Influence of Cyclic Operation on PEM Fuel Cell Catalyst Stability

Paik, C. H.; Saloka, George; Graham, George W.

doi:10.1149/1.2400204

Cited by 79 publications

(72 citation statements)

References 14 publications

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“…For UPLs less than or equal to 1.0 V RHE a decrease in the Cdl is observed, which may be associated with the loss of the platinum surface area observed in Figure 1a and 2a. For UPLs > 1.0 V RHE the Cdl initially shows an increase, which is believed to be caused by the generation of hydrophilic oxygenated carbon surface groups from the surface oxidation 11,14,15,16 in Eq. 5.…”

Section: Observations Inmentioning

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 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: 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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“…4 vs. The results data obtained in [184,185] were at much higher level than the measurements of [186]. ) [189], 25% after 400 cycles [187], and ~50% after 2400 cycles [190].…”

Section: Pt and Ionomer Dissolutionmentioning

confidence: 67%

“…These changes, also known as the loss in the active surface area of the catalyst, were associated in previous studies [179][180][181] Potential cycling is considered to be the main cause of coarsening and coalescence of Pt particles in the catalyst. The effect of cycling becomes more noticeable with an increased number of applied cycles [186][187][188][189][190] as well as with changing the profile and frequency of these cycles [182][183][184][185]. In [183] it has been reported a 75% loss of Pt surface area after varying the cell voltage between 0.65 and 1.05V for 10,000 potential cycles.…”

Section: Pt and Ionomer Dissolutionmentioning

confidence: 99%

“…Carbon corrosion was detected in many occasions following the operation of the cell under potential cycling [182,184,188,194], start-up and shutdown [176], localised fuel starvation [195,196], and extended OCV [197]. Wilson et al [194] presented TEM images showing how potential cycling causes considerable dissipation of Pt particles from their carbon support in the catalyst.…”

Section: Carbon Corrosionmentioning

confidence: 99%

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

Ous

Arcoumanis

2013

Journal of Power Sources

132

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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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“…Following Rand and Woods' report on the dissolution of platinum, [9] there have been several reports on the durability of fuel cell catalysts. [10][11][12][13][14][15][16] According to the report of Rand and Woods, [9] platinum is dissolved above 1.08 V and the evolution of molecular oxygen occurs above 1.46 V, whereas gold is not dissolved at 1.4 V. Dissolved platinum can then either deposit on existing platinum particles to form larger particles (Ostwald ripening) or diffuse into an electrochemically inaccessible portion of the membrane electrode assembly (e.g., into the gas diffusion layer), and the resulting electrochemical active surface area will accordingly decrease. [13,[17][18][19] Shao-Horn and co-workers described a potential mechanism for the loss of electrochemical active surface area.…”

mentioning

confidence: 99%