Thermally Driven SOFC Degradation in 4D: Part I. Microscale

Abstract

© The Author(s) 2018. Published by ECS. Solid oxide fuel cells (SOFCs) still suffer from many performance and lifetime issues due to complex degradation mechanisms such as sintering and delamination, particularly when exposed to high thermal ramp rates. This work presents the first of a two-part study investigating such degradation with a focus on the microscale. It is found that, compared to long-duration operation, nickel sintering during start-up and shut-down is minor even at low ramp-rates (3◦C·min−1). Moreover, thermal ramp-rates during heating have a negligible influence on the extent of particle-particle delamination during operational cycling; a similar magnitude of Ni-YSZ interfacial particle contact loss is observed after each thermal cycle for ramp rates from 3−30◦C·min−1. Tortuosity-factor and percolation values remain consistent after the first thermal cycle, where Ni mobility may homogenize the structure during low ramp-rates. Both sintering and delamination are correlated to the triple-phase boundary (TPB) losses but for operational thermal cycling with minor dwell times, the particle-particle delamination is the prominent mechanism. This two-part study is the first report of an extended 4D analysis into the effects of thermal cycling on the anode structure with sub-micron resolution using only lab-based instruments. These findings will lead to improved cell designs, ultimately extending device lifetimes.