Study On Preparation Of Pt/C Catalyst By Hydrogen Pressure Reduction Method And Its Electrochemical Properties

The slow rate of cathodic oxygen reduction reaction（ORR）process limits the development of fuel cell research.A highly efficient cathode catalyst is needed to improve the ORR rate.Pt/C catalyst is currently recognized as the best performance and most widely used commercial cathode catalyst.In this paper,Pt/C catalyst was prepared by hydrogen pressure reduction method,which has the advantage of short reaction time,no impurity introduction in the reaction process,and low requirements for equipment.The main contents and conclusions were as follows:（1）With the increase of the solution p H,the morphology of the Pt powder presented irregular structures.The agglomeration of Pt powder intensified at high temperature.The particle size of Pt powder prepared was mostly in the range of 50～200 nm.The addition of dispersant could improve the dispersion of Pt powder,and the average particle size of Pt powder was significantly decreased to 2.79 nm.（2）The catalyst prepared without dispersant had better catalytic activity.In the pretreatment process of carbon materials,When ECP600JD was used as catalyst carrier calcined in air at 350℃,the catalyst prepared had the highest catalytic activity.Raman spectroscopy was used to analyze the defect degree on the surface of carbon carrier.It was found that for the same carbon material,the greater the I_D/I_Gvalue,the better the catalyst activity.（3）Single factor experiment of pressure hydrogen reduction method.The optimal experimental conditions for the preparation of 20 wt%Pt/C catalyst were determined as follows:reaction temperature was 90°C,hydrogen partial pressure was 0.4 MPa,stirring speed was 400 rpm,reaction time was 120 min,and solution p H was 6.34.The catalyst prepared under optimized conditions was named Pt/C-_20%.The limiting current density of Pt/C-_20%is as high as 6.34 m A cm^-2;The ORR half-wave potential(E_1/2)of Pt/C-_20%is 0.91V;The Mass Activity（MA）of Pt/C-_20%is up to 0.190 A mg_Pt^-1at 0.9 V（vs.RHE）,which is 4.2 times of commercial Pt/C.Through transmission electron microscopy（TEM）characterization,the average diameter of Pt particle on Pt/C-_optimizationis4.05 nm.Compared with commercial Pt/C catalyst,The larger Pt particle size on Pt/C-_20%may be the reason for the smaller Electrochemical Active Surface Area（ECSA）.（4）Preparation of 50 wt%Pt/C catalyst.the optimal experimental conditions of stirring speed of 400 rpm,reaction time of 120 min and solution p H of 6.39,which were the same as those prepared by 20%Pt/C catalyst.This indicates the applicability of the optimized experimental conditions for preparing Pt/C catalyst by pressure hydrogen reduction method.The catalyst prepared under optimized conditions was named Pt/C-_50%.The limiting current density of Pt/C-_50%is as high as 6.59 m A cm^-2;The ORR E_1/2of Pt/C-_50%is 0.88 V;The MA of Pt/C-_50%is up to 0.105A mg_Pt^-1at 0.9 V（vs.RHE）.Through X-ray photoelectron spectroscopy（XPS）Characterization of Pt/C-_20%and Pt/C-_50%,and it was found that the Pt⁰4f_7/2binding energy is correlated with the catalyst activity:the higher the catalyst activity is,the larger the corresponding Pt⁰4f_7/2binding energy is.There are 51 figures,3 tables and 118 references in this thesis.