Controlling Concentration and Nature of Oxygen Defects in Layered Cuprate-Based Materials by Electrical Bias

Both the nature and concentration of oxygen defects in oxide materials can have a significant impact on their physical and chemical properties, as well as key interfacial reaction kinetics such as oxygen exchange with the atmosphere. Mostcommonly,thedesiredoxygendefect concentration, or equivalently oxygen nonstoichiometry, is attained in a given material by controlling the oxygen partial pressure and temperature in which it is equilibrated or annealed. This approach, however, is limited by the range of oxygen partial pressures readily experimentally achievable and requires knowledge of the applicable defect chemical model.

In this study, we fine-tune oxygen defect concentrations in promising rare earth cuprate (RE2CuO4: RE = rare earth) solid oxide fuel cell (SOFC) cathode materials by application of electrical potentials across a yttria-stabilized zirconia (YSZ) supporting electrolyte. These layered perovskites can incorporate both oxygen interstitials and vacancies, thereby broadening the range of investigations. Here, we show a strong correlation between oxygen nonstoichiometry values (which are determined by in situ measurement of chemical capacitance) and oxygen surface exchange kinetics (which is inversely proportional to the area-specific-resistance). Both types of oxygen defects -- interstitials and vacancies -- dramatically enhance surface kinetics. These studies are expected to provide further insight into the defect and transport mechanisms that support enhanced SOFC cathode performance.