Modeling hydrogen starvation conditions in proton-exchange membrane fuel cells

Ohs, Jan Hendrik; Sauter, Ulrich; Maaß, Susanne; Stolten, Detlef

doi:10.1016/j.jpowsour.2010.06.038

Cited by 57 publications

(33 citation statements)

References 14 publications

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“…• Model prediction: To overcome the disadvantages in the experimental measurements mentioned above, some researchers have developed mathematical models to obtain the electrolyte potential profile for this phenomenon [47,57,58]. The results can assist researchers in clearly understanding degradation mechanisms.…”

Section: Reverse Currentmentioning

confidence: 99%

“…In addition to measuring or mathematically predicting the high cathode potential experienced during the startup and shutdown processes, researchers have also conducted other related tests, such as measuring the current distribution in segmented cells [60][61][62], monitoring the concentration of CO or CO 2 during startup and shutdown [59,63], evaluating the effect of cell design (flow field structure and GDL thickness) on start-stop phenomena [64,65], and conducting modeling studies [58,[66][67][68][69][70][71][72][73] on water management and carbon-corrosion during startup and shutdown. All the test results have confirmed performance degradation during the startup and shutdown processes of PEMFCs.…”

Section: Reverse Currentmentioning

confidence: 99%

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A review on performance degradation of proton exchange membrane fuel cells during startup and shutdown processes: Causes, consequences, and mitigation strategies

Wang

et al. 2012

Journal of Power Sources

272

150

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a b s t r a c tPerformance degradation during startup and shutdown is considered an important issue affecting the durability and lifetime of proton exchange membrane fuel cells (PEMFCs). Due to the high potentials experienced by the cathode during startup and shutdown, the conventional carbon support for the cathode catalyst is prone to oxidation by reacting with oxygen or water. This paper presents an overview of the causes and consequences of performance degradation after frequent startup-shutdown cycles. Mitigation strategies are also summarized, including the use of novel catalyst supports and the application of system strategies to prevent performance degradation in PEMFCs. It is found from the literature review that improvements in catalyst supports to prevent oxidation come at the expense of high cost, and the novel supports developed to date are not sufficient to completely prevent carbon oxidation in fuel cell engines. System strategies, including potential control and reaction gas control, have been developed and applied in fuel cell engines to alleviate or even avoid performance decay. This review aims to provide a clear understanding of the mechanisms related to degradation behaviors during the startup and shutdown processes, thereby helping fuel cell material or system developers in their efforts to prevent performance degradation and prolong the lifetime of PEMFCs.Crown

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Section: Reverse Currentmentioning

confidence: 99%

Section: Reverse Currentmentioning

confidence: 99%

A review on performance degradation of proton exchange membrane fuel cells during startup and shutdown processes: Causes, consequences, and mitigation strategies

Wang

et al. 2012

Journal of Power Sources

272

150

View full text Add to dashboard Cite

show abstract

“…An inappropriate perimeter-placed reference is sometimes 20 used. 17,18 But most commonly, the ORR characteristics are simply assumed to dominate the signal to justify the use of a twoelectrode setup, which appears reasonable given the higher exchange current density of the HOR. However, Kuhn et al 19 separated the contributions with a pseudo reference electrode 25 sandwiched between the electrodes and found that the HOR impedance was not negligible under their conditions, but of the same order of magnitude across the entire cell impedance range.…”

Section: Introductionmentioning

confidence: 99%

Electrocatalytic performance of fuel cell reactions at low catalyst loading and high mass transport

Zalitis

Kramer

Kucernak

2013

Phys. Chem. Chem. Phys.

