Georgia Institute of Technology Materials Science and Engineering

Tuesday, July 27, 2021, 12:00 PM,

Committee Members:

Prof. Meilin Liu, Advisor, MSE

Prof. Thomas Fuller, ChBE

Prof. Mark Losego, MSE

Prof. Matthew McDowell, ME/MSE

Prof. Preet Singh, MSE

“Enhancing the Stability and Performance of Solid Oxide Cells by Tailoring Surfaces and Interfaces through Surface Modification”

Abstract:

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. Wide spread use is limited by energy loss due to sluggish electrode reactions and inadequate durability of key materials for prolonged operation, causing increased system costs. This work focuses on improving the stability and performance of reversible solid oxide cells through surface modification of different interfaces within the cell.

The air electrode is one area of focus, as the kinetics of oxygen reduction and evolution reactions are notorious sluggish, resulting in large overpotentials and low energy efficiency. Further, the problem is often exacerbated by reactions with contaminates commonly encountered in ambient air (e.g., H2O and CO2) and from other cell components (e.g., Cr), leading to degradation in performance over time. To combat these problems, a surface sol-gel (SSG) process will be developed to achieve layer-by-layer deposition of catalytically active catalysts (e.g., PrOx and BaO) on the surface of a porous air electrode, decreasing the polarization resistance and increasing the stability of the electrode. The advantages of the SSG process over conventional surface modification methods  include excellent control of the composition, thickness, uniformity, and conformality of the coatings. Development of the SSG surface modification will focus on the fabrication and analysis of the catalyst coating, determining optimal catalyst compositions and morphologies for high performing cells. The surface modification will be evaluated with scanning electron microscopy (SEM), x-ray diffraction (XRD), transmission electron microscopy (TEM), and quartz crystal microbalance, while the electrochemical performance of catalyst-coated electrodes will be evaluated with electrochemical impedance spectroscopy (EIS). The optimized surface modifications (including materials and coating processes) will finally be demonstrated on working single cells.

The interface between the electrolyte and the air electrode is the other area of focus, where the electrolyte experiences degradation due to high concentrations of water present during water electrolysis. Here, a dense and highly stable electrolyte composition is deposited on the surface of the bulk electrolyte prior to the application of the electrode, creating an electrolyte protection layer. This layer prevents reactions between the highly conductive but less stable bulk electrolyte material and water present in the air electrode.  For this protection layer, extensive development will be performed to determine the fabrication techniques and parameters required to fabricate the desired films. XRD, SEM, EDX, and EIS will be utilized to investigate the structure, composition, and electrochemical performance of the surface modified electrolytes. Finally, the optimized electrolyte protection layer will be demonstrated in solid oxide electrolysis cells.

Overall, this work will demonstrate the power of surface modification in enhancing both performance and durability of revisable solid oxide cells. Modification of the air electrode surface will improve performance and stability by catalyzing the ORR and protecting the electrode from degradation. Modification of the electrolyte/electrode interface will protect the electrolyte from degradation in high concentrations of steam. Thus the performance and stability of RSOCs will be improved by tailoring the properties of the surfaces and interfaces.