Comparative study of oxygen reduction reaction on RuxMySez (MÂ =Â Cr, Mo, W) electrocatalysts for polymer exchange membrane fuel cell

Electrochemical evaluation of the RuxMySez (M = Cr, Mo, W) type electrocatalysts towards the oxygen reduction reaction (ORR) is presented. The electrocatalysts were synthesized by reacting the corresponding transition metal carbonyl compounds and elemental selenium in 1,6-hexanediol under refluxing conditions for 3 h. The powder electrocatalysts were characterized by scanning electron microscopy (SEM), and X-ray diffraction (XRD). Results indicate the formation of agglomerates of crystalline particles with nanometric size embedded in an amorphous phase. The particle size decreased according to the following trend: RuxCrySez > RuxWySez > RuxMoySez. Electrochemical studies were performed by rotating disk electrode (RDE) and rotating ring-disk electrode (RRDE) techniques. Kinetic parameters exhibited Tafel slopes of 120 mV dec−1; exchange current density of around 1 × 10−5 mA cm−2 and apparent activation energies between 40 and 55 kJ mol−1. A four-electron reduction was found in all three cases. The catalytic activity towards the ORR decreases according to the following trend: RuxMoySez > RuxWySez > RuxCrySez. However this trend was not maintained when the materials were tested as cathode electrodes in a single polymer exchange membrane fuel cell, PEMFC. The RuxWySez electrocatalyst showed poor activity compared to RuxMoySez and RuxCrySez which were considered suitable candidates to be used as cathode in PEMFCs.