Modeling of wetting phenomena in cathode catalyst layers for PEM fuel cells

Olbrich, Wolfgang; Kadyk, Thomas; Sauter, Ulrich; Eikerling, Michael

doi:10.1016/j.electacta.2022.140850

Cited by 15 publications

(13 citation statements)

References 49 publications

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“…Another explanation could link this observation to cell flooding and the heterogeneous wettability of the pore network in the catalyst layers, containing both hydrophilic and hydrophobic surfaces. This effect was observed and modelled by several groups, [28][29][30][31][32] where it is assumed that the pore surface shifts from hydrophilic to hydrophobic behavior, depending on its coverage with ionomer and/or Pt. This shift can be attributed to the orientation of the ionomer side chains, and their interaction with Pt located on the carbon surface.…”

Section: Resultsmentioning

confidence: 99%

The Effect of Ionomer to Carbon Ratio and Relative Humidity on Cathode Catalyst Degradation in PEM Fuel Cells

Schneider,

Scherzer,

Storey

et al. 2023

J. Electrochem. Soc.

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The effect of ionomer to carbon (I/C) weight ratio and relative humidity (RH) on cathode catalyst degradation was investigated by comprehensive in situ characterization. Membrane electrode assemblies (MEA) with I/C ratios of 0.5, 0.8 and 1.2 were subjected to an accelerated stress test performed at 40, 70 and 100% RH. The results show an increasing loss in electrochemical active surface area (ECSA) for both higher I/C ratios and RH during voltage cycling. To differentiate between ionomer and water connected ECSA, carbon monoxide stripping measurements were performed at varying RH. Before degradation, all MEAs show comparable total ECSA values, while higher I/C ratios lead to a larger fraction of ionomer connected ECSA. After degradation, ECSA measurements of the lowest I/C ratio showed a relatively higher loss of Pt in contact with ionomer than Pt in contact with water, while an opposite trend was observed for higher I/C ratios. H2/N2 impedance measurements showed drastically increasing protonic catalyst layer resistances for decreasing RH especially at low I/C ratios, which might hinder Pt2+ ion diffusion towards the membrane, hence decreasing the ECSA loss. Limiting current measurements show increasing molecular O2 diffusion resistances at end of test for samples with higher I/C ratios and higher ECSA loss.

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Section: Resultsmentioning

confidence: 99%

The Effect of Ionomer to Carbon Ratio and Relative Humidity on Cathode Catalyst Degradation in PEM Fuel Cells

Schneider,

Scherzer,

Storey

et al. 2023

J. Electrochem. Soc.

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show abstract

“…Considering that wettability reflects the hydrophilicity of a surface, with α ≪ 1 for hydrophobic materials, and α ≫ 1 for hydrophilic materials, the chosen value of α = 1.08 indicates a relatively wettable structure. Although carbon materials are generally hydrophobic, the surface of HSC carbon supports in Pt/C catalyst powder and its primary pores can have several functional groups, making it more wettable. − Given that the Pt surface is also highly wettable, ,,,,, assuming the average wettability between Pt and carbon surfaces as uniform wettability with α = 1.08 is considered reasonable in this study.…”

Section: Resultsmentioning

confidence: 99%

Water Condensation in the Nanoscale Pores of Pt/C Catalyst Particles and Its Impact on Catalyst Utilization: A Simulation Based on a Reconstructed Structure from Nanoimaging

Otic,

Katayama,

Arao

et al. 2024

ACS Appl. Mater. Interfaces

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In polymer electrolyte membrane fuel cells, carbonsupported platinum (Pt/C) catalyst particles require sufficient water condensation within the nanoscale pores to effectively utilize the interior Pt catalysts. Since experimental visualizations with nanoscale precision of this phenomenon are not yet possible, we utilized a Pt/C catalyst particle reconstructed from segmented nanoimaging of a catalyst powder, which served as the computational domain for lattice density functional theory (LDFT) simulation of water condensation. Paired with experimental water uptake data, LDFT successfully simulated high-resolution water condensation, capturing both thin-film and capillary water condensation phenomena. Using a simple proton movement method within the water network, we reproduced the Pt utilization data from a CO stripping experiment. Our findings highlight that at low relative humidity (RH), Pt utilization is influenced by thin water film formations, mainly dictated by the wettability properties of surfaces within primary pores and the Pt/C catalyst particle's exterior. Conversely, at high RH, Pt utilization is attributed to capillary water condensation in medium-to-large sized pores. This approach contributes a qualitative and quantitative discussion on hypotheses regarding the mechanism of Pt utilization, supporting recent studies (e.g.,

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“…Figure 12 comprehensively depicts the relevant phenomena, model systems, and approaches. Physical models can be devised to rationalize impacts on performance, durability and economic viability that are exerted by (1) the catalyst material's electronic structure, (2) the catalyst surface atomic structure and chemisorption state, (3) the local reaction environment (LRE) at the catalyst-electrolyte interface, (4) catalyst-support interactions, (5) a near-surface ionomer-skin layer [175], (6) pore size and contact angle distributions in the CL [175,176], (7) percolation-controlled transport properties [177].…”

Section: Theory and Computationmentioning

confidence: 99%

2023 Roadmap on molecular modelling of electrochemical energy materials

Zhang,

Cheng,

Chen

et al. 2023

J. Phys. Energy

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New materials for electrochemical energy storage and conversion are the key to the electrification and sustainable development of our modern societies. Molecular modelling based on the principles of quantum mechanics and statistical mechanics as well as empowered by machine learning techniques can help us to understand, control and design electrochemical energy materials at atomistic precision. Therefore, this roadmap, which is a collection of authoritative opinions, serves as a gateway for both the experts and the beginners to have a quick overview of the current status and corresponding challenges in molecular modelling of electrochemical energy materials for batteries, supercapacitors, CO2RR, and fuel cell applications.

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Modeling of wetting phenomena in cathode catalyst layers for PEM fuel cells

Cited by 15 publications

References 49 publications

The Effect of Ionomer to Carbon Ratio and Relative Humidity on Cathode Catalyst Degradation in PEM Fuel Cells

The Effect of Ionomer to Carbon Ratio and Relative Humidity on Cathode Catalyst Degradation in PEM Fuel Cells

Water Condensation in the Nanoscale Pores of Pt/C Catalyst Particles and Its Impact on Catalyst Utilization: A Simulation Based on a Reconstructed Structure from Nanoimaging

2023 Roadmap on molecular modelling of electrochemical energy materials

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