Highly Connected Oxygen Ion Conduction Pathways for Solid Oxide Fuel Cells Operating in Intermediate Temperatures with Fuel Flexibility

Abstract

Solid oxide fuel cells are promising eco-friendly power generating devices directly utilizing various fuels such as hydrogen, methane, and carbon dioxide. However, a technical breakthrough is required for further commercialization by lowering the high operating temperature to the intermediate temperature regime. Introducing the anode functional layer (AFL) between the electrolyte and anode is one of the crucial methods in the development of high performance solid oxide fuel cells by maximizing the triple phase boundary (TPB) sites. To activate the TPB sites, ensuring the continuous oxygen ion conduction from the electrolyte to the TPB sites is essential to maximize their utilization for hydrogen oxidation reactions (HORs). In this study, we modify the connectivity of oxygen ion conduction pathways in the AFL by controlling the microstructure in AFLs. We calculated active reaction site using image processing of cross-sectional scanning electron microscopy (SEM) image and the strong correlation between the electrochemical performance and calculated active reaction site is revealed. The modified AFL with highly connected oxygen ion conduction pathways exhibits substantially higher maximum power density (MPD) compared with conventional AFL: ~1.7-fold higher MPD of 1.51 Wcm-2 at 550 ℃ with hydrogen and ~3.5-fold higher MPD of 1.11 Wcm-2 at 550 ℃ with methane and carbon dioxide, surpassing previously reported values. Moreover, excellent carbon tolerance is observed in the modified AFL, exhibiting nearly no degradation at 550 ℃ for 130 h. This result substantiates the role of connectivity of the oxygen ion conduction pathways in the HOR and carbon tolerance in AFLs. Figure 1