| Electrochemical reduction of oxygen is one of the most important electrocatalytic reations. Polytetrafluoroethylene (PTFE) bonded carbon-based oxygen electrode are widely used in many important electrochemical technologies, such as fuel cells, matal/air batteries, organic electrosynthetic processes and electrochemical devices for decontamination of wastewaters. Based on the review of research and development of fuel cells and oxygen electrodes, electrochemical performances of oxygen electrodes made from activated carbon (AC) and multi-walled carbon nanotubes (MWNTs) as well as electrochemical reduction behavior of oxygen at the surface of MWNTs were investigated by different material characterization methods and electrochemical techniques, such as SEM, XRD, TPD, TG, N2 adsorption, linear polarization, cyclic voltammetry and electrochemical impedance spectroscopy.In the third chapter of this dissertation, the effects of the preparation conditions, such as the compositions of catalyst layer and hydrophobic layer, and different electric conductors on the performance of gas diffusion electrode were studied by using linear polariztion technique. The experimental results showed that the performance of gas diffusion electrode is greatly depended on its preparation conditions, and the electrodes with better performance can be obtained with the following prepartion conditions: mass ratio of PTFE to activated carbon in catalyst layer is 0.15:0.85; mass ratio of PTFE, acetylene black and Na2SO4 in hydrophobic layer is 1:1:1; 80 mesh nickel net is used as electric conductor; each part of the electrode is pressed together at 10 MPa for 1 min.In the fourth chapter, the techniques of N2 adsorption and TPD were used to examine the texture and surface chemical properties of activated carbon before and after treatment of nitric acid and air oxidation, and effects on the performance of gas diffusion electrode were also studied. It is found that the performance of oxygen diffusion electrode declines with the increasing of oxygen functional groups at the carbon surface.In the fifth chapter, electrochemical reduction behavior of dissolved oxygen in alkaline solution at the surface of MWNTs and graphite were investigated by using cyclic voltammetric method. Compared with other carbon materials, MWNTs showhigher electrocatalytic activity for oxygen reduction, and the reduction of O2 to HO2-is a quasi-reversible process at MWNTs electrode. The reduction of O2 to HO2- andthe further reduction of HO2- to OH- at graphite electrode are controlled by thediffusion of reative species in the solution, while at MWNTs electrode, both reactions are controlled by adsorptive process. This can be ascribed to the great difference of the surface texture between MWNTs and graphite powders.Furthermore, it has been found that the tops of MWNTs can be opened by air oxidation and concentric nitric acid treatment, which resuts in the appearance of pores with diameter of 2-4 nm and the great increasement of BET surface of MWNTs. However, the electrode performance of treated MWNTs does not improve remarkably, on the contrary, the decline of the electrode performance of air oxidized MWNTs is observed. These can be partly attributed to the destruction of topological defects on the MWNTs surface after air oxidation.In the sixth chapter, the polarization behavior of MWNTs oxygen diffusion electrode was investigated by linear polarization and electrochemical impedance spectroscopy (EIS). It is found that two Tafel linear parts exist in the polarization curves of MWNTs oxygen diffusion electrode. Tafel slope at low overpotential is -0.055--0.061 V dec-1, and the corresponding reaction is first order for oxygen partial pressure. EIS of gas diffusion electrode depends on the carbonaceous materials of catalyst layer. The Nyquist plots of MWNTs gas diffusion electrode show a linear region with a phase angle of 45 in the high frequency range and a depressed semicircle at lower frequencies. The linear behavior at higher frequency implies a...
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