A pore-scale model of oxygen reduction in ionomer-free catalyst layers of PEFCs

  1. Get@NRC: A pore-scale model of oxygen reduction in ionomer-free catalyst layers of PEFCs (Opens in a new window)
DOIResolve DOI: http://doi.org/10.1149/1.3505042
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Journal titleJournal of the Electrochemical Society
SubjectApproximate analytical solutions; Catalyst layers; Cylindrical nanopores; Electrode potentials; Electrokinetic; Electrostatic interactions; Free channels; Helmholtz; Key determinants; Local current density; Materials selection; Metal phase; Metal surfaces; Nanostructural; Oxygen distribution; Oxygen Reduction; Platinum utilization; Poisson-Nernst-Planck theories; Polarization data; Polymer electrolyte fuel cells; Polymer electrolyte membranes; Pore wall; Pore-scale model; Potential distributions; Potential of zero charge; Proton migration; Stern model; Transport equation; Ultra-thin; Upscaling; Catalysts; Electrochemical electrodes; Electrolytic reduction; Fuel cells; Oxygen; Platinum; Poisson distribution; Polyelectrolytes; Pore pressure; Protons; Quay walls; Nanopores
AbstractWe present a model for oxygen reduction in water-filled, cylindrical nanopores with platinum walls. At one end, the pores are in contact with a polymer electrolyte membrane. The electrostatic interaction of the protons with the charged pore walls drives proton migration into the ionomer-free channels. We employ the Stern model to relate the surface charge density at the pore walls to the electrode potential. Proton and potential distributions within the pores are governed by the Poisson-Nernst-Planck theory and the oxygen distribution by Ficks law. Assuming a small local current density from oxygen reduction, we found an approximate analytical solution to the transport equations. The metal surface charge density and the corresponding proton conductivity of the pores are tuned by the deviation of the electrode potential from the potential of zero charge of the metal phase, which is the key determinant of the effectiveness of platinum utilization. Other determinants of pore performance are the Helmholtz capacitance, electrokinetic parameters, and pore size and length. Upon upscaling, the model is consistent with polarization data for ionomer-free, ultrathin catalyst layers in polymer electrolyte fuel cells (PEFCs). We discuss the implications of the model for the materials selection and nanostructural design of such catalyst layers. © 2010 The Electrochemical Society.
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AffiliationNational Research Council Canada (NRC-CNRC); NRC Institute for Fuel Cell Innovation (IFCI-IIPC)
Peer reviewedYes
NPARC number21271510
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Record identifier3d20a9b3-b832-4ace-a860-d416d97ee648
Record created2014-03-24
Record modified2016-05-09
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