Oxygen activation over engineered surface grains on YDC/YSZ interlayered composite electrolyte for LT-SOFC

Abstract

This paper reports the role of surface grain boundaries in enhancing oxygen incorporation kinetics on oxide ion conducting yttria-doped ceria (YDC) ceramic electrolyte. Thin YDC interlayered (similar to 400 nm) YSZ composite electrolyte was successfully fabricated by pulsed laser deposition (PLO) on the cathode side of 100 mu m-thick polycrystalline substrate. Oxygen isotope exchange experiment was conducted employing secondary ion mass spectrometry (SIMS) with high spatial resolution (50 nm). Surface mapping result of (18)O/(16)O shows that high activity at surface grain boundary regions indicating that the grain boundary regions are electrochemically active for oxygen incorporation reaction. In addition, fuel cell current-voltage measurements and electrochemical impedance spectroscopy study were performed in the temperature range of 350-450 degrees C on surface-engineered electrode-membrane assemblies (MEA) having different YDC surface grain sizes. Results from both dc and ac measurements confirm again that fuel cell MEAs having smaller surface grain size show better performance than large grain surfaces. Up to 4-fold increase was observed in power density and correspondingly lower electrode interface resistance. The collective results of SIMS and electrochemical measurements indicate that the YDC grain boundary regions at the cathode side are electrochemically active for oxygen surface kinetics. The results of this study provide an opportunity and incentive for designing high performing LT-SOFCs by surface engineering of YSZ electrolyte with nano-granular, catalytically superior thin YDC cathodic interlayers.