Impact of Hydrophobic Coating on Mass Transport Losses in PEFCs

Biesdorf, Johannes; Forner‐Cuenca, Antoni; Schmidt, Thomas J.; Boillat, Pierre

doi:10.1149/2.0861510jes

Cited by 40 publications

(38 citation statements)

References 57 publications

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“…• C for 2 hours (flow rates anode/cathode: 300/750 ml/min 31 , stoichiometries ≥ 30/≥ 30), followed by cooling down of the cell, activating potential cycles and a repetition of the first step (at 80…”

Section: Methodsmentioning

confidence: 99%

Durability of Unsupported Pt-Ni Aerogels in PEFC Cathodes

Henning

Herranz

Ishikawa

et al. 2017

J. Electrochem. Soc.

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The commercial success of polymer electrolyte fuel cells (PEFCs) depends on the development of Pt-based oxygen reduction reaction (ORR) catalysts with greater activity and stability to reduce the amount of expensive noble metal per device. To advance toward this goal, we have tested a novel class of unsupported bimetallic alloy catalysts (aerogels) as the cathode material in PEFCs under two accelerated stress test conditions and compared it to a state-of-the-art carbon-supported benchmark (Pt/C). The investigated Pt 3 Ni aerogel shows little degradation under high potential conditions (> 1.0 V) which can occur during fuel starvation and start-up/shutdown of the cell. If tested under the same conditions, the Pt/C benchmark displays significant losses of electrochemical surface area and ORR activity due to carbon support corrosion as observed in cross section and transmission electron microscopy analysis. When testing the durability upon extended load cycling (0.6-1.0 V), Pt 3 Ni aerogel demonstrates less stability than Pt/C which is related to the severe Ni leaching from the alloy under such conditions. These findings highlight the advantages of using unsupported ORR catalysts in PEFCs and point to the reduction of non-noble metal dissolution as the next development step. Polymer electrolyte fuel cells (PEFCs) currently rely on large amounts of carbon-supported platinum (Pt/C) catalysts (≈0.4 mg Pt /cm 2 electrode ) to reduce the voltage losses due to the sluggish kinetics of the cathodic oxygen reduction reaction (ORR).1 Recent advancements in minimizing the Pt loading and associated costs were achieved by alloying platinum with other metals like Ni, Cu and Co which increases the Pt mass-specific ORR activity.2 On the other hand, these catalysts suffer from significant corrosion of the carbon support and Pt nanoparticles during PEFC operation which compromises their long-term efficiency and reliability.3 To specifically mitigate the issue of support stability, researchers have developed alternative corrosionresistant supports (e.g. conductive metal oxides 4-7 ), extended metal surfaces (e.g. 3 M nanostructured thin film catalysts 8 ) and unsupported materials (e.g. Pt-coated Ni, Co or Cu nanowires 9-11 ). Pursuing this last strategy, unsupported bimetallic Pt-Ni electrocatalysts with high specific surface area (≈30 m 2 /g Pt ) and nanochain network structure, referred to as aerogels, were synthesized in a previous work. 12These materials reach the U.S. Department of Energy target (DOE; i.e. 440 A/g Pt at 0.9 V vs. the reversible hydrogen electrode (V RHE )) for automotive PEFC application when tested as thin films by the rotating disk electrode (RDE) technique, 13 which is the standard tool employed by the majority of researchers in this field for initial assessment of catalyst activities. Considering that performance figures derived from such RDE experiments, often do not translate fully to the technical system, it is fundamental to also assess activity and durability in PEFCs to evaluate the real application p...

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Section: Methodsmentioning

confidence: 99%

Durability of Unsupported Pt-Ni Aerogels in PEFC Cathodes

Henning

Herranz

Ishikawa

et al. 2017

J. Electrochem. Soc.

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“…This translates to very high stoichiometries (λ > 60 at 1 A cm −2 ) to allow for the so-called "differential cell" operation. 29,30 The individual cells were machined in aluminum and coated with a protective layer (25 μm Ni, 10 μm Au). They have 1 cm 2 of active area and the flow field is composed of five parallel channels (1 mm wide, −2 on the cathode, respectively, were used for every experiment.…”

