Spontaneous oscillations of cell voltage, power density, and anode exit CO concentration in a PEM fuel cell

Lü, Hui; Rihko‐Struckmann, Liisa; Sundmacher, Kai

doi:10.1039/c1cp21984g

Cited by 23 publications

(20 citation statements)

References 33 publications

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“…From a technical point of view, the occurrence of oscillatory kinetics can be thought of as an autonomous self‐cleaning process that can prevent the anode becoming completely poisoned by adsorbed carbon monoxide, as is the case under conventional, non‐oscillatory conditions. In fact, it has been reported that operating a fuel cell under an oscillatory regime can result in higher average power densities than those obtained at a steady state …”

Section: Introductionsupporting

confidence: 71%

“…It can be seen that the differences between the Pd‐Pt/C and Pd/C systems studied herein, and their differences relative to the Pt‐Ru/C system, which is widely discussed in the literature, reflect different adsorption/oxidation kinetic constants of CO and of H 2 , in addition to the H 2 O dissociation on the catalyst surface for the formation of OH ad . As first proposed by Lopes et al., CO‐stripping voltammetry can be used to estimate the mean amplitude of oscillation.…”

Section: Resultsmentioning

confidence: 99%

“…[11] An interesting aspect of these devices is that the reactions that occur on the surface of these catalysts and the adsorption/desorptionp rocesses are interrelated through the anode potential, and this delicate interplay can result in oscillatory behavior. [13][14][15] In addition, oscillatory dynamics in aPEMFC are not restricted to systems with aP t-Ru/C anode, [16][17][18][19][20][21][22][23][24][25][26][27][28] and the occur-rence on Pd-Pt/C [29] and on Pt [30,31] anodes has also been reported.…”

Section: Introductionmentioning

confidence: 99%

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Voltage Oscillations in a Polymer Electrolyte Membrane Fuel Cell with Pd‐Pt/C and Pd/C Anodes

Nogueira

Varela

2017

ChemistryOpen

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Polymer electrolyte membrane fuel cells (PEMFC) fed with H2 contaminated with CO may exhibit oscillatory behavior when operated galvanostatically. The self‐organization of the anodic overpotential is interesting because it can be accompanied by an increase in the average performance. Herein we report experimental studies of voltage oscillations that emerge in a PEMFC equipped with a Pd/C or PdPt/C anode and fed with H2 contaminated with CO (100 ppm). We used on‐line mass spectrometry to investigate how the mass fragments associated with CO2 and CO (m/z 44 and 28, respectively) varied with the voltage oscillations. Overall, we observed that oscillations in the anodic overpotential are in phase with that of the CO and CO2 signals. This fact is consistent with an autonomous adsorption–oxidation cyclic process. For both anodes, it has been observed that, in general, an increase in current density implies an increase in oscillatory frequency. By using CO stripping, we also discuss how the onset of CO oxidation is related to the maximum overpotential reached during a cycle, whereas the minimum overpotential can be associated with the catalytic activity of the electrode for H2 oxidation.

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Section: Introductionsupporting

confidence: 71%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Voltage Oscillations in a Polymer Electrolyte Membrane Fuel Cell with Pd‐Pt/C and Pd/C Anodes

Nogueira

Varela

2017

ChemistryOpen

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“…The Pd1 catalyst is the only catalyst that exhibits spontaneous oscillations of the fuel cell potential. These oscillations may be explained as follows [46]: electrooxidation of impurities of the formic acid to CO ads strongly adsorbed on Pd surface causing the decrease of the FC voltage and power, but at sufficiently low voltage the rate of oxidation of CO ads to CO 2 increases cleaning the surface of the catalyst what results in an increase of FC voltage and power. The other explanation may be that formic acid is directly electrooxidised to CO 2 , which is periodically removed from the catalyst layer [10].…”

Section: Fuel Cell Testsmentioning

confidence: 99%

Deactivation resistant Pd–ZrO2 supported on multiwall carbon nanotubes catalyst for direct formic acid fuel cells

