Highly Porous and Preferentially Oriented {100} Platinum Nanowires and Thin Films
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AbstractHighly {100} oriented Pt deposits were prepared by electrodeposition from a 10 mM HCl, 100 mM KCl and Na2PtCl6.xH2O 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 H2SO4. The effect of the deposition potential, Edep, temperature of the electrolyte, Tdep, platinum salt concentration [Na2PtCl6.xH2O], and nature of the substrate were investigated. It was shown that the proportion of {100} oriented Pt surfaces reaches a maximum for Edep = ‐0.35 V vs SCE. Moreover, this proportion increases steadily as Tdep and [Na2PtCl6.xH2O] are decreased from 75 to 25 °C 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 Pt4+ is limited. Due to the predominance of {100} facets, the normalized electrocatalytic activity (μA cm−2Pt) for the electro‐oxidation of hydrazine and ammonia is higher than non‐oriented polycrystalline Pt by a factor of 4 and 2.7, respectively.
