Unraveling two-phase transport in porous transport layer materials for polymer electrolyte water electrolysis

Angelis, Salvatore De; Schuler, Tobias; Charalambous, Margarita A.; Marone, Federica; Schmidt, Thomas J.; Büchi, Félix N.

doi:10.1039/d1ta03379d

Cited by 38 publications

(31 citation statements)

References 41 publications

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“…In this scenario, it is essential to utilize the available catalyst as efficiently as possible. Recent studies have shown that the structure of the PTL can have an essential impact on CL utilization. − Several studies have investigated the bulk properties of the PTL − and the respective fluidic transport during operation. − A significant influence affecting CL utilization is related to the surface properties of the PTL rather than the bulk features. ,,− This is linked to two main reasons: (i) the poor electronic in-plane (IP) conductivity of typical CLs, caused by the disruption of the electronic percolation network of the CL structure and (ii) the in-plane mass transport limitation in the porous structure of the CL under the contact points between PTL and CL.…”

Section: Introductionmentioning

confidence: 99%

How the Porous Transport Layer Interface Affects Catalyst Utilization and Performance in Polymer Electrolyte Water Electrolysis

Weber

Wrubel

Gubler

et al. 2023

ACS Appl. Mater. Interfaces

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Cost reduction and fast scale-up of electrolyzer technologies are essential for decarbonizing several crucial branches of industry. For polymer electrolyte water electrolysis, this requires a dramatic reduction of the expensive and scarce iridium-based catalyst, making its efficient utilization a key factor. The interfacial properties between the porous transport layer (PTL) and the catalyst layer (CL) are crucial for optimal catalyst utilization. Therefore, it is essential to understand the relationship between this interface and electrochemical performance. In this study, we fabricated a matrix of two-dimensional interface layers with a well-known model structure, integrating them as an additional layer between the PTL and the CL. By characterizing the performance and conducting an in-depth analysis of the overpotentials, we were able to estimate the catalyst utilization at different current densities, correlating them to the geometric properties of the model PTLs. We found that large areas of the CL become inactive at increasing current density either due to dry-out, oxygen saturation (under the PTL), or the high resistance of the CL away from the pore edges. We experimentally estimated the water penetration in the CL under the PTL to be ≈20 μm. Experimental results were corroborated using a 3D-multiphysics model to calculate the current distribution in the CL and estimate the impact of membrane dry-out. Finally, we observed a strong pressure dependency on performance and high-frequency resistance, which indicates that with the employed model PTLs, a significant gas phase accumulates in the CL under the lands, hindering the distribution of liquid water. The findings of this work can be extrapolated to improve and engineer PTLs with advanced interface properties, helping to reach the required target goals in cost and iridium loadings.

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Section: Introductionmentioning

confidence: 99%

How the Porous Transport Layer Interface Affects Catalyst Utilization and Performance in Polymer Electrolyte Water Electrolysis

Weber

Wrubel

Gubler

et al. 2023

ACS Appl. Mater. Interfaces

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“…The challenge of anodic CL microstructure analysis lies in the difficulties of achieving high-quality 3D reconstructions, considering the small feature size (< 1 µm 6 ). While three-dimensional reconstructions of PTLs can be easily found in literature for both ex situ 3,7 and operando studies 8 , only one recent publication can be found where a PEWE CL reconstruction was obtained 6 . In 6 , the authors used focused ion beam-scanning electron microscopy (FIB-SEM) to reconstruct a CL employing an unsupported Ir-Ru catalyst.…”

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confidence: 99%

Understanding the microstructure of a core–shell anode catalyst layer for polymer electrolyte water electrolysis

Angelis

Schuler

Sabharwal

et al. 2023

Sci Rep

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Reducing precious metal loading in the anodic catalyst layer (CL) is indispensable for lowering capital costs and enabling the widespread adoption of polymer electrolyte water electrolysis. This work presents the first three-dimensional reconstruction of a TiO2-supported IrO2 based core shell CL (3 mgIrO2/cm2), using high-resolution X-ray ptychographic tomography at cryogenic temperature of 90 K. The high data quality and phase sensitivity of the technique have allowed the reconstruction of all four phases namely pore space, IrO2, TiO2 support matrix and the ionomer network, the latter of which has proven to be a challenge in the past. Results show that the IrO2 forms thin nanoporous shells around the TiO2 particles and that the ionomer has a non-uniform thickness and partially covers the catalyst. The TiO2 particles do not form a percolating network while all other phases have high connectivity. The analysis of the CL ionic and electronic conductivity shows that for a dry CL, the ionic conductivity is orders of magnitudes lower than the electronic conductivity. Varying the electronic conductivity of the support phase by simulations, reveals that the conductivity of the support does not have a considerable impact on the overall CL electrical conductivity.

