Tolerance and Recovery of Ultralow-Loaded Platinum Anode Electrodes upon Carbon Monoxide and Hydrogen Sulfide Exposure

Prass, Sebastian; Friedrich, K. Andreas; Zamel, Nada

doi:10.3390/molecules24193514

Cited by 23 publications

(12 citation statements)

References 31 publications

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“…Most studies in literature employ CV scan rates between 1 and 100 mV/s [20,21,26,42,43]. At higher scan rates, current magnitudes arising from electrochemical surface processes generally increase.…”

Section: Resultsmentioning

confidence: 99%

“…Platinum loadings of 50 μg/cm 2 are already often considered state-of-the-art, with even lower (ultra-low) loadings forecasted for the near future. Although the majority of studies in literature focuses on the cathode electrode including higher catalyst loadings and its decay during accelerated stress tests (ASTs), the anode electrode is of interest especially when investigating the effect of startup/shutdown cycles [24] or impurities [25,26] on the anode compartment, or the cell reversal tolerance upon freeze start-ups and successional reversal effects [27,28]. Therefore, thorough understanding of CVs of low-and ultra-low-loaded electrodes is of great interest.…”

Section: Introductionmentioning

confidence: 99%

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Hydrogen Oxidation Artifact During Platinum Oxide Reduction in Cyclic Voltammetry Analysis of Low-Loaded PEMFC Electrodes

et al. 2020

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An artifact appearing during the cathodic transient of cyclic voltammograms (CVs) of low-loaded platinum on carbon (Pt/C) electrodes in proton exchange membrane fuel cells (PEMFCs) was examined. The artifact appears as an oxidation peak overlapping the reduction peak associated to the reduction of platinum oxide (PtOx). By varying the nitrogen (N2) purge in the working electrode (WE), gas pressures in working and counter electrode, upper potential limits and scan rates of the CVs, the artifact magnitude and potential window could be manipulated. From the results, the artifact is assigned to crossover hydrogen (H2X) accumulating in the WE, once the electrode is passivated towards hydrogen oxidation reaction (HOR) due to PtOx coverage. During the cathodic CV transient, PtOx is reduced and HOR spontaneously occurs with the accumulated H2X, resulting in the overlap of the PtOx reduction with the oxidation peak. This feature is expected to occur predominantly in CV analysis of low-loaded electrodes made of catalyst material, whose oxide is inactive towards HOR. Further, it is only measurable while the N2 purge of the WE is switched off during the CV measurement. For higher loaded electrodes, the artifact is not observed as the electrocatalysts are not fully inactivated towards HOR due to incomplete oxide coverage, and/or the currents associated with the oxide reduction are much larger than the spontaneous HOR of accumulated H2X. However, owing to the forecasted reduction in noble metal loadings of catalyst in PEMFCs, this artifact is expected to be observed more often in the future.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Hydrogen Oxidation Artifact During Platinum Oxide Reduction in Cyclic Voltammetry Analysis of Low-Loaded PEMFC Electrodes

et al. 2020

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“…All of these species are included in the hydrogen fuel standard [5]. For CO and H 2 S, a lower Pt or PtRu catalyst loading generally leads to an increase in the anode overpotential [6][7][8][9][10]. However, it was reported that for H 2 S, the catalyst loading effect disappears for values equal to or below 25 µg cm −2 [10].…”

Section: Introductionmentioning

confidence: 99%

“…For CO and H 2 S, a lower Pt or PtRu catalyst loading generally leads to an increase in the anode overpotential [6][7][8][9][10]. However, it was reported that for H 2 S, the catalyst loading effect disappears for values equal to or below 25 µg cm −2 [10]. An effect was not observed with the weak contaminant CO 2 , which is attributed to a concentration that was substantially lower (1%) [7] than in a typical reformate (10-20%) [11].…”

Section: Introductionmentioning

confidence: 99%

Impact of the Cathode Pt Loading on PEMFC Contamination by Several Airborne Contaminants

