The effect of pretreatment of Vulcan XC-72R carbon on morphology and electrochemical oxygen reduction kinetics of supported Pd nano-particle in acidic electrolyte

The influence of chemical pretreatment of carbon support for oxygen reduction on palladium nano-particles in acidic electrolyte was studied. Vulcan XC-72R carbon as catalyst support for palladium nano-particles was pretreated with 5% HNO3, 0.07 M H3PO4, 0.2 M KOH and 10% H2O2. The effect of treatment on the properties of the carbon support was studied by N-2 adsorption and X-ray photoelectron spectroscopy (XPS). It was found that chemical treatment significantly changed the surface chemical properties and surface area of the carbon support. The surface area and pore volume of 5% HNO3 and 10% H2O2 treated carbon supports were drastically decreased due to the oxidative nature of treatment. Ethylene glycol (EG) reduction method was used to synthesise 20% Pd on pr-treated and un-treated carbon supports. Differences in catalyst morphology were characterized using X-ray diffraction, energy dispersive X-ray analysis and transmission electron microscope techniques. It was observed that by using a mild reducing agent, namely EG, well-dispersed and nano-size Pd particles could be achieved during catalyst synthesis. The electrocatalytic activity of different Pd/C catalysts towards the oxygen reduction reaction (ORR) was examined by cyclic voltammetry (CV) on a rotating ring-disc electrode (RRDE) and compared with E-Tek 20% Pd/C catalyst under identical experimental conditions. The kinetics of ORR on these electrocatalysts predominantly involved a four-electron step reduction with the first electron transfer being the rate-determining step. However, the observed specific activity, mass activity and amount of hydrogen peroxide produced during ORR were greatly influenced by the pretreatment employed for carbon support. (C) 2010 Elsevier B.V. All rights reserved.