Making Pt-shell Pt30Ni70 nanowires by mild dealloying and heat treatments with little Ni loss

Abstract

Dealloying treatment is one way to make a Pt rich shell on Pt alloy through chemically depleting the surface of non-noble metals. However, this treatment usually causes more than half of the non-noble metal to be lost before the catalyst forms an effective protective surface. This process may cause unfavorable morphology and size change of the alloy catalyst. Our research indicates that a mild dealloying treatment in acid combined with an annealing treatment could make an effective Pt rich surface layer when only a little non-noble metal is dissolved from the alloy surface. Pt–Ni alloy nanowires are chosen as the treatment target because long nanowires are mechanically more stable than nanoparticles, which tend to migrate, agglomerate and lose surface area during working. Pt–Ni nanowires are made by electrospinning followed by a mild dealloying treatment and a post-heat treatment to make a core–shell structure in which Ni loses only ∼10 atom% and the resultant Pt-shell could prevent nickel (>70 atom% of the whole wire) in the core from dissolving in 1 M hot sulfuric acid. These long nanowires have diameters around 10–20 nm and form a self-supporting net.