Effect of Surface Defect Engineering on Proton Conductivity in Yttrium-Doped Barium Zirconate Thin Films

Yttrium-doped barium zirconate (BZY) has been considered as a potential electrolyte candidate for intermediate-to-low temperature protonic ceramic fuel cell applications. However, the transport properties of BZY are often limited by the formation of highly resistive space charge zones at lattice discontinuities, such as lattice defects and surfaces. Unlike lattice defects, how to reduce the space charge effects at surfaces remains less explored. In this regard, surface defect engineering can be a meaningful way to regulate the proton transport of BZY by tailoring the space charge distribution close to the surface. Here, the Ar and/or O2 plasma was used to prepare BZY thin films with different levels of surface defects. The results of electrochemical impedance spectroscopy and detailed structural characterization suggest that the plasma treatment is effective in improving the proton conductivities and lowering the activation energy of BZY thin films through the generation of negatively charged barium vacancy defects and the enrichment of yttrium dopants on the surface.