Durability and Performance of High Performance Infiltration Cathodes

Abstract

The performance and durability of solid oxide fuel cell (SOFC) cathodes consisting of a porous Ce0.9Gd0.1O1.95 (CGO) infiltrated with nitrates corresponding to the nominal compositions La0.6Sr0.4Co1.05O3–δ (LSC), LaCoO3–δ (LC), and Co3O4 are discussed. At 600 °C, the polarization resistance, Rp, varied as: LSC (0.062 Ω cm2) < LC (0.079 Ω cm2) < Co3O4 (0.27 Ω cm2). High temperature X‐ray diffraction revealed a number of different phases in LSC and LC. The electrochemical performance of the LSC‐infiltrated CGO cathode was found to depend on the infiltrate firing temperature and is suggested to originate from a complex interplay between the formation, percolation, and surface area of electronically conducting and catalytically active phases. Simplified models that predict the Rp of LSC‐infiltrated CGO were applied and showed that the performance is not only characterized by the nanoscale size of the infiltrate but also from a better surface exchange property. A 450 h test of an LSC‐infiltrated CGO cathode showed an Rp with final degradation rate of only 11 mΩ cm2 kh–1. An SOFC with an LSC‐infiltrated CGO cathode tested for 1,500 h at 700 °C and 0.5 A cm–2 (60% fuel, 20% air utilization) revealed no measurable degradation.

Advances in Cathode Materials for Solid Oxide Fuel Cells: Complex Oxides without Alkaline Earth Metal Elements

“…[ 446 ] Recently, Samson et al directly infi ltrated Co 3 O 4 into a porous Ce 0.9 Gd 0.1 O 1.95 framework, and a surprisingly low ASR of 0.27 Ω cm 2 was obtained at 600 °C. [ 447,448 ] Under similar conditions, the ASRs of La 0.6 Sr 0.4 Co 1.05 O 3-δ and LaCoO 3-δ infi ltrated GDC electrolyte were 0.062 Ω cm 2 and 0.079 Ω cm 2 , respectively, which were just slightly better than that of the Co 3 O 4 infi ltrated GDC. The authors attributed the high performance of Co 3 O 4 infi ltrated electrode to the beneficial interplay between the GDC and Co 3 O 4 , which seemed to greatly enhance the surface exchange properties.…”

“…[ 442 ] Some other alkaline earth metal element free oxide materials were also tried with infi ltration method to prepare high-performance oxygen reduction electrodes. [443][444][445][446][447][448] With high electrical conductivity (≈190 S cm −1 ) and compatible TEC (12.2 × 10 −6 K −1 ) but low oxygen ionic conductivity, [ 443 ] the spinel Cu 1.25 Mn 1.75 O 4 phase was impregnated into an YSZ framework to form a new composite cathode, [ 444 ] and an infi ltration amount of 50 wt% was found to exhibit the lowest polarization resistance of 0.3 Ω cm 2 at 750 °C, which was much lower than 8.5 Ω cm 2 from a LSM infi ltrated YSZ cathode. In addition, the charge transfer process was likely to be the rate determining step at above 750 °C.…”

“…The authors attributed the high performance of Co 3 O 4 infi ltrated electrode to the beneficial interplay between the GDC and Co 3 O 4 , which seemed to greatly enhance the surface exchange properties. [ 447,448 ] …”

Reversible Decomposition of Secondary Phases in BaO Infiltrated LSM Electrodes—Polarization Effects

“…During the infiltration step, a material is added in the form of an aqueous precursor solution to an existing scaffold, where the desired material forms during subsequent conditioning of the electrode . An unintended consequence of this approach can be the formation of minor secondary phases, either from the infiltrate itself or from reactions between the infiltrate and the scaffold . Recent investigations on La 1− x Sr x CoO 3− δ (LSC)‐based electrodes have indicated that the presence of minor secondary phases may even improve electrode performance due to the formation of hetero‐interfaces .…”

“…An unintended consequence of this approach can be the formation of minor secondary phases, either from the infiltrate itself or from reactions between the infiltrate and the scaffold . Recent investigations on La 1− x Sr x CoO 3− δ (LSC)‐based electrodes have indicated that the presence of minor secondary phases may even improve electrode performance due to the formation of hetero‐interfaces . These and other studies of secondary phases often draw conclusions correlating electrode composition with performance based on ex situ studies and in operando electrochemical characterization.…”