Characteristics of electrolyte supported micro-tubular solid oxide fuel cells with GDC-ScSZ bilayer electrolyte

Abstract

In this study, a gadolinia-doped ceria (GDC)-supported micro tubular SOFC (T-SOFC) was fabricated using extrusion and dip-coating techniques (Cell A). The effects of inserting a scandium-stabilized zirconia (ScSZ) layer as an electron blocking layer between the GDC layer and the GDC-Ni anode layer were also explored (Cell B). The microstructures and electrochemical performances of Cell A and Cell B were investigated and compared. The layer thicknesses of the GDC and ScSZ bi-layer electrolytes were approximately 285 μm and 8 μm respectively. With the inserted ScSZ layer, both the ohmic resistance and the polarization resistance significantly increased at all the operating temperatures. The increase in the ohmic resistance of Cell B was predominantly due to the interfacial resistance, while the substantial escalation in the polarization resistance was mainly because of the low bulk oxygen diffusion process in the ScSZ layer and the smaller charge transfer processes occurring at the interfaces. The OCV of Cell B showed a slight decrease from 1.06 to 0.98 V and that of Cell A experienced an obvious decline from 0.92 to 0.76 V as the temperature rose from 650 to 800 °C. The ScSZ layer of Cell B successfully inhibited the OCV loss caused by the electronic conduction in GDC. The maximum power densities (MPDs) of Cell A at 650, 700, 750, and 800 °C were 0.20, 0.27, 0.33, and 0.36 Wcm−2, and those of Cell B 0.16, 0.23, 0.32, and 0.42 Wcm−2. The MPD of Cell B was improved at temperatures above 750 °C but remained inferior to that of Cell A below 750 °C. This is due to the fact that, as operating temperature increased above 750 °C, the benefit of the higher OCV in Cell B surpassed the deficiency of the higher cell resistance, thereby leading to a higher MPD.