The Influence of the Oxygen Partial Pressure on the Oxygen Reduction Reaction Kinetics for the Low Platinum Loading Catalysts

Two different platinum catalysts (8.3 and 12.4wt% Pt based on molybdenum carbide derived carbon) were characterized by the high resolution transmission electron microscopy and X-ray diffraction methods. The oxygen reduction reaction (ORR) kinetics was studied on synthesized catalysts and commercially available 20wt% Pt-Vulcan in 0.1M KOH electrolyte solution saturated with oxygen or various O2/N2 gas mixtures at atmospheric pressure. The current density values increase five-fold as the oxygen concentration increases from 20% to 100%. This refers to first-order reaction with respect of oxygen for all catalyst studied. Two different approaches have been proposed for calculating the reaction order. The ORR electrochemical activity for catalysts increases in the following sequence: 8.3wt% Pt-C (half of the loading) ≤ 20wt% Pt-Vulcan < 8.3wt% Pt-C ≈ 12.4wt% Pt-C at all O2 partial pressures studied. The most promising catalyst for ORR was found to be 8.3 wt% Pt-C.