Novel processing of La0.58Sr0.4Co0.2Fe0.8O3−δ cathodes for metal-supported fuel cells

Abstract

Metal-supported solid oxide fuel cells (MSCs) have gained high attention as they offer a possibility to utilize solid oxide fuel cells (SOFCs) in mobile applications such as auxiliary power units in heavy duty vehicles. Cathode reliability is one of the main issues of MSC development, since cathodes tend to degrade rapidly after being in-situ activated during onset of the stack operation. In the present study, a novel sintering route for La 0.58 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ (LSCF) cathode material was developed. Sintering of the screen printed cathodes was performed before stack operation at 950 °C in reducing Ar atmosphere for 3 h. Under these conditions, severe oxidation of the metallic substrate and the Ni in the anode was avoided reliably. For proof of concept, phase stability and microstructure of the MSC cathodes were characterized. The results reveal that cathode layers sintered in Ar exhibit substantially improved adherence and mechanical stability compared to conventionally processed MSC cathodes, making them ready for systematic investigation of electrochemical performance.

High-Performance Metal-Supported Solid Oxide Fuel Cells by Advanced Cathode Processing

“…Sintering behavior.-Initial experiments for investigating the sintering behavior of LSCF were reported in a previous article. 51 As expected, sintering activity of the mixed ionic electronic conducting (MIEC) material was found to considerably increase with increasing temperature. Additionally, further increased sintering activity, compared to sintering in air, was observed when the oxygen partial pressure was reduced during the thermal treatment by using an Ar atmosphere (p O2 ≈ 10 −5 bar).…”

“….-A critical issue in the procedure of developing an ex situ sintering route for MSC full-cells is the resulting cathode layer stability. As observed in the previous publication, 51 slight changes in processing conditions may lead to failure of the cathode layers. Therefore, further investigation focused on identifying the cause of failure.…”

“…Phase stability under reducing conditions.-In the previously reported work, it was found that screen-printed layers exhibit slightly higher sensitivity regarding the onset of phase decomposition compared to pressed pellets, which were used for dilatometry measurements and subsequently analyzed by XRD. 51 It was concluded that, due to the high porosity and high specific surface area, the apparent atmosphere can penetrate the thin cathode layer and cause significantly more pronounced phase transformation. In contrast, for the pressed samples where porosity is drastically reduced, the critical oxygen content of the sintering atmosphere is shifted to lower values.…”

“…In contrast, for the pressed samples where porosity is drastically reduced, the critical oxygen content of the sintering atmosphere is shifted to lower values. 51 Hence, further investigation of the phase stability was preferentially conducted on screen-printed layers as they correspond more closely to the real application. Additional experiments revealed that the reversibility of the phase transformation went further than initially expected.…”

Dual-Phase Cathodes for Metal-Supported Solid Oxide Fuel Cells: Processing, Performance, Durability

“…6,19 Recently, an ex situ sintering procedure was developed for LSCF cathodes. 14,[20][21][22] The sintering of entire cells in argon at 950°C clearly improved cathode adherence. At the same time, detrimental oxidation of the metal support and the Ni in the anode was prevented reliably.…”