Electrochemical Performance Investigation Of Cu-based Anode For Direct Borohydride Fuel Cell

Direct borohydride fuel cell(DBFC) is a novel type of fuel cell directly using alkaline borohydride as anode fuel.In recent years, the DBFC has been considered to be a promising potential power sources in mobile and portable applications, for its high theoretical energy density(9.3Wh/g), theoretical open circuit voltage(1.64V) and theoretical conversion efficiencies(0.91). Meanwhile, it has the significant advantages in anodic reaction kinetic, fuel storage and transportation.Theoretically, the direct electro-oxidation of BH4- is an eight-electron exchange reaction; however, for the majority of anodic catalysts, the borohydride oxidation and hydrolysis reaction progressed simultaneously. Due to the existence of the hydrolysis reaction, theoretical eight-electron exchange can not fully realized. It has been proved that the anodic oxidation reactions of BH4- is actually involved with a complex reaction system of three chemical states of hydrogen valence transformation among protide(H")-protium (H0*)-proton(H+), so the mechanism of the BH4- oxidation remains unresolved. Because the anocic oxidation process of BH4- accompanied with the hydrogen generation process, it will not only reduces fuel transformation efficiency but also leads to lower battery performance. Therefore, in the study of BH4- anodizing oxidation process, preparing lower costs anode catalysts which can inhibit BH4- hydrolysis at the same time improve the BH4- direct oxidation reaction, is a key problem for DBFC commercial application.In this dissertation, we firstly explored the possibility of the low-cost Cu metal as the anode catalyst materials for DBFC.The electrochemical oxidation behavior and reaction kinetics of sodium borohydride on Cu electrode was studied in basic solution by cyclic voltammetry(CV). The CV results showed that Cu electrode had obvious catalytic activities on the BH4- hydrolysis and direct electro-oxidation reaction which belongs to’catalytic’electrode materials. According the CV results, we calculated different kinetic parameters, and a reaction mechanism was proposed to explain the anodic properties of BH4- on Cu electrodes.On that basis, Cu/C, Pd/C and Cu-Pd/C catalysts with various mass ratios and were prepared by using impregnation method.The structure and morphology of catalysts were examined by transmission electron microscopy(TEM) and X-ray diffraction(XRD). The BH4- electrochemical oxidation behavior on different carbon-supported catalysts had been studied by different electrochemical methods, such as cyclic voltammogram(CV), Chronoamperometry(CA), Chronopotentiometry(CP) and electrochemical impedance spectra(EIS). All the testing results showed that the Cu-Pd/C alloy catalysts could significantly improve the electro-oxidation of BH4". The DBFC was fabricated with different carbon-supported catalysts as anode catalysts. It was found that the cell using the 4Cu-1Pd/C had a higher electrochemical activity. The cell power density reached to 7.94mW cm-2 which was five times as high as that of Cu/C(1.45mW cm-2). So, Cu-Pd/C alloy catalysts which was made by adding a certain amount of Pd to the Cu, could improve the electro-oxidation property apparently. The experimental results provided a basis and ideas for the research of non-precious metal as the DBFC anode catalysts.