Effect Of Nickel-based Catalysts On Direct Oxidation Of Sodium Borohydride

Direct borohydride fuel cell?DBFC? is a kind of new fuel cell, which employs borohydride sodium/potassium in alkaline solution as anodic fuel. Theoretically, the electrochemical oxidation of BH₄^- is 8e reaction, but the number of electrons released is associated with the performance of anode catalysts. It is an important way for the reduction of DBFC cost and commercialization that develops non-noble metal anode catalysts. Here the performance of nickel-based catalysts with low price was researched systematically, and the effect of the deposition of Ni catalysts on the direct oxidation of BH₄^-.Firstly, the performance of Ni foil catalyst and Ni catalyst by electrodeposited on nickel substrate on the direct oxidation of BH₄^- was researched in alkaline medium. Only one oxidized peak in the cyclic voltammetry of BH₄^- electro-oxidation on Ni electrode and the peak potential was about-0.7 V. The current value of the first 3 cycles of BH₄^- electro-oxidation in Ni foil catalyst was 23, 15 and 3 m A. Under the similar conditions, it was 116, 63 and 23 m A with Ni catalyst by electrodeposited on nickel substrate, which was 5, 4 and 7 times of the Ni foil. The discharge time of BH₄^- was 1.4×103 s under the Ni foil catalyst with the discharge efficiency of 4%, while the BH₄^-discharge time was 7.2×104 s under the electrodeposited Ni catalyst with the discharge efficiency of 23%, almost increase 6 times. Therefore, the oxidation peak current and the constant current discharge time of BH₄^- were increased significantly with electrodeposited Ni catalyst, and the discharge efficiency and fuel utilization rate were also increased significantly. Since the surface morphology of the catalyst was changed by the electrodeposited of Ni, the specific surface area and the active catalytic site increased. The optimal conditions for the preparation of Ni catalyst on nickel were as following: the Ni2+ concentration was 0.2 mol/L, the electrodeposition potential was-1.0 V, and the electrodeposition time was 100 s.Secondly, the deposition of Ni catalyst in alkaline solution is corroded easily and soon lost the catalytic activity on the electrochemical oxidation of BH₄^-. The effects of different electrolyte additives on the catalytic performance of electrodeposited Ni were researched by cyclic voltammetry, electrochemical impedance spectroscopy, chronopotentiometry and so on. The results confirmed that TEA was not only inhibited effectively the corrosion of Ni in alkaline medium, but also promoted the electrochemical oxidation of BH₄^-. The optimal concentration ranges of TEA were 0.018⁰.025 mol/L. The discharge time was 9.0×104 s at the optimum concentration, with the discharge efficiency of 29%. The electro-oxidation of BH₄^- was also promoted by TU, but the corrosion of Ni in alkaline electrolyte was not inhibited well. The optimal concentration ranges of TU were 0.21 ?mol/L. The discharge time was 7.3×104 s at the optimum concentration with the discharge efficiency of 23%. Comparison of two kinds of additives, TEA was the better option forus.