Oxygen Electroreduction on PtCo₃, PtCo and Pt₃Co Alloy Nanoparticles for Alkaline and Acidic PEM Fuel Cells

Pt-Co alloy nanoparticles have emerged as one of the most promising electrocatalysts for the oxygen reduction reaction (ORR) in hydrogen fuel cells. Our study presents a comprehensive structural, compositional and electrochemical characterization linked with ORR activity for carbon supported PtCo3, PtCo, and Pt3Co alloy nanoparticle catalysts in 0.1 M HClO4 and 0.1 M KOH. Surface-sensitive cyclic voltammetry was used to investigate the changes of composition of outermost atomic layers of Pt-Co alloys. Our electrochemical results in alkaline media clearly show the stability and voltage-induced accumulation of Co on the particle surface, whereas in 0.1 M HClO4 the voltage cycling initiates the rapid dissolution of Co to form a Pt-enriched surface surrounding by alloy core. We correlated the ECSA and ORR activity with the as-synthesized chemical composition of Pt-Co alloys. In results, after electrochemical treatment in 0.1 M HClO4 the Pt mass based activities (jmass) increase according: Pt(HT) < PtCo < Pt3Co < PtCo3 at comparable particle size. Unlike to acid, after voltage cycling in 0.1 M KOH jmass increase according: PtCo3 < Pt(HT) < PtCo < Pt3Co. However, in 0.1 M KOH activated PtCo3 core-shell catalyst shows 4–5 fold higher mass activity compared to pure Pt and Pt(HT).