Characterizing the Structural Degradation in a PEMFC Cathode Catalyst Layer: Carbon Corrosion

Young, A. P.; Stumper, Jürgen; Gyenge, Előd L.

doi:10.1149/1.3139963

Cited by 171 publications

(120 citation statements)

References 28 publications

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“…Observed previously, 11 the CV and EIS Cdl measurements differed by a factor of 1 to 2. It is clarified here that the pseudo-capacitance part of the Pt oxide reduction peak may convolute the Cdl measured during CV.…”

Section: Observations Inmentioning

confidence: 61%

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A Semi-Empirical Two Step Carbon Corrosion Reaction Model in PEM Fuel Cells

Young

Colbow

Harvey

et al. 2013

J. Electrochem. Soc.

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The cathode CL of a polymer electrolyte membrane fuel cell (PEMFC) was exposed to high potentials, 1.0 to 1.4 V versus a reversible hydrogen electrode (RHE), that are typically encountered during start up/shut down operation. While both platinum dissolution and carbon corrosion occurred, the carbon corrosion effects were isolated and modeled. The presented model separates the carbon corrosion process into two reaction steps; (1) oxidation of the carbon surface to carbon-oxygen groups, and (2) further corrosion of the oxidized surface to carbon dioxide/monoxide. To oxidize and corrode the cathode catalyst carbon support, the CL was subjected to an accelerated stress test cycled the potential from 0.6 V RHE to an upper potential limit (UPL) ranging from 0.9 to 1.4 V RHE at varying dwell times. The reaction rate constants and specific capacitances of carbon and platinum were fitted by evaluating the double layer capacitance (Cdl) trends. Carbon surface oxidation increased the Cdl due to increased specific capacitance for carbon surfaces with carbon-oxygen groups, while the second corrosion reaction decreased the Cdl due to loss of the overall carbon surface area. The first oxidation step differed between carbon types, while both reaction rate constants were found to have a dependency on UPL, temperature, and gas relative humidity. Early polymer electrolyte membrane fuel cell (PEMFC) research used platinum black as the catalyst for both the cathode and anode electrodes. These electrodes were costly due to their very high Pt loadings (>>1.0 mg/cm 2 ). One of the ways of reducing the platinum loading was to replace platinum black with dispersed platinum nanoparticles on a carbon support. The smaller platinum particles on carbon enabled a reduced Pt loading of the cathode to less than 0.5 mg/cm 2 , while maintaining the required platinum surface area required for high fuel cell performance. Although cost was reduced, the durability of the fuel cell was negatively impacted. At potentials greater than 0.2 V RHE (reversible hydrogen electrode), the carbon support is thermodynamically unstable and able to oxidize to carbon dioxide (CO 2 ) and/or carbon monoxide (CO) [Eqs. 1-3], 1 leaving the platinum unsupported and inactive. Furthermore, due to the loss of support the platinum particles have been shown to agglomerate into larger particles, dissolve into the ionomer, or get washed out of the system.Even in the presence of platinum, the kinetics of carbon oxidation/corrosion is relatively slow; therefore, carbon is quite stable under normal PEMFC operating conditions. In practice, elevated cathode potentials of greater than 1.2 V RHE are required to oxidize carbon at reaction rates high enough to cause significant structural degradation. Normal PEMFC operation occurs between 0-1.0 V RHE ; however, upon fuel starvation or gas switching conditions (start-up and shutdown operation due to infiltration of oxygen into the normally hydrogen filled anode compartment during fuel cell off conditions) the cathode potential can exceed ...

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Section: Observations Inmentioning

confidence: 61%

“…The EIS spectra were fit to an equivalent circuit representing a transmission line network of the porous CL. As discussed elsewhere 11 in greater detail, the fitted parameters consisted of the high frequency cell resistance, the cathode CL protonic resistance, and the Cdl.…”

mentioning

confidence: 99%

A Semi-Empirical Two Step Carbon Corrosion Reaction Model in PEM Fuel Cells

Young

Colbow

Harvey

et al. 2013

J. Electrochem. Soc.

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“…The resulting spike in the cathode voltage to a potential of about 1.5 V vs. SHE produces severe corrosion of the carbon support material of the cathode catalyst, with associated damage by electrode layer thinning and disintegration, platinum nanoparticle agglomeration, and the loss of catalytically active platinum surface area. [6][7][8] Surface oxides may also form, making the cathode layer more hydrophilic and prone to water flooding, which drastically reduces oxygen access to active catalytic sites. 9 System control strategies have been sought to minimize these voltage spikes, but no practical solutions have emerged to eliminate the problem.…”

mentioning

confidence: 99%

Power Output and Durability of Electrospun Fuel Cell Fiber Cathodes with PVDF and Nafion/PVDF Binders

