Analysis of Ice Formation Process in Cathode Catalyst Layer of PEFC at Cold Start

Tabe, Yutaka; Ichikawa, Ryosuke; Chikahisa, Takemi

doi:10.1016/j.egypro.2012.08.036

Cited by 21 publications

(18 citation statements)

References 10 publications

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“…These observations support the previous suggestion that the oxygen supply does not dominate the ice distribution, and suggest that the different ice distributions reported by Thompson et al using pure oxygen 14 and Li et al using air 15 were caused mainly by the magnitude of the current density, not by the cathode gas conditions. Simplified analyses using the agglomerate and the CL models developed by the authors 20 suggest that a steep reduction in oxygen diffusivity in the CL pores due to ice formation, something which is difficult to estimate by conventional models, is necessary to change the ice formation rate throughout the CL at relatively-low current densities of cold startup. Further, even if a drastic reduction is possible, the similar durations of operation until the shutdown and the similar ice distributions in the CL under the various cathode gas conditions cannot be explained by the oxygen transport.…”

Section: Resultsmentioning

confidence: 99%

“…The proton conductivity of a polymer electrolyte decreases at lower temperatures, 19 and the higher reaction rate near the membrane interface is estimated to be due to the significant decrease in the proton conductivity of the ionomer in the CL below freezing, even in the range of relatively-low current densities at cold startup. 20 As protons are supplied from the anode side through the membrane, there is a lower reaction rate in the region far from the membrane interface, and the unevenness of the reaction rate becomes more pronounced with higher current densities. The observed ice formation early in the freezing (in Figs.…”

Section: Resultsmentioning

confidence: 99%

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Ice Formation Processes in PEM Fuel Cell Catalyst Layers during Cold Startup Analyzed by Cryo-SEM

Tabe

Yamada

Ichikawa

et al. 2016

J. Electrochem. Soc.

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For further improvements in the startup ability below freezing and the durability of polymer electrolyte fuel cells, understanding the ice formation mechanism during cold startup is particularly significant. This study observes cross-sectional ice distributions in a catalyst layer (CL) during isothermal galvanostatic operation at −20 • C using a cryo-scanning electron microscope. The effects of current density, cathode gas conditions, initial water content of the membrane, and cell temperature on the cold start characteristics and the ice formation process in the CL are evaluated. The observational results show that at higher current densities, the region with active ice formation moves from the membrane to the gas diffusion layer sides during the freezing period and vacant pores remain near the membrane even after cell shutdown, while the pores are completely filled with nearly-uniformly growing ice at lower current density operation. This is consistent with the experimental finding from the cold start characteristics that the estimated amount of ice accumulated in the cell until the shutdown decreases as the current density increases. Contrary to expectations, these changes are largely independent of cathode gas conditions, even with pure oxygen. Additional factors controlling the ice formation process are discussed based on the experimental results. The polymer electrolyte fuel cell (PEFC) is a potential candidate for automotive power sources and portable electricity generators because of its characteristics of high efficiency, high power density, low operating temperature, and other advantageous characteristics. In cold climates, however, ensuring startup and durability of PEFCs at subfreezing conditions is a critical issue for the practical use of PEFC. It has been reported that freezing of water produced by the cathode reaction induces shutdown (voltage failure) during startup at subfreezing temperatures, and this freezing causes various kinds of degradation of the cell performance.1-3 Therefore, a number of practicable strategies based on thermal management and control of the residual water present in the cell before cooling and starting have been developed. However, a basic understanding of details of the ice formation process at cold startup, which is particularly-significant for further improvements in the cold startup ability and durability, remains insufficiently addressed in the literature.Some modeling studies have been conducted to describe the heat and mass transfer, and ice formation during cold startup. [4][5][6][7] The research group of the authors has investigated the performance of a PEFC at temperatures below the freezing point by both simulation and experiments.4 That study identified the initial temperature at which self-starting becomes possible, and this is determined by the balance of the produced heat and water generated due to the reaction. With regard to freezing at temperatures closer to zero, like −10• C, it was reported that the produced water is present in a supercooled state, a...

