Nanoporous silver cathode surface treated by atomic layer deposition of CeO_xfor low-temperature solid oxide fuel cells

Abstract

We evaluated the performance of solid oxide fuel cells (SOFCs) with a 50 nm thin silver (Ag) cathode surface treated with cerium oxide (CeO(x)) by atomic layer deposition (ALD). The performances of bare and ALD-treated Ag cathodes were evaluated on gadolinia-doped ceria (GDC) electrolyte supporting cells with a platinum (Pt) anode over 300 °C-450 °C. Our work confirms that ALD CeO(x) treatment enhances cathodic performance and thermal stability of the Ag cathode. The performance difference between cells using a Ag cathode optimally treated with an ALD CeO(x) surface and a reference Pt cathode is about 50% at 450 °C in terms of fuel cell power output in our experiment. The bare Ag cathode completely agglomerated into islands during fuel cell operation at 450 °C, while the ALD CeO(x) treatment effectively protects the porosity of the cathode. We also discuss the long-term stability of ALD CeO(x)-treated Ag cathodes related to the microstructure of the layers.

Review on process-microstructure-performance relationship in ALD-engineered SOFCs

“…The peak power density of the cell with a Ag cathode, with two cycles of ALD CeO 2 overlayer, was about 50% higher than that of a Pt-only cathode. The thermal stability improvement was also observed in the ALD CeO 2 overlayer [33].…”

“…Nanoporous structures of metals and ceramic, in combination with nanoparticles, are employed. However, the mechanical and chemical stability of electrode structures with high surface-to-volume ratio, especially nanostructures, may become a serious issue at elevated temperatures [27][28][29][30][31][32][33].…”

“…(1) ALD oxide on metallic cathode ALD oxide overlayers (or overcoatings, capping layers), e.g., MnO x [31], ZrO 2 [28], SnO 2 [29], doped ZrO 2 [30,32], CeO x [33], on metal cathodes have been actively researched in recent years [28][29][30][31][32] because they can compensate for the low thermal stability of porous metal electrodes, and in some cases, can also improve the ORR activity. While oxide overlayers can be fabricated by using other techniques (sputtering [136][137][138], infiltration [139][140][141]), the conformal nature of the ALD process may further help to enhance the stability of metallic electrodes.…”

Developing metallic cathode for low-temperature solid oxide fuel cell applications

“…will be lost per year at 800 °C) 67 . Therefore, Ag was seldom used in pure metallic form at the temperature above 500 °C, and rather it was presented as a constitute of the composite with perovskites or ion-conducting electrolytes 91,92,[105][106][107][108][109][110][111][112] . However, with the low operating temperature of µ-SOFCs, the technical feasibility of using Ag as a cathode is reconsidered.…”

“…Electrolyte materials such as zirconia, YSZ, or ceria are often used for surface modification on metallic cathodes because of their high thermal stability and ion conductivity. By introducing these thermally stable protective layers on a metallic cathode, the thermal stability of thin-film electrode can be improved at operating temperature below 500 ˚C 10,63,91,92 . The ion-conducting material capping on the surface can also serve as an extension of the electrolyte and provides ion-conducting pathways, resulting in higher TPB density.…”