Preparation And Performance Study Of Pd-based Anode Catalysts For Direct Liquid Fuel Cells

Direct liquid fuel cells(DLFCs)have great development potential in portable power and electric vehicles on account of their fast-starting speed,low operating temperature,high energy density,convenient fuel storage and transportation.Yet,palladium(Pd)electrocatalyst with limited activity and poor stability seriously hinders the practical application.Therefore,it is necessary to synthesize novel high activity and stability catalysts.Morphology control at the nanoscale attract much attention in recent years,besides,materials surface structure is closely related to electrocatalytic properties of catalysts.Ultrathin Two-dimensional(2D)nanosheets possesses unique electronic properties and high surface area with a number of active sites,improving the current density of electrooxidation peak.The assembly of 2D structures into three-dimensional(3D)nanomaterials with porous structure,providing additional active sites,which can not only maintain the high specific surface area of the 2D structure,but also have high electrochemical and structural stability.In this work,3D layered palladium tungsten nanosheet assemblies(L-PdW NAs),PdIr nanosheet(PdIr NSs)and Pd nanocrystalline assemblies(Pd NAs)were synthesized,respectively.The morphology,electrocatalytic properties and catalytic enhancement mechanism of all catalysts were characterized and studied.The main contents are as follows:(1)L-PdW NAs have been synthesized using carbon monoxide(CO)as a structural guide and reducing agent,exhibiting much higher catalytic activity and stability toward both ethanol oxidation reaction(EOR)and methanol oxidation reaction(MOR)compared to palladium nanosheets(Pd NSs)and commercial Pd/C.It is discovered that the tungsten hexacarbonyl(W(CO)₆)in the synthetic system displays a decisive key in forming the layered nanosheet structure.The catalytic enhancement mechanism should attribute to the synergetic effects between the introduced W and novel architecture of layered nanosheet assembles and the bifunctional mechanism between Pd and W.(2)PdIr NSs were prepared with CO as the structural guide and reducing agent and ascorbic acid as the co-reducing agent,exhibiting excellent catalytic performance for MOR and formic acid oxidation reaction(FAOR).The MOR mass activity of PdIr NSs is 1.26times and 2.32 times that of Pd NSs and commercial Pd/C,respectively.The FAOR mass activity of PdIr NSs is 1.48 times and 2.65 times that of Pd NSs and commercial Pd/C,respectively.The catalytic enhancement mechanism can be attributed to the electronic effect and the bifunctional effect between the introduced Ir and Pd.(3)Pd NAs have been synthesized via galvanic reduction method in Zn/H₂O system.The method is fast,simple and pollution-free.The FAOR mass activity and the specific surface area of Pd NAs are about 3 times and 2.5 times that of commercial Pd/C,respectively.The initial oxidation potential