A pore network model of porous electrodes in electrochemical devices

Abstract

• A PNM is computationally efficient for analysing flow and transport processes in electrodes. • The concentration profile of electrolyte is non-uniform across the 3D electrode. • Pore size distribution and connectivity influence the intrusion of electrolyte in the electrode. • Current density across the electrode is non-uniform and related to the concentration profiles. A computationally efficient pore network model (PNM) has been developed to incorporate the transport and electrochemical phenomena occurring within porous electrodes. This PNM is validated on a synthetic cubic structure and subsequently run on a network obtained from X-ray computed tomography (X-CT) images of a sample of commercial porous carbon paper commonly used in electrochemical devices. The carbon paper's physical characteristics (pore-size distribution, permeability, porosity and electroactive surface area) are discussed. The concentration distribution of active species is examined considering solely the transient convective and diffusive transport processes initially, and subsequently is compared to the concentration of active species when migration and reactive transport factors are included. The results show non-uniformity in the concentration and pressure distributions in the electrode when considering the pure convective/diffusive transport processes. The migration and reactive processes are subsequently considered and are shown to be influenced by the rate in which the convective/diffusive flow permeates the electrode. A uniform steady decline in volume-averaged state of charge is shown, followed by a pore-scale non-uniform current density and state of charge distribution upon discharge. These results were obtained on a standard single core workstation highlighting the benefits of using a computationally inexpensive model.