The Research On Preparation Of Pt/C Catalysts With Freeze-Drying Method

The preparation and developments of Pt/C electrocatalysts for proton exchange membrane fuel cell (PEMFC) are reviewed. The emphases of discussion are on the preparation of Pt/C electrocatalysts with freeze-drying method. The freeze-drying method is first investigated at first. And then the comparison of the freeze-drying method and heat-drying method is carried out. At last, The effects on the electrocatalysts by pretreatments of carbon support, dispersant and precursor are studied. Cyclic Voltammetry (CV) in sulphuric acid solution and dimethyl ether solution is employed to characterize the catalytic activity of the electrocatalysts; Transmission Electron Microscopy (TEM) and X-ray Diffraction are employed to characterize the microstructure of the electrocatalysts; The electrochemical characteristics of the direct dimethyl ether fuel cells (DDFC) made from the electrocatalysts are tested by Arbin Fuel Cell Test Systems.The Ratio of isopropyl alcohol and pure water and temperature in the process of freezing are considerated in the research of the preparation of the Pt/C electrocatalysts with freeze-drying method. The result shows, when we use 300mL pure water to wash the carbon (40mg) in isopropyl alcohol (20ml) to alter the ratio of isopropyl alcohol and pure water, we get the electrocatalysts with high catalytic activity; The use of the liquid nitrogen (-196℃) to freeze the suspension (carbon and precursor solution) can make the Pt/C electrocatalysts in high dispersion. Through the comparison between freeze-drying and heat-drying, the agglomeration and the desorption of the precursor on carbon support can be alleviated with freeze-drying method.The effects on the electrocatalysts by pretreatments of carbon support, dispersant and precursor are studied. The result shows that pretreatment of the carbon support by KMnO₄ can add oxygen-containing functional groups on the surface of carbon, which can reduce the hydrophobicity of the carbon support, and then make it much easier for carbon to dissolve in water to form suspension; Isopropyl alcohol can make the carbon support in high dispersion in the precursor solution, which can make the precursor absorbed on the surface of the carbon...