Georgia Institute of Technology Materials Science and Engineering

Committee Members: 

Prof. Meilin Liu, Advisor, MSE

Prof. Hamid Garmestani, MSE

Prof. Preet Singh, MSE

Enhancing Air Electrode Performance of Solid Oxide Cells by Surface Modification

Abstract:

Proton conducting reversible solid oxide cells (P-rSOCs) offer an efficient and clean option for energy storage and conversion. However, one issue holding back this renewable technology is the sluggish oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) kinetics that take place at the air electrode. The air electrode in a P-rSOC is also subject to harsh high steam environments that can cause degradation over time. Catalyst infiltration into the air electrode offers a possible solution to each of these issues. Several catalyst candidates were investigated using the state-of-the-art double perovskite air electrode material, PrBa0.8Ca0.2Co2O5+δ (PBCC), as the air electrode backbone. Symmetrical cells with catalyst coated PBCC electrode were primarily used to screen catalyst solutions and isolate the air electrode performance. Electrochemical impedance spectroscopy (EIS) was utilized to measure the electrochemical performance, as well as the long-term stability of catalyst infiltrated symmetrical cells under various testing conditions containing either steam and/or Cr contaminants. Electrochemical performance of single cells with a catalyst coated PBCC electrode were measured in both the fuel cell mode and the electrolysis cell mode. X- ray diffraction (XRD), Scanning electron microcopy (SEM) and Raman spectroscopy were conducted to characterize surface morphology changes and to gain understanding of surface mechanisms causing degradation to the air electrode during testing.  Symmetrical cells infiltrated with a PrCoO3-δ catalyst demonstrated excellent stability and electrochemical performance (as low as 0.147 Ω cm2 and no degradation across 500 hrs) against various sources of Cr contaminations at steams concentrations as high as 30% in 600 °C. Single cells infiltrated with PrCoO3-δ  that were run in fuel cell mode exhibit a power density of 2.02 W cm-2 at 650°C, a 35.5% increase in performance from the bare single cells. When run in electrolysis mode these same infiltrated single cells demonstrate a current density of -3.22 A cm-2 at 650 °C, a 22.4% improvement from the performance of the bare PBCC single cells.  The PrCoO3-δ infiltrated proton conducting reversible single cell was among the best performing P-rSOCs reported in literature.