Preparation And Electrochemical Properties Of Carbon-supported Pt And Pd-based Fuel Cell Anode Catalysts

Fuel cell is a device that can directly convert the chemical energy into electric energy.Compared with the traditional energy,it has many obvious advantages such as non-combustion involved in the use process,high efficiency and low pollutant emission.However,the high price and the low performances of electrocatalysts for fuel oxidation would prevent its applications in daily life.In this paper,Pt and Pd based catalysts with low platinum and palladium loads were successfully prepared by NaBH4 as a reducing agent and were observed in the oxidation process of formic acid and ethanol,respectively.The details are as follows:(1)Honeycomb porous carbon materials(GC)were firstly synthesized by using Stober method with silica spheres as hard templates,mixed with hydrogels of biomass nitrogen source gelatin and Hummers graphene oxide as raw materials,and then self-assembly with silica nanospheres.The BET specific surface area of GC can reach to be 1104.5 m2g-1.Two kinds of catalysts of Pd/G and Pd/GC were prepared with graphene(G)and porous carbon material GC as supports for each by ultrasonic technique assisted liquid phase reduction.The influence of Pd contents and concentration of formic acid on the catalytic oxidation performance of formic acid were investigated.It was found that the high catalytic oxidation activity and the stability of Pd/GC catalyst prepared by adjusting the mixture ratio among Stober SiO2,gelatin and Hummers graphene oxide can be obtained.(2)The PtxPdy/SnO2/GC nanocatalysts with different molar ratios of Pt and Pd for formic acid oxidation were prepared by ultrasonic assisted liquid phase reduction method,in which,the support of SnO2/GC was fabricated firstly by the ethylene glycol reduction method.Compared with PtPd/GC,PtSn02/GC and Pt/GC catalysts,Pt1Pd1/SnO2/GC has a relatively larger the electrochemical activity area(ECSA)with 528.93 cm2/mg,and the positive sweep peak current density(Ip)reached 2258.45 mA/mgpt at 0.75V.The steady current density(Is)at 3000s is 195 mA/mgPt.The results suggested that the addition of SnO2 will significantly improve the electrocatalytic oxidation activity and stability of the catalyst.Microstructure analysis showed that the catalyst particle size is only about 3 nm.When Pt:Pd=1:1,nanoparticles were uniformly deposited on the GC surface,leading to increase the electrochemical activity area of the catalyst and improving its catalytic performances.(3)PdSnP/GC catalyst was prepared by ultrasound-assisted liquid phase reduction method and used for the ethanol catalytic oxidation.The ECSA,Ip and Is values of PdSnP/GC catalysts were 198.5 m2/g,2853 mAmgpd-1 and 796 mAmgpd-1,respectively.It means the electrochemical performances were better than that of Pd/GC,PdP/GC and PdSn/GC.In addition,it was also found that the ECSA with 203.4 m2/g was obtained when Pd:Sn=2:1.Meanwhile,Ip attained 2677 mA/mgPd,and Is wtih 490 mA/mgPd.The influences of pH values of the solution for preparing PdSnP/GC catalysts on electrochemical performances were investigated.Results showed that the maximum value of Ip can be received and to be 3562 mA/mgPd in-the condition of pH=10.And the highest Is value was 598.5mg/mgPd.Microstructure observation showed that PdSnP/GC catalyst have two particle sizes,one is 43 nm,the other is 5nm.These nanoparticles were uniformly dispersed on the GC surface.Mechanism analysis shows that the introduction of non-metallic P and Sn would reduce the d-band center of Pd and further change the adsorption property of CO molecules on the surface of Pd,thus promoting the electrocatalytic activity of Pd.