Contamination mechanisms of proton exchange membrane fuel cells - Mass transfer overpotential origin
Keith Bethune, Jean St-Pierre, Jacob LaManna, Daniel S. Hussey, David L. Jacobson
Several experimental methods were used to identify the cause of the concurrent increase in kinetic and mass transfer overpotentials during the contamination of proton exchange membrane fuel cells outfitted with a commercially relevant cathode catalyst loading of 0.1 mg Pt per cm2. Neutron images demonstrated that the transport of liquid water through gas diffusion electrode materials was subtly affected by the presence of propene and methyl methacrylate in air at ppm levels (25 to 100 ppm propene, 12.5 to 50 ppm methyl methacrylate). Multioxidant polarization curves were obtained to isolate overpotentials (O2, 21% O2 + 79% He, and air). For all cases, neat air, 50 ppm propene in air, and 25 ppm methyl methacrylate in air, only kinetic and mass transfer overpotentials increased (O2 reduction on a Pt supported on C catalyst, O2 diffusion through the catalyst layer ionomer). Also, only the O2 mass transfer coefficient associated with diffusion in the catalyst layer ionomer increased in the presence of 50 ppm propene and 25 ppm methyl methacrylate. Contaminant species adsorbed on the catalyst decrease the active surface area and increase both the real current density and the O2 reduction kinetic overpotential. The smaller active surface area also brings the real current density closer to the limiting value, inducing an increase of the mass transfer overpotential connected with O2 movement in the ionomer layer covering the catalyst. This mechanism was supported by a mathematical contamination model focused on contaminant and O2 processes on the catalyst surface (adsorption, reaction, desorption).
, St-Pierre, J.
, LaManna, J.
, Hussey, D.
and Jacobson, D.
Contamination mechanisms of proton exchange membrane fuel cells - Mass transfer overpotential origin, Journal of Physical Chemistry C, [online], https://doi.org/10.1021/acs.jpcc.0c06233, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=930393
(Accessed December 9, 2023)