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Ice Formation Processes in PEM Fuel Cell Catalyst Layers during Cold Startup Analyzed by Cryo-SEM

Tabe

Yamada

Ichikawa

et al. 2016

J. Electrochem. Soc.

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“…Thompson et al [110] experimentally determined the oxygen reduction reaction kinetics for PEMFCs operating at subfreezing temperatures and no significant change in the oxygen reduction reaction kinetics was observed. Tabe et al [107] investigated the ice distribution in a cathode CL during the process of cold start. The results showed that at higher startup current densities, ice grew from the membrane side to the GDL side.…”

Section: Experimental Work On Cold Start Of Pemfcmentioning

confidence: 99%

“…More and more experimental studies [11][12][13]42,44,[48][49][50]55,[96][97][98][99][100][101][102][103][104][105][106][107][108][109][110] have been performed simultaneously with numerical simulations to study the cell structure parameters and working conditions. Thompson et al [11] launched the research of the impact of F/T cycle on MEA, and the results showed that for membranes with water contents above λ = 8, the calorimetry and conductivity curves merged at low temperature, suggesting the formation of a common acid hydrate with similar network connectivity.…”

Section: Experimental Work On Cold Start Of Pemfcmentioning

confidence: 99%

A Review on Cold Start of Proton Exchange Membrane Fuel Cells

et al. 2014

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Successful and rapid startup of proton exchange membrane fuel cells (PEMFCs) at subfreezing temperatures (also called cold start) is of great importance for their commercialization in automotive and portable devices. In order to maintain good proton conductivity, the water content in the membrane must be kept at a certain level to ensure that the membrane remains fully hydrated. However, the water in the pores of the catalyst layer (CL), gas diffusion layer (GDL) and the membrane may freeze once the cell temperature decreases below the freezing point (T f ). Thus, methods which could enable the fuel cell startup without or with slight performance degradation at subfreezing temperature need to be studied. This paper presents an extensive review on cold start of PEMFCs, including the state and phase changes of water in PEMFCs, impacts of water freezing on PEMFCs, numerical and experimental studies on PEMFCs, and cold start strategies. The impacts on each component of the fuel cell are discussed in detail. Related numerical and experimental work is also discussed. It should be mentioned that the cold start strategies, especially the enumerated patents, are of great reference value on the practical cold start process. OPEN ACCESSEnergies 2014, 7 3180

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“…3 It was reported that at higher startup current densities, ice grew from the membrane to the GDL, while the ice distribution in the cell was nearly uniform at a lower current density. 27,28 Faster ice growth was observed under lands and at the interface of the cathode CL and GDL. 29 Cold starts at low current density allowed full utilization of cathode CL pore volume for ice storage, thereby enhancing cold start performance.…”

mentioning

confidence: 99%

Durability of Polymer Electrolyte Membrane Fuel Cells Operated at Subfreezing Temperatures

Macauley

Lujan

Spernjak

et al. 2016

J. Electrochem. Soc.

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The structure, composition, and interfaces of membrane electrode assemblies (MEA) and gas-diffusion layers (GDLs) have a significant effect on the performance of single-proton-exchange-membrane (PEM) fuel cells operated isothermally at subfreezing temperatures. During isothermal constant-current operation at subfreezing temperatures, water forming at the cathode initially hydrates the membrane, then forms ice in the catalyst layer and/or GDL. This ice formation results in a gradual decay in voltage. High-frequency resistance initially decreases due to an increase in membrane water content and then increases over time as the contact resistance increases. The water/ice holding capacity of a fuel cell decreases with decreasing subfreezing temperature (−10 • C vs. −20 • C vs. −30 • C) and increasing current density (0.02 A cm −2 vs. 0.04 A cm −2 ). Ice formation monitored using in-situ highresolution neutron radiography indicated that the ice was concentrated near the cathode catalyst layer at low operating temperatures (≈−20 • C) and high current densities (0.04 A cm −2 ). Significant ice formation was also observed in the GDLs at higher subfreezing temperatures (≈−10 • C) and lower current densities (0.02 A cm −2 ). These results are in good agreement with the long-term durability observations that show more severe degradation at lower temperatures (−20 • C and −30 • C).

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Analysis of Ice Formation Process in Cathode Catalyst Layer of PEFC at Cold Start

Cited by 21 publications

References 10 publications

Ice Formation Processes in PEM Fuel Cell Catalyst Layers during Cold Startup Analyzed by Cryo-SEM

Ice Formation Processes in PEM Fuel Cell Catalyst Layers during Cold Startup Analyzed by Cryo-SEM

A Review on Cold Start of Proton Exchange Membrane Fuel Cells

Durability of Polymer Electrolyte Membrane Fuel Cells Operated at Subfreezing Temperatures

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