Relationship Between Interface Structure And Properties Of High Conductive Carbon Fiber Electrode Materials

At present, the lead alloy and titanium are the main substrate materials of the electrodes used in the field of hydrometallurgy and electrochemistry. However, it is known that the lead alloy electrode has high oxygen evolution potential, big energy consumption used as anodes, and high dissolubility used to zinc electrowinning. According to statistics, the consumption of lead electrode plates is 0.2 blocks per ton electrolytic zinc. The total electrolytic zinc consumption of lead plates is more than 1.5 million pieces each year in China. These consumption has increased the costs of the electrolytic metallurgical industry. It is easily for lead electrodes in the zinc electrowinning process to pollute the electrolyte, pollute the cathode products and reduce the quality of the cathode products. Moreover, the titanium substrate of the Ti-based coating electrodes possesses high internal resistance. The Ti-based coating electrodes can not avoid the passivation of Ti-base when anodized in the sulfuric acid system, so their further application is confined. Therefore, it becomes an important issue in the filed of hydrometallurgy to develop a new electrode material with wide adaptability, strong corrosion resistance and low cost.The carbon fibers are used as the new electrode substrate material to solve the existing problems of the electrode substrate material themselves above and to reach the target of large-scale production in the future. And the substrate of the new coating electrode material has many advantages, such as light quality, good conductivity, high corrosion resistance, high strength, large specific area, et al. In this study, a new electrode material based on the carbon fiber cloth of light wight, low cost and wide adaptability was prepared by galvanostatic electrodeposition method. The PbO2 was directly deposited onto the pretreated carbon fiber cloth without the intermediate layer.The surface chemical properties, surface morphology of the carbon fibers and the interface structures of the composite electrode material were characterized in order to investigate the effects of the pretreatments of hot-air oxidation and liquid oxidation on the carbon fibers. The interface structures of the electrode materials before and after surface treatments were studied. And the compositions of the interface structures were analyzed by energy dispersive spectrometer. Then the effects of electrodeposition conditions of Pb(NO3)2 concentration, electrodeposition current density and electrodeposition time on the active layer morphology and the interface performance including interface characteristic, adhesion and conductivity of the CF/β-PbO2 electrode were studied later. The relationship between the morphology and interface performance with the electrochemical properties and corrosion resistivity was analyzed. On this basis, the electrochemical properties and corrosion resistivity of the CF/β-PbO2 electrode and traditional lead alloy electrode were studied. Finally, the rare earth Sm was doped into the active layer in order to homogenize the surface morphology, refine the grains, improve the interfacial bonding properties between the carbon fiber matrix and β-PbO2, and to obtain the better electrochemical performance of the CF/β-PbO2 electrode.The research results show that the oxygen-containing functional groups and O/C ratio on the surface of the carbon fibers can be increased in a short time after the surface pretreatments of hot-air oxidation and liquid phase oxidation. Meanwhile, the surface roughness of the carbon fibers increases with many corrosion pits and grooves caused by oxidation etching. The carbon fibers get the largest number of the oxygen-containing functional groups, biggest O/C ratio and best chemical activity at the hot-air oxidation temperature of 400 ℃ and the liquid phase oxidation time of 60 min. The interface bonding strength of the active coating and the pretreated carbon fibers is bigger than the untreated carbon fibers. The EDS result indicates that there is no new compounds generated in the interface between the active coating and carbon fibers matrix. Thus, the interface bonding mechanism was figured out with mechanical chimeric way based on Van Der Waals force. The electrodeposion process of PbO2 mainly include these steps to ger the smooth, dense homogeneous active coating of the electrode, such as, the formation of PbO2 particles, wrapping the carbon fibers, filling the gaps of the carbon fiber cloth and covering the whole carbon fiber cloth.The XRD result shows that the active layer of the coating electrode based on carbon fibers obtained by electrodeposition method is P-PbO2. The optimum electrodeposition condition of the CF/β-PbO2 electrode are as followed:Pb(NO3)2 concentration of 150 g·L-1, electrodeposition current density of 40 mA·cm-2 and electrodeposition time of 100 min. The interface bonding strength of the CF/β-PbO2 electrode obtained under the optimum electrodeposition condition is the biggest and the interfacial resistivity of 6.75×10-5Ω·m is the lowest, respectively. The electrochemical properties and corrosion resistivity of the CF/β-PbO2 electrode obtained under the optimum electrodeposition condition are superior to other conditions. Compared with the traditional lead alloy electrode, the quality of the CF/β-PbO2 electrode reduced by 70.2% with the same area and volume. The CF/β-PbO2 electrode has better electrocatalytic activity than the traditional lead alloy electrode with the negative shift value of polarization potential of 98 mV. The CF/β-PbO2 electrode has higher corrosion potential of 1.085 V and lower corrosion current density of 2.074×10-4 A·cm-2 than those of the traditional lead alloy electrode. The CF/β-PbO2 electrode has stronger corrosion resistance and the corrosion rate is only 1/5 of that of the traditional lead alloy electrode. Considering the advantages of light wight, strong electrocatalytic activity and high corrosion resistance of the CF/β-PbO2 electrode, the cost and stability of the electrode materials will be reduced and increased, respectively.The surface of the active layer of the CF/PbO2 electrode doped with rare earth Sm is more uniform, dense and smooth than the undoped electrode. The carbon fibers are covered better with the PbO2 particles doped with Sm. The CF/Sm-PbO2 electrode has higher interface bonding strength and lower electrical resistivity which reduced with 5.81%. The CF/Sm-PbO2 electrode doped with Sm has better electrocatalytic acitivity with the negative shift value of polarization potential of 85 mV than the CF/β-PbO2 electrode. In addition, the doping Sm can improve the stability and corrosion resistance of the electrode and the corrosion rate was reduced by 11.8%.