Synthesis, Characterization And Electrochemical Properties Of BiOX (X=C1, Br, I) As Catalysts For Cathode Reaction Of Aluminum-air Battery

Abstract:The development and problems at present of Aluminum-air full cell, air electrode and air electrode catalyst are introduced. BiOCl micro-assembled consisting of ultrafine nanoplates and ultrathin nanosheets BiOX (X=Cl, Br, I) were respectively prepared by hydrothermal method, and BiOX(X=Cl, Br) flower spherical microspheres was prepared by solvent-thermal method. The crystallinity of BiOX (X=Cl, Br, I) are examined using X-ray powder diffraction (XRD), and the surface morphologies of BiOX (X=C1, Br, I) are examined using scanning electron microscope (SEM) and transmission electron microscopy (TEM). The effects of different catalyst on the performance of the air electrode are investigated by polarization and discharge curves respectively. The air electrodes loaded with these catalysts are studied by cyclic voltammetry and electrochemical impedance spectroscopy. The electron transfer pathway in oxygen reduction process is examined using oxygen reduction kinetics. The main results are as follows:(1) Under condition of the precursor concentration0.18mol·L-1, reaction temperature180℃, reaction time6h and pH=3, the BiOCl(0.18) micro-assembled consisting of ultrafine nanoplates is synthesized by hydrothermal method, it performs slightly better than other samples as catalyst for air electrode application. Through the polarization curves, BiOCl (0.18) micro-assembled consisting of ultrafine nanoplates can significantly reduce electrode polarization, the oxygen reduction current density is557mA℉cm-2, the electrochemical properties is better than the currently MnO2catalyst. In the constant current discharge curve, the voltage of the air electrode loaded with BiOCl (0.18) is always higher than the air electrode loaded with MnO2. Under condition of high current density, the voltage of the air electrode loaded with BiOCl (0.18) is still up to1.28V. The oxygen reduction kinetics results showed that BiOCl (0.18) takes2-electron transfer pathway. Through extensive researches, BiOCl catalytic activity is closely related to the oxygen vacancy concentration, while the oxygen vacancy concentration of (001) plane is the highest. Therefore, the85%percentage of (001) plane of BiOCl (0.18) is the key factor resulting high catalytic activity, much higher than other BiOCl samples.(2) BiOX (X=Cl, Br, I) ultrathin nanosheets is synthesized by hydro-thermal method. BiOCl ultrathin nanosheets perform slightly better than other samples as catalyst for air electrode application. Through the polarization curves, BiOCl ultrathin nanosheets can significantly reduce electrode polarization, the oxygen reduction current density is483mA℉cm-2, the electrochemical properties better than BiOX (X=Br, I). By AC impedance test, BiOCl ultrathin nanosheets compare with BiOBr and BiOI ultrathin nanosheets exhibits lower resistance. Oxygen reduction kinetics study results show that ultrathin nanosheets BiOCl take4-electron transfer pathway, while ultrathin nanosheets BiOI and BiOBr take2-electron transfer pathway.(3) BiOX (X=Cl, Br) flower spherical microspheres is synthesized by solvothermal method. BiOBr flower spherical microspheres perform slightly better than BiOCl flower spherical microspheres as catalyst for air electrode application. By the polarization curves test, the oxygen reduction current density of the air electrode loaded with BiOBr flower spherical microspheres is434mA·cm-2. In AC impedance test, under the condition of open-circuit voltage or the bias voltage-0.3V, the BiOBr flower spherical microspheres relative to the BiOCl exhibits lower resistance.