Abstract
Driven by the demand for the commercialization of fuel cell (FC) technology, we describe the design and fabrication of a highly durable FC electrocatalyst based on double-polymer-coated carbon nanotubes for use in polymer electrolyte membrane fuel cells. The fabricated electrocatalyst is composed of Pt-deposited polybenzimidazole-coated carbon nanotubes, which are further coated with Nafion. By using this electrocatalyst, a high FC performance with a power density of 375 mW/cm2 (at 70 ˚C, 50% relative humidity using air (cathode)/H2(anode)) was obtained, and a remarkable durability of 500,000 accelerated potential cycles was recorded with only a 5% loss of the initial FC potential and 20% loss of the maximum power density, which were far superior properties compared to those of the membrane electrode assembly prepared using carbon black in place of the carbon nanotubes. The present study indicates that the prepared highly durable fuel cell electrocatalyst is a promising material for the next generation of PEMFCs.
Highlights
IntroductionChemical oxidation of the Multi-walled carbon nanotubes (MWNTs) with strong acids is a conventional activation technique for MWNTs to create surface functional groups, such as oxygen containing groups, e.g., C=O and COOH, for homogeneous Pt-NP loading[10]
We developed a novel technique of improving the proton conductivity of the FC electrocatalyst[22], in which (PyPBI)-wrapped Multi-walled carbon nanotubes (MWNTs) were further coated with a proton conducting ionomer, polyvinylphosphonic acid (PVPA), through an acid-base reaction between PyPBI and PVPA
The spectra of both the Nafion-treated MWNT/PyPBI/Pt (MWNT/PyPBI/Pt/Nafion) and Nafion-treated CB/PyPBI/Pt (CB/PyPBI/Pt/Nafion) show the characteristic peaks of Nafion such as F1s at 689 eV, while no Nafion peak was recognized on the Nafion-treated CB/Pt; namely, the narrow scans of the F1s region (Supplementary Fig. 5) indicated the absence of Nafion on the Nafion-treated commercial-CB/Pt composite obtained after rinsing with methanol and 2-propanol
Summary
Chemical oxidation of the MWNTs with strong acids is a conventional activation technique for MWNTs to create surface functional groups, such as oxygen containing groups, e.g., C=O and COOH, for homogeneous Pt-NP loading[10] Such an oxidation technique sacrifices the pristine MWNT structure, resulting in fast degradation of the prepared electrocatalyst during FC operating conditions[11]. Pristine MWNTs are unable to provide good binding sites for sufficient attachment of such an ionomer When using such an ionomer, it leaches from the MEA during long term FC operating conditions, resulting in a lower FC performance[21]. The Nafion ionomer was added to support a good proton transfer and to improve the triple phase boundary structure of the electrocatalyst, and facilitates a good oxygen reduction reaction (see the schematic illustration of Fig. 1d). We describe the possible reasons of the prolonged durability for the MWNT/PyPBI/Pt/Nafion-based MEA
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