Oxygen reduction at platinum nanoparticles supported on carbon cryogel in alkaline solution

The oxygen reduction reaction was investigated in 0.1 M NaOH solution, on a porous coated electrode formed of Pt particles supported on carbon cryogel. The Pt/C catalyst was characterized by the X-ray diffraction (XRD), transmission electron microscopy (TEM) and cyclic voltammetry techniques. The results demonstrated a successful reduction of Pt to metallic form and homogenous Pt particle size distribution with a mean particle size of about 2.7 nm. The ORR kinetics was investigated by linear sweep polarization at a rotating disc electrode. The results showed the existence of two E - log j regions, usually referred to polycrystalline Pt in acid and alkaline solution. At low current densities (lcd), the Tafel slope was found to be close to -2.3RT/F, while at high current densities (hcd) it was found to be close to -2?2.3RT/F. It is proposed that the main path in the ORR mechanism on Pt particles was the direct four-electron process, with the transfer of the first electron as the rate determining step. If the activities are expressed through the specific current densities, a small enhancement of the catalytic activity for Pt/C was observed compared to that of polycrystalline Pt. The effect of the Pt particle size on the electrocatalysis of oxygen reduction was ascribed to the predominant (111) facets of the platinum crystallites. . Kinetika reakcije redukcije kiseonika je ispitivana na nanocesticama platine dispergovanim na ugljenicnom nosacu, u 0.1 mol dm-3 NaOH, na 25 ?C. Za sintezu Pt katalizatora (Pt/C) je primenjena modifikovana poliol metoda iz rastvora etilen glikola, dok je kao nosac koriscen ugljenicni kriogel. Tako dobijeni katalizator je okarakterisan primenom BET metode, difrakcije X-zraka (XRD) i transmisione elektronske mikroskopije (TEM). Dobijeni rezultati su pokazali veoma homogenu raspodelu nanocestica Pt, sa prosecnom velicinom cestica oko 2,7 nm. Za ispitivanje kinetike reakcije redukcije kiseonika su koriscene stacionarna polarizaciona metoda i metoda ciklicne voltametrije. Pokazano je da oblast malih gustina struje na krivoj polarizacije karakterise vrednost Tafelovog nagiba oko -60 mV dek-1, dok je u oblasti vecih gustina struje ova vrednost bliska -120 mV dek-1. Prema dobijenim rezultatima, glavni reakcioni put u mehanizmu redukcije kiseonika je direktna cetvoroelektronska izmena, pri cemu je stupanj koji odredjuje ukupnu brzinu reakcije prenos prvog elektrona. Poredjenjem kataliticke aktivnosti, izrazene preko gustine struje po realno