Objective: Preparation of Pt and Pt-Co (70-30) alloys by Mechanical alloying (MA) and chemical vapour deposition (MOCVD) and determine their performance for the ORR in alkaline media.
Methode: The Pt and Pt-Co (70-30) were obtained by Mechanical alloying (MA) of platinum and cobalt powders and by MOCVD from acetylacetonates of Pt and Co and deposited as thin films on glassy carbon. They were characterized by X rays Diffraction, Scanning Electronic Microscopy and Energy dispersive X-ray (EDX). Their performance for the oxygen reduction reaction (ORR) was evaluated in KOH 0.5. Cyclic voltammetry and Rotating disk electrode (RDE) techniques were used.
Results: The PtCo (MA) alloy in tetragonal form (JCPDS-43-1358), with agglomerated particles formed by 20-25 nm crystallites. However by EDX some iron was determined: 0.9% in Pt and 3.1% in Pt-Co. The MOCVD films has about 250 nm and the particle size was 30 ± 2 n nm for Pt particles and 19 nm ± 2 for Pt-Co particles. The kinetic parameters for the ORR obtained from Tafel plots showed that: the PtCo alloys obtained by both techniques showed higher exchange current densities than Pt obtained in the same experimental conditions. The Koutecky-Levich plots were obtained and compared with 2 and 4 electron pathways for the ORR. Pt CVD has a 2 electron pathway and Pt-Co CVD mostly 4 electron pathway.
Conclusions: Both techniques MA and CVD forms crystallites in the range of 19 to 30 nm, the best material for the ORR was the Pt-Co obtained by MA.