Shape-regulated high yield synthesis of electrocatalytically active branched Pt nanostructures for oxygen reduction and methanol oxidation reactions

Abstract

We describe a shape regulated synthesis of branched Pt nanostructures (nPts) by a simple polyol method using 1,3-propanediol as solvent and poly(diallyldmethylammonium chloride) (PDDA) as stabilizing agent and their electrocatalytic activity in the oxygen reduction and methanol oxidation reactions. The transmission electron microscopic measurements show that the nanoparticles have multiple branches. The size of the branched nanostructures ranges from 10 to 15 nm and the branches have the width of 3-5 nm. The X-ray diffraction measurement indicates the existence of face centered cubic structure of Pt. UV-vis spectroscopic measurement suggests that the reduction of Pt(IV) proceeds through the formation of Pt(II) species. The solvent and the stabilizing agent plays vital role in the growth of nPts. Aggregated nanoparticles were obtained in the absence of PDDA. The traditional solvent ethylene glycol in the presence of PDDA yields only spherical nanoparticles. The nPts were loaded onto the walls of multiwall carbon nanotube (MWCNT) to examine their electrocatalytic activity. The nanoparticles on MWCNT retain their initial shape, size and morphology. The electrocatalytic activity of nPts toward oxygen reduction reaction (ORR) was evaluated in terms of kinetic current density using rotating-ring-disk electrode (RRDE) system. The nanostructured electrocatalyst favors the 4-electron pathway for the reduction of oxygen at a more positive potential with a kinetic current density of 11.97 mA cm(-2). The electrocatalytic performance of the catalyst in the methanol oxidation reaction (MOR) was studied with chronoamperometry and potential dependent electrochemical impedance spectroscopy measurements. The nPts show high specific activity in the ORR and MOR. The electrocatalytic activity of nPts towards ORR and MOR is compared with the commercial catalyst and spherical nanoparticles.