Małolepszy

Mazurkiewicz

Stobiński

et al. 2015

International Journal of Hydrogen Energy

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“…Instabilities, such as these oscillations are quite common in electrochemical systems when there are competing reactions. Several studies have reported spontaneous potential oscillations recorded for PEM PtRu anodes exposed to H 2 and CO. [15][16][17][18] The frequency of such oscillations has been shown to depend on conditions such as current density, gas mixture composition, cell temperature, and gas flow velocity. To our knowledge, this is the first report of current oscillations in a CO 2 /H 2 on PEM PtRu anodes.…”

Section: Resultsmentioning

confidence: 99%

Influence of Hydrogen and Operation Conditions on CO2 Adsorption on Pt and PtRu Catalyst in a PEMFC

Kortsdottir¹,

Domínguez²,

Lindström³

2013

ECS Electrochemistry Letters

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CO 2 is a major component in reformate gas and can, as a source of CO, be a catalyst poison in polymer electrolyte membrane fuel cells. The effect of CO 2 on cell performance is not fully understood in the presence of hydrogen. This paper addresses the influence of hydrogen on CO 2 adsorption on Pt/C and PtRu/C catalysts. The results show that the reduction and adsorption of CO 2 is slow but increases if hydrogen is present, especially on PtRu/C. Further, exposure to a CO 2 and H 2 mixture at 0.15 V on PtRu/C results in current oscillations, which are dependent on operation conditions. Reformate gas inevitably contains 10-30% CO 2 and traces of CO, even after several purification steps. While numerous studies exist on the influence of CO on fuel cell performance, see reviews 1-3 and references therein, the effect of CO 2 is less studied. Although CO 2 is potentially harmless in a fuel cell, studies have shown 4,5 that 20-25% CO 2 in the hydrogen fuel induces performance losses that cannot be explained by dilution only. It is generally argued that CO 2 is transformed to CO in the fuel cell, due to the reverse water-gas shift (RWGS) reaction 4or by an electrochemical reduction mechanism, 6 such asalthough the latter has been questioned due to its low standard potential of −0.2 V. 7 According to thermodynamic calculations the RWGS reaction would give rise to CO concentrations of about 15-100 ppm in equilibrium with a 20-25% CO 2 /H 2 gas mixture 2,8,9 depending on temperature and humidity. However, the moderate effects of CO 2 in operating fuel cells 8,10 indicates that much lower concentrations must be present, presumably due to slow kinetics of both the RWGS reaction 9,11 and the electroreduction of CO 2 8 at PEM fuel cell conditions. Using PtRu as a catalyst instead of Pt has been shown to improve the tolerance of CO 2 in the hydrogen gas, 4,5,9,12 but there is some controversy as to whether it is only due to the improved tolerance to CO,11,12 or if Ru somehow hinders the transformation of CO 2 to CO. 4,9 This study sheds further light on the interplay between hydrogen and CO 2 in a fuel cell both on Pt/C and PtRu/C catalyst and how this is affected by operation conditions, in particular the influence of relative humidity and the presence or absence of H 2 . ExperimentalMembrane electrode assemblies (MEA) were prepared using Tanaka catalysts (TEC10E40E, 36% Pt, and TEC61E54, 29.7% Pt and 23.0% Ru (1:1.5) both on high surface carbon) and N115 membranes, as previously described. 13,14 The experimental setup was identical to that used in a previous study, 14 with a cell housing from ElectroChem, Inc connected to a PAR potentiostat. The MEA was activated according to the previously described procedure, 13,14 except for the adjustment of the higher potential limit in the case of PtRu from 1.2 to 0.9 V, to avoid Ru oxidation and subsequent dissolution and loss of catalyst.As a standard experiment, CO 2 was allowed to enter the cell at a potential hold at 0.15 V for 30 min followed by a 5 min purge with N 2 . These time...

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Spontaneous oscillations of cell voltage, power density, and anode exit CO concentration in a PEM fuel cell

Cited by 23 publications

References 33 publications

Voltage Oscillations in a Polymer Electrolyte Membrane Fuel Cell with Pd‐Pt/C and Pd/C Anodes

Voltage Oscillations in a Polymer Electrolyte Membrane Fuel Cell with Pd‐Pt/C and Pd/C Anodes

Deactivation resistant Pd–ZrO2 supported on multiwall carbon nanotubes catalyst for direct formic acid fuel cells

Influence of Hydrogen and Operation Conditions on CO2 Adsorption on Pt and PtRu Catalyst in a PEMFC

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