Elucidating the Impact of the Ionomer Equivalent Weight on a Platinum Group Metal-Free PEMFC Cathode via Oxygen Limiting Current

Hao Wang, Luigi Osmieri, Haoran Yu, Michael Zachman, Jae Park, Nancy Kariuki, Firat Cetinbas, Sunilkumar Khandavalli, Scott Mauger, Deborah Myers, David Cullen, Kenneth Neyerlin

Research output: Contribution to journalArticlepeer-review


Leveraging the interactions between ionomer and catalyst can increase the performance of proton exchange membrane fuel cells. The impacts of the equivalent weight (EW) of perfluorosulfonic acid-based ionomers on the platinum group metal-free electrode structure and fuel cell performance have not been fully explored. Four membrane electrode assemblies (MEAs) were prepared by using a commercial Fe-N-C catalyst, two perfluorosulfonic acid ionomers with different EWs, that is, Aquivion 720 (A720) and Nafion 1100 (N1100), and two ionomer-to-catalyst (I/C) ratios. The four MEAs were characterized to understand the impact of the ionomer EW and content on the capacitance, proton conductivity, and mass transport on the cathode. The mass transport resistance was measured for the first time using a new oxygen reduction reaction limiting current method enabling to couple the effects of oxygen diffusion with liquid water generation. Low EW ionomer combined with a moderate I/C results in improved performance due to its enhanced proton conductivity. However, when used at high I/C, it can cause severe water flooding at high current density due to the enhanced liquid water uptake, especially at high relative humidity, resulting in lower catalyst utilization and higher mass transport resistance.
Original languageAmerican English
Pages (from-to)72-90
Number of pages19
Issue number1
StatePublished - 2023

NREL Publication Number

  • NREL/JA-5900-85471


  • ionomer equivalent weight
  • limiting current
  • mass transport
  • oxygen reduction reaction
  • PGM-free catalyst
  • proton exchange membrane fuel cell


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