180

194

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An alternative approach to the rotating disk electrode (RDE) for characterising fuel cell electrocatalysts is presented. The approach combines high mass transport with a flat, uniform, and homogeneous catalyst deposition process, well suited for studying intrinsic catalyst properties at realistic operating conditions of a polymer electrolyte fuel cell (PEFC). Uniform catalyst layers were produced with loadings as low as 0.16 μg Pt cm -2 and thicknesses as low as 200 nm. Such ultra thin catalyst layers are considered 10 advantageous to minimize internal resistances and mass transport limitations. Geometric current densities as high as 5.7 A cm -2 Geo were experimentally achieved at a loading of 10.15 μgPt cm -2 for the hydrogen oxidation reaction (HOR) at room temperature, which is three orders of magnitude higher than current densities achievable with the RDE. Modelling of the associated diffusion field suggests that such high performance is enabled by fast lateral diffusion within the electrode. The electrodes operate over a wide 15 potential range with insignificant mass transport losses, allowing the study of the ORR at high overpotentials. Electrodes produced a specific current density of 31 ± 9 mA cm -2Spec at a potential of 0.65 V vs. RHE for the oxygen reduction reaction (ORR) and 600 ± 60 mA cm -2 Spec for the peak potential of the HOR. The mass activities of Pt/C catalysts towards the ORR was found to exceed a range of literature PEFC mass activities across the entire potential range. The HOR also revealed fine structure in 20 the limiting current range and an asymptotic current decay for potentials above 0.36 V. These characteristics are not visible with techniques limited by mass transport in aqueous media such as the RDE. IntroductionUnderstanding the kinetics of the oxygen reduction reaction 25 (ORR) and hydrogen oxidation reaction (HOR) on platinum nano-particles is vital for polymer electrolyte fuel cell (PEFC) development. Each platinum nano-particle within the electrode should have optimal proton access, gas access and an electronic path to study intrinsic electrocatalytic properties of the catalyst. 30 These three criteria should be maintained throughout the working conditions (e.g., temperature, humidity and potential). If a reaction site is starved for any of the three, its activity will be reduced, which skews the average activity and introduces an error. It is paramount to minimize the number of underperforming 35 catalyst sites to determine intrinsic catalyst properties. Ideally, the catalyst layer should be made as thin as possible. Thus, all the catalyst particles will be close to the perfluorosulfonic acid (PFSA) membrane for ionic access and close to the gas diffusion layer (GDL) for gas access and an electronic path, removing 40 internal limitations. Mass transport limitations lead to concentration polarization across thick electrodes, 1-3 limiting the active thickness to about 5 μm at high current densities, regardless of how thick the catalyst layer is. 1 The majority of ORR and ...

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“…101 The model shows that the formation of surface oxides on platinum and carbon support is a key feature in the degradation reaction. In order to resolve local carbon corrosion anode 102 and cathode 103 two dimensional models have been developed which link corrosion to distribution of local current density. A one dimensional model along the channel was applied to model carbon corrosion in dead end mode PEFC 104 with good qualitative agreement.…”

Section: Degradation Modelsmentioning

confidence: 99%

Accelerated Degradation of High-Temperature Polymer Electrolyte Fuel Cells: Discussion and Empirical Modeling

Reimer

Schumacher

Lehnert

2014

J. Electrochem. Soc.

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Accelerated stress tests are commonly applied in order to obtain a prediction of fuel cell life time within a short testing period. The stress test in this work considers a fuel cell which is constantly under load with frequent periods of very high current. Four different cells were operated each with a specific load profile. As a result severe performance degradation was observed in the region of high current densities. A short overview over the phenomena which may contribute to this specific fuel cell degradation is compiled from literature. Based on this overview major degradation modes are identified and combined with a simple polarization curve model. The modeling results allow for two different interpretations. Carbon corrosion reactions can explain the observed effects if cell voltage is assumed as the driving force for degradation. A better fit was obtained by using the overall heat flux as degradation criterion. In this case an increase in local temperature could lead to redistribution and loss of phosphoric acid from the MEA. The expected lifetime of a polymer electrolyte fuel cell (PEFC) ranges from 5 000 h for mobile application to 40 000 h for stationary application.1,2 In order to gain information about time dependent degradation in advance accelerated test protocols are used.3,4 Depending on the design of these tests valuable information about the nature of the main degradation mode under the applied operation conditions can be obtained. Despite the difference in operation conditions for PEFC, HT-PEFC and PAFC the structure and material of the electrodes are almost the same. Consequently, observed degradation phenomena show strong similarities.5 A good description of these phenomena can be found in several review papers 6-13 as well as in at least four books 1,2,14,15 where recent experimental facts and interpretations are summarized. A compact description can also be found in a recent review paper on modeling transport phenomena in PEFCs. 16 The purpose of this paper is to present the results of a specific accelerated degradation test for high temperature polymer electrolyte fuel cells (HT-PEFC) with phosphoric acid doped polybenzimidazole (PBI/H 3 PO 4 ) membranes. The fuel cell is constantly under load with frequent periods of very high current. In order to accelerate degradation effects the fuel cell is operated beyond it's point of maximum power. A simple polarization curve model is used as starting point for the analysis of data. Based on this first analysis a degradation model is proposed which allows for a straightforward physical interpretation. The complexity of degradation effects which occur simultaneousy usually leads to models which either resolve a specific mechanism in depth or describe more general effects. This paper aims at general effects which requires a broader understanding of degradation. In the following it is attempted to provide an overview over the phenomena which may contribute to fuel cell degradation. Based on this overview major degradation modes are identified and ...

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Modeling hydrogen starvation conditions in proton-exchange membrane fuel cells

Cited by 57 publications

References 14 publications

A review on performance degradation of proton exchange membrane fuel cells during startup and shutdown processes: Causes, consequences, and mitigation strategies

A review on performance degradation of proton exchange membrane fuel cells during startup and shutdown processes: Causes, consequences, and mitigation strategies

Electrocatalytic performance of fuel cell reactions at low catalyst loading and high mass transport

Accelerated Degradation of High-Temperature Polymer Electrolyte Fuel Cells: Discussion and Empirical Modeling

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