Probing local electrochemical activity within yttria-stabilized-zirconia via in situ high-temperature atomic force micro
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Carlos R. Pérez Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
Tae-Sik Oh, Rainer Küngas,b) and John M. Vohs Department of Chemical and Biomolecular Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
Dawn A. Bonnell Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
Stephen S. Nonnenmanna) Department of Mechanical and Industrial Engineering, University of Massachusetts, Amherst, Engineering Lab I, Amherst, Massachusetts 01003, United States (Received 20 June 2014; accepted 15 September 2014)
Considerable interest in understanding interfacial phenomena occurring across nanostructured solid oxide fuel cell (SOFC) membrane electrode assemblies has increased demand for in situ characterization techniques with higher resolution. We briefly outline recent advancements in atomic force microscopy (AFM) instrumentation and subsystems in realizing real time imaging at high temperatures and ambient pressures, and the use of these in situ, multi-stimuli probes in collecting local information related to physical and fundamental processes. Here we demonstrate direct probing of local surface potential gradients related to the ionic conductivity of yttria-stabilized zirconia (YSZ) within symmetric SOFCs under intermediate operating temperatures (500–600 °C) via variable temperature scanning surface potential microscopy (VT-SSPM). The conductivity values obtained at different temperatures are then used to estimate the activation energy. These locally collected conductivity and activation energy values are subsequently compared to macroscopic electrochemical impedance results and bulk literature values, thus supporting the validity of the approach. I. INTRODUCTION
Excellent chemical to electrical conversion efficiency,1 fuel flexibility,2 and relatively high power output3 make solid oxide fuel cells (SOFCs) a viable alternative resource to help alleviate increasing global energy demands. To ensure reaction efficiencies and sufficient electrolyte ionic conductivity, SOFCs typically operate in a temperature range of 500–1000 °C, which leads to high degradation rates and slow startup times.4 One crucial limitation hindering the reduction of operating temperature is the low ionic conductivity of the electrolyte at lower temperatures. Yttria-stabilized zirconia (YSZ) is the most popular electrolyte ceramic owing to its pure oxygen ion conduction over very broad temperature and oxygen partial pressure a)
Address all correspondence to this author. e-mail: [email protected] b) Current address: Topsoe Fuel Cell A/S, Nymøllevej 66, DK-2800 Kgs., Lyngby, Denmark. DOI: 10.1557/jmr.2014.295
ranges5 as well as the low cost of manufacturing the material. A maximum conductivity value of 101 S/cm is observed for bulk YSZ at a temperature as high as 1000 °C.68 In recent years, significant effort has focused on reducing the operating temperature of SOFCs throu
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