Coherent hexagonal platinum skin on nickel nanocrystals for enhanced hydrogen evolution activity

Metastable noble metal nanocrystals may exhibit distinctive catalytic properties to address the sluggish kinetics of many important processes, including the hydrogen evolution reaction under alkaline conditions for water-electrolysis hydrogen production. However, the exploration of metastable noble metal nanocrystals is still in its infancy and suffers from a lack of sufficient synthesis and electronic engineering strategies to fully stimulate their potential in catalysis. In this paper, we report a synthesis of metastable hexagonal Pt nanostructures by coherent growth on 3d transition metal nanocrystals such as Ni without involving galvanic replacement reaction, which expands the frontier of the phase-replication synthesis. Unlike noble metal substrates, the 3d transition metal substrate owns more crystal phases and lower cost and endows the hexagonal Pt skin with substantial compressive strains and programmable charge density, making the electronic properties particularly preferred for the alkaline hydrogen evolution reaction. The energy barriers are greatly reduced, pushing the activity to 133 mA cm_geo^-2 and 17.4 mA μg_Pt^-1 at -70 mV with 1.5 µg of Pt in 1 M KOH. Our strategy paves the way for metastable noble metal catalysts with tailored electronic properties for highly efficient and cost-effective energy conversion.

The reactivity of water and OH on Pt-Ni(111) films

Bimetallic Pt catalysts are of interest as water redox catalysts in low temperature fuel cells. Here we compare water and hydroxyl adsorption on Pt-Ni(111) films and a PtNi(111) alloy surface with the behaviour on the pure metals. Whereas water adsorbs and desorbs intact from close packed Pt and Ni, it dissociates on PtNi surfaces to form adsorbed hydroxyl and hydrogen. Reactivity to water increases in the order Pt(111) < monolayer Pt-Ni(111) < multilayer (2-6 ML) Pt-Ni(111) ∼ PtNi(111) surface alloy and does not scale directly with the Pt strain. Hydroxyl can also be formed by reaction with pre-adsorbed O and is less stable than on pure Pt, decomposing to water and O in a broad peak near 180 K, 20 K lower than on Pt(111). The reduced stability of OH on Pt-Ni(111) films is common to all the PtNi surfaces and consistent with bimetallic PtNi surfaces showing less blocking by OH during the oxygen reduction reaction.

Mo@Pt overlayers as efficient catalysts for hydrodeoxygenation of guaiacol and anisole

Silica alumina supported Mo@Pt overlayer catalysts were prepared via the directed deposition technique and evaluated for hydrodeoxygenation (HDO) of guaiacol and anisole.