Modelling and advanced quantification of inhomogeneous 3D current distribution in SOFC electrodes at the particle level

It is widely accepted that electrode microstructural characteristics significantly affect the electrochemical performance as well as the durability of solid oxide fuel cells. 3D tomography allows for the reconstruction and simulation of electrochemical phenomena within the real three-dimensional electrode microstructures. However, despite the availability of the full three-dimensional structural details, so far the microstructural analysis has been largely focused to obtaining averaged properties, such as the three-phase boundary density or the tortuosity factor, while 3D simulations have been mainly used to predict polarization curves and voltage profiles, something that can also be done with high fidelity by 1D continuum models. In order to overcome these limitations, we have recently introduced a completely new methodology for advanced microstructural characterization [1]. First we solve for the transport and electrochemical reactions of charged and gas species within the 3D electrode microstructure (Figure 1a), thus obtaining the electric potential, current density and gas concentration in every point of the corresponding phase. Then, each phase is resolved into individual particles and pores, allowing for the quantification of the statistical distribution of current and other truly-three-dimensional quantities 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 (Figure 1b). These two classes of particles are mutually exclusive, so that up to the 30% of solid electrode volume is shown to be underutilized. These behaviours are confirmed in both real and synthetic microstructures. The insight gained by the exploitation of all the information contained in 3D microstructural datasets enhances the understanding of the reasoning behind inhomogeneous current distribution, with its consequent impact on lifetime, suggesting strategies for the design of more durable SOFC electrodes. The approach is also applicable to lithium-ion batteries and other electrochemical energy systems.