Heat-Treated PtCo₃ Nanoparticles as Oxygen Reduction Catalysts

PtCo 3 /C catalysts for oxygen reduction were prepared and heat-treated between 350 and 1000 °C under reductive conditions. The catalysts were activated by cyclic voltammetry, which resulted in the partial oxidative leaching of cobalt. Subsequent rotating disk electrode measurements showed a maximum mass activity for samples tempered at 800 °C, which yielded a 2.4 times higher activity than commercial PtCo x /C. TEM images revealed that the particle size of the PtCo 3 /C catalysts remains almost constant until a temperature of 600 °C is reached; a further temperature increase leads to a noticeable particle growth and a broadening of the particle size distribution. XRD measurements showed that heat treatment leads to the formation of fcc-Pt, Pt 3 Co, fct-PtCo, fcc-PtCo, and cobalt. The fct- and fcc-PtCo phases are present in samples with the highest catalytic activities.