Controlled synthesis and characterization of carbon-supported Pd₄Co nanoalloy electrocatalysts for oxygen reduction reaction in fuel cells

Carbon-supported Pd₄Co nanoalloy samples (denoted as Pd₄Co/C) have been synthesized by a modified polyol reduction process, involving a mixture of ethylene glycol (a polyol) and a small amount of sodium borohydride as reducing agents, and evaluated as electrocatalysts for the oxygen reduction reaction (ORR) in fuel cells. The synthesis process offers Pd₄Co nanoparticles with an average particle size of 4.6 nm and a narrow size distribution, which increases to 7.3 and 11.0 nm on annealing, respectively, at 350 and 500 °C in 10% H₂–90% Ar. Although the as-prepared Pd₄Co/C sample exhibits instability during ORR, annealing at 350 and 500 °C enhances the stability significantly due to an increasing degree of alloying between Pd and Co and increasing particle size. While both Pd/C and Pt/C exhibit a drastic decline in catalytic activity on annealing at 350 and 500 °C due to a significant increase in particle size, the Pd₄Co/C sample maintains high catalytic activity even after annealing at 350 °C due to an increase in the degree of alloying. The Pd₄Co/C catalyst offers an added advantage of excellent tolerance to methanol poisoning and lower cost compared to the conventional Pt/C catalyst.