Exploiting the full potential of 3D simulations through novel characterization metrics at the particle level

It has been widely recognized that electrode microstructural characteristics significantly affect the electrochemical performance and durability of solid oxide fuel cells. The advent of 3D tomography has opened the scope for the reconstruction and simulation of electrochemical phenomena within real three-dimensional electrode microstructures. Yet, despite the availability of full three-dimensional details, so far the microstructural analysis has been largely limited to obtaining averaged properties, such as the tortuosity factor or the three-phase boundary density, while 3D simulations have been mainly used to predict voltage profiles and polarization curves, something that can also be done with 1D continuum models. In this study we introduce a completely new methodology for advanced microstructural characterization. First we solve for the transport and electrochemical reactions of charged and gas species within the 3D electrode microstructure, to obtain the electric potential, current density and gas concentration in every point of the corresponding phase. Then, the microstructure is resolved into individual particles, allowing for the quantification of the statistical distribution of current and other truly-three-dimensional properties at the particle level. The analysis allows for the identification of two classes of particles: particles which transfer more current than average, characterized by 10-40% more contacts than average, and particles which produce more current than average, which show ~2.5 times more three-phase boundary length than average. These two classes of particles are mutually exclusive, so that up to the 30% of solid electrode volume is shown to be underutilized. These behaviors are shown in both real and synthetic microstructures. The insight gained by the exploitation of all the information contained in 3D microstructural datasets enhances our understanding of the reasoning behind inhomogeneous current distribution, with its consequent impact on lifetime, suggesting strategies for the design of more durable SOFC electrodes.