Ion and Water Transport Characteristics in Membranes for Polymer Electrolyte Fuel Cells Containing  H  +  and Ca2 +  Cations

Okada, Tatsuhiro; Nakamura, Norito; Yuasa, Makoto; Sekine, Isao

doi:10.1149/1.1837890

Cited by 103 publications

(127 citation statements)

References 9 publications

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“…Once the cations enter the ionomer, they displace protons resulting in reduced ionic conductivity and water content, as well as lower gas permeability of the ionomer. 5,6,[13][14][15][16][17][18] Other researchers confirmed the findings of Okada group as well. 9,20,25,31,33 23 Pozio et al 19 investigated the degradation in PEFC that was caused by iron contamination from SS316L end plates and reported that contamination of the membrane electrode assemblies with iron led to degradation of the ionomer, revealed by a massive fluoride losses.…”

supporting

confidence: 62%

Thinning of Cathode Catalyst Layer in Polymer Electrolyte Fuel Cells Due to Foreign Cation Contamination

Banas

Uddin

Park

et al. 2018

J. Electrochem. Soc.

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Four hundred hour fuel cell tests were performed on commercial, as-received and Ca 2+ contaminated catalyst coated membranes (CCMs) to evaluate the effects of long term exposure of foreign cations on fuel cell performance and degradation. Following testing, significant thinning of the cathode catalyst layer was observed across the entire active area in the contaminated cell, while only localized thinning was observed in the as-received baseline CCM. Analysis of the elemental maps and line intensity profiles of platinum (Pt) obtained from energy dispersive X-ray spectrum (EDX) shows minimal change in total platinum content across the thickness of the catalyst layer, and hence loss of carbon is suspected to be the cause of the thinning. A numerical model is employed to show the foreign cation redistribution during testing, which shows proton depletion in the cathode catalyst layer when the CCM is contaminated with foreign cations. We hypothesize that this lack of protons leads to accelerated carbon corrosion in the cathode to supply protons to oxygen reduction where foreign cations block transport of protons. A carbon corrosion scheme is presented which shows that under the operating potentials of the cell, carbon oxidation can occur, leading to the observed thinning. The polymer electrolyte fuel cell (PEFC), a promising clean energy source for automobile application, still needs to overcome durability issues originating from various sources.1 Cationic impurities originated from either ambient air (e.g. roadside contaminants) or from the corrosion of stack and balance of plant components can significantly decrease the performance and life time of PEFCs. [1][2][3][4] In this paper, we report on the influence of foreign cationic contamination on the thinning of the cathode catalyst layer during non-accelerated testing. Long duration (400hr) testing was conducted using commercial catalyst coated membranes which showed significant catalyst layer thinning in a calcium cation contaminated cell, this thinning of the cathode catalyst layer was not observed in a non-contaminated baseline. While foreign cations are known to cause several degradation mechanisms in PEFCs, no study has examined the influence of cationic contamination on carbon corrosion, which we believe causes the thinning of the catalyst layer.To understand the impact and mechanism of cation contamination in PEFC, several modeling 5-11 and experimental studies 12-33 have been conducted, including ex-situ contamination of the polymer membrane with various cations before the test as well as injecting cations into the air or fuel stream during the cell test. Okada and co-workers extensively investigated the effect of various metal cations (Li + , Na + , Ca 2+ , Fe 2+ , Ni 2+ , Cu 2+ , Rb 2+ , Cs + ) on the transport properties of perfluorosulfonic acid (PFSA) membranes, thermodynamics and oxygen reduction reaction (ORR) kinetics. 5,[13][14][15][16][17][18] They reported that, with the exception of Li + , all foreign cations have higher affinity toward the sulfo...

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supporting

confidence: 62%

Thinning of Cathode Catalyst Layer in Polymer Electrolyte Fuel Cells Due to Foreign Cation Contamination

Banas

Uddin

Park

et al. 2018

J. Electrochem. Soc.

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“…In the literature, the major observation about metal ions' impact on fuel cell performance is their effect on membrane conductivity [17][18][19][20][21]. Unfortunately, how metal ions affect fuel cell catalysts has received very little attention.…”

Section: Introductionmentioning

confidence: 99%

Effect of Co2+ on oxygen reduction reaction catalyzed by Pt catalyst, and its implications for fuel cell contamination