Brodt

Dale

Pintauro

2016

J. Electrochem. Soc.

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Membrane-electrode-assemblies (MEAs) with electrospun nanofiber mat electrodes (0.10 mg/cm 2 Pt loading) and a Nafion 211 membrane were prepared and tested in a H 2 /air fuel cell at 100% and 40% relative humidity. The cathode binder was either neat poly(vinylidene fluoride) (PVDF) or a Nafion/PVDF blend (20 to 80 wt% Nafion) and the anode binder was Nafion with poly(acrylic acid). Polarization curves were recorded at 80 • C and ambient pressure before, intermittently, and after a carbon corrosion voltage cycling experiment. The Nafion/PVDF cathode MEA with the smallest amount of PVDF (80/20 Nafion/PVDF weight ratio) produced the highest maximum power at beginning-of-life (BoL), 545 mW/cm 2 at 100% RH, which was 35% greater than that for a conventional MEA with a neat Nafion binder. Carbon corrosion scaled inversely with cathode PVDF content, with a 33/67 Nafion/PVDF cathode binder MEA producing the highest end-of-life (EoL) power (330 mW/cm 2 ). MEAs with < 50 wt% PVDF in the cathode binder exhibited a power density decline during carbon corrosion, whereas the power increased during/after carbon corrosion for nanofiber cathodes with binders containing > 50 wt% PVDF due to favorable increases in the hydrophilicity of the carbon support and Pt mass activity, coupled with a lower carbon loss. The hydrogen/air proton-exchange membrane fuel cell is a promising candidate for emission-free automotive power plants, but issues remain regarding the high cost and durability of membrane-electrodeassemblies (MEAs).1 For commercialization, the Pt loading of fuel cell MEAs (particularly the cathode) must be reduced while maintaining high power output and the catalytic activity of the cathode for electrochemical oxygen reduction must be maintained during long-term operation with various power cycles and numerous stack start-ups and shut-down events. 2In a series of recent papers, Pintauro and coworkers have shown that an electrospun nanofiber cathode, composed of Pt/C particles and a binder of Nafion + poly(acrylic acid) (abbreviated as PAA) performs remarkably well in a hydrogen/air proton exchange membrane fuel cell.3-5 For example, a nanofiber electrode MEA with 0.055 mg Pt /cm 2 at the cathode and 0.059 mg Pt /cm 2 at the anode (Johnson Matthey Pt/C catalyst) produced more than 900 mW/cm 2 at maximum power in a H 2 /air fuel cell at 80• C, 100% RH, and high feed gas flow rates at 2 atm backpressure. 4 In a recent collaborative study between Vanderbilt University and Nissan Technical Center North America, Brodt et al. 5 showed that MEAs with an electrospun particle/polymer cathode generated high beginning-of-life power and also exhibited excellent durability, as determined from end-of-life polarization curves after an accelerated start-stop voltage cycling (carbon corrosion) test. Thus, after 1,000 simulated start-stop cycles, a nanofiber MEA with Johnson Matthey Pt/C catalyst and a binder of Nafion + PAA maintained 53% of its initial power at 0.65 V and 85% of its maximum power, as compared to a 28% power retention at 0.65...

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“…Despite the majority of studies blaming voltage cycling of the cell for the carbon corrosion in PEMFC [184, 185, 187-189, 218, 243], some studies have associated its cause to the presence of liquid water in the catalyst [248][249][250][251][252]. Maass et al [249] found that the corrosion rate of carbon is linearly dependant on the molar water concentration.…”

Section: Corrosionmentioning

confidence: 99%

Degradation aspects of water formation and transport in Proton Exchange Membrane Fuel Cell: A review

Ous

Arcoumanis

2013

Journal of Power Sources

137

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This is the accepted version of the paper.This version of the publication may differ from the final published version. Permanent repository link AbstractThis review paper summarises the key aspects of Proton Exchange Membrane Fuel Cell (PEMFC) degradation that are associated with water formation, retention, accumulation, and transport mechanisms within the cell. Issues related to loss of active surface area of the catalyst, ionomer dissolution, membrane swelling, ice formation, corrosion, and contamination are also addressed and discussed. The impact of each of these water mechanisms on cell performance and durability was found to be different and to vary according to the design of the cell and its operating conditions. For example, the presence of liquid water within Membrane Electrode Assembly (MEA), as a result of water accumulation, can be detrimental if the operating temperature of the cell drops to sub-freezing.The volume expansion of liquid water due to ice formation can damage the morphology of different parts of the cell and may shorten its life-time. This can be more serious, for example, during the water transport mechanism where migration of Pt particles from the catalyst may take place after detachment from the carbon support. Furthermore, the effect of transport mechanism could be augmented if humid reactant gases containing impurities poison the membrane, leading to the same outcome as water retention or accumulation.Overall, the impact of water mechanisms can be classified as aging or catastrophic. Aging has a longterm impact over the duration of the PEMFC life-time whereas in the catastrophic mechanism the impact is immediate. The conversion of cell residual water into ice at sub-freezing temperatures by the water retention/ accumulation mechanism and the access of poisoning contaminants through the water transport mechanism are considered to fall into the catastrophic category. The effect of water mechanisms on PEMFC degradation can be reduced or even eliminated by (a) using advanced materials for improving the electrical, chemical and mechanical stability of the cell components against deterioration, and (b) implementing effective strategies for water management in the cell.

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Characterizing the Structural Degradation in a PEMFC Cathode Catalyst Layer: Carbon Corrosion

Cited by 171 publications

References 28 publications

A Semi-Empirical Two Step Carbon Corrosion Reaction Model in PEM Fuel Cells

A Semi-Empirical Two Step Carbon Corrosion Reaction Model in PEM Fuel Cells

Power Output and Durability of Electrospun Fuel Cell Fiber Cathodes with PVDF and Nafion/PVDF Binders

Degradation aspects of water formation and transport in Proton Exchange Membrane Fuel Cell: A review

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