Cobalt-free composite cathode for SOFCs: Brownmillerite-type calcium ferrite and gadolinium-doped ceria

Abstract

A cobalt-free composite Ca2Fe2O5 (CFO) - Ce0.9Gd0.1O1.95 (GDC) is investigated as a new cathode material for intermediate-temperature solid oxide fuel cells (IT-SOFCs) based on a Gd0.1Ce0.9O1.95 (GDC) electrolyte. The cathodes had brownmillerite structure with x wt.% Gd0.1Ce0.9O1.95 (GDC) - (100 x) wt.% Ca2Fe2O5 (CFO), where x = 0, 10, 20, 30 and 40. The effect of GDC incorporation on the thermal expansion coefficient (TEC), electrochemical properties and thermal stability of the CFO-GDC composites is investigated. The composite cathode of 30 wt.% GDC - 70 wt.% CFO (CG30) coated on Gd0.1Ce0.9O1.95 electrolyte showed the lowest area specific resistance (ASR), 0.294 Omega cm(2) at 700 degrees C and 0.122 Omega cm(2) at 750 degrees C. The TEC of the CG30 cathode was 13.1 x 10(-6) degrees C-1 up to 900 degrees C, which is a lower value than for CFO alone (13.8 x 10(-6) degrees C-1). Long-term thermal stability and thermal cycle testing of CG30 cathodes were performed. Stable ARS values were observed during both tests without delamination at the cathode-electrolyte interface. An electrolyte-supported single cell with a 300-mu m-thick GDC electrolyte and an anode-supported single cell with similar to 10-mu m-thick yttria-stabilized zirconia (YSZ) with a GDC buffer layer attained maximum power densities of 395 mW cm(-2) at 750 degrees C and 842 mW cm(-2) at 800 degrees C, respectively. The unique composite composition of CG30 demonstrates enhanced electrochemical performance and good thermal stability for IT-SOFCs. Copyright (c) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.