Highly Porous and Preferentially Oriented {100} Platinum Nanowires and Thin Films

摘要

Highly {100} oriented Pt deposits were prepared by electrodeposition from a 10 mM HCl, 100 mM KCI and Na_2PtCI_6.xH_2O electrolyte. The deposits were prepared in the form of thin films and array of nanowires. A qualitative assessment of the proportion of {100} oriented Pt surfaces was obtained through X-ray diffraction measurements and cyclic voltammetry in 0.5 M H_2SO_4. The effect of the deposition potential, E_(dep), temperature of the electrolyte, T-(dep), platinum salt concentration [Na_2PtCl_6.xH_2O], and nature of the substrate were investigated. It was shown that the proportion of {100} oriented Pt surfaces reaches a maximum for E_(dep) = -0.35 V vs SCE. Moreover, this proportion increases steadily as T_(dep) and [Na_2PtCl_6.xH_2O] are decreased from 75 to 25 ℃ and from 2.5 to 0.25 mM, respectively. Scanning electron microscopy and high-resolution transmission electron microscopy micrographs indicate that the more oriented samples are made of pine tree-like structures that are effectively single crystals, and that the growth facets appear to be close to the {001} plane. This observation also clearly indicates that the plane exposed during the CV experiment is also {001}. As suggested by these micrographs, the films and nanowires are highly porous and roughness factors as large as 1000 were obtained on highly {100} oriented Pt nanowires. The predominance of {100} facets is attributed to their energetically favoured growth in the presence of hydrogen, and is shown to be significantly enhanced when the mass transport of Pt~(4+) is limited. Due to the predominance of {100} facets, the normalized electrocatalytic activity (μA cm~(-2)p,) for the electro-oxidation of hydrazine and ammonia is higher than non-oriented polycrystalline Pt by a factor of 4 and 2.7, respectively.