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 La0.6Sr0.4Co0.8Fe0.2O3–x (LSCF)-infiltrated Ce0.9Gd0.1O1.95 (GDC) solid oxide fuel cell (SOFC) cathodes. Both coated and uncoated cathodes displayed initial 650 °C polarization resistance (Rp) values of 0.09 ± 0.03 Ω cm2. However, improved stability was observed for cells with zirconia overcoats ≤5 nm thick. Specifically, 1000 h, symmetric cell, open-circuit, 650 °C Rp degradation rates decreased from 45%/kh for uncoated LSCF-GDC nanocomposite cathodes (NCCs) to 28%/kh, 18%/kh, and 12%/kh 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 Rp degradation rates of 87%/kh. 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 h 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 “cleanup” 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