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Published February 2015 | Published + Supplemental Material
Journal Article Open

Platinum-decorated carbon nanotubes for hydrogen oxidation and proton reduction in solid acid electrochemical cells

Abstract

Pt-decorated carbon nanotubes (Pt-CNTs) were used to enhance proton reduction and hydrogen evolution in solid acid electrochemical cells based on the proton-conducting electrolyte CsH_2PO_4. The carbon nanotubes served as interconnects to the current collector and as a platform for interaction between the Pt and CsH_2PO_4, ensuring minimal catalyst isolation and a large number density of active sites. Particle size matching was achieved by using electrospray deposition to form sub-micron to nanometric CsH_2PO_4. A porous composite electrode was fabricated from electrospray deposition of a solution of Pt-CNTs and CsH_2PO_4. Using AC impedance spectroscopy and cyclic voltammetry, the total electrode overpotential corresponding to proton reduction and hydrogen oxidation of the most active electrodes containing just 0.014 mg cm^(−1) of Pt was found to be 0.1 V (or 0.05 V per electrode) at a current density of 42 mA cm^(−2) for a measurement temperature of 240 °C and a hydrogen-steam atmosphere. The zero bias electrode impedance was 1.2 Ω cm2, corresponding to a Pt utilization of 61 S mg^(−1), a 3-fold improvement over state-of-the-art electrodes with a 50× decrease in Pt loading.

Additional Information

© 2015 The Royal Society of Chemistry. This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence. Received 30 Sep 2014, Accepted 10 Dec 2014, First published online 22 Dec 2014. This work was supported by the Dow-Bridge Program through the Resnick Sustainability Institute at Caltech, as well as by a Resnick Graduate Student Fellowship (R.E.U.). We thank Dr Tim Davenport, Michael Ignatowich, and Webster Guan for their assistance in TGA measurements, and Nate Thomas and Anupama Khan for their assistance in imaging. We also acknowledge Prof. George R. Rossman for his assistance with Raman Spectroscopy, Ben Myers from Northwestern University's Atomic and Nanoscale Characterization Experimental Center (NUANCE) for SEM imaging (Fig. 2). In addition, we acknowledge Caltech's Kavli Nanoscience Institute (KNI) for access to additional imaging instrumentation and the Molecular Materials Research Center at Caltech for the use of the Cahn C-35 Ultra-Microbalance.

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