Modulation of the Shape of Platinum Nanoparticles by Using Different Oleylamine/Polyvinylpyrrolidone Amounts

This study deals with the synthesis of cubic shape platinum nanoparticles (Pt NPs) by adjusting the oleylamine (OAm):polyvinylpyrrolidone (PVP) ratio in the solution media. The mass ratios between the OAm:PVP were respectively set to the 1:2, 1:1, 2:1 values. Platinum acetylacetonate (Pt(acac)2) was used as Pt precursor and the reduction of this salt to the metallic Pt was provided by microwave irradiation technique. It is seen that increasing amount of OAm triggers the formation of cubic shape Pt NPs. The average sizes of the Pt NPs fall in the range of 6-8 nm. The unsupported Pt NPs were directly used as a catalyst for the oxygen reduction reaction (ORR). According to the hydrodynamic ORR voltammograms of the catalysts, the Pt NPs prepared with 1:2 (OAm:PVP) exhibit the highest current density at all stirring rates of rotating disc electrode (RDE). Besides, Pt NPs prepared with 2:1 (OAm:PVP) have the minimum charge transfer resistance based on electrochemical impedance spectroscopy (EIS) analysis conducted at 0.9 V. After all these analyses, Pt NPs were synthesized using extra five different ratios (1.5:1, 1:1.5, 2.5:1, 3:1, 1:3) of (OAm:PVP) for thoroughly examining the optimum value for the ORR catalytic activity. As a result, the Pt NPs prepared with a 2.5:1 (OAm:PVP) ratio provided the best performance among all the catalysts.