Progress in 3D electrode microstructure modelling for fuel cells and batteries: transport and electrochemical performance

Electrode microstructure plays an important role in the performance of electrochemical energy devices including fuel cells and batteries. Building a clear understanding of how the performance is affected by the electrode microstructure is necessary to design the optimal electrode microstructure, to achieve better device performance. 3D microstructure modelling enables us to perform simulations directly on a 3D electrode microstructure and thus link structure with performance. This paper provides an extensive review on the current state of the art in 3D microstructure modelling of transport and electrochemical performance for four promising electrochemical energy technologies: solid oxide fuel cells (SOFCs), proton exchange membrane fuel cells (PEMFCs), redox flow batteries (RFBs) and lithium ion batteries (LIBs). Each technology has different electrode microstructures and processes, and thus presents different challenges. The most commonly used modelling methods including the finite element method (FEM) and the finite volume method (FVM) are reviewed, together with the developing lattice Boltzmann method (LBM), with the advantages and disadvantages of each method revealed. Whilst FEM and FVM have been extensively applied in simulating SOFC and LIB electrodes where the methods are capable of dealing with single phase (gas or liquid) transport, they face challenges in simulating the multiphase phenomenon present in PEMFC and some RFB electrodes. LBM is, on the other hand, well suited in simulating gas-liquid two phase flow and applications in PEMFCs and RFBs, as well as single-phase phenomenon in SOFCs and LIBs. The review also points to current challenges in 3D microstructure modelling, including the simulations of nanoscale gas transport and phase transition, moving interfaces associated with structural changes, accurate reactions kinetics, experimental validation, and how to make 3D microstructure modelling truly impactful through the design of better electrochemical devices.