Contamination Mechanisms of Proton Exchange Membrane Fuel Cells - Mass Transfer Overpotential Origin

Abstract

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).

Development of an Oxygen Mass Transport Coefficient Measurement and Separation Method for Proton Exchange Membrane Fuel Cells

“…However, since this offset is similar for all oxygen concentrations and equal for all diluent gases, an impairment to the separation method is not expected. Third, the assumption of a positive linear slope for ke versus cO2, which was first observed and described in (6) and explained by an increased oxygen blockage due to product water removal, could be insufficient and needs further investigation. Other approaches are considered to analyze the present dataset.…”

“…For the last step, the linear correlation between the lumped ionomer permeability and Knudsen diffusion mass transport resistance 1/ke+K and the oxygen concentration c (1 to 7 %) is extrapolated to the origin, which yields the Knudsen diffusion mass transport coefficient kK, shown in Figure 1 d). This approach to isolate the Knudsen contribution is novel (6). In the present work, 1/ke is evaluated at 7 % oxygen but can be extrapolated to 21 % oxygen.…”

Low-Grade Thermal Energy Harvesting and Self-Powered Sensing Based on Thermogalvanic Hydrogels

“…Nevertheless, the maximum power output is also governed by various overpotentials within the system during cell operation [ 57 , 58 , 59 , 60 ]. Theoretically, the performance of a given cell is also determined by three major overpotentials within the thermogalvanic cell: ohmic overpotential, charge transfer overpotential, and mass transfer overpotential [ 61 , 62 , 63 ]. The further complexity in the thermogalvanic arises from the temperature dependence of each of these overpotentials.…”

“…Inexpensive and environmentally friendly electrode and electrolyte materials form simple device structures, as well as excellent thermoelectric power performance [ 30 , 31 , 32 ]. As shown in Figure 1 , the number of publications and citations using hydrogels to harvest and sense thermal energy has increased from 2000 to 2022 [ 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 , 62 , ...…”

Perspective—Oxygen-Based Fuel Cell and Reversible Systems for Heavy-Duty Motive and Stationary Applications

“…64 As oxygen is relatively pure, 51 contamination is not a concern especially because oxygen will compete more effectively against contaminants that can adsorb on the catalyst surface and reduce their impact. 65 The overall impact of oxygen on degradation is unclear because mechanisms are positively (contamination), negatively (Pt dissolution and agglomeration, catalyst support oxidation, ionomer, and membrane decomposition), minimally (mass transfer related degradation, carbon and composite bipolar plate degradation), or indeterminately (degradation of metallic bipolar plates) affected. Limited durability tests conducted under steady state conditions without or with periodic interruptions indicate very low degradation rates.…”