High performance modeling of heterogeneous SOFC electrode microstructures using the MOOSE framework: ERMINE (Electrochemical Reactions in MIcrostructural NEtworks).

Electrochemical energy devices, such as batteries and fuel cells, contain active electrode components that have highly porous, multiphase microstructures for improved performance. Predictive electrochemical models of solid oxide fuel cell (SOFC) electrode performance based on measured microstructures have been limited to small length scales, a small number of simulations, and/or relatively homogeneous microstructures. To overcome the difficulty in modeling electrochemical activity of inhomogeneous microstructures at considerable length scales, we have developed a high-throughput simulation application that operates on high-performance computing platforms. The open-source application, named Electrochemical Reactions in MIcrostructural NEtworks (ERMINE), is implemented within the MOOSE computational framework, and solves species transport coupled to both three-phase boundary and two-phase boundary electrochemical reactions. As the core component, this application is further incorporated into a high-throughput computational workflow. The main advantages of the workflow include:•Straightforward image-based volumetric meshing that conforms to complex, multi-phased microstructural features•Computation of local electrochemical fields in morphology-resolved microstructures at considerable length scales•Implementation on high performance computing platforms, leading to fast, high-throughput computations.

Quantitative interpretation of impedance spectroscopy data on porous LSM electrodes using X-ray computed tomography and Bayesian model-based analysis.

It is broadly understood that strontium-doped lanthanum manganate (LSM) cathodes for solid oxide fuel cells (SOFCs) have two pathways for the reduction of oxygen: a surface-mediated pathway culminating in oxygen incorporation into the electrolyte at the triple-phase boundary (TPB), and a bulk-mediated pathway involving oxygen transfer across the electrode-electrolyte interface. Patterned electrode and thin film experiments have shown that both pathways are active in LSM. Porous electrode geometries more commonly found in SOFCs have not been amenable for precise measurement of active electrode width because of the difficulty in precisely measuring the electrode geometry. This study quantitatively compares a reaction-diffusion model for the oxygen reduction reaction in LSM to the impedance spectrum of an experimental LSM porous electrode symmetric button cell on a yttria-stabilized zirconia (YSZ) electrolyte. The porous microstructure was characterized using computed tomography (nano-CT) and Bayesian model-based analysis (BMA) was used to estimate model parameters. BMA produced good fits to the data, with higher than expected values for the interfacial capacitance at the LSM-YSZ interface and vacancy diffusion activation energy; these results may indicate that the active width of the electrode is on a similar scale with that of the space-charge width at the LSM-YSZ interface. The analysis also showed that the active width and proportion of current moving through the bulk pathway is temperature dependent, in accordance with patterned electrode results.

Gas Transport Resistance in Polymer Electrolyte Thin Films on Oxygen Reduction Reaction Catalysts.

Significant reductions in expensive platinum catalyst loading for the oxygen reduction reaction are needed for commercially viable fuel cell electric vehicles as well as other important applications. In reducing loading, a resistance at the Pt surface in the presence of thin perfluorosulfonic acid (PFSA) electrolyte film, on the order of 10 nm thick, becomes a significant barrier to adequate performance. However, the resistance mechanism is unresolved and could be due to gas dissolution kinetics, increased diffusion resistance in thin films, or electrolyte anion interactions. A common hypothesis for the origin of the resistance is a highly reduced oxygen permeability in the thin polymer electrolyte films that coat the catalyst relative to bulk permeability that is caused by nanoscale confinement effects. Unfortunately, the prior work has not separated the thin-film gas transport resistance from that associated with PFSA interactions with a polarized catalyst surface. Here, we present the first characterization of the thin-film O2 transport resistance in the absence of a polarized catalyst, using a nanoporous substrate that geometrically mimics the active catalyst particles. Through a parametric study of varying PFSA film thickness, as thin as 50 nm, we observe no enhanced gas transport resistance in thin films as a result of either interfacial effects or structural changes in the PFSA. Our results suggest that other effects, such as anion poisoning at the Pt catalyst, could be the source of the additional resistance observed at low Pt loading.

Spatially resolved, in situ potential measurements through porous electrodes as applied to fuel cells.

We report the development and use of a microstructured electrode scaffold (MES) to make spatially resolved, in situ, electrolyte potential measurements through the thickness of a polymer electrolyte fuel cell (PEFC) electrode. This new approach uses a microfabricated apparatus to analyze the coupled transport and electrochemical phenomena in porous electrodes at the microscale. In this study, the MES allows the fuel cell to run under near-standard operating conditions, while providing electrolyte potential measurements at discrete distances through the electrode's thickness. Here we use spatial distributions of electrolyte potential to evaluate the effects of Ohmic and mass transport resistances on the through-plane reaction distribution for various operating conditions. Additionally, we use the potential distributions to estimate the ionic conductivity of the electrode. Our results indicate the in situ conductivity is higher than typically estimated for PEFC electrodes based on bulk polymer electrolyte membrane (PEM) conductivity.