Tsay

Wang

et al. 2010

Electrochimica Acta

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The oxygen reduction reaction (ORR) catalyzed by Pt was studied in the presence of Co 2+ using cyclic voltammetry (CV), rotating disk electrode (RDE), and rotating ring-disk electrode (RRDE) techniques in an effort to understand fuel cell cathode contamination caused by Co 2+ . Findings indicated that Co 2+ could weakly adsorb on the Pt surface, resulting in a slight change in ORR exchange current densities. However, this weak adsorption had no significant effect on the nature of the ORR rate determining steps. The results from both RDE and RRDE indicated that the overall electron transfer number of the ORR in the presence production. The fuel cell performance drop observed in the presence of Co 2+ could be attributed to the reduction in overall electron transfer number and the increase in H 2 O 2 production. Higher production could intensify the attack by H 2 O 2 and its radicals on membrane electrode assembly components, including the ionomer, carbon support, Pt particles, and membrane, leading to fuel cell degradation.Crown

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“…Proton flux to the cathode is reduced not only due to proton site occupancy but also decreased proton mobility caused by cationic interaction. [14][15][16] Strong interactions between the cations and sulfonic acid sites may also induce ionic cross-linking throughout the ionomer network. In addition, the reduced hydrophilicity of metal cations in comparison to protons reduces the water content (λ) in the membrane.…”

mentioning

confidence: 99%

Electrode Edge Cobalt Cation Migration in an Operating Fuel Cell: An In Situ Micro-X-ray Fluorescence Study

Cai

Ziegelbauer

Baker

et al. 2018

J. Electrochem. Soc.

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PtCo-alloy cathode electrocatalysts release Co cations under operation, and the presence of these cations in the membrane electrode assembly (MEA) can result in large performance losses. It is unlikely that these cations are static, but change positions depending on operating conditions. A thorough accounting of these Co cation positions and concentrations has been impossible to obtain owing to the inability to monitor these processes in operando. Indeed, the environment (water and ion content, potential, and temperature) within a fuel cell varies widely from inlet to outlet, from anode to cathode, and from active to inactive area. Synchrotron micro-X-ray fluorescence (μ-XRF) was leveraged to directly monitor Co 2+ transport in an operating H 2 /air MEA for the first time. A Nafion membrane was exchanged to a known Co cation capacity, and standard Pt/C electrocatalysts were utilized for both electrodes. Co Kα 1 XRF maps revealed through-plane transient Co transport responses driven by cell potential and current density. Because of the cell design and imaging geometry, the distributions were strongly impacted by the MEA edge configuration. These findings will drive future imaging cell designs to allow for quantitative mapping of cation through-plane distributions during operation. In pursuit of vehicle electrification, considerable efforts have been devoted to elucidating the degradation mechanisms of proton exchange membrane (PEM) fuel cells. [1][2][3][4][5][6][7] While the majority of these studies are based around post-mortem analyses of fuel cell materials (e.g. changes in nanoparticle sizes and shape distributions), a full accounting of the losses that contribute to membrane-electrode assembly (MEA) performance degradation requires looking beyond wellresearched catalyst nanoparticle degradation processes.2,8 Indeed, the performance of a PEM fuel cell is affected by many internal and external factors, such as fuel cell design and assembly, material degradation, operational conditions, and impurities or contaminants.9 The above-mentioned factors interact, and they are closely related to the cation activities in the fuel cell. In the current PEM fuel cell system, in addition to protons, various other cations are introduced from a variety of sources. For example, cerium ions are intentionally introduced to the MEA to improve membrane durability by neutralizing radical species before they attack the ionomer. 10,11 In contrast, when Pt-alloy catalysts are used, cobalt, nickel, or other 3d transition metal cations can leach out during fuel cell operation.1,3,5 Finally, cell component corrosion or impurities in the reactant/fuel flows may serve as additional cation sources. 12,13 In general, these cations exhibit greater affinities for the sulfonic acid groups in the ionomers than protons. Proton flux to the cathode is reduced not only due to proton site occupancy but also decreased proton mobility caused by cationic interaction.14-16 Strong interactions between the cations and sulfonic acid sites may also induce io...

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Ion and Water Transport Characteristics in Membranes for Polymer Electrolyte Fuel Cells Containing H + and Ca2 + Cations

Cited by 103 publications

References 9 publications

Thinning of Cathode Catalyst Layer in Polymer Electrolyte Fuel Cells Due to Foreign Cation Contamination

Thinning of Cathode Catalyst Layer in Polymer Electrolyte Fuel Cells Due to Foreign Cation Contamination

Effect of Co2+ on oxygen reduction reaction catalyzed by Pt catalyst, and its implications for fuel cell contamination

Electrode Edge Cobalt Cation Migration in an Operating Fuel Cell: An In Situ Micro-X-ray Fluorescence Study

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