Journal of Physical Chemistry C 114 16499 (2012)
The structure, stability and the catalytic activity of a number of single and double-wall platinum (n,m) nanotubes ranging in diameter from 0.3-2.0 nm were studied using plane-wave based density functional theory in the gas phase and water environment. The change in the catalytic activity towards the oxygen reduction reaction (ORR) with the size and chirality of the nanotube was studied by calculating equilibrium adsorption potentials for ORR intermediates and by constructing free energy diagrams in the ORR dissociative mechanism network. In addition, the stability of the platinum nanotubes is investigated in the terms of electrochemical dissolution potentials and by determining the most stable state of the material as a function of pH and potential, as represented in Pourbaix diagrams. Our results show that the catalytic activity and the stability towards electrochemical dissolution depend greatly on the diameter and chirality of the nanotube. Based on the estimated overpotentials for ORR we conclude that smaller, approximately 0.5 nm in diameter single-wall platinum nanotubes consistently show a huge, up to 400 mV larger overpotential than platinum indicating very poor catalytic activity toward ORR. This is the result of substantial structural changes induced by the adsorption of any chemical species on these tubes. Single-wall n=m platinum nanotubes with diameter larger than 1 nm have smaller ORR overpotentials than bulk platinum for up to 180 mV and thus show improved catalytic activity relative to bulk. We also predict that these nanotubes can endure the highest cell potentials but dissolution potentials are still for 110 mV lower than for the bulk indicating a possible corrosion problem.
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