St‐Pierre

Zhai

2020

Molecules

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Proton exchange membrane fuel cells (PEMFCs) with 0.1 and 0.4 mg Pt cm −2 cathode catalyst loadings were separately contaminated with seven organic species: Acetonitrile, acetylene, bromomethane, iso-propanol, methyl methacrylate, naphthalene, and propene. The lower catalyst loading led to larger cell voltage losses at the steady state. Three closely related electrical equivalent circuits were used to fit impedance spectra obtained before, during, and after contamination, which revealed that the cell voltage loss was due to higher kinetic and mass transfer resistances. A significant correlation was not found between the steady-state cell voltage loss and the sum of the kinetic and mass transfer resistance changes. Major increases in research program costs and efforts would be required to find a predictive correlation, which suggests a focus on contamination prevention and recovery measures rather than contamination mechanisms.Molecules 2020, 25, 1060 2 of 15 focusing on the cathode catalyst loading effect were found [19,20]. However, contamination data in [19] are not directly comparable because both the catalyst layer design and catalyst loading were concurrently altered. The authors also refer to 10 ppb SO 2 data obtained by another group that showed more severe fuel cell damage with a catalyst loading decrease from 0.4 to 0.3 mg Pt cm −2 . In contrast, the effect of 2,6-diaminotoluene, a species that leaches out of the fuel cell system balance of plant materials, was more impactful after the Pt catalyst loading was lowered from 0.4 to 0.1 mg Pt cm −2 [20]. In comparison to the anode, the higher cathode potential is expected to affect the contamination mechanism with, for example, a different Pt surface charge, altered contaminant adsorbates and reaction intermediates, catalyst coverage, and cell voltage loss. This situation is exacerbated with a catalyst loading change, which affects the overpotential of the irreversible oxygen reduction reaction and the cathode potential. Information about chemical and electrochemical reactions for specific contaminants may be available in the literature. However, the presence of relevant cathode reactants, oxygen and water, may not be considered. For instance, novel intermediates or products were not detected with chlorobenzene in air [21]. However, the presence of acetylene in air led to small amounts of methane [22] that were not expected based on acetylene chemistry and electrochemistry. Therefore, tests completed under these significantly different operating conditions are needed in part because contaminant reactions are not currently predictable in assessing catalyst coverage and cell voltage loss.This report documents the impact of the cathode Pt catalyst loading effect for PEMFCs contaminated with seven model organic airborne species, which were previously evaluated and selected from a larger pool of 21 contaminants [23]: Acetonitrile (nitrile), acetylene (alkyne), bromomethane (halocarbon), iso-propanol (alcohol), methyl methacrylate (ester), naphthalene (polycyclic ...

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“…Finally, we note that alternative strategies, such as hydrogen purification, can contribute to the restriction of CO poisoning in H 2 -PEMFCs. Prass et al [163] investigated platinum catalyst layers with ultralow metal loadings (50, 25, and 15 µg cm −2 ) in order to mitigate CO contamination according to the Hydrogen Quality Standard ISO 14687-2:2012 limits for PEMFCs. The authors, based on the relatively high overpotentials that occurred due to CO poisoning and their assumption that the use of slightly anodic loadings is inevitable for PEMFC commercialization, suggested that the research community should consider focusing on reducing the CO concentration limits of the Hydrogen Quality Standard.…”

mentioning

confidence: 99%

Carbon Monoxide Tolerant Pt-Based Electrocatalysts for H2-PEMFC Applications: Current Progress and Challenges

Molochas

Tsiakaras

2021

Catalysts

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The activity degradation of hydrogen-fed proton exchange membrane fuel cells (H2-PEMFCs) in the presence of even trace amounts of carbon monoxide (CO) in the H2 fuel is among the major drawbacks currently hindering their commercialization. Although significant progress has been made, the development of a practical anode electrocatalyst with both high CO tolerance and stability has still not occurred. Currently, efforts are being devoted to Pt-based electrocatalysts, including (i) alloys developed via novel synthesis methods, (ii) Pt combinations with metal oxides, (iii) core–shell structures, and (iv) surface-modified Pt/C catalysts. Additionally, the prospect of substituting the conventional carbon black support with advanced carbonaceous materials or metal oxides and carbides has been widely explored. In the present review, we provide a brief introduction to the fundamental aspects of CO tolerance, followed by a comprehensive presentation and thorough discussion of the recent strategies applied to enhance the CO tolerance and stability of anode electrocatalysts. The aim is to determine the progress made so far, highlight the most promising state-of-the-art CO-tolerant electrocatalysts, and identify the contributions of the novel strategies and the future challenges.

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Tolerance and Recovery of Ultralow-Loaded Platinum Anode Electrodes upon Carbon Monoxide and Hydrogen Sulfide Exposure

Cited by 23 publications

References 31 publications

Hydrogen Oxidation Artifact During Platinum Oxide Reduction in Cyclic Voltammetry Analysis of Low-Loaded PEMFC Electrodes

Hydrogen Oxidation Artifact During Platinum Oxide Reduction in Cyclic Voltammetry Analysis of Low-Loaded PEMFC Electrodes

Impact of the Cathode Pt Loading on PEMFC Contamination by Several Airborne Contaminants

Carbon Monoxide Tolerant Pt-Based Electrocatalysts for H2-PEMFC Applications: Current Progress and Challenges

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