Pt-SnO2−Pd/C Electrocatalyst with Enhanced Activity and Durability for the Oxygen Reduction Reaction at Low Pt Loading: The Effect of Carbon Support Type and Activation

A simple-to-use method of carbon support surface activation using a PdCl 2 −SnCl 2 solution (referred to as the Shipley solution) was developed, for improving the activity and durability of low Pt loading (0.1 mg cm −2 ) catalysts toward the oxygen reduction reaction (ORR). Three types of carbon supports were investigated: Denka, Graphitized Carbon (GC) and Vulcan XC-72R. Pt nanoparticles were synthesized by a modified polyol process and adsorbed on Shipley solution treated carbon supports. The resulting catalyst composition was Pt-SnO 2 −Pd/C with beneficial atomic ratios of Pt/Sn ≥ 12 and Sn/Pd ≥ 2. Employing extensive potential cycling as accelerated degradation testing, we found that the Pt-SnO 2 −Pd/C catalysts maintained excellent electrocatalytic activity for ORR with respect to control samples without carbon support treatment (both commercial and in-house prepared). The Pt area-specific oxygen reduction current density at 0.9 V RHE and 25 °C was most improved in the case of the GC support. The activity of commercial Pt/GC after stability testing decreased by 21.5% to 0.055 A m −2 Pt while for Pt-SnO 2 −Pd/GC, 0.078 A m −2 Pt was measured, identical to that of the fresh catalyst. The electrochemical results are supported by detailed surface analysis. Pt−Pd bimetallic nanoclusters were identified, and the kinetically beneficial role of the partially reduced SnO 2 surface for oxygen and water adsorption is discussed. The oxygen mass transfer limiting current densities in the porous rotating disk electrodes (PRDE) were qualitatively correlated with changes of the catalyst layer morphology during stability testing in terms of the Bonnecaze and Ahlberg models.