The effect of hydrogen on the breakdown of the protective oxide scale in solid oxide fuel cell interconnects

ACS Appl. Energy Mater.

et al. 2021

One challenge for the commercialization of protonic ceramic fuel cells (PCFCs) is the lack of sealing technology for fabricating PCFC stacks, while related studies are limited. In this study, the Ag−CuO braze is employed to successfully join the BaZr 0.1 Ce 0.7 Y 0.1 Yb 0.1 O 3-δ (BZCYYb) electrolyte to AISI 441 interconnect for the PCFCs. The wettability of Ag−CuO braze on the BZCYYb surface can be tailored by changing the CuO content. The influence of CuO content and brazing temperature on the joint microstructure is analyzed. Sufficient wettability of the braze and limited interfacial reaction can be achieved using Ag-2 mol % CuO at 970−1000 °C. Under this condition, a reaction layer (Cu 2 Yb 2 O 5 , BaCr 2 O 4 ) is formed at the BZCYYb interface, and an oxide layer ((Cu, Cr, Fe) 3 O 4 , Cr 2 O 3 ) is observed at the AISI 441 interface. In addition, the long-term stability of as-brazed joints is assessed by aging in both wet oxidizing (50% air−50% H 2 O) and reducing (4% H 2 −96% Ar) atmospheres for 300 h at 600 °C. After aging tests, the joints remain intact and dense, indicating that the Ag−CuO braze system is applicable for fabricating PCFC stacks. KEYWORDS: protonic ceramic fuel cells, BaZr 0.1 Ce 0.7 Y 0.1 Yb 0.1 O 3-δ , interfacial microstructure, Ag−CuO braze, corrosion

Section: Resultsmentioning

confidence: 94%

Joining the BaZr_0.1Ce_0.7Y_0.1Yb_0.1O_3-δ Electrolyte to AISI 441 Interconnect for Protonic Ceramic Fuel Cell Applications: Interfacial Microstructure and Long-Term Stability

ACS Appl. Energy Mater.

et al. 2021

“…A thin and dense oxide layer (~ 2 µm) is formed between Ag and AISI 441 (Fig. 2a 2 ), which has been proved to be composed of (Fe, Mn, Cr) 3 O 4 and Cr 2 O 3 by many studies [25,[40][41][42]. It is worth noting that the oxide layer formed at the stainless steel interface by the traditional RAB method is typically thicker than 20 µm [25,32,33], which is 10 times wider than the above oxide layer.…”

Section: Resultsmentioning

confidence: 99%

Joining YSZ electrolyte to AISI 441 interconnect for solid oxide cells using the Ag interlayer: Enhanced mechanical and aging properties

et al. 2021

Preprint

Conventional Ag-CuO braze can lead to two electrolyte/interconnect joining issues: over-oxidation at the steel interconnect and hydrogen-induced decomposition of CuO. This work demonstrates that a pure Ag interlayer, instead of Ag-CuO braze, can join YSZ electrolyte to AISI 441 interconnect in air. Reliable joining between YSZ and AISI 441 can be realized at 920 °C. A dense and thin oxide layer (~2 μm) is formed at the AISI 441 interface. Also, an interatomic joining at the YSZ/Ag interface is detected by TEM observation. Obtained joints display high shear strengths (~86.1 MPa), 161% higher than that of joints brazed by Ag-CuO braze (~33 MPa). After aging in reducing and oxidizing atmospheres (800 °C/300 h), joints remain tight and dense, indicating a better aging performance. This technique eliminates the CuO-induced issues, which will extend lifetimes for SOFC/SOEC stacks and other ceramic/metal joining applications.

“…A thin and dense oxide layer (~2 µm) formed between Ag and AISI 441 (Figure 3(a 2 )), which has been proven to be composed of (Fe, Mn, Cr) 3 O 4 and Cr 2 O 3 in many studies [31,[47][48][49]. It is worth noting that the oxide layer formed at the stainless steel interface by the traditional RAB method is typically thicker than 20 µm [31,37,38], which is 10 times wider than the above oxide layer.…”

Section: Interfacial Microstructure and Formation Mechanism Of Ysz/ai...mentioning

confidence: 99%

Joining 3YSZ Electrolyte to AISI 441 Interconnect Using the Ag Particle Interlayer: Enhanced Mechanical and Aging Properties

et al. 2021

Crystals

Reactive air brazing has been widely used in fabricating solid oxide fuel/electrolysis cell (SOFC/SOEC) stacks. However, the conventional Ag–CuO braze can lead to (I) over oxidation at the steel interconnect interface caused by its adverse reactions with the CuO and (II) many voids caused by the hydrogen-induced decomposition of CuO. The present work demonstrates that the Ag particle interlayer can be used to join yttria-stabilized zirconia (YSZ) electrolytes to AISI 441 interconnect in air instead of Ag–CuO braze. Reliable joining between YSZ and AISI 441 can be realized at 920 °C. A dense and thin oxide layer (~2 μm) is formed at the AISI 441 interface. Additionally, an interatomic joining at the YSZ/Ag interface was observed by TEM. Obtained joints displayed a shear strength of ~86.1 MPa, 161% higher than that of the joints brazed by Ag–CuO braze (~33 MPa). After aging in reducing and oxidizing atmospheres (800 °C/300 h), joints remained tight and dense, indicating a better aging performance. This technique eliminates the CuO-induced issues, which may extend lifetimes for SOFC/SOEC stacks and other ceramic/metal joining applications.