PhD Prospectus Defense: Toluwalope John

TITLE: ROLE OF INFILTRATES ON ANODIC AND CATHODIC POLARIZATION RESISTANCES IN SOLID OXIDE CELL ELECTRODES

ABSTRACT: The growing need to mitigate instability in power grids due to the intermittent nature of renewable energy sources has driven significant interest toward eIicient and scalable energy conversion and storage technologies. Solid oxide cells (SOCs) emerge as particularly promising solutions, providing high eIiciency for electricity generation while operating solid oxide fuel cells (SOFC) and producing hydrogen while operating as solid oxide electrolyzer cells (SOEC). However, conventional SOC technologies operate at high temperatures (800–1000 °C), leading to severe material compatibility, mechanical, and structural stability challenges. The oxygen electrode, in particular, experiences significant degradation under these conditions with more adverse eIects in the SOEC operating mode. Lowering operational temperatures to intermediate ranges (600-750°C) can mitigate these issues; however, this approach results in reduced catalytic activity, predominantly aIecting the oxygen electrode due to the high activation energy associated with oxygen reduction and evolution reactions. Although conventional oxygen electrodes such as LSM-YSZ and LSCF have been extensively studied for high-temperature applications, their performance substantially declines at intermediate temperatures due to insuIicient catalytic activity. To overcome these limitations, electrodes with enhanced catalytic properties and mixed ionic- electronic conduction (MIEC) properties are essential. Among potential candidates, Ruddlesden- Popper (RP) nickelate oxides have garnered attention for their superior catalytic activity, excellent oxygen ionic and electronic conductivity, and moderate thermal expansion coeIicients. Nevertheless, chemical incompatibility with conventional electrolytes typically necessitates additional barrier layers, complicating fabrication and raising production costs. This research aims to address the chemical incompatibility by utilizing an infiltration technique to incorporate rare-earth nickelates (Ln2NiO4, Ln = La, Nd, Pr) into conventional LSM-YSZ electrode scaIolds. The infiltration approach enables significantly reduced calcination temperatures, thereby preventing the formation of detrimental secondary phases and eliminating the requirement for barrier layers. In this study, the electrochemical performance, structural stability, and durability of infiltrated Ln2NiO4-LSM-YSZ electrodes are systematically evaluated and compared with baseline LSM–YSZ electrodes and barrier-layered nickelate configurations. A key focus is the identification of rate- limiting steps in oxygen electrocatalysis using Distribution of Relaxation Times (DRT) analysis of impedance spectra, with particular attention to how these processes are influenced by the infiltrated phases. These insights aim to inform the design of high-performance oxygen electrodes and advance the practical implementation and industrial viability of solid oxide electrolysis and fuel cell systems at intermediate temperatures.

COMMITTEE: ADVISOR/CHAIR Professor Srikanth Gopalan, ME/MSE; Professor Uday Pal, ME/MSE; Professor Soumendra Basu, ME/MSE; Professor Joerg Werner, ME/MSE