Size-controlled synthesis, characterization and electrocatalytic behaviors of polymer-protected nickel nanoparticles: a comparison with respect to two polymers

A facile reduction of nickel chloride in aqueous solution with sodium borohydride leads to fairly monodisperse, and electrochemically active nickel nanoparticles by the separate use of a capping polymer like polyvinyl pyrrolidone (PVP) and polyacrylic acid (PAA). The resulting nanoparticles have been characterized by transmission electron microscopy, powder X-ray diffraction, Fourier transform infrared spectroscopy, and cyclic voltammetry. The size of the Ni nanoparticles is very small (1.2-6.1 nm) and can be readily tuned by changing the polymer as well as its concentration in each case. PVP bearing bulky pyrrolidone moieties leads to the formation of smaller nanoparticles than PAA at the chosen concentrations of polymers providing similar numbers of monomer units. In alkaline medium graphite-supported Ni nanoparticles form Ni(OH)(2) and then NiOOH which are electrocatalytically active towards the electro-oxidation of methanol. The study reveals that at high positive potential the polyacrylate anion interacts more with the catalyst nanoparticles as compared to PVP resulting in lowering of the current density at higher concentrations of polymer. Thus the catalyst nanoparticles are capable of exhibiting competing effects of size- and particle-surface-environment in electrocatalysis and possess alcohol sensing properties for alkaline oxidation of methanol.