Preparation Of Carbon Supported Pd Anodic Catalyst And Kinetic Study Of Formic Acid Electrooxidation

In this thesis the electro-oxidation behaviors of formic acid at the Pt/C or Pd/C electrode in direct formic acid fuel cell (DFAFC) were mainly investigated. The electro-oxidation characters of formic acid at Pt/C or Pd/C electrode and the kinetic process of electro-oxidation was studied deeply, and the related kinetic parameters are obtained by different techniques. Furthermore, the best method and conditions of preparation of Pd/C catalyst were explored and characterized by X-ray diffraction(XRD), transmission electron microscopy(TEM), Energy Disperse Spectroscopy(EDS), Thermogravimetry (TG) and electro-surface area techniques.The electro-oxidation of formic acid at Pt/C electrode is carried out by forming COad in indirect path and the electro-oxidation of formic acid at Pd/C electrode is carried out by forming CO2 in direct path. So Pd/C electrode can not easily be poisoned by COad and have higher electro-catalytic activity to the oxidation of formic acid.The oxidation rate of formic acid at Pt/C or Pd/C electrodes is increased with increasing the concentration of formic acid, and the orders of reaction is 0.5 on Pt/C and 1 on Pd/C electrode. The oxidation rate of formic acid at Pd/C electrode is decreased with increasing H+ concentration at some extent. The apparent negative reaction order with respect to H+ is about ?0.18 or ?0.04 in H2SO4 or HClO4 solution respectively. The activation energy of the oxidation of formic acid at Pt/C or Pd/C electrode is significantly increased as the potential rose. It means formic acid oxidation is more sensitive to temperature at relatively higher potential.The oxidation of formic acid at Pt/C or Pd/C electrode is completely irreversible kinetic process. The apparent peak current density of formic acid oxidation increases with the increase in the scan rate and the peak potential shift positively. Some kinetic parameters were obtained by calculation: to the oxidation of formic acid at Pt/C electrode, the slope of Tafel is 340mV, the charge transfer coefficient is 0.32, apparent diffusion coefficient is 8.9×10-7 cm2?s-1; to the oxidation of formic acid at Pd/C electrode, the slope of Tafel is 174mV, the charge transfer coefficient is 0.22, apparent diffusion coefficient is 6.5×10-7 cm2?s-1. Normal pulse voltammetry consists of a series of pulses of increasing amplitude applied to the electrode. Because of the short pulse duration and sufficiently long waiting time (2s) at base potential, cyclic renewal of the diffusion layer can be achieved. The process can be expressed by the Cottrell equation. Thus, some kinetic parameters of the oxidation of formic acid at Pd/C electrode can also be obtained by NPV.The effects of electro-catalytic activity of formic acid caused by Pd/C catalysts prepared by different conditions are also investigated. Finally the best method and conditions of preparation of Pd/C catalyst are found. Besides, adding Au to Pd/C catalyst is helpful to enhance electro-catalytic activity.