Study On Synthesis And Electrochemical Characteristics Of Au-Ni Alloy Anode Catalyst For Direct Borohydride Fuel Cell

Fuel cells, as electrochemical devices, convert fuels such as hydrogen into electricitywithout combustion; they create virtually no pollution and hold the key to futureprosperity and a healthy global environment. Fuel cell using sodium borohydride （NaBH₄）aqueous solution as fuel has received growing attention because the direct borohydridefuel cell （DBFC） has special advantages, including the chemical stability of solid statefuel （NaBH₄）, non-combustible, high cell voltage （1.64V）, and a specific capacity of5.7Ah g^-1higher than that of methanol (5.03Ah g^-1). Although BH₄-is a promising fuel,there are significant problems with the anode oxidation reaction of DBFC, on the most ofmetals studied in relation to BH₄-oxidation, the complete8e-exchange is not achieveddue to hydrolysis of borohydride. This makes the number of electrons released by perBH₄-anion （faradaic efficiency） decrease. The result leads to a decrease in the energydensity of DBFC, thus lowers the expected fuel efficiency of an8-electron oxidation. Itwas well reported that high coulombic numbers near8e-were obtained by using Auanodes due to its inactivity towards the hydrolysis reaction. However, the Au electrodeusually demonstrates slow electrode kinetics and thus low current and power output.Therefore, improving the electrochemical activity of oxidation of BH₄-on Au anode hasbecome the focus of the studies on DBFC.In this paper, around Au-Ni alloy, the selection and optimization of the preparationmethods of Au-Ni Material, the electrochemical oxidation behavior of BH₄-on the Au-Nianode, doped with a small amount of Pt to improve the electrocatalytic activity of Au-Nialloy for BH₄-oxidation, has been studied.1. The relatively simple aqueous phase preparation method and reverse micellespreparation method were chosed to synthesis the Au-Ni alloy materials. Comparedelectrochemical oxidation behaviors of BH₄-on the two Au-Ni alloys prepared bydifferent methods, it was found that the catalytic activity of Au-Ni alloy prepared by thereverse micelles method was better. To summarize the affections of the water tosurfactant ratio Rω for Au-Ni nanoparticle size and surface electrochemical activitysurface composition, the Rω in reverse micelles method has been changed. The resultsshow that using reverse micelles method the higher of BH₄-electrochemical oxidationcatalytic activity of Au-Ni catalyst can be prepared in the condition of Rω=5.2. Using the reverse micelles method Au/C and Au-Ni/C catalysts were prepared in the preparation condition R_ω=5. Compared the catalytic performance of Au/C and Au-Ni/C,the Au-Ni/C not only reduced the Au/C cost but also compensated the Au slow kineticrate and enhanced the activity of the catalyst. Through electrochemical techniques theelectrochemical catalytic oxidation behaviors of BH₄-on Au-Ni/C materials underdifferent operating conditions have been studied. The studies found that theelectrochemical oxidation of BH₄-on Au-Ni/C electrode was hybrid controlled by theirreversible electron transfer process and the diffusion process. Conditions such as theconcentration of NaOH or NaBH₄and temperature can affect the catalytic behavior ofAu-Ni/C electrochemical oxidation of BH₄-. The impacts of NaOH or NaBH₄concentration and temperature on cell performance have been discussed; the resultsshowed that the best composition of anolyte is1M NaBH43M NaOHand in a certaintemperature range, the cell performance increased with the increase of temperature.3. Doping a small amount of Pt in the Au-Ni alloys, the Au_0.49Ni_0.49Pt_0.02/C,Au_0.475Ni_0.475Pt_0.05/C and Au_0.46Ni_0.46Pt_0.08/C catalysts were prepared. Three types ofnanopaticles are spherical, and their diameters were3.9nm,3.7nm,4.0nm, respectively.Electrochemical tests showed that the material catalytic activity improved significantlywith doping a small amount of Pt. Using the Au-Ni/C, Au_0.49Ni_0.49Pt_0.02/C,Au_0.475Ni_0.475Pt_0.05/C and Au_0.46Ni_0.46Pt_0.08/C as anode assembled direct sodiumborohydride-hydrogen peroxide fuel cell （DBPFC）, respectively. It is found that theDBPFC using Au_0.475Ni_0.475Pt_0.05/C as anode and Au/C as cathode can give an optimal cellperformance; the maximum power is68.36mW cm^-2.