No abstract

No abstract

In this work, a Lattice-Boltzmann-Method (LBM) model for simulating hysteresis in a proton exchange membrane fuel cell (PEMFC) electrode is presented. One of the main challenges hindering study of the cathode catalyst layer (CCL) in PEMFCs is the lack of understanding of two-phase transport and how it affects electrochemical performance. Previously, the microstructure details needed to build an accurate mesoscale model to examine such phenomena have eluded researchers; however, with advances in tomography and focused-ion-beam scanning-electron-microscopy (FIB-SEM), reconstruction of the complex porous media has become possible. Using LBM with these representations, the difficult problem of catalyst layer capillary hysteresis can be examined. In two-phase capillary hysteresis, both the equilibrium saturation position as well as its absolute value depends on the wetting history. Based on the models, it is ascertained that at lower capillary numbers, the liquid begins to undergo capillary fingering—only above a capillary pressure of 5 MPa, a regime change into stable displacement is observed. As capillary fingering does not lead to uniform removal of liquid, the prediction is that because high capillary pressures are needed to change to the regime of stable displacement, wicking is not as effective as the primary means of water removal.

The ionomer, which is responsible for proton transport, oxygen accessibility to reaction sites, and binding the carbon support particles, plays a central role in dictating the catalyst layer performance. In this work, we study the effect of ionomer distribution owing to the corrosion induced degradation mode in the catalyst layer based on a combined mesoscale modeling and experimental image-based data. It is observed that the coverage of the ionomer over the platinum-carbon interface is heterogeneous at the pore-scale which in turn can critically affect the electrode-scale performance. Further, an investigation of the response of the pristine as well as degraded microstructures that have been exposed to carbon support corrosion has been demonstrated to highlight the kinetic-transport underpinnings on the catalyst layer performance decay.

Proton-exchange membranes fuel-cells (PEMFC) electrochemical performance insights are predicated on a detailed understanding of species transport in the cathode catalyst layer (CCL). Traditionally, CCL microstructure considerations were approached through approximations with unresolved pore-scale features. Such simplifications cause the loss of predictability for improving the economic feasibility via lower Pt-loading or non-noble metal catalysts. With advances in visualization, microstructure resolved mesoscale models become possible. A judicious combination of lattice Boltzmann (LBM) and finite volume (FVM) is an appropriate strategy for direct numerical simulation (DNS) of the physicochemical fields that remain unresolved due to spatiotemporal limitations.