Section: Methodsmentioning

confidence: 99%

Advanced Water Management in PEFCs: Diffusion Layers with Patterned Wettability

Forner‐Cuenca

Biesdorf

Manzi-Orezzoli

et al. 2016

J. Electrochem. Soc.

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Following our two previous publications on material synthesis and on ex situ characterization, we present an experimental in situ study to evaluate the effects of using gas diffusion layers with patterned wettability at the cathode side of polymer electrolyte fuel cells. The operando performance was assessed using traditional electrochemical diagnostics (such as polarization curves) combined with the pulsed gas analysis (PGA) method, which allows measuring the mass transport losses. Neutron radiography was performed simultaneously in order to image the water distribution during operation. Using this methodology, the effects of changing the pattern, including a microporous layer (MPL), and varying the operation conditions (temperature and relative humidity of the cathode gas) have been systematically evaluated. It has been confirmed that water redistributes according to the engineered pattern and that the power density is significantly increased thanks to reduced mass transport losses under various conditions. © The Author Several attempts have been reported in the literature to develop porous materials for fuel cells with optimized liquid/gas transport characteristic.1,2 The variation of microstructure 3,4 and the optimization of hydrophobic coatings and their content permitted significant improvements in performance, 5-9 while the inclusion of microporous layers led to the state-of-the-art materials that we know today. 10-17However, these materials do not have dedicated pathways for liquid and gas transport, but randomly distributed transport paths defined by the pore size and coating distributions.The perforation of GDLs in specific locations showed improved performances under certain operating conditions. 18,19 The local application of hydrophobic coatings was reported to improve oxygen diffusivity using an ex situ test rig combined with X-ray tomography. [20][21][22] An in situ study by the same research group demonstrated clear improvements when combining these hybrid GDLs with micro-grooved gas channels, but the isolated effect of hybrids GDLs did not lead to significant performance improvements. 23 Recently, we reported a method to produce GDLs with patterned wettability 24,25 based on radiation induced chemical grafting, and were the first to publish operando data with such patterned materials, showing a significant improvement when using them on the cathode of a PEFC. 25 Here, we present a comprehensive study on the impact of GDLs having patterned wettability on the water distribution and performance of the cell. The varied parameters include the dimensions of the pattern, the presence or absence of an MPL, and operating parameters such as humidity and temperature, respectively. This work currently rounds up a series of three papers including a detailed study on the material synthesis parameters (Part I) 26 and the analysis of the impact of various material parameters (substrate, coating load, grafting chemistry, pattern dimensions) on the water distribution in capillary injection experiments (Part II...

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“…1,2 To reduce cost, the high power densities are required for mobile and automotive applications implying cell operation at high current densities, which in turn increases water production within the cell. [3][4][5] At these operational conditions, mass transport losses become dominant and lead to decreased power output and fuel cell component degradation due to an uneven distribution of heat and current density.…”

Section: Introductionmentioning

confidence: 99%

Determination of oxygen transport resistance in gas diffusion layer for polymer electrolyte fuel cells

Wan

Zhong²,

Liu³

et al. 2018

Int J Energy Res

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Summary Gas diffusion layer (GDL) plays an important role in the performance of membrane electrode assembly (MEA) in polymer electrolyte fuel cells. In this work, 2‐type MEAs were prepared by 2 different GDLs of 29 BC and 29‐WUT, and the performance were investigated using polarization curve methods. The performance of MEA with 29‐WUT was 120 mV higher than 29 BC at 1600 mA/cm2. Electrochemical impedance spectroscopy (EIS) was applied to measure the mass transport resistance of 2‐type MEAs under normal running condition. The results of EIS showed that the mass transport resistance of 29 BC was 3.15 times higher than that of 29‐WUT at 1600 mA/cm2. To clarify this phenomenon, limiting current methods were applied under diluting oxygen concentration, low humidity, and high flow rate conditions. The results of limiting current methods showed that both the total oxygen transport resistance and the molecular diffusion resistance in the GDL of 29 BC were larger than that of 29‐WUT due to the lower porosity of gas diffusion substrate in 29 BC. As a result, EIS can be well combined with limiting current methods to analyze oxygen transport resistance in GDLs of fuel cells.

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Impact of Hydrophobic Coating on Mass Transport Losses in PEFCs

Cited by 40 publications

References 57 publications

Durability of Unsupported Pt-Ni Aerogels in PEFC Cathodes

Durability of Unsupported Pt-Ni Aerogels in PEFC Cathodes

Advanced Water Management in PEFCs: Diffusion Layers with Patterned Wettability

Determination of oxygen transport resistance in gas diffusion layer for polymer electrolyte fuel cells

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