Enhanced catalytic activity and stability of sofc electrodes through plasma-driven surface modification

Abstract

Solid oxide fuel cells (SOFCs) are pivotal for sustainable energy systems, offering eco-friendly electricity generation from chemical energy of injected fuels. Commercial viability mandates SOFC operation at intermediate temperatures (450 – 650 °C) for material diversification, cost reduction, and augmented thermal compatibility and longevity. However, this lowered operational temperature concurrently amplifies polarization resistance due to the intrinsic thermal activation of the oxygen reduction reaction. The resultant increase in resistance poses a formidable challenge in the development of electrodes with optimal performance. Additionally, the presence of an oxidizing atmosphere during the annealing process, commonly employed in the fabrication and treatment of conductive perovskite oxides used as oxygen electrode materials, leads to the accumulation of Sr and the formation of Sr-rich clusters on their surfaces, thereby degrading electrode performance. In this dissertation, I introduce plasma processes as a strategic avenue for developing oxygen electrodes with heightened activity and durability. The first strategy involves room temperature ex-solution achieved via remote plasma treatment. Conventional exsolution necessitates high-temperature reduction heat treatment. This method often lacks control over nanoparticle growth, leading to extended processing times and potential phase disruption in certain materials. To address these drawbacks, I explored room temperature exsolution using H2N2 remote plasma, aiming to mitigate the limitations associated with conventional exsolution methods. SEM analysis confirmed the emergence of nanoparticles on both the thin film and the porous structure subsequent to plasma treatment. Furthermore, XPS analysis identified the precipitated surface nanoparticles as Co. Moreover, an increase in oxygen vacancy was substantiated through XRD following plasma exposure. In summary, this study successfully demonstrated room temperature exsolution on the surface of the LSCF electrode facilitated by remote plasma in a concise 10-minute duration. The second strategy is surface amorphization through direct plasma treatment. To suppress Sr segregation, an innovative approach leveraging Ar plasma to amorphize porous oxide electrode surfaces is proposed. Investigating the effects of plasma treatment on the morphology, chemical composition, and crystallinity of an LSCF electrode surface reveals substantial changes in its electrochemical properties. Remarkably, a mere 5-minute plasma exposure achieves a 43% reduction in initial LSCF electrode polarization resistance and significantly improves durability at 650 °C, compared to the bare LSCF. This study demonstrates the viability of plasma-driven surface modification in high-temperature processes, and represents the first application of an amorphization strategy to a practical electrode in the field of SOFCs. This approach presents substantial promise for practical SOFC implementations, signifying a pivotal step toward successful commercialization. Consequently, I am confident that plasma treatment not only holds significant industrial value due to its capability for large-scale production but also stands as an exceptional method with vast potential to address multifaceted challenges in the realm of SOFC technology.