Performance estimation by multiphase-field simulations and transmission-line modeling of nickel coarsening in FIB-SEM reconstructed Ni-YSZ SOFC anodes I: Influence of wetting angle

Abstract

FIB-SEM measurements of as-processed Ni-YSZ solid oxide fuel cell (SOFC) anodes are conducted. Based on the reconstructed volume as initial condition, multiphase-field simulations of nickel coarsening are performed to investigate the microstructure under operating conditions. The effect of the wettability of nickel on YSZ is discussed to span a possible range of different operating conditions. Effective properties including nickel particle size distributions, mean particle diameters, tortuosities and triple-phase boundary lengths (TPBL) serve as quantitative indicators for possible degradation and failure. The resulting data is used in a transmission-line model (TLM) to estimate anode performance and long-term stability. Generally, the simulations show that Ni coarsening at 750°C takes place mainly in the first 100 hours. It is found that nickel coarsening is enhanced when nickel shows dewetting on YSZ. Among other findings, the TPBL decreases significantly during the simulations for all parameter sets and is insusceptible to variations in wetting angle. The TLM considers the reduction of TPBL as the main factor for degradation. Loss of nickel connectivity can lead to a further significant drop in anode performance occurring predominantly for low wettability of nickel on YSZ.