RUI: Using graph theory measures to probe oxygen vacancy and proton conduction in perovskites and double perovskites

Mount Holyoke College, South Hadley MA

Investigators

Abstract

NONTECHNICAL SUMMARY The Division of Materials Research and the Chemistry Division contribute funds to this award, which supports theoretical research and education on the conduction properties of materials used in fuel- and solar cells. Limitations in the supply of fossil fuels, environmental considerations, and the relative inefficiency of burning fuel to produce electricity have sparked considerable efforts in developing alternative sources of energy. Combustion is inherently inefficient due to the number of energy transfer steps. Fuel cells avoid the entire combustion process by directly converting chemical energy into electricity, significantly increasing efficiency. Solar cells directly convert light energy into electrical energy and, while not as efficient as fuel cells, they make use of a renewable resource. Both processes emit significantly fewer pollutants than combustion and reduce dependence on petroleum products. A solid oxide fuel cell is comprised of two electron-conductive surfaces (electrodes) sandwiching a conductor (electrolyte) of ions. Electricity production is substantially determined by how fast the ions move through the electrolyte. In solar cells, electricity production is limited by missing oxygen atoms in the material, which comprise mobile atom-lattice defects. Overall, understanding ion or ion-defect motion through a material is important for optimizing the performance of these devices. This project will clarify how changes in structure near an ion or vacancy influence conduction pathways. Simulations of specific materials as well as the simulation methods developed in this project will be useful in furthering our knowledge and understanding of conduction, and help engineer more efficient conductors for use in fuel- and solar cells. This project will include training undergraduate women at Mount Holyoke College in computational chemistry, programming, and the associated mathematics. These undergraduates will attend the annual MERCURY conference organized for undergraduates doing research in computational chemistry by the MERCURY consortium, of which the PI is one of the founding members. An extension to the PI's Passport to Chemistry Adventure outreach program targeting high-school students will be developed and sent to the eleven western Massachusetts libraries participating in the program. TECHNICAL SUMMARY The Division of Materials Research and the Chemistry Division contribute funds to this award, which supports computational research and education on oxygen-vacancy and proton conduction in perovskites and double perovskites. Charged-defect conduction is essential to the functioning of many devices. For example, protons and oxygen vacancies are sometimes the main conductors in fuel-cell membranes; oxygen-vacancy transport is essential for oxygen reduction at the cathode of a fuel cell. Furthermore, band gaps in solar cells are sometimes tuned by oxygen-vacancy concentration. The project will further computational investigations to understand how charged-defect conduction paths in perovskite and double-perovskite materials change with lattice restructuring near the defect, as well as with charge-defect correlation during the conduction process. The project will extend the uses of the PI's defect conduction path finding methods and centrality measures based on time. Centrality measures will be used to not only predict traps, key nexuses, and pathways, but to also predict correlated motion including proton/proton correlation and proton/oxygen-vacancy correlation in acceptor-doped barium zirconate. Complementary techniques such as accelerated dynamics techniques on an empirical potential will be used to determine how well graph-theory-based methods work. This project will include training undergraduate women at Mount Holyoke College in computational chemistry, programming, and the associated mathematics. These undergraduates will attend the annual MERCURY conference organized for undergraduates doing research in computational chemistry by the MERCURY consortium, of which the PI is one of the founding members. An extension to the PI's Passport to Chemistry Adventure outreach program targeting high-school students will be developed and sent to the eleven western Massachusetts libraries participating in the program.