Atomic Layer Deposited Zirconia Overcoats as On-Board Strontium Getters for Improved Solid Oxide Fuel Cell Nanocomposite Cathode Durability

Here, a flow type Atomic Layer Deposition (ALD) reactor was used to deposit 1-10 nm thick porous ZrO₂ overcoats within the pores of conventional La_0.6Sr_0.4Co_0.8Fe_0.2O_3-x (LSCF)-infiltrated Ce_0.9Gd_0.1O_1.95 (GDC) Solid Oxide Fuel Cell (SOFC) cathodes. Here, both coated and uncoated cathodes displayed initial 650 °C polarization resistance (R_p) values of 0.09 ± 0.03 Ω cm². However, improved stability was observed for cells with zirconia overcoats ≤ 5 nm thick. Specifically, 1000-hour, symmetric cell, open-circuit, 650 °C R_p degradation rates decreased from 45 %/khrs for uncoated LSCF-GDC Nano-Composite Cathodes (NCCs) to 28 %/khrs, 18 %/khrs, and 12 %/khrs for identical LSCF-GDC NCCs with 1, 2, and 5 nm of zirconia overcoat, respectively. In contrast, identical LSCF-GDC NCCs with 10 nm of zirconia overcoat displayed 650 °C R_p degradation rates of 87 %/khrs. Scanning Electron Microscopy and controlled atmosphere impedance tests showed no significant changes in the LSCF infiltrate particle size or microporosity gas concentration polarization resistance with 1000 hours of 650 °C aging. Instead, X-ray Photoelectron Spectroscopy indicated that zirconia overcoats decreased the amount of “surface Sr” on the LSCF, and X-ray Diffraction detected SrZrO₃ in samples with 5 or 10 nm thick zirconia overcoats. Hence, the lower degradation rates of LSCF-GDC NCCs with 1-5 nm thick zirconia overcoats were attributed to “clean up” of deleterious “surface Sr” from the LSCF surface via the formation of SrZrO₃, while the higher degradation rates of LSCF-GDC NCCs with 10 nm thick zirconia overcoats were attributed to the accumulation of excessive amounts of SrZrO₃ hindering oxygen incorporation into the LSCF.