Silicon Contamination of the Praseodymium Doped Ceria Oxygen Surface Exchange Coefficient

Abstract

Chemical oxygen surface exchange coefficients are used to quantify and rank the performance of oxygen exchange catalysts used in solid oxide fuel cell, solid oxide electrolysis cell, oxygen separation membrane, catalytic converter, and other oxygen-exchange-enabled devices. Unfortunately, during the manufacture and operation of these devices it is easy to introduce siliceous contaminants that degrade their oxygen exchange performance. Surprisingly, despite the well-known negative impact siliceous impurities have on the oxygen transport properties of ceria-based materials, quantitative measurements of how siliceous impurities impact the chemical oxygen surface exchange coefficient of praseodymium doped ceria are largely absent from the literature. In this work, the crystal structure, film thickness, surface composition, bulk composition, and chemical oxygen exchange coefficient of (100)-oriented PCO thin films with, and without, surface silica contaminants were evaluated via X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), X-ray Photoelectron Spectroscopy (XPS), Secondary Ion Mass Spectroscopy (SIMS), and Curvature Relaxation (κR) experiments, respectively. The results show that siliceous surface phases only a few nanometers thick are capable of (1) reducing the PCO chemical oxygen surface exchange coefficient by approximately 3 orders of magnitude and (2) approximately doubling the activation energy for oxygen exchange.