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)) MnO_(3- 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