Effect of Water Adsorption on Conductivity in Epitaxial Sm0.1Ce0.9O2-δ Thin Film for Micro Solid Oxide Fuel Cells Applications

The growing demand for miniaturized systems for energy conversion and storage has prompted extensive research aimed at fabricating electrochemical devices, such as solid oxide fuel cells for portable applications (μ-SOFCs). This goal requires reducing the operating temperature by producing components as thin films. Nowadays, there is a huge gap between macroscopic device-level electrochemical techniques and microscopic electrochemical techniques to study atomic-level diffusion and transport process.

Recently, a new scanning probe microscopy technique, named electrochemical strain microscopy (ESM) has been developed in order to study the structure and physical properties on the microscopic level. After applying the dc bias to the tip, the oxygen vacancies and protons injection or annihilation can occur, depending on the working conditions and the material properties. The subsequent oxygen ion or proton movement results in localized strain under the tip, which can be detected through dynamic surface displacement.[1] This technique can be very useful to investigate the electrochemical activity at the nano-scale in ionic or proton conductors.

In this presentation, I will discuss several examples of high-resolution studies of pure and Sm-doped CeO₂ epitaxial thin films surfaces which allowed to understand water interaction and conductivity mechanisms on the nanoscale. In particular I will show:

(1) The effect of the different doping concentrations on Sm_1-xCe_xO_2-a in terms of different transport mechanism and  different type of charge carriers [2].

(2) The role of granularity and porosity on the oxygen ion or proton conduction 20% Sm doped CeO₂ nanocrystalline films [3].

(3) The bias dependent mechanisms of irreversible cathodic and anodic processes on a pure CeO₂ film.[4]

 [1] A. Kumar et al. Nature Chemistry, 2011, 3,707.

[2] Nan Yang et al. ACS Nano DOI: 10.1021/nn505345c (2014)

[3] S. Doria, Nan Yang, et al. Appl. Phys. Lett. 103, 171605 (2013)

[4] Nan Yang et al. Nanotechnology 25, 075701 (2014).