface decoration, and compn., it is possible to probe reaction pathways, decouple bulk and surface properties, and rapidly screen hundreds of chem. compns. to discover trends and identify new high performing catalysts. Here we introduce the capabilities of this new instrument by using it to measure geometrically graded microdot electrodes of the solid-oxide fuel-cell (SOFC) cathode material (La_(0.8)Sr_(0.2))0.95MnO3-δ (LSM). We collect A.C. impedance spectra from several hundred microdots with diams. ranging from 30 to 500 μm and thicknesses from 30 to 300 nm over the temp. and oxygen partial pressure ranges of 700 to 800 °C and 3.2 × 10^(-4) to 1 atm, resp. Automated data anal. using a phys. motivated equiv. circuit model yields phys. parameters for each dot at each measurement condition. The LSM surface reaction resistance and bulk ionic resistance both exhibited a power law dependence on dot diam. with an exponent close to -2, indicative of a surface reaction pathway that encompasses the entirety of the dot surface. The slight deviation from -2 is attributed to local cooling of the sample by the microprobe tip, which slightly increases the resistances for smaller diam. microelectrodes. A surprising increase in surface reaction resistance with microelectrode thickness was obsd., tentatively assigned to an obsd. increase in film roughness with thickness. The results set the stage for exploration of a wide range of gradient types, from compn. to growth temp. to catalyst coating, while the use of impedance spectroscopy implies that a broad range of properties, from ionic cond. to material nonstoichiometry, can be extd

Focus topics for the ECFA study on Higgs / Top / EW factories

In order to stimulate new engagement and trigger some concrete studies in areas where further work would be beneficial towards fully understanding the physics potential of an $e^+e^-$ Higgs / Top / Electroweak factory, we propose to define a set of focus topics. The general reasoning and the proposed topics are described in this document

Focus topics for the ECFA study on Higgs / Top / EW factories

International audienceIn order to stimulate new engagement and trigger some concrete studies in areas where further work would be beneficial towards fully understanding the physics potential of an $e^+e^-$ Higgs / Top / Electroweak factory, we propose to define a set of focus topics. The general reasoning and the proposed topics are described in this document

Focus topics for the ECFA study on Higgs / Top / EW factories

International audienceIn order to stimulate new engagement and trigger some concrete studies in areas where further work would be beneficial towards fully understanding the physics potential of an $e^+e^-$ Higgs / Top / Electroweak factory, we propose to define a set of focus topics. The general reasoning and the proposed topics are described in this document

Focus topics for the ECFA study on Higgs / Top / EW factories

International audienceIn order to stimulate new engagement and trigger some concrete studies in areas where further work would be beneficial towards fully understanding the physics potential of an $e^+e^-$ Higgs / Top / Electroweak factory, we propose to define a set of focus topics. The general reasoning and the proposed topics are described in this document