Towards more representative test methods for corrosion resistance of PEMFC metallic bipolar plates

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Abstract

Metallic bipolar plates are of increasing interest to automotive polymer electrolyte membrane fuel cell (PEMFC) manufacturers due to their low cost, high power density, ease of manufacture, high conductivity and good mechanical properties but minimising the undesirable effects of corrosion remains a key challenge. Unfortunately, reliable assessment of the applicability of stainless steels with a range of coatings and surface treatments has been hampered by a lack of representative ex situ test methods. Here we characterise the local environment experienced by a bipolar plate during fuel cell operation via in situ measurement of pH and corrosion potential for an uncoated 316L stainless steel bipolar plate in a single cell PEMFC. We demonstrate that the degradation mode is more akin to corrosion in relatively dilute thin liquid layers, rather than the fully immersed conditions employed in conventional ex situ screening tests. A key observation is that the corrosion potential of the bipolar plate is only weakly coupled to the potential of the nearest Pt electrode due to the low ionic conductivity of the discontinuous aqueous phase in the gas diffusion layer (GDL). However, localised polarisation of the steel can occur in the presence of oxygen as a result of galvanic coupling with the carbon GDL at wetted interfaces, a process which may be enhanced by the creviced geometry. The implications for development of more representative ex situ test protocols are discussed. 

LanguageEnglish
Pages2785-2791
Number of pages7
JournalInternational Journal of Hydrogen Energy
Volume40
Issue number6
DOIs
Publication statusPublished - 19 Feb 2015

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Proton exchange membrane fuel cells (PEMFC)
corrosion resistance
fuel cells
Corrosion resistance
corrosion
electrolytes
Corrosion
membranes
gaseous diffusion
Diffusion in gases
polymers
stainless steels
Stainless steel
Ionic conductivity
in situ measurement
surface treatment
ion currents
Surface treatment
radiant flux density
Fuel cells

Keywords

  • bipolar plate
  • corrosion
  • PEMFC
  • stainless steel
  • test methods
  • corrosion resistance

Cite this

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abstract = "Metallic bipolar plates are of increasing interest to automotive polymer electrolyte membrane fuel cell (PEMFC) manufacturers due to their low cost, high power density, ease of manufacture, high conductivity and good mechanical properties but minimising the undesirable effects of corrosion remains a key challenge. Unfortunately, reliable assessment of the applicability of stainless steels with a range of coatings and surface treatments has been hampered by a lack of representative ex situ test methods. Here we characterise the local environment experienced by a bipolar plate during fuel cell operation via in situ measurement of pH and corrosion potential for an uncoated 316L stainless steel bipolar plate in a single cell PEMFC. We demonstrate that the degradation mode is more akin to corrosion in relatively dilute thin liquid layers, rather than the fully immersed conditions employed in conventional ex situ screening tests. A key observation is that the corrosion potential of the bipolar plate is only weakly coupled to the potential of the nearest Pt electrode due to the low ionic conductivity of the discontinuous aqueous phase in the gas diffusion layer (GDL). However, localised polarisation of the steel can occur in the presence of oxygen as a result of galvanic coupling with the carbon GDL at wetted interfaces, a process which may be enhanced by the creviced geometry. The implications for development of more representative ex situ test protocols are discussed. ",
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AB - Metallic bipolar plates are of increasing interest to automotive polymer electrolyte membrane fuel cell (PEMFC) manufacturers due to their low cost, high power density, ease of manufacture, high conductivity and good mechanical properties but minimising the undesirable effects of corrosion remains a key challenge. Unfortunately, reliable assessment of the applicability of stainless steels with a range of coatings and surface treatments has been hampered by a lack of representative ex situ test methods. Here we characterise the local environment experienced by a bipolar plate during fuel cell operation via in situ measurement of pH and corrosion potential for an uncoated 316L stainless steel bipolar plate in a single cell PEMFC. We demonstrate that the degradation mode is more akin to corrosion in relatively dilute thin liquid layers, rather than the fully immersed conditions employed in conventional ex situ screening tests. A key observation is that the corrosion potential of the bipolar plate is only weakly coupled to the potential of the nearest Pt electrode due to the low ionic conductivity of the discontinuous aqueous phase in the gas diffusion layer (GDL). However, localised polarisation of the steel can occur in the presence of oxygen as a result of galvanic coupling with the carbon GDL at wetted interfaces, a process which may be enhanced by the creviced geometry. The implications for development of more representative ex situ test protocols are discussed. 

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