Oxygen Transport Bulk or Surface

In a porous electrode, reaction takes place most easily at the gas—electrodeelectrolyte boundaries (triple-phase boundary, TPB). Oxygen adsorbed on the electrode must be transported to the electrolyte through the surface or bulk diffusion. Bulk diffusivity has been studied for various perovskites and related oxides. 

Kawada et al. [12] attempted to obtain the surface diffusion coefficient on an oxide electrode by measuring the surface oxygen potential gradient under current flow. An oxygen potential microprobe was fabricated by coating a porous yttrium-stabilized zirconia (YSZ) layer on a tip of a thin Pt-Rh wire probe (TA Instruments thermal probe) (Fig. 7.4). They estimated the surface diffusion coefficient on Lao.8Sro,2Mn03 to be around 10 at 700 C. Due to the difficulties in experimental setup, uncertainties remained in the obtained values. Further studies are necessary to clarify the contribution of surface diffusion. 

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