Mechanistic Studies of High Temperature Oxygen Electrodes with Simultaneous High Activity and Stability

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TECHNICAL SUMMARY:Materials research for the advanced energy systems (e.g. fuel cells and batteries) has been driven by the recognition that multifunctionalities in constituent materials are needed in order to achieve higher power density, faster kinetics, and larger energy density. For instance, mixed electronic and ionic conducting oxides are used as oxygen reduction electrode - cathode. In an active cathode, both oxygen ions and electron holes move out of the electrode in a substantial flux, which creates a gradient in the electronic transference number with position inside grains that form the electrode, resulting in local oxidation or reduction. As a consequence, cation kinetic demixing takes place, along with possible phase transition, amorphorization, or even solid-state reaction. This Solid State and Materials Chemistry supported program is to investigate the evolution of electrode materials under electrochemical potential, particularly cation kinetic demixing. Of particular interest will be the electrodes based on (1) perovskite family oxides with presence of oxygen vacancies, (2) perovskite family oxides with presence of cation vacancies, and (3) Ruddlesden-Popper type complex oxides with presence of oxygen interstitials. The research concentrates on the investigation of charge exchange and transport in the presence of external loads to elucidate the role of electrochemical potential gradients on oxygen reduction NON-TECHNICAL SUMMARY:Next generation of fuel cells and batteries requires higher power, faster kinetics, and larger energy density, which necessitate the use of complex materials to achieve multifunctionalities and activity. The dichotomy is that the active constituents are often not stable; and the stable components are not very active. This project, supported by the Solid State and Materials Chemistry program in the National Science Foundation is to investigate the origin of this activity/stability conjugation. The knowledge gained in this program will be translated into design guidelines of new electrodes with simultaneously high efficiency and high performance stability for fuel cells and batteries, so that they can store more energy, recharge faster, and their performance degrades more slowly. This will be accomplished through systematically theoretical and experimental studies, along with active recruitment of four graduate/undergraduate students to build a diverse group that includes women and members of underrepresented minority groups. The students will be trained to be the future leading researchers in the area of energy materials and solid-state electrochemistry. In addition, the chemistry teachers from local high schools will be aligned with the research experience to transfer demonstrations and experiments into their classrooms, and to promote high school students to enter the science disciplines.