Relationships between PEMFC Cathode Kinetic Losses and Contaminants’ Dipole Moment and Adsorption Energy on Pt

St‐Pierre, Jean; Zhai, Yunfeng; Ge, Junjie

doi:10.1149/2.1061603jes

Cited by 12 publications

(5 citation statements)

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“…On the cathode side, a chemical air filter may be required to remove potential contaminants (SO x , H 2 S, NO x , volatile organic compounds, etc.) from intake air [111,112]. In addition to external contaminants, degradation products (sulfate and organic compounds from the membrane [66,[113][114][115]; cobalt from the catalyst [116,117]) from within the fuel cell MEA can also decrease fuel cell cathode performance.…”

Section: Durability Of Low-pt Fuel Cellmentioning

confidence: 99%

Proton-Exchange Membrane Fuel Cells with Low-Pt Content

Kongkanand¹,

Gu²,

Mathias

2017

Encyclopedia of Sustainability Science and Technology

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Widespread commercialization of fuel cell electric vehicles (FCEV) relies on further reduction of PGM (platinum group metals) usage. Although enhancements in the activity and stability of the catalyst are necessary, those alone are insufficient. In a fuel cell with low PGM content, transport of reactants (oxygen and protons) to a small area of catalyst can cause large performance loss at high power. Because it is this high-power point that determines the required fuel cell area, these losses drive up the size, and thus the cost, of the fuel cell stack. This entry discusses fuel cell cost reduction with special focus on the challenges and opportunity associated with Pt reduction. Proton-Exchange Membrane Fuel Cells with Low-Pt Content, Fig. 1 Impact of fuel cell vehicles on Pt consumption (Reprinted with permission from Ref. [7].

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Section: Durability Of Low-pt Fuel Cellmentioning

confidence: 99%

Proton-Exchange Membrane Fuel Cells with Low-Pt Content

Kongkanand¹,

Gu²,

Mathias

2017

Encyclopedia of Sustainability Science and Technology

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“…Table 1 indicates that conversion is below 43 and 49% at 0.55 V for propene and methyl methacrylate, respectively. Therefore, for the lower cell voltages of 0.46 and 0.44 V, contaminant conversion is expected to be even lower than at 0.55 V. Table 1 data were obtained with similar MEAs (ohmic resistance of approximately 0.056 Ω•cm 2 at 1 A•cm −2 ), 49 which is comparable to an average of 0.064 Ω•cm 2 at 1 A•cm −2 for the present work (Section 3.2). The estimated cathode potentials from ref 48 and the present report data are similar because a hydrogen electrode was also used for both cases (anode potential of ∼0 V versus the RHE).…”

Section: Resultsmentioning

confidence: 91%

“…Most contaminants are not fully oxidized at a 0.55 V cell voltage (Table ), which is in part supported by contaminant reduction and oxidation potentials . This situation ensures that a supply of unaltered contaminant is available for adsorption.…”

Section: Methodsmentioning

confidence: 99%

“…Most contaminants are not fully oxidized at a 0.55 V cell voltage (Table 1), which is in part supported by contaminant reduction and oxidation potentials. 49 This situation ensures that a supply of unaltered contaminant is available for adsorption. Tests completed with different contaminant concentrations and a momentary contaminant injection have demonstrated that the current distribution may be altered.…”

Section: Introductionmentioning

confidence: 99%

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Contamination Mechanisms of Proton Exchange Membrane Fuel Cells - Mass Transfer Overpotential Origin

et al. 2020

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Several experimental methods were used to identify the cause of the concurrent increase in kinetic and mass transfer overpotentials during the contamination of proton exchange membrane fuel cells outfitted with a commercially relevant cathode catalyst loading of 0.1 mg Pt per cm2. Neutron images demonstrated that the transport of liquid water through gas diffusion electrode materials was subtly affected by the presence of propene and methyl methacrylate in air at ppm levels (25 to 100 ppm propene, 12.5 to 50 ppm methyl methacrylate). Multioxidant polarization curves were obtained to isolate overpotentials (O2, 21% O2 + 79% He, and air). For all cases, neat air, 50 ppm propene in air, and 25 ppm methyl methacrylate in air, only kinetic and mass transfer overpotentials increased (O2 reduction on a Pt supported on C catalyst, O2 diffusion through the catalyst layer ionomer). Also, only the O2 mass transfer coefficient associated with diffusion in the catalyst layer ionomer increased in the presence of 50 ppm propene and 25 ppm methyl methacrylate. Contaminant species adsorbed on the catalyst decrease the active surface area and increase both the real current density and the O2 reduction kinetic overpotential. The smaller active surface area also brings the real current density closer to the limiting value, inducing an increase of the mass transfer overpotential connected with O2 movement in the ionomer layer covering the catalyst. This mechanism was supported by a mathematical contamination model focused on contaminant and O2 processes on the catalyst surface (adsorption, reaction, desorption).

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“…The absence of a correlation is not surprising, considering the effects of cell design and operating conditions on contamination. Several parameters were mentioned in an earlier attempt to correlate the effect of contaminants on oxygen reduction kinetics [65], including contaminant partial pressure and temperature, exposed Pt surface features (crystal faces, edges), Pt state (reduced or oxidized), phase in contact with the Pt surface (air, ionomer), adsorption isotherms for O 2 , contaminants, and related intermediates and products, and elementary chemical and electrochemical reactions and associated rate constants for O 2 reduction and contaminant oxidation or reduction. This list is enlarged by factors affecting ohmic and mass transfer losses, including cation and neutral molecules' absorption isotherms influencing ionomer and membrane ionic conductivity and oxygen permeability by swelling and changing the distance between sulfonate groups, and contaminant scavenging by liquid water modifying the effective contaminant concentration [12,13,[66][67][68][69][70][71].…”

Section: Contaminant Effect Predictionmentioning

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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Relationships between PEMFC Cathode Kinetic Losses and Contaminants’ Dipole Moment and Adsorption Energy on Pt

Cited by 12 publications

References 77 publications

Proton-Exchange Membrane Fuel Cells with Low-Pt Content

Proton-Exchange Membrane Fuel Cells with Low-Pt Content

Contamination Mechanisms of Proton Exchange Membrane Fuel Cells - Mass Transfer Overpotential Origin

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

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