Uncovering Performance Improvements of Ni/GDC Anode for Low Temperature SOFC—DFT Study

Low-temperature solid oxide fuel cells (SOFCs) offer several advantages, such as improved material stability and operating cost reduction. However, achieving optimal performance and commercial viability requires overcoming various challenges. One significant issue with commonly used electrode materials is the decrease in catalytic activity at low temperatures. Ceria-based anodes are renowned for their robust thermal stability and facile redox ability, thereby contributing to their excellent performance. To further improve these abilities, doping ceria with lanthanide elements such as Gd or Sm enhances ion conductivity and facilitates the creation of oxygen vacancies. Recently, nickel catalysts supported by gadolinium-doped ceria (Ni/GDC) have shown superior performance to conventional Ni-YSZ electrodes. However, the specific reasons behind this improvement still remain unclear.<br/>Therefore, we performed DFT calculations to explore the key factors contributing to the catalytic performance of Ni/GDC. According to DFT studies, oxygen vacancy formation plays a crucial role in explaining intrinsic electronic conductivity. Since easier oxygen vacancy formation (represented by the low oxygen vacancy formation energy (E_ovf) in DFT calculations) results in high electronic conductivity, this is expected to further improve the reaction activity. Through E_ovf calculations for Ni/GDC, we confirmed that oxygen vacancies form more easily near the Gd sites compared to the Ni or Ce sites. This indicates that near the Gd sites serve as active sites, facilitating electron transfer and reactions. The key finding is that introducing Ni onto the GDC increases the exposure of electronically conductive Gd on the surface. This enrichment of active Gd sites is expected to enhance the catalytic activity, as revealed by the segregation energy calculations. The DFT-predicted enhancement in catalytic activity was validated by experiments. These findings help to overcome low catalytic activity issues in low-temperature SOFC electrodes and contribute to the commercialization of cost-effective electrodes.