A comparative investigation of chromium deposition at air electrodes of solid oxide fuel cells

Deposition processes of chromium (Cr) species were investigated for the O2 reduction on (La,Sr)MnO3 (LSM), Pt and (La,Sr)(Co,Fe)O3 (LSCF) electrodes in the presence of chromia-forming alloy metallic interconnect at 900oC under air flow. For the reaction on LSM electrodes, deposition of Cr species preferentially occurred on the zirconia electrolyte surface, forming a distinct deposit ring at the edge of the LSM electrode while at LSCF electrodes, Cr species deposited on the electrode and electrolyte surface, forming isolated Cr particles. In contrast, there was no detectable deposition of Cr species either on the electrode or electrolyte surface for the O2 reduction reaction on Pt electrodes. The results clearly demonstrated that deposition of Cr species in solid oxide fuel cells is not an electrochemical reduction of high valent Cr vapor species to Cr2O3 in competition with O2 reduction. Cr deposition at SOFC cathodes is basically a chemical dissociation reaction and is controlled by the nucleation reaction between the nucleation agent and the gaseous Cr species. The nature of the nucleation agent strongly depends on the electrode material and impurities which may be introduced during electrode and electrolyte fabrication processes.