High-throughput Characterization of Oxides’ Electrochemistry

HUANG, RUIYUN

doi:https://doi.org/10.21985/n2-hf4b-m421

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High-throughput Characterization of Oxides’ Electrochemistry

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Throughout history, the development of materials has relied heavily on the empirical judgment of scientists and engineers and on prolonged experiments proton to errors. Due to the complexity of material behavior, successful discovery of new candidates has been serendipitous, and down-selection of candidates remains a time-consuming process that requires repetitive characterization using a consistent experimental design. In recognition of the urgent demand to meet today’s materials needs on a much more rapid time scale, increasing attention is being directed towards high-throughput characterization approaches. Such an approach enables one to collect experiment data of a wide variety of parameters to rapidly establish chemical trends and physical laws, which in turn, expedite the materials development cycle.1, 2 Multiple areas, including catalysts3, 4, organic coatings5, electronic materials6, and sensing polymers, have seen benefits from this approach7. However, high-throughput characterization methods of solid-state ionic materials still lack development, especially in the field of electrochemistry for energy applications. Accordingly, this work is focused on the high-throughput characterization of solid-state ionic materials with potential application in high-temperature electrochemical energy technologies. Pure oxygen ionic conductors and mixed ion and electronic conductors (MIECs) with potential applications in solid oxide fuel cells (SOFCs), oxygen sensors, and thermocycling fuel production are evaluated. Two approaches were developed: first, high-throughput characterization of electrolyte materials was realized via a careful selection of sample geometry that enables accurate conductivity measurement across a compositionally graded material deposited as a thin film on an electronically conductive substrate. The method was applied to the discovery of the optimal dopant concentration in Lu-stabilized zirconia where the 15% doing resulted a highest conductivity. The 15% Lu-stabilized zirconia showed comparative conductivity as Sc-stabilized zirconia at 600 °C (~0.01 S/cm) and second highest conductivity among other dopant for zirconia at 1000 °C. Second, a new electrochemical approach for the measurement of oxygen nonstoichiometry with high precision was established that has the potential to dramatically cut the measurement time compared to thermogravimetric analysis, the most commonly used method for probing nonstoichiometry. Here, the a.c. electrical impedance response of candidate materials deposited on a pure oxygen ion conducting electrolyte is measured to determine the chemical capacitance. A new formalism for recovering the oxygen nonstoichiometry from these capacitance values is reported. The approach is applied to undoped and zirconia-substituted ceria, materials which are inherently of interest for their potential applications and which present a range of transport and thermodynamic properties. The study of ceria, a benchmark material, reproduced the literature enthalpy and entropy of reduction to within 94%. The study of zirconia-substituted ceria (Ce0.8Zr0.2O2-δ) produced nonstoichiometry results with higher accuracy than previously available, and also revealed the ionic conductivity in this predominantly electronically conducting material. A preliminary study of Sr(Ti0.5Mn0.5)O3-δ was also performed, and the material requirements for high throughput characterization of this material established. These studies lay the groundwork for the rapid discovery of electrochemical properties in oxide and other materials.

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