Study On Synthesis And Electrochemical Characteristics Of Pd-based Anode Catalysts For Direct Borohydride Fuel Cell

Fuel cell is an electrochemical power generation appliance, which could directly convert chemical energy to electrical energy not by burning. With some outstanding features such as non-toxic, easy storage, high open circuit potential, low operation temperature and high power density, direct borohydride fuel cell (DBFC) has attracted increasing attentions recently. It is significant to develope high electronic utilization anode catalyst since BH4? hydrolysis reaction coexists in the process of BH4? electrochemical oxidation reaction. At present, the anode catalysts of direct borohydride fuel cell mainly employ precious metals Pt, which could hardly reduce the costs and achieve theoretical reaction electronic number.In this paper, in order to prepare the anode electrocatalysts with high electrochemical catalytic activity and low costs, the carbon supported nanosized Pd-based anode catalysts of DBFC were prepared. The main contents are as follow:1. Nanosized Pd-Au alloys were prepared by impregnation method. The size of the Pd-Au alloys particles was about 5 nm, which was apparently less than that of the usual Au particles. The results showed that the Pd-Au/C catalysts had higher catalytic activity and lower overpotential for the direct oxidation of NaBH4 than pure Au/C catalyst, especially Pd₂Au/C showed the highest catalytic activity among the three Pd-based catalysts. A simple direct borohydride-hydrogen peroxide fuel cell (DBHFC) was fabricated in which the Au/C was used as the cathode catalyst and the Pd₂Au/C as the anode catalyst, as high as 56.8 mW cm^-2 power density at a current density of 70 mA cm^-2 can be obtained. The effects of NaBH₄ concentrations and temperature on BH₄^- electro-oxidation process had been discussed.2. The carbon supported bimetallic Pd-Au catalyst with core-shell structure was prepared by successive reduction method. The core-shell structure and surface morphology were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and ultraviolet-visible absorption spectroscopy (UV-vis spectrum). The results showed that the spheroidal nanoparticles were homogeneously dispersed on the surface of the carbon and the calculated Pd shell thickness was about 0.375 nm. The Pd-Au/C catalyst with core-shell structure exhibited much higher catalytic activity for the direct oxidation of NaBH4 than pure Au/C and Pd/C catalyst and the catalyst was not poisoned with the increase of the discharge time. A direct borohydride-hydrogen peroxide fuel cell (DBHFC), in which the Pd-Au/C with core-shell structure was used as the anode catalyst and the Au/C as the cathode catalyst, showed as high as 71.8 mW cm^-2 power density at a current density of 90 mA cm^-2 at 0.798 V.3. A series of nanosized Pd_x-Co_100-x alloys on VXC-72R carbon were prepared by impregnation method. The results showed that supported Pd_x-Co_100-x alloys catalysts had similar catalytic activity for the direct oxidation of BH4? to Pd/C catalyst, though Co/C have been proved no catalytic activity for BH4? oxidation. The DBHFC used Pd₇₀Co₃₀/C as the anode catalyst showed as high as 72.98 mW cm^-2 power density at a current density of 95 mA cm^-2 and a discharge capacity of 1.54 Ah g^-1.