Effect Of Binary Catalysts On The Direct Oxidation Of Sodium Borohydride

The direct borohydride fuel cell （DBFC） has been high attention in the world dueto its high theoretical voltage, specific capacity and conversion efficiencies, andremoving the store and transportion of hydrogen gas and eliminating the safety concernsowing to not using pure hydrogen gas. The direct oxidation ofBH₄^-is8e reactiontheoretically, but the number of electrons of the reaction is not8owing to hybridelectric potential resulting from the hydrolysis reaction ofBH₄^-in operation of DBFC.The hydrolysis reaction ofBH₄^-could be inhibited and the direct oxidationofBH₄^-promoted by using appropriate anode catalysts. In this work, the Ni-Crcatalysts-based on the non-precious metal nickel was prepared, and the effect of theNi-Cr catalysts on the direct oxidation ofBH₄^-was studied systematically.Firstly, the catalytic performance of Pt and Ni on the direct oxidation ofBH4was researched by cyclic voltammetry in alkaline medium. It was found that the directoxidation ofBH₄^-could be catalyzed by both Ni and Pt. However, the peak potentialofBH₄^-direct oxidation shifted to more negative and the process was simple underthe action of Ni catalyst, but the peak current was lower relatively.Secondly, the catalytic performance of Ni-Cr on the direct oxidation ofBH4was researched by cyclic voltammetry. It was found the peak currents ofBH₄^-directoxidation could be increased two or three times using Ni-Cr binary catalysts, comparedwith the single metal Ni catalyst, and the direct oxidation ofBH₄^-was enhancedobviously. Although the direct oxidation ofBH₄^-could not be catalyzed by Cr, theadsorbance ofBH₄^-on the electrode surface was reduced due to the unevendistribution of electrodepositing Cr on the surface of Ni, so two or three hydrogen atomsof a tetrahedronBH₄^-could be oxidized and the catalyst activity enhance significantly.The research also showed that the optimum condition of electrodeposition was theCr3+concentration of0.2mol/L, the electrodeposition potential of-0.100V and theelectrodeposition time of1s. In addition to, the peak current ofBH₄^-direct oxidationcould be increased with the increase of Ni-Cr catalysts area and the experimenttemperature, but the temperature was not too high.Lastly, the difference of catalytic performances between Ni-Cr and Ni catalystswere studied by cyclic voltammetry （CV）, electrochemical impedance spectroscopy（EIS）, chronopotentiometry （CP） and so on. It was found that the direct oxidation of BH4not only could be promoted, but also the stability of catalyst improved usingNi-Cr binary catalysts. Besides, by electrodepositing Cr on Ni, the impedance of thesystem was reduced, the electrochemical performance of electrode reaction wasimproved and the operation voltage of DBFC was increased.