Preparation And Electrochemical Properties Of NaBH₄-H₂O₂ Fuel Cell Catalysts

Direct Sodium borohydride-hydrogen peroxide fuel cell?DBHPFC?is a new type of direct liquid fuel cell with borohydride as anode fuel and hydrogen peroxide as cathode oxidant.Sodium borohydride is a kind of hydrogen storage material with very high hydrogen content which has the fast oxidation kinetics and high specific energy.Compared with gaseous oxygen the liquid H₂O₂ is easy to store and has high volume ratio energy density.Moreover,DHPFC using hydrogen peroxide directly does not produce CO₂ gas and carbonate during the work process which is very suitable for application underwater.At present,the research of NaBH₄-H₂O₂ fuel cell is mainly focused on the selection and preparation of electrode materials.In this thesis,perovskite oxides La_1-xSr_xCoO₃,Ag/C@TiO₂,Pd C@TiO₂ and Pd-Ag/C@TiO₂,Pt C/@TiO₂,Au/C@TiO₂ electrode were used as catalysts to study the electrochemical reduction and oxidation reaction of H₂O₂ andNaBH₄.XRD,SEM,TEM and EDS measurements are conducted to investigate the morphology and physical structure of the electrodes.The electrochemical performance of the electrodes is studied by cyclic voltammetry?CV?,linear scanning?LSV?,chronoamperometry?CA?.The experimental results are analyzed and the conclusions are as follows:1.La_1-xSr_xCo O₃ powder electrodes were synthesized by a sol-gel method.The optimum calcination temperature is 650?.Results revealed that La_0.6Sr_0.4CoO₃ electrodes exhibite highest activity for the reduction of H₂O₂.The current density reaches 123 mA·cm^-2 when the electrode potential is-0.4 V with the H₂O₂ concentration of 0.6 mol·L^-1.2.C@TiO₂ nanowire arrays are obtained by a method of chemical vapor deposition method.The Ag/C@TiO₂ and Pd/C@TiO₂ electrodes are prepared by depositing Ag and Pd respectively on C@TiO₂ substrate.The catalytic performance of electrode was studied for by CV and CA.The optimum NaOH concentration of Ag/C@TiO₂ electrode for electrocatalytic reduction of H₂O₂ was 1 mol·L^-1,and the current density on the Ag/C@TiO₂ electrode increases with the H₂O₂ concentration rising.Resulsts also reveal that the Ag/C@TiO₂electrode exhibits a good stability toward the reduction of H₂O_2.According to the characterization and test,the optimal H₂SO₄ concentration of Pd/C@TiO₂ electrode for electrocatalytic reduction current density of H₂O₂ is 2mol·L^-1.The current density reaches 120mA·cm^-2 when the electrode potential is 0.2 V.The current density on the Pd/C@TiO₂electrode also shows a rising trend with the H₂O₂ concentration increasing.3.Different proportions of Pd-Ag/C@TiO₂ electrodes with core-shell structures are prepared by thermal evaporation and potentiostatic deposition.The results show that the performance of Pd-Ag?2:1?/C@TiO₂ core/shell nanorods is best and the current density reached 672 mA cm^-2 in 3 mol·L^-1NaOH+0.20 mol L^-1 NaBH₄.The current density can remain 210 mA·cm^-2 in 0.05 mol·L^-1NaBH₄+3 mol·L^-1NaOH when potential was-0.1V.The decay of the current curve is very small in the 1200s test time,which indicates that the PdAg/C@TiO₂ electrode has a high electrochemical activity and stability for NaBH₄oxidation.4.C@TiO₂ nanowire arrays are prepared by electrodeposition of particle Pt as anode catalyst.The electrode shows the best catalytic performance in 1 mol·L^-1NaOH+0.4mol·L^-1NaBH₄.The current density reaches 545 mA·cm^-2 when the electrode potential is 0V.The current density remains in 131 mA·cm^-2 when the electrode potential is 0.0 V in the 1000s test time.The decay of the current curve is very small,which indicates that the Pt/C@TiO₂electrode has a high electrochemical activity and stability for NaBH₄ oxidation.5.The 3D structure of Au/C@TiO₂ electrode is prepared by electrodeposition of Au on the C@TiO₂ nanowire arrays.Cyclic voltammetry shows that the Au/C@TiO₂ electrode has higher catalytic activity for the electrooxidation of NaBH₄.The Au/C@TiO₂ electrode has good stability by chronoamperometry.The electrocatalytic oxidation of NaBH₄ on Au eletrode is an irreversible system.It is found that the number of transferred electrons is 6.2.The results show that the oxidation efficiency of NaBH₄ on the Au electrode is higher.