Preparations of Highly Stable RuCo/CNTs Electrocatalysts for Oxygen Reduction Reaction

The carbon nanotubes (CNTs) supported ruthenium cobalt alloy (Ru_xCo) nanoparticles (Ru_xCo/CNTs) were prepared with different Ru/Co ratios (x=Ru/Co=0.5, 1.0, 2.0, 3.0) by impregnated method using less expensive metal chlorides (CoCl₂ and RuCl₃) as precursors. The heat treatments were carried at the temperatures of 300°C, 400°C, 500°C and 700°C for comparison. It was found that the as prepared Ru_xCo nanoparticles were uniformly dispersed on the CNTs support and exhibited mainly hexagonal alloyed phase with small amounts of metal oxides being presented at the surface. The mean particle sizes were smaller than 10 nm and the potentials corresponding to oxygen reduction reaction (ORR) were 0.67~0.73 V with the electron transfer numbers (n) of 3.0~4.0 by varying the Ru/Co ratios from 0.5 to 3.0. The amounts of Co presented in the alloy significantly influenced the growth of Ru_xCo nanoparticles and the defects of CNTs support. The best ORR activity with high stability in an acid solution was achieved with the Ru₂Co/CNTs when heat-treated at 400°C under H₂ for 2 h.