Use of gaseous Cr species to diagnose surface and bulk process for O2 reduction in solid oxide fuel cells

Oxygen reduction reactions on Sr-doped LaMnO3 (LSM), Sr-doped La(Co,Fe)O-3 (LSCF) and Pt electrodes have been investigated in the absence and presence of gaseous Cr species at 900 degreesC in air. Gaseous Cr species were introduced by using chromia-forming alloy interconnect in contact with the electrode. In the presence of gaseous Cr species, the electrode processes for the O-2 reduction on LSM and Pt electrode were significantly inhibited while on LSCF electrodes, the inhibiting effect was much smaller. It has been shown that gaseous Cr species primarily inhibited the electrode surface process of the O-2 reduction reaction and the inhibiting effect can be quantitatively related to the oxygen diffusion coefficient of the electrode material. The results demonstrated that gaseous Cr species can be used to distinguish between the surface and bulk process kinetics for the O-2 reduction reaction under solid oxide fuel cells operation conditions.