The world-wide interest in reducing the dependency on fossil fuels demands the development of energy storage systems with high power density from abundant materials, which would enable wide-spread industrial deployment of grid-scale renewable energy systems, as well as the progressive advancement of high-powered electric vehicles (EVs). Perovskite oxide ceramics attracted significant attention as a strong candidate for bi-functional electrocatalyst for metal-air batteries. There has been consistent investigation on the viability of bi-functional electrocatalysts, because energy storage systems cannot operate rechargeably without the proper bi-functional electrocatalyst. Among various electrocatalysts for both oxygen evolution and reduction, making nanoparticles from these materials for practical applications is a great challenge. The newly introduced pervovskite electrocatalyst of ~50 nm size preferentially reduced oxygen to water (< 5 % peroxide yield), exhibited more than 20 times higher gravimetric activity (A/g) than IrO2 in an OER half-cell test, and surpassed the charge/discharge performance of Pt/C (20 wt%) in a zinc-air full cell test. This study describes substantially the systematic engineering of perovskite ceramics into such a bifunctional nanosized electrocatalyst with high stability and activity, which was also explained in detail from the aspect of defect chemistry. Highly efficient bifunctional oxygen electrocatalysts are indispensable to the development of highly efficient regenerative fuel cells and rechargeable metal-air batteries, which could power future electric vehicles. Although perovskite oxides are known to have high intrinsic activity, large particle sizes rendered from traditional synthesis routes limit their practical use due to low mass activity. We report the synthesis of nano-sized perovskite particles with a nominal composition of L ax(Ba0.5Sr0.5)1-xCo0.8Fe0.2O3-d (BSCF), where lanthanum concentration and calcination temperature were controlled to influence oxide defect chemistry and particle growth. This approach produced a bifunctional perovskite electrocatalyst of ~50 nm size with supreme activity and stability for both the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). The electrocatalyst preferentially reduced oxygen to water (<5 % peroxide yield), exhibited more than 20 times higher gravimetric activity (A/g) than IrO2 in an OER half-cell test (0.1 M KOH), and surpassed the charge/discharge performance of Pt/C (20 wt%) in a zinc-air full cell test (6 M KOH).Our work provides a general strategy for designing perovskite oxides as inexpensive, stable and highly active bifunctional electrocatalysts for future electrochemical energy storage and conversion devices.The world-wide interest in reducing the dependency on fossil fuels demands the development of energy storage systems with high power density from abundant materials, which would enable widespread industrial deployment of grid-scale renewable energy systems, as well as the progressive advancement of...

La0.3(Ba0.5Sr0.5)0.7Co0.8Fe0.2O3d is a promising bifunctional perovskite catalyst for the oxygen reduction reaction and the oxygen evolution reaction. This catalyst has circa 10 nm-scale rhombohedral LaCoO3 cobaltite particles distributed on the surface. The dynamic microstructure phenomena are attributed to the charge imbalance from the replacement of A-site cations with La3+ and local stress on Cosite sub-lattice with the cubic perovskite structure.

DC flash sintering of both pure and 0.5 mol. % Bi 2 O 3 -doped ZnO at a relatively high activating field of 300 V/cm has been investigated. It is demonstrated that even high-purity ZnO single crystals can "flash" at ~870 C. In comparison, flash sintering occurs at a substantially lower onset temperature of ~550 C in ZnO powder specimens, indicating the important roles of surfaces and/or grain boundaries. A model has been developed to forecast the thermal runaway conditions and the predictions are in excellent agreements with the observed onset flash temperatures, attesting that the flash starts as a thermal runaway in at least these ZnO based systems. Interestingly, enhanced grain growth is observed at the anode side of the pure ZnO specimens with an abrupt change in the grain sizes, indicating the occurrence of electricpotential-induced abnormal grain growth. With a large current density, the growth of aligned hexagonal single-crystalline rods toward the anode direction is evident in the ZnO powder specimen. Moreover, Bi 2 O 3 doping defers the onset of flash sintering, which can be explained from the formation of space charges at grain boundaries, and it homogenizes the microstructure due to a liquid-phase sintering effect. The key scientific contributions of this study include the development of a model to predict the thermal runaway conditions that are coincident with the observed onset flash sintering temperatures, the clarification of how flash starts in ZnO based specimens, and the observation and explanation of diversifying phenomena of sintering and microstructural development under applied electric currents.

Grain growth in 8 mol% Y 2 O 3 -stabilized zirconia ceramics (8YSZ) under an electric current has been investigated. Enhanced grain growth on the cathode side starts at 1150°C, well below the conventional sintering temperature, while grain growth is dormant on the anode side until 1400°C. In fully dense samples, the grain size undergoes an abrupt transition, differing by a factor of more than 10 on the two sides. Porous samples also experience faster densification on the cathode side, but grain growth is postponed until full density is first reached. Estimated grain boundary diffusivity on the cathode side has an apparent activation energy about 1 eV lower than that of normal grain boundary diffusion. These results are attributed to supersaturated oxygen vacancies accumulated on the cathode side, causing cation reduction that lowers their migration barrier.