Observation of Preferential Pathways for Oxygen Removal through Porous Transport Layers of Polymer Electrolyte Water Electrolyzers

Abstract

Summary Understanding the relationships between porous transport layer (PTL) morphology and oxygen removal is essential to improve the polymer electrolyte water electrolyzer (PEWE) performance. Operando X-ray computed tomography and machine learning were performed on a model electrolyzer at different water flow rates and current densities to determine how these operating conditions alter oxygen transport in the PTLs. We report a direct observation of oxygen taking preferential pathways through the PTL, regardless of the water flow rate or current density (1-4 A/cm 2 ). Oxygen distribution in the PTL had a periodic behavior with period of 400 μm . A computational fluid dynamics model was used to predict oxygen distribution in the PTL showing periodic oxygen front. Observed oxygen distribution is due to low in-plane PTL tortuosity and high porosity enabling merging of oxygen bubbles in the middle of the PTL and also due to aerophobicity of the layer.

Insights into Interfacial and Bulk Transport Phenomena Affecting Proton Exchange Membrane Water Electrolyzer Performance at Ultra‐Low Iridium Loadings

“…First, we note that the performance of all five PEMWE, irrespective of PTL and low loading are the highest reported and consistent with our previous work, [ 5 ] however we see intriguing, substantial differences in performance between different PTLs, as much as 80 mV at 3 A cm −2 , indicating that the PTL structural differences have an even bigger impact on the cell Ohmic resistance and mass transport resistance than kinetics, as expected. [ 20 ]…”

“…[ 5 ] The current understanding in literature is that catalyst layer utilization is controlled by a combination of poor catalyst layer electronic conductivity and the poor interfacial area due to porous PTLs requiring microporous layers (MPL). [ 16 , 17 , 18 ] This narrative is at odds with recent work showing that i) oxygen transport through the titanium PTL may be a crucial limiting factor contributing to performance decline, [ 19 , 20 ] ii) high performance at ultra‐low loadings without MPLs is possible, [ 5 ] iii) catalyst layer ionic resistance dominates over electronic resistance when ionomer volume fraction is higher than 20%. [ 21 ]…”

Continuum Modeling of Porous Electrodes for Electrochemical Synthesis

“…One of the advantages of the method is that it does not need to track interfaces for two-phase systems, resulting in better solution convergence, compared to CFD methods. Like PNMs, LBM models have been mostly applied to study water and oxygen transport in the PTL of water electrolyzers. , The LBM is applied over the reconstructed 3-D domain, commonly obtained with X-ray computed tomography, FIB-SEM, or other imaging tools . While application of the LBM beyond computational fluid dynamics and calculation of the flow field are still quite rare, the LBM has recently been applied in the electrochemical community to study both species transport in porous components and their reactivity. , Kamali et al developed a boundary condition for simulation of a surface reaction rate possessing a reaction order of 1 .…”

Resolving Anodic Current and Temperature Distributions in a Polymer Electrolyte Membrane Water Electrolysis Cell Using a Pseudo-Two-Phase Computational Fluid Dynamics Model

“…The high value is lower than values measured by other authors. Satjaritanun et al 22 used operando X-ray computed tomography (CT) experiments to measure ε g values between 0.2 and 0.4 using a 0.320 mm activated carbon PTL. Thinner anode PTL materials such as the 0.19 mm Toray paper used by Lee et al 23 led to a consistent steady-state ε g of 0.2 at the anode.…”