Mechanism of improving oxygen transport resistance of polytetrafluoroethylene in catalyst layer for polymer electrolyte fuel cells

Wan, Zhaohui; Liu, Sufen; Zhong, Qing; Jin, Aiping; Pan, Mu

doi:10.1016/j.ijhydene.2018.01.091

Cited by 24 publications

(15 citation statements)

References 31 publications

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“…Besides heat-treating Nafion, introducing hydrophobic/hydrophilic particles ( e . g ., PTFE/SiO 2 ) into the catalyst layer − and modifying carbon support of the catalyst are also methods to change the hydrophobicity of the catalyst layer. These studies showed common observations that making the catalyst layer hydrophilic will improve the performance under low-humidity conditions, , while making the catalyst layer hydrophobic will help the water management and increase the maximum power density, , though some argued that the improvement was mainly due to the change in primary porosity .…”

Section: Resultsmentioning

confidence: 99%

Electrocatalyst Performance at the Gas/Electrolyte Interface under High-Mass-Transport Conditions: Optimization of the “Floating Electrode” Method

Lin

Zalitis

Sharman

et al. 2020

ACS Appl. Mater. Interfaces

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The thin-film rotating disk electrode (TF-RDE) is a well-developed, conventional ex situ electrochemical method that is limited by poor mass transport in the dissolved phase and hence can only measure the kinetic response for Pt-based catalysts in a narrow overpotential range. Thus, the applicability of TF-RDE results in assessing how catalysts perform in fuel cells has been questioned. To address this problem, we use the floating electrode (FE) technique, which can facilitate high-mass transport to a catalyst layer composed of an ultralow loading of catalyst (1–15 μgPt cmgeo –2) at the gas/electrolyte interface. In this paper, the aspects that have critical effects on the performance of the FE system are measured and parametrized. We find that, in order to obtain reproducible results with high performance, the following factors need to be taken into account: system cleanliness, break-in procedure, hydrophobic agent, ionomer type, and the measurements of catalyst surface area and loading. For some of these parameters, we examined a range of different approaches/materials and determined the optimum configuration. We find that the gas permeability of the hydrophobic agent is an important factor for improving the hydrogen oxidation reaction (HOR) and oxygen reduction reaction (ORR) performance. We provide evidence that the suppression of the HOR and ORR introduced by the Nafion ionomers is more than a local mass transport barrier but that a mechanism involving the adsorption of the sulfonate on Pt also plays a significant role. The work provides intriguing insights into how to manufacture and optimize electrocatalyst systems that must function at the gas/electrolyte interface.

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Section: Resultsmentioning

confidence: 99%

Electrocatalyst Performance at the Gas/Electrolyte Interface under High-Mass-Transport Conditions: Optimization of the “Floating Electrode” Method

Lin

Zalitis

Sharman

et al. 2020

ACS Appl. Mater. Interfaces

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“…However, too much PTFE addition would cover the catalyst surface and reduce the porosity of the catalyst layer, which leads to the oxygen shortage for active sites. [18] We also see that the resistances of the sample DM-8 % and DM-11 % are much higher than those of DM-2 %, DM-5 % (Figure 6b) and samples of PM-x ( Figure 3c) and IM-y (Figure 4c). In the durability test (Figure 6c), no matter what the current density is at the beginning, the current density of all DM-z series CCLs will decay to a very close value, about 140~160 mA cm À 2 .…”

Section: Ccls Prepared By Decal Methodsmentioning

confidence: 66%

Effect of Catalyst Layer Hydrophobicity on Fe−N−C Proton Exchange Membrane Fuel Cells

2020

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The hydrophobicity of the cathode catalyst layer (CCL) affects the performance of the proton exchange membrane fuel cell (PEMFC) by adjusting the water management of the catalyst layer, which has been extensively studied in Pt-based catalysts.Here, the effect of the hydrophobicity of FeÀ NÀ C CCL on the performance of the PEMFC is investigated. The hydrophobicity of the FeÀ NÀ C CCL is tuned by polytetrafluoroethylene (PTFE) by using three addition methods: 1) coat PTFE on FeÀ NÀ C powder and heat-treat; 2) mix PTFE emulsion with FeÀ NÀ C ink and then brush the electrode; and 3) transfer a ground PTFE/ FeÀ NÀ C composite film onto the gas diffusion layer by the decal method. For each PTFE addition method, the optimized PTFE amount can increase the power density of FeÀ CÀ N PEMFC by 15.1 %, 26.6 %, and 87.2 %, respectively. At the same time, it is found that enhanced hydrophobicity reduces the initial current decay rate of the FeÀ NÀ C CCLs, but their residual current densities are close after a 50 h durability test at 0.5 V in a H 2 -O 2 PEMFC. It can be concluded that the hydrophobicity of the FeÀ NÀ C CLL has a great influence on the power density of the fuel cell, but the influence on the long-term durability of the fuel cell is negligible.

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“…Improving the transport properties of the cathode electrolytic layer towards faster moisture removal, it is possible to increase the limiting current and enlarge the working range of the SPE oxygen pump. The introduction of PTFE particles into the cathode catalytic layer promotes the formation of a system of channels, which enable the efficient removal of excessive moisture from the layer [ 31 , 50 ] with more efficient oxygen transport to active catalyst sites [ 51 , 52 ]. In the submitted work, cathode electrocatalysts were synthesized on the basis of carbon black modified with PTFE particles as a support.…”

Section: Resultsmentioning

confidence: 99%

“…6b and passes through a maximum corresponding to the optimal value of 10 wt %. The modification of the carbon support with the optimal PTFE content essentially improves water transport in the cathode electrocatalytic layer, prevents its premature flooding, facilitates oxygen access to active catalyst sites, and increases the degree of Pt utilization [ 31 , 50 , 51 ]. A further increase in the PTFE content leads to the growth of Pt nanoparticles in size, a decrease in the catalyst EASA, and an appreciable decrease in the proton conductivity of the catalytic layer (due to a decrease in the proton-conducting polymer content [ 55 ]) and seems to worsen the oxygen pump IV curve.…”

Section: Resultsmentioning

confidence: 99%

The Study of the Solid Polymer Electrolyte Oxygen Concentrator with Nanostructural Catalysts Based on Hydrophobized Support

et al. 2020

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Mechanism of improving oxygen transport resistance of polytetrafluoroethylene in catalyst layer for polymer electrolyte fuel cells

Cited by 24 publications

References 31 publications

Electrocatalyst Performance at the Gas/Electrolyte Interface under High-Mass-Transport Conditions: Optimization of the “Floating Electrode” Method

Electrocatalyst Performance at the Gas/Electrolyte Interface under High-Mass-Transport Conditions: Optimization of the “Floating Electrode” Method

Effect of Catalyst Layer Hydrophobicity on Fe−N−C Proton Exchange Membrane Fuel Cells

The Study of the Solid Polymer Electrolyte Oxygen Concentrator with Nanostructural Catalysts Based on Hydrophobized Support

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