Palladium–vanadium alloy electrocatalysts for oxygen reduction: Effect of heat treatment on electrocatalytic activity and stability

Carbon black (Vulcan XC72R)-supported palladium–vanadium electrocatalysts for the oxygen reduction reaction (ORR) were synthesized by wet chemical reduction of metal chloride salts. The nominal compositions of the electrocatalysts were 60:40, 70:30 and 80:20 (Pd/V atomic ratio). The electrocatalysts were treated at a range of temperatures in 10% H2 in Ar and the effect of heat treatment on particle morphology was characterised using powder X-ray diffraction and transmission electron microscopy. These analyses showed that high temperatures caused an increase in the average particle size. The electrocatalytic activities of the electrocatalysts for the ORR were determined using rotating disk electrode voltammetry, which revealed a marked enhancement in the electrocatalytic activity of the Pd70V30 electrocatalyst after heat treatment. The electrochemical stability of the electrocatalysts was examined using an accelerated stability test, which showed a loss of electrochemical surface area upon electrochemical cycling, the extent of which depended on the nominal composition of the electrocatalysts. Electrocatalyst testing after the stability test showed a loss of electrocatalytic performance and microscopic analysis revealed significant morphological changes in the electrocatalyst particle dimensions and dispersion on the carbon support after the stability test.