(Georgia Institute of Technology, 2022-07-21)
Kane, Nicholas John
Reversible solid oxide cells (RSOCs) are an extremely promising solution for efficient electric grid storage; however, breakthroughs in materials innovation are required for RSOCs to be implemented on a large scale, as several challenges remain to be fully resolved. The air electrode is one area of focus, as the kinetics of oxygen reduction and evolution reactions are notoriously sluggish, resulting in low energy efficiency. To combat these problems, a surface sol-gel (SSG) process was developed to achieve layer-by-layer deposition of catalytically active catalysts (e.g., PrOx and BaO) on the surface of a porous air electrode, reducing the polarization resistance while increasing the stability of the electrode. For example, the application of an SSG coating of PrOx to a La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) electrode reduced the polarization resistance from 1.136 to 0.117 Ω cm2 at 600 °C and the degradation rate from 1.13×10-3 to 2.67×10-4 Ω cm2 h-1 at 650 °C. The interface between the electrolyte and the air electrode is the other area of focus, where the electrolyte experiences degradation due to exposure to high concentrations of water during water electrolysis. Here, a dense and highly stable electrolyte composition, BaHf0.8Yb0.2O3 (BHYb), was deposited on the surface of a more conductive electrolyte, BaZr0.1Ce0.7Y0.1Yb0.1O3-δ, creating a bilayer electrolyte. The epitaxial, dense, and uniform BHYb layer is effective in preventing electrolyte degradation against high concentrations of steam and CO2 present in the air electrode, greatly enhancing the chemical stability while maintaining high electrochemical performance.