Europium-Doped Ceria Nanowires as Anode for Solid Oxide Fuel Cells

Shuai Li,Liquan Chen,Xia Lu,Yusheng Zhao,Siqi Shi,Zhaoxiang Wang

doi:10.3389/fchem.2020.00348

Abstract

CeO2-based materials have been studied intensively as anodes for intermediate temperature solid oxide fuel cells (IT-SOFCs). In this work, pristine and europium (Eu)-doped CeO2 nanowires were comprehensively investigated as anode materials for IT-SOFCs, by a combination of theoretical predictions and experimental characterizations. The results demonstrate: (1) Oxygen vacancies can be energetically favorably introduced into the CeO2 lattice by Eu doping; (2) The lattice parameter of the ceria increases linearly with the Eu content when it varies from 0 to 35 mol.%, simultaneously resulting in a significant increase in oxygen vacancies. The concentration of oxygen vacancies reaches its maximum at a ca. 10 mol.% Eu doping level and decreases thereafter; (3) The highest oxygen ion conductivity is achieved at a Eu content of 15 mol.%; while the 10 mol.% Eu-doped CeO2 sample displays the highest catalytic activity for H2-TPR and CO oxidization reactions. The conducting and catalytic properties benefit from the expanded lattice, the large amount of oxygen vacancies, the enhanced reactivity of surface oxygen and the promoted mobility of bulk oxygen ions. These results provide an avenue toward designing and optimizing CeO2 as a promising anode for SOFCs.

Highlights

Solid oxide fuel cells (SOFCs) are a kind of high-efficiency and environmental-friendly energy conversion device (Steele and Heinzel, 2001; Brandon et al, 2003; Ormerod, 2003; Choudhury et al, 2013)
Traditional SOFCs based on yttrium stabilized zirconium (YSZ) electrolytes have to work above 800◦C due to the low conductivity of the electrolytes and the low catalytic activity of the electrodes (Jacobson, 2010; Coduri et al, 2018; Sreedhar et al, 2019)
Before the experimental synthesis and characterization of pristine and Eu-doped CeO2 samples, first-principle density functional theory (DFT) simulations were performed to explore the formation mechanism and formation energy of oxygen vacancies in the fluorite CeO2 structure with/without dopants, which could be used as a good guide for the subsequent experimental investigations

Summary

Introduction

Solid oxide fuel cells (SOFCs) are a kind of high-efficiency and environmental-friendly energy conversion device (Steele and Heinzel, 2001; Brandon et al, 2003; Ormerod, 2003; Choudhury et al, 2013). 10 mol.% Eu doping level and decreases thereafter; (3) The highest oxygen ion conductivity is achieved at a Eu content of 15 mol.%; while the 10 mol.% Eudoped CeO2 sample displays the highest catalytic activity for H2-TPR and CO oxidization reactions. - The oxygen vacancies were indicated by theoretical calculations, and quantitatively determined by Raman spectroscopy of the Eu-doped CeO2 samples.

Results

Conclusion