Stabilization of Iron-Based Fuel Cell Catalysts by Non-Catalytic Platinum

Abstract

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Stable, Active, and Methanol-Tolerant PGM-Free Surfaces in an Acidic Medium: Electron Tunneling at Play in Pt/FeNC Hybrid Catalysts for Direct Methanol Fuel Cell Cathodes

“…53,54 The present hybrid Pt/FeNC catalysts are therefore promising for application at the cathode of DMFC, being tolerant to methanol crossover from the anode to the cathode and much more durable than FeNC alone, as previously shown in PEMFC. 46 The effect of cell temperature was first investigated, highlighting strong improvement from 80 to 100°C (Figure 1b). The cell performance obtained with Pt 1.0 Fe 1.0 d and Pt 2.0 Fe 1.0 d is comparable, the difference lying within the reproducibility error.…”

“…In particular, the cell performance at high voltage (kinetically controlled region) is very similar for both cathode catalysts, as expected from our previous work. 46 Since the content of 1 wt % Pt was shown in PEMFC to be the lower-end limit for complete durability over at least 50 h in PEMFC, 46 we then focused the DMFC measurements on the Pt 2.0 Fe 1.0 d cathode.…”

“…In a recent study, we reported on the stabilization of FeNC by minute amounts of platinum (1-2 wt %). 46 The addition of 1-2 wt % Pt to a given FeNC catalyst resulted in Pt/FeNC composites with similar ORR activity, but with dramatically improved durability in PEMFC. While the ORR activity of FeNC at 0.8 V was divided by ca four after PEMFC operation for 50 h at 0.5 V, no measurable change in ORR activity was observed after functionalization of the same FeNC material with 1-2 wt % Pt.…”

“…In the present work, two Pt/FeNC catalysts were prepared as previously reported, 46 and further investigated with 57 Fe Mössbauer spectroscopy at 5 K and scanning transmission electron microscopy (STEM) coupled with energy-dispersive X-ray spectroscopy (EDXS). They were also electrochemically characterized for ORR catalysis with a rotating disk electrode (RDE) in the presence of methanol, as well as at the cathode of DMFC.…”

Effect of Pyrolysis Atmosphere and Electrolyte pH on the Oxygen Reduction Activity, Stability and Spectroscopic Signature of FeNx Moieties in Fe-N-C Catalysts

“…While significantly more durable than NH 3 -pyrolyzed catalysts, they also suffer from a slow but steady linear decline with duration of operation in PEMFC. 26,29 Two main degradation mechanisms of such materials have been identified: (1) irreversible iron leaching from Fe particles imperfectly embedded in carbon or from FeN 4 active sites; 30 and (2) reversible degradation induced by the hydrogen peroxide by-product formed during ORR in acidic medium; 31,32 Mechanism (1) was investigated with online mass-spectrometry and revealed that Fe leaching resulted from carbon corrosion during startup/shutdown AST, while Fe leaching during load-cycling AST mainly originated from Fe particles imperfectly surrounded by a N-C layer. The FeN 4 moieties were mostly stable during load-cycling AST in inert-gas saturated acidic medium, in a broad range of temperature and up to 10,000 cycles.…”