Preparation of Pt-Sn / graphene catalysts and their activities for ethanol electrooxidation in polyol synthesis

Pt-Sn/ graphene catalysts were prepared by heat treatment of a dispersion of graphene oxide, SnCl₂ and H₂PtCl₆ in ethylene glycol at 130°C for 3h after its pH value had been adjusted to 12 by NaOH, followed by centrifuging, washing with ethanol and water, and cryodrying. The pH value of the heat-treated dispersion was controlled by adding dilute nitricacid to 2, 4 and 6 to mediate the properties of the catalysts and its effects on the compositions, microstructure and catalytic activities of the resulting catalysts in ethanol electrooxidation. These were investigated by XRD, ICP, TEM and cyclic voltammetry. Results indicated that with decreasing pH values the Sn content increased, the Pt/ Sn atom ratio decreased and the electrochemical activity increased. The current density for ethanol electrooxidation was increased by 120% at the pH value of 2 compared for the sample without nitric acid. The improvement of the catalytic activity can be ascribed to an increased loading of Sn and Pt since the oxidative product of ethylene glycol in the heat treatment acted as a chelating agent for metal nanoparticles under high pH values. A very simple acid-treatment-assisted polyol route to prepare graphene supported Pt-Sn nanoparticles were developed. To evaluate the composition, microstructure and electrochemical activity of catalysts treated with different pH values of acid solution have been characterized by XRD、ICP、TEM and cyclic voltammetry. And the changes of Pt and Sn metal particles loading on the surface of graphene were discussed. The results show that graphene is a good support. With the increase of pH values, the Sn content of catalysts increased and the electrochemical activity was improved. As the pH values of acid solution was decreased to 2, the synergistic effect of Pt and Sn reached its maximum, and the current densities of ethanol electrooxidation with the catalysts were about 120% higher than that of original Pt-Sn/ G catalysts, which also reached the maximum.