XRD and electrochemical investigation of particle size effects in platinum-cobalt cathode electrocatalysts for oxygen reduction

Pt-Co/C electrocatalysts with Pt loadings close to 30 wt.% prepared by the impregnation method in water–ethylene glycol solutions were investigated by X-ray diffraction and correlated with electrochemical measurements. We show that composition of the binary solvent controls the average particle size and its distribution. The unit cell parameter of the Pt3Co alloy decreases nonlinearly with decreasing particle size. The ORR activity of the prepared Pt-Co/C catalysts in H2SO4 solution enhances with decreasing particle size and unit cell parameter as well as with narrowing of the particle size distribution. Corrosion treatment of the synthesized Pt-Co/C materials brings about an increase of ca. 1 nm in the average grain size accompanied by broadening of the grain size distribution and a decrease in the Co content. All of the synthesized Pt-Co/C materials show higher ORR activities compared with commercial Pt/C electrocatalysts.