(400l) Atomically Deposited Sintering Aids: Assessing the Effects of Al2O3 Particle ALD on the Sintering and Performance of SOFC Electrolytes
Yttria-stabilized cubic zirconia (YSZ) is the most-common electrolyte material for solid oxide fuel cells (SOFC) due to its reasonable oxygen-ion conductivity and chemical stability across a wide range of environments. To achieve suitable ionic conductivity, YSZ electrolytes must be near theoretical density; this necessitates high sintering temperatures, often exceeding 1450 °C. This high sintering temperature limits the viability of low-cost one-step sintering during manufacturing and thus increases the cost of SOFC fabrication. Previous researchers have successfully lowered the required YSZ sintering temperature through incorporation of aluminum oxide (Al2O3) particles with the YSZ. While this technique has proven to be successful in reducing the sintering temperature, the presence of Al2O3 in the electrolyte can reduce YSZ ionic conductivity. In this work, we report on the use of atomic layer deposition (ALD) to precisely and conformally coat individual YSZ particles with the desired amount of Al2O3. Constant-rate-of-heating (CRH) experiments were conducted using a horizontal push-rod dilatometer to extract the activation energy of sintering in the initial stage and also gain mechanistic insights into the active diffusion mechanisms as a function of ALD film thickness. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were used to characterize the as-deposited thin Al2O3 films and the effects of the Al2O3 films on grain growth and microstructure during densification. Finally, electrochemical impedance spectroscopy was used to characterize the ionic conductivity of dense YSZ electrolytes.