Abstract
Long-term stability of nanostructured thin film (NSTF) catalysts at operating potentials has been investigated. Compared to high surface area Pt/C catalysts, NSTF electrodes show 20-50x smaller F- emission rates (FER) because of their high specific activity for oxygen reduction reaction (ORR), but are susceptible to poisoning by the products of membrane degradation because of their low electrochemically active surface area (ECSA). The observed voltage degradation rates at potentials corresponding to 1-1.5 A/cm2 current density are much higher than the allowable 13-14 μV/h. Although F- is not itself responsible for performance decay, cumulative fluoride release (CFR) is a good marker for catalyst surface contamination. The observed performance decay is not only due to loss of active Pt sites but also adsorbed impurities impeding ORR kinetics. There is a strong correlation between measured CFR and observed decrease in specific ORR activity and limiting current density and increase in mass transfer overpotentials. The correlations indicate that the target of <10% lifetime performance degradation can be achieved by restricting CFR in NSTF electrodes to 0.7 μg/cm2, as may be possible with more stable membranes, higher surface area NSTF catalysts, and cell operation at lower temperatures and higher relative humidities.
| Original language | English |
|---|---|
| Pages (from-to) | F306-F320 |
| Journal | Journal of the Electrochemical Society |
| Volume | 164 |
| Issue number | 4 |
| DOIs | |
| State | Published - 2017 |
Funding
This work was supported by the Fuel Cell Technologies Office of the U.S. Department of Energy's (DOE) Office of Energy Efficiency and Renewable Energy. Dr. Nancy Garland is the DOE Technology Development Manager for this work. Argonne is a DOE, Office of Science Laboratory operated under Contract No. DE-AC02-06CH11357 by the UChicago Argonne, LLC. Darren Miller, Michael Kurkowski, and Andrei Komlev of 3M Energy Components Program are also recognized for assistance with test execution and F- ion analysis. The U.S. Government retains for itself, and others acting on its behalf, a paid-up nonexclusive, irrevocable worldwide license in said article to reproduce, prepare derivative works, distribute copies to the public, and perform publicly and display publicly, by or on behalf of the Government.