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“…In 2022, Kulkarni et al 9 utilized X-ray micro-CT and investigated the oxygen content distribution with different catalyst loadings. De Angelis et al 47 in 2021 unraveled two-phase (water/oxygen) transport via X-ray micro-CT, figuring out four different connection types of oxygen clusters and how isotropic/anisotropic microstructure could influence the electrolysis performance. One more imaging research interest is to distinguish electrode components within assemblies, which may require combination of Xray CT and other imaging characterization techniques such as ptychography and fluorescence.…”

Section: Why We Need X-ray Ct In Electrocatalysismentioning

confidence: 99%

“…This enables the identification of water saturation in the anode of water electrolyzers, as has been shown in previous studies. 47 Traditionally, neutron imaging has been limited to 2D radiography in the in-plane or through-plane direction of the membrane electrode assembly, owing to low resolution (>5 μm) and long exposure times. However, recent advances in imaging resolution 89 and time scale 90 have enabled the accomplishment of 3D neutron tomography.…”

Section: Iibii X-ray Ct With Neutron Ctmentioning

confidence: 99%

“…Additionally, systems containing pumped fluid motion, such as redox flow batteries or PEM electrolyzers, require additional considerations toward pressure fluctuations in the liquid phase due to deformation of the connecting tubes during cell rotation at high scan speeds. However, they do offer a unique design opportunity that staining agents , can be used to generate contrast. Figure presents a typical operando vanadium redox flow battery setup tested with X-ray micro-CT at Canadian Light Sources, with connections of four inlet/outlet fluid tubes and two electrical cables.…”

Section: Why We Need X-ray Ct In Electrocatalysismentioning

confidence: 99%

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A Viewpoint on X-ray Tomography Imaging in Electrocatalysis

et al. 2023

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With the emerging demands for clean energy and an economy with net-zero greenhouse gas emissions, electrocatalysis areas have attracted tremendous interest in recent years. The electrochemical devices that use electrocatalysis, such as fuel cells, electrolyzers, and flow batteries, consist of hierarchical structures, requiring comprehension and rational designs across scales from millimeter and micrometer all the way down to atomic scale. In past decades, electron microscopy techniques such as scanning electron microscopy (SEM) and transmission electron microscopy (TEM) have been extensively utilized for imaging different scales of these devices in both two and three dimensions. However, electron-based techniques for high-resolution imaging require uninterrupted maintenance of a high-vacuum environment, leading to difficulties of sample preparation and lack of integrated observation without intrusion/ disassembly. To overcome these disadvantages, more and more efforts have been dedicated to the development of X-ray imaging techniques recently, specifically absorption-based two-dimensional (2D) transmission X-ray microscopy and three-dimensional (3D) X-ray tomography, due to much better transmission behaviors of X-rays than electrons. X-ray tomography imaging mostly focuses on answering questions related to morphology and morphological changes at the microscale or near 1 μm resolution and nanoscale of 30 nm resolution. The method is nondestructive and it allows for the visualization of operando electrochemical devices, such as fuel cells, electrolyzers, and redox flow batteries. Operando X-ray microscopic tomography typically focuses on catalyst layers and morphology changes during degradation, as well as mass transport. Nanoscale tomography still predominantly is used for ex situ studies, as multiple challenges exist for operando studies implementation, including X-ray beam damage, sample holder design, and beamline availability. Both microscale and nanoscale tomography beamlines now couple various spectroscopic techniques, enabling electrocatalysis studies for both morphology and chemical transformations. This viewpoint highlights the recent advances in X-ray tomography for electrocatalysis, compares it to other tomographic techniques, and outlines key complementary techniques that can provide additional information during imaging. Lastly, it provides a perspective of what to anticipate in coming years regarding the method use for electrocatalysis studies.

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Unraveling two-phase transport in porous transport layer materials for polymer electrolyte water electrolysis

Abstract: In polymer electrolyte water electrolysis (PEWE), reducing mass-transport losses is crucial for lowering both PEWE capital and operational costs, allowing the widespread commercialization of the technology. In this work, we...

Cited by 38 publications

References 41 publications

How the Porous Transport Layer Interface Affects Catalyst Utilization and Performance in Polymer Electrolyte Water Electrolysis

How the Porous Transport Layer Interface Affects Catalyst Utilization and Performance in Polymer Electrolyte Water Electrolysis

Understanding the microstructure of a core–shell anode catalyst layer for polymer electrolyte water electrolysis

A Viewpoint on X-ray Tomography Imaging in Electrocatalysis

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