Prediction of Electrolyte Distribution in Technical Gas Diffusion Electrodes: From Imaging to SPH Simulations

Abstract

The performance of the gas diffusion electrode (GDE) is crucial for technical processes like chlorine-alkali electrolysis. The function of the GDE is to provide an intimate contact between gaseous reactants, the solid catalyst, and the liquid electrolyte. To accomplish this, the GDE is composed of wetting and non-wetting materials to avoid electrolyte breakthrough. Knowledge of the spatial distribution of the electrolyte in the porous structure is a prerequisite for further improvement of GDE. Therefore, the ability of the electrolyte to imbibe into the porous electrode is studied by direct numeric simulations in a reconstructed porous electrode. The information on the geometry, including the information on silver and PTFE distribution of the technical GDE, is extracted from FIB/SEM imaging including a segmentation into the different phases. Modeling of wetting phenomena inside the GDE is challenging, since surface tension and wetting of the electrolyte on silver and PTFE surfaces must be included in a physically consistent manner. Recently, wetting was modeled from first principles on the continuum scale by introducing a contact line force. Here, the newly developed contact line force model is employed to simulate two-phase flow in the solid microstructures using the smoothed particle hydrodynamics (SPH) method. In this contribution, we present the complete workflow from imaging of the GDE to dynamic SPH simulations of the electrolyte intrusion process. The simulations are used to investigate the influence of addition of non-wetting PTFE as well as the application of external pressure differences between the electrolyte and the gas phase on the intrusion process.

Operando Laboratory X-Ray Imaging of Silver-Based Gas Diffusion Electrodes during Oxygen Reduction Reaction in Highly Alkaline Media

“…The microstructure of the GDEs shows silver grains with deposited PTFE at their grain boundaries and a complex open pore system extending through the whole electrode (Figure 7). Previous investigations showed that this microstructure is homogenous over the whole cross section of the GDE [22]. Moreover, the laboratory X-ray radiographies and the FIB cuts demonstrate that large pores with sizes of about 40 µm form regularly between the Ni mesh (Figure 2).…”

Experimental and Model‐Based Analysis of Electrolyte Intrusion Depth in Silver‐Based Gas Diffusion Electrodes

“…Comparing the graded electrode with the highest silver loading (45 mg Ag cm −2 ) and the full silver electrode, there is still a significant difference in the limiting current density. This proves, that the active part of the full silver electrode is thicker than 75 μm and thus the electrolyte must intrude much deeper than expected from other simulation approaches [15–17] . Unfortunately, the electrolyte penetration depth cannot be determined exactly for the full silver electrode and will only be revealed by operando tomography experiments.…”

“…This proves, that the active part of the full silver electrode is thicker than 75 μm and thus the electrolyte must intrude much deeper than expected from other simulation approaches. [15][16][17] Unfortunately, the electrolyte penetration depth cannot be determined exactly for the full silver electrode and will only be revealed by operando tomography experiments. Nevertheless, we proved experimentally and with our model-based analysis that large parts of the full silver GDE are intruded by the electrolyte and are utilized for the ORR in high alkaline media.…”

“…However, these membrane‐supported electrodes have a completely different structure than conventional GDE made from silver and PTFE particles. While Kunz et al [15] . hardly found any electrolyte imbibition in a silver‐based pore system without application of a large differential pressure in their simulations, Röhe et al [16,17] .…”

“…However, these membranesupported electrodes have a completely different structure than conventional GDE made from silver and PTFE particles. While Kunz et al [15] hardly found any electrolyte imbibition in a silverbased pore system without application of a large differential pressure in their simulations, Röhe et al [16,17] determined small intrusion depths of the electrolyte based on their dynamic model approach. In summary, quite contradictory information can be found in the literature, although the electrolyte distribution and the penetration depth is of fundamental importance for understanding the processes in GDE with liquid electrolyte.…”