Elimination of Surface Adsorbates on Gadolinium Doped Ceria for Electrochemical Strain Microscopy

Use of solid oxide fuel cells for the conversion of electrochemical energy has a number of advantages over current technologies.  These systems offer high efficiencies for energy conversion, a choice of inexpensive hydrocarbon fuels, and environmentally friendly operation.  The mechanisms which govern the functionality of these materials may be elucidated using scanning probe microscopy based techniques.  However, the formation of surface adsorbates complicates their use.  One such technique, electrochemical strain microscopy, quantifies the mechanical response of a surface resulting from the application of an AC bias through a cantilever.  We have used this methodology in conjunction with a number of strategies to understand the behavior of gadolinium doped ceria, a widely used electrolyte material, while circumventing the issues that arise at the material surface.  Sections of the ceria sample were ablated using a focused ion beam to expose a surface previously shielded from the ambient environment, then subsequently studied with electrochemical strain microscopy.  We find that the ablation process produced a surface morphology exhibiting an enhanced electromechanical response similar to polycrystalline ceria at the grain boundaries that has previously been attributed to the space-charge effect.  Thermogravimetric analysis, between 20°C and 400°C, revealed a plateau in weight around 200°C and 350°C, suggesting these are points that surface adsorbates may be removed from the electrolyte.  We are currently studying the ablated regions at 250°C in a controlled environment to analyze the strain response under these conditions.