The laser ablation of a bulk CoCrFeMnNi high-entropy alloy immersed in liquid yields colloidal nanoparticles with diameters below 5 nm. Both, the chemical composition and the crystal lattice of the bulk material is preserved in the nanoparticles.

Understanding of the NH 3 oxidation poisoning mechanism at Pt(100) is key to tackling a drawback of a reaction important to wastewater decontamination, electrochemical NH 3 sensors, and NH 3 fuel cells. Here we present a detailed study of poisoning adsorbates generated by NH 3 at Pt(100) thin films and identify new key species (1) by comparison to NO 2 − reduction adsorbates and (2) using literature FTIR and DEMS (differential electrochemical mass spectrometry) data. We show that NH 3 and NO 2 − generate identical intermediates at the same electrochemical potentials, suggesting that reactions as disparate as NH 3 oxidation and NO 2 − reduction follow a universal catalytic pathway for N-containing compounds at Pt(100). This represents a significant paradigm shift from 45 years of thought that suggested the two pathways were completely separate. We then use the behavior of poisoning, adsorbed intermediates to develop an in situ cleaning procedure that allows improvements in performance and lifetime for NH 3 electro-oxidation technologies. The in situ cleaning procedure, demonstrated for 1200 cleaning cycles over 2 h, required neither H 2 production nor Pt oxide formation. The latter trait allowed the employment of Pt(100) films without risk of immediate catalyst deorientation to a polycrystalline state. Article pubs.acs.org/JPCC

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Highly {100} oriented Pt deposits were prepared by electrodeposition from a 10 mM HCl, 100 mM KCl and Na 2 PtCl 6 .xH 2 O electrolyte. The deposits were prepared in the form of thin fi lms 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 2 SO 4 . The effect of the deposition potential, E dep , temperature of the electrolyte, T dep , platinum salt concentration [Na 2 PtCl 6 .xH 2 O], 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 2 PtCl 6 .xH 2 O] 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 fi lms 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 signifi cantly enhanced when the mass transport of Pt 4 + is limited. Due to the predominance of {100} facets, the normalized electrocatalytic activity ( μ A cm − 2 Pt ) for the electro-oxidation of hydrazine and ammonia is higher than non-oriented polycrystalline Pt by a factor of 4 and 2.7, respectively.