Process development of BaZrO3-BaCeO3 based electrolytes for proton-conducting solid oxide fuel cells
Date of Issue2017-04-04
School of Mechanical and Aerospace Engineering
Low-temperature solid oxide fuel cells (LT-SOFCs) have attracted signiﬁcant attention because of their better long-term stability, shorter start-up times and potential applications in small-scale portable devices. Proton-conducting ceramics are regarded as promising electrolyte materials for LT-SOFCs since they show smaller activation energy for proton conduction and larger ionic conductivities at low temperature range than conventional oxygen-ion conducting electrolytes. However, the high processing temperatures and the lack of economical and scalable fabrication method for proton-conducting electrolytes have restricted the commercial development of proton-conducting SOFCs. To address these problems, this thesis aims at developing economical and scalable methods to fabricate BaZrO3-BaCeO3 based proton-conducting electrolytes at reduced processing temperatures. In the first part, a single-step slurry spray coating method has been developed to prepare proton-conducting BaCe 0.7Zr0.1Y0.2O3 (BCZY) membranes on the pre-annealed porous anode substrates. The effects of sintering temperature on the electrolyte membrane and anode microstructure, proton conductivity of the resulted films, and their fuel cell performances have been investigated. Dense BCZY membranes with improved anode microstructure and high proton conductivity have been obtained at reduced temperature. SOFCs using spray-coated electrolyte films gave stable OCV and good performance. In the second part, chemical solution deposition (CSD) method has been proposed to realize a scalable and cost-effective fabrication of sub-micrometer scale proton-conducting electrolyte thin film. Different chemical solution synthesis routes and heat treatment processes have been investigated to obtain dense and crack-free BaZr0.8Y0.2O3 (BZY) thin film. The crystallinity, microstructure and gas tightness of BZY thin films have been studied. Compared to the sophisticated vacuum-based thin film deposition techniques, this cost effective and scalable CSD method is a promising way for mass production of electrolyte thin films for micro-SOFCs.