The Effect Of Additive On The Electro- Chemical Behavior Of Sodium Borohydride

Direct sodium borohydride fuel cell (DBFC) use sodium borohydride (NaBH4) alkaline solution as the anode fuel. And with the hydrogen storage material NaBH4 hydrogen content that is as high as 11% (m/m) in solids), 7.4%(m/m) in saturated sodium borohydridesolution, respectively. NaBH4 reactions faster than the kinetics of methanol oxidation, the energy density and cell voltage is better than methanol.On the base of theory, the direct electrochemical oxidation NaBH4 as 8e-reaction, is greater than methanol 6e-reaction, has higher specific capacity.Additionally, NaBH4 is non-flammable, low toxicity, and it does not produce carbon dioxide.However, the biggest problem of NaBH4 in the direct oxidation is hydrolysis produces hydrogen gas. One hand the hydrogen gas produced in hydrolysis reduces the fuel usage,on the other hand because of that hydrogen bubbles will impede the migration of ions, as a result, the battery's performance is reduced. Inhibition of hydrolysis of sodium borohydride is the best way to dissolve in the alkaline solution, and appropriate alkaline optimum conditions differ because of the different working electrode. According to the results of previous experiments, the thesis chose concentration to:0.27 mol/L NaBH4 +1.5 mol/L NaOH. Inhibiting the hydrolysis of sodium borohydride and to improve the direct electrochemical oxidation NaBH4 to 8e- reaction is the main problem solved of the research.First of all, the thesis deals with Linear Sweep Voltammetry(LSV) and cyclic voltammetry curves(CV) of the catalytic electrode materials are:gold, platinum, nickel in 0.27 mol/L NaBH4+1.5mol/L NaOH alkali solution, the electrochemical oxidation experimental temperature was 40℃, the results show that when gold is used as catalytic electrode materials, a direct oxidation reaction takes place, gold as the catalytic oxidation electrode materials, the direct electrochemical oxidation can be reach 8e-reaction, nevertheless, the gold catalytic electrode materials polarized more seriously; when platinum used as catalyst, two consecutive oxidation reactions take place in 0.27 mol/L NaBH4+1.5mol/L NaOH alkaline solution, which occurred at-0.09V in the vicinity of the direct oxidation of BH4-reaction process, while BH4- hydrolysis generated intermediate BH3OH- followed in the near +0.29 V oxidation; nickel as catalytic electrode materials, as compared with platinum, NaBH4 direct electrochemical oxidation potential is more negative, the reaction starts faster. NaBH4 in alkaline solution will form comparatively more stable nickel hydroxide, nickel prevented the further oxidation of NaBH4.Secondly,the effect of different additives on the electrochemical behavior in alkaline solution NaBH4 on platinum electrode was investigated by cyclic voltammetry curves(CV),electrochemical impedance spectroscopy(EIS) and chronopotentiometry(CP).The experimental results show that additives when appropriate amount of the additive is beneficial to the oxidation of sodium borohydride in alkaline solution on platinum electrode and these three kinds of additives can reduce the platinum electrode BH4- adsorption capacity, improve the oxidation current of NaBH4, and increase the NaBH4 catalytic oxidation activity, and enhance the discharge efficiency.The further study showed that the best additives were 6μmol/L melamine,15μmol/L hexamethylene tetramine,and 30μmol/L toluene sulfonamide.