Study On Nanoporous Carbon Supported Anode Catalysts For Direct Borohydride-hydrogen Peroxide Fuel Cell

The direct borohydride-hydrogen peroxide fuel cell(DBHFC) that utilizes directly the sodium borohydride(NaBH4) in aqueous alkaline medium as a fuel has attracted considerable attention, since its unique advantages, e.g. high energy density(9.3 Wh g-1) and high theoretical open circuit voltage(OCV) of 3.01 V. However, the DBHFC has a long way to become commercially viable for applications, because it still suffers from high cost caused by precious metal-based electrocatalysts(e.g., Pt, Au or Pd). The anode performance of the DBHFC is crucial to minimize the electrocatalyst cost and improve the fuel utilization. Usually, the properties of the support can substantially affect the performances of synthesized electrocatalysts, such as electrochemical active area, morphology, stability, etc. Thus, to improve the catalyst support is an effectively approach to enhance the catalytic activity of catalyst.The metal-organic frameworks(MOFs) with tunable pore sizes and multiple structures have been demonstrated as promising templates. And the resultant nanoporous carbons present large pore volume, high specific surface area, and good electrochemical properties in wide applications, which are essential for a good catalyst carrier in fuel cells. Therefore, in this paper the nanoporous carbon(NPC) has been prepared by template metal-organic framework-5(MOF-5, Zn4O(OOCC6H4COO)3) with furfuryl alcohol(FA) as carbon source and used as the support for the anode catalyst in DBHFC. The paper mainly focuses on:The NPC supported Pt anode catalyst(Pt/NPC) is prepared by impregnation reduction method. The obtained Pt/NPC catalyst is characterized by cyclic voltammetry(CV), chronopotentiometry and fuel cell test. The results show that the Pt/NPC exhibits much higher catalytic activity for borohydride oxidation than the Vulcan XC-72 carbon supported Pt(Pt/XC-72). Besides, the DBHFC using the Pt/NPC as anode electrocatalyst shows the maximum power density as high as 54 mW cm-2, and in the case of the single cell with the Pt/XC-72 anode catalyst, the corresponding maximum power density is only 34 mW cm-2.The activated nanoporous carbon(A-NPC) is synthesized via KOH activation of the NPC. The specific surface area and microstructure of the nanoporous carbon before and after activation treatment are derived from their corresponding N2 adsorption-desorption isotherms. It has been found that the A-NPC achieves a surface area up to 2296 m2 g-1 and a pore volume of 1.59 cm3 g-1. The electrochemical oxidation behaviors of BH4- on the A-NPC supported Au(Au/A-NPC), NPC supported Au(Au/NPC) and Vulcan XC-72 carbon supported Au(Au/XC-72) catalysts are compared via electrochemical measurements. The results show that the Au/A-NPC catalyst presents a superior catalytic activity for borohydride oxidation to other two catalysts.The PtxCu/NPC and Pdx Zn/NPC with various molar rations are synthesized via impregnation reduction method. The catalytic activitives for borohydride oxidation of the PtxC u/NPC and Pdx Zn/NPC catalysts are tested using electrochemical characterizations. The results show that both the PtxCu/NPC and Pdx Zn/NPC catalysts display much higher activities for borohydride oxidation than that of the corresponding monometallic catalysts. Especially, the Pt2Cu/NPC and Pd2Zn/NPC catalysts exhibit the highest catalytic activity among PtxCu/NPC and Pdx Zn/NPC catalysts, respectively. Besides, the DBHFC equipped with the Pt2Cu/NPC and Pd2Zn/NPC anode catalysts also present an excellent cell performance with the maximum power density as high as 89 mW cm-2 and 104 mW cm-2.