Comparative study of oxygen reduction reaction on RuxMySez (M = 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 3h. 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 x 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 Ru(x)Mo(y)se(z) and RuxCrySez which were considered suitable candidates to be used as cathode in PEMFCs. (C) 2008 Elsevier B.V. All rights reserved.