Simulation of the reduction process of solid oxide fuel cell composite anode based on phase field method

Abstract

It is known that the reduction process influences the initial performances and durability of nickel-yttria-stabilized zirconia composite anode of the solid oxide fuel cell. In the present study, the reduction process of nickel-yttria stabilized zirconia composite anode is simulated based on the phase field method. An three-dimensional reconstructed microstructure of nickel oxide-yttria stabilized zirconia composite obtained by focused ion beam-scanning electron microscopy is used as the initial microstructure for the simulation. Both reduction of nickel oxide and nickel sintering mechanisms are considered in the model. The reduction rates of nickel oxide at different interfaces are defined based on the literature data. Simulation results are qualitatively compared to the experimental anode microstructures with different reduction temperatures.

Phase field modeling of microstructure evolution and concomitant effective conductivity change in solid oxide fuel cell electrodes

“…Therefore, a multiphase-multigrain model that treats all the interfaces in SOFC electrodes in a universal framework is needed for the simulation of microstructure evolution in SOFC electrodes. Li et al has proposed a multiphase-multigrain model that has the potential to be applied to a wide range of SOFC electrode materials [27][28][29][30]. However, the tunability of the interfacial energy in their model is limited as discussed in Appendix A.…”

Achievements of NEDO Durability Projects on SOFC Stacks in the Light of Physicochemical Mechanisms

“…The present results on the anode degradations are different from those obtained from button cells or those anode‐support cells/stacks fabricated and operated mainly in Europe . Some trends in the anode degradations can be extracted from observations in the previous and the present NEDO projects as following categories: those stacks which do not use alloys in the anode compartment exhibit essentially no degradation (MHPS, Kyocera, NGK).…”

“…Above different behaviors in stacks should be discussed in terms of those physicochemical properties which are used in the fundamental approaches based on button cells or single cells. In the present project, UTokyo group made a series of experiments and simulations to make clear the Ni cermet anode behaviors in the SOFC environment , . In contrast to industrial anodes, those anodes exhibit significant grain growth and the morphological changes in microstructure which are confirmed by the combined FIB‐SEM analyses and 3D reconstruction of the electrode microstructure.…”

“…In contrast to industrial anodes, those anodes exhibit significant grain growth and the morphological changes in microstructure which are confirmed by the combined FIB‐SEM analyses and 3D reconstruction of the electrode microstructure. To take into account those behaviors in terms of surface/interface energies of Ni and oxide in addition to diffusion properties of Ni, simulations have been made with success in reproducing experimental morphological changes and also electrochemical anode performance , .…”

“…The stack degradation issues have been extracted from the stack performance tests made by CRIEPI on respective stacks with the same technique of separating measured voltage losses into several different contributions and their degradation rates and also by Tokyo Gas on thermal cycle characteristics . Degraded parts have been carefully examined by means of detailed analyses on changes in electrode microstructure with combined focussed ion beam scanning electron microscopy (FIB‐SEM) and 3D reconstruction technique by KyotoU, in deposited impurities at electrochemically active sites detected with secondary‐ion mass spectroscopy (SIMS) by AIST, with scanning transmission electron miscroscopy (STEM) by KyushuU and in electro‐chemo‐mechanical features by TohokuU. Such combined and systematic efforts in understanding degradations of SOFC stacks have revealed interesting general features of SOFCs as follows: Stack degradation behaviors are, in many cases, different from those in single or button cells.…”