Sonochemical Synthesis of Platinum Catalysts Supported on Carbonized Polyaniline for Proton Exchange Membrane Fuel Cell

Abstract

Carbon supported catalysts usually have high catalytic efficiency due to a low metal loading and large surface area. Thus the platinum catalyst loaded on the carbon black has been widely used for PEMFC(proton exchange membrane fuel cell), and it makes enormous development possible in the field of fuel cell. The methods used for making platinum catalyst loaded on carbon could be divided into two categories. One is to reduce metal precursor by mixing it with supporting material, and the other is to mix supporting materials with pre-reduced metal colloids.1Both of them have been successfully used for making Pt/C catalyst.In making a supported metal catalyst, there has been reported a method based on a sonochemical process, not chemical reduction. Cu/polyaniline catalyst was synthesized by irradiating ultrasound to the organic solution composed of Cu precursor and aniline(solute)2. Aniline was polymerized and Cu precursor was reduced with the ultrasound irradiation simultaneously. The Cu/carbonized polyaniline catalyst was also synthesized by pyrolyzing the Cu/polyaniline. This method has the possibility of being applicable in making a Pt/carbonized polyaniline catalyst for fuel cell application because a carbonized polyaniline could be used as a support as reported in a previous result3 and Pt precursor is able to be reduced with the ultrasound irradiation4. Thus the development of Pt/carbonized polyaniline catalyst and its application in PEMFC were studied in this research.We used H2PtCl6·6H2O as a Pt precursor and aniline as a solvent for making catalyst of Pt/polyaniline. The mixture of Pt precursor and aniline was irradiated by ultrasound, and the product was perfectly dried in vaccum oven. The dried product was heated to carbonize polyaniline.Fig. 1 shows the X-ray diffraction (XRD) pattern of synthesized Pt/carbonized polyaniline. The pattern is identical with critical peaks of Pt metal. This result confirms a successful reduction of Pt precursor. The size of Pt particle was measured as 12.37 nm by treating Pt(111) peak with using Scherrer equation. The SEM-EDS (scanning electron microscope – energy dispersive spectroscopy, not shown here) analysis directly shows well dispersed Pt on carbonized polyaniline. Fig. 2 is XPS (X-ray photoelectron spectroscopy) data of Pt/carbonized polyaniline catalyst. The presence of metallic Pt was also confirmed with XPS data. The electrochemical properties Pt/carbonized polyaniline were evaluated through CV(cyclic voltammetry) and ORR (oxygen reduction reaction) tests. Furthermore, the performance of single cell made with Pt/carbonized polyaniline was measured and compared to that obtained with a conventional Pt/C catalyst.In this presentation, all the results investigated in the research will be presented with in-depth discussion.