Long-Term Stability of Nanostructured Thin Film Electrodes at Operating Potentials

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/cm 2 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/cm 2 , as may be possible with more stable membranes, higher surface area NSTF catalysts, and cell operation at lower temperatures and higher relative humidities.

Strong Activity Changes Observable during the First Pretreatment Cycles of Trimetallic PtNiMo/C Catalysts

“…This could be attributed to ongoing morphological changes and loss of 111‐facets as well as the leaching of Ni and Mo [7,23] . Additionally during cycling, impurities can accumulate on the electrode and result in lower observed SA [38] …”

“…[7,23] Additionally during cycling, impurities can accumulate on the electrode and result in lower observed SA. [38] Figure 3c gives insights into the reproducibility. While the initial SA development show higher deviations (6-15 %) up to the 9th ORR-cycle, a continuous cycling leads to a converge of the average SA result.…”

“…While the initial SA development show higher deviations (6-15 %) up to the 9th ORR-cycle, a continuous cycling leads to a converge of the average SA result. The deviations in absolute activity might stem not only from the usual aspects in RDE testing, such as ink preparation and electrode coverage homogeneity, [38,39] but also from the undefined starting point (Figure S3b in Supporting Information). No additional pretreatment was carried out during these studies, thus an equilibration of the catalyst before starting the experiment is missing.…”

Anode-Design Strategies for Improved Performance of Polymer-Electrolyte Fuel Cells with Ultra-Thin Electrodes

“…A typical 50-cm 2 electrode area, quad-serpentine test cell obtained from Fuel Cell Technologies was used for the cell testing. All MEAs were first conditioned using a process referred to as ''thermal cycling'' and as described in Ahluwalia et al 47 See Supplemental Experimental Procedures for further details on cells and materials.…”

Impact of Platinum Loading on Performance and Degradation of Polymer Electrolyte Fuel Cell Electrodes Studied in a Rainbow Stack

“…Qi et al varied the wt% of Pt/C and found that 20% Pt/C and 30% Nafion is best combination in case of the E‐TEK catalyst material. Other groups optimized performance of low loaded MEAs by using ionomer‐free NSTF (nanostructured thin films) to reduce the oxygen transport resistance , . Others have studied catalyst layer preparation techniques or have used stable carbon composite catalysts for catalyst layer preparation .…”