Our research seeks to understand and design dynamic behavior in a class of inorganic materials called “solid state ionics.” These materials enable carbon-neutral energy technologies including fuel/electrolysis cells and batteries, which store and convert energy between chemical and electrical forms cleanly. In order to enable widespread deployment of these technologies, the efficiencies/rates and lifetimes must be improved. Instead of trial-and-error approaches, we develop the scientific foundation that enables us to engineer key materials properties controlling energy conversion/storage efficiency and lifetime: 1) chemical expansivity, 2) ionic/electronic conductivity, and 3) interfacial reaction kinetics. These properties are governed by atomic-scale anomalies in the materials, so we uncover design principles for behavior through the lens of defect chemistry. To achieve our vision of “defects by design,” our approach comprises 5 pillars: a) precise synthesis with defect-level control, b) in situ characterization of model materials in controlled temperature, gas atmosphere, illumination, and electric fields, c) new frontiers of defect description beyond the traditional focus on dilute, bulk equilibrium, d) data-driven, high-throughput materials search and analysis, and e) coupled behavior. Our recent work has sought to uncover and leverage the operando coupling among electrical, chemical, mechanical, and optical states of solid-state-ionic materials, which is essential to tailor the key properties for improved device performance.

Our recent work has been focusing on development of design principles for high anion/cation conductivity, fast oxygen/steam surface exchange kinetics, and low chemical expansivity in ceramics that “breathe.” We measure surface oxygen and proton exchange kinetics on model thin films fabricated by pulsed laser deposition, using a novel optical transmission relaxation technique and in situ ac-impedance spectroscopy. Controlled variation of overall film defect chemistry, outermost surface chemistry, orientation, crystallinity, and microstructure has enabled a better understanding of the relative importance of each. We study chemical expansion behavior across multiple length scales using in situ X-ray and neutron diffraction, X-ray absorption spectroscopy, thermogravimetric analysis, and dilatometry, with comparison to atomistic computational simulations. Such studies have enabled identification of structural and chemical factors that can be applied to tailor chemical expansion behavior. We apply ac-impedance spectroscopy, equivalent circuit analysis, and microstructure models like the nano-Grain-Composite Model to evaluate and separate local interface/bulk ionic and electronic transport and polarization in bulk ceramic, thin film, heterostructured, and nanostructured materials. Overall, approaches to lower the chemical expansion coefficients (for durability) and increase the surface exchange kinetics and ionic/electronic transport (for efficiency) are being actively identified. Lastly, we apply high-throughput screening and combinatorial library synthesis/characterization to expedite discovery of promising materials.