Coupling Study Of Mesoscale Reversible Fuel Electrode Sintering And Multiphysics Processes

Reversible solid oxide fuel cell(rSOFC)can produce and store energy through dual-mode operating,which is promising for balancing the conflicts between power supply and requirements.One of the key issues in the development of rSOFC is the development of highly efficient reversible electrodes,which is highly related to the microstructure evolution of electrode materials during sintering process and the complex multiphysics transport process with meso-scale elementary reactions during dual-mode operating.La-doped strontium titanate(LST),one kind of reversible electrode materials,is often sintered together with Gd-doped ceria(GDC)for composite electrode.It is needed to understand the mechanisms of sintering process in micron/nano level,including the electrode particle interactions and structure changes.Accordingly,a molecular dynamics method is developed to simulate the sintering process for the LST/GDC nanoparticle systems in this paper.It is found that a high sintering temperature is beneficial for increasing TPB(TriplePhase boundary)length,but not for the effective surface area of catalyst particles.A mass fraction of 0.5~0.6 is predicted as the optimal LST composition for the TPB length,active surface area,and compatible thermal expansion coefficient.The heat capacity and thermal conductivity increase in the high sintering temperature and high mass fraction of LST conditions.The methodology and findings can provide a guideline on optimization of the sintering conditions for LST/GDC electrodes,which may promote the commercialization of rSOFC technology.A two-dimensional mathematical model is developed for a single-cell based on the planar configuration and validated by relevant experimental data,with an aim to describe the coupling phenomena of the multiphysics transport processes and the meso-scale elementary reactions.It is revealed that desorption and adsorption reactions in the electrode mostly take place near the electrolyte and the channel,respectively;the distribution of the surface species depends on the gas diffusion in the porous electrode affected by the thickness and microstructure of the electrode.The electrochemical reactions are centralized in about 100 μm thick electrode from the electrolyte.Nis and COs are the major surface species in both fuel cell(FC)and electrolysis cell(EC)modes.Os is higher in the FC mode,particularly near the electrolyte due to the desorption and charge transfer reactions.The microscopic structure properties,including average porosity,tortuosity and particle size,are also influential on the elementary reactions due to the gas diffusion through the tortuous pathways and elementary reaction properties at the active sites on the catalyst surfaces.It is also found that the performance predicted in the global reaction models is often overestimated,which means the elementary reaction models is more reasonable.