Abstract
Degradation of carbon-supported Pt nanocatalysts in fuel cells and electrolyzers hinders widespread commercialization of these green technologies. Transition between oxidized and reduced states of Pt during fast potential spikes triggers significant Pt dissolution. Therefore, designing Pt-based catalysts able to withstand such conditions is of critical importance. We report here on a strategy to suppress Pt dissolution by using an organic matrix tris(aza)pentacene (TAP) as an alternative support material for Pt. The major benefit of TAP is its potential-dependent conductivity in aqueous media, which was directly evidenced by electrochemical impedance spectroscopy. At potentials below ∼0.45 VRHE, TAP is protonated and its conductivity is improved, which enables supported Pt to run hydrogen reactions. At potentials corresponding to Pt oxidation/reduction (>∼0.45 VRHE), TAP is deprotonated and its conductivity is restricted. Tunable conductivity of TAP enhanced the durability of the Pt/TAP with respect to Pt/C when these two materials were subjected to the same degradation protocol (0.1 M HClO4 electrolyte, 3000 voltammetric scans, 1 V/s, 0.05–1.4 VRHE). The exceptional stability of Pt/TAP composite on a nanoscale level was confirmed by identical location TEM imaging before and after the used degradation protocol. Suppression of transient Pt dissolution from Pt/TAP with respect to the Pt/C benchmark was directly measured in a setup consisting of an electrochemical flow cell connected to inductively coupled plasma-mass spectrometry.
Highlights
Hydrogen-fed fuel cells are expected to find a broad application in both stationary and mobile devices.[1,2] Usage of scarce and expensive Pt-based catalysts to run both hydrogen oxidation reaction (HOR) at the anode[3,4] and oxygen reduction reaction (ORR) at the cathode[5,6] impedes widespread commercialization of these devices
Electrochemical stability and Pt dissolution from the Pt/TAP composite and from the Pt/C benchmark were studied by subjecting these catalysts to the same degradation test (3000 voltammetric scans, 1 V/s, 0.05−1.4 VRHE, 0.1 M HClO4)
Pt/C suffered notable degradation, as revealed by the decay of both the Pt electrochemical surface area (ESA) and its catalytic activity for hydrogen evolution reaction (HER), which was used as a test reaction
Summary
Hydrogen-fed fuel cells are expected to find a broad application in both stationary and mobile devices.[1,2] Usage of scarce and expensive Pt-based catalysts to run both hydrogen oxidation reaction (HOR) at the anode[3,4] and oxygen reduction reaction (ORR) at the cathode[5,6] impedes widespread commercialization of these devices. As discussed earlier, such selective catalytic behavior of a fuel cell anode is beneficial for the overall device lifetime.[12,13,22] Another benefit of the restricted conductivity of TAP at higher potentials could be a suppression of electrochemical oxidation/reduction of supported Pt, which means that aggressive Pt transient dissolution should be limited with respect to state-of-the-art catalysts comprised of Pt nanoparticles dispersed on high-surface-area carbon. Improved stability of Pt/TAP is a consequence of potential-dependent conductivity of TAP support, which is evidenced directly by in situ electrochemical impedance spectroscopy (EIS) measurements
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