Comparative study of oxygen reduction reaction on Ru x M y Se z (M=Cr, Mo, W) electrocatalysts for polymer exchange membrane fuel cell

Abstract: Electrochemical evaluation of the Ru x M y Se z (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: Ru x Cr y Se z >Ru x W y Se z >Ru x Mo y Se z . Electrochemical studies were performed by rotating disk electrode (RDE) and rotating ring-disk electrode (RRDE) techniques. Kinetic parameters exhibited Tafel slopes of 120mVdec−1; exchange current density of around 1×10−5 mAcm−2 and apparent activation energies between 40 and 55kJmol−1. A four-electron reduction was found in all three cases. The catalytic activity towards the ORR decreases according to the following trend: Ru x Mo y Se z >Ru x W y Se z >Ru x Cr y Se z . However this trend was not maintained when the materials were tested as cathode electrodes in a single polymer exchange membrane fuel cell, PEMFC. The Ru x W y Se z electrocatalyst showed poor activity compared to Ru x Mo y Se z and Ru x Cr y Se z which were considered suitable candidates to be used as cathode in PEMFCs. [Copyright &y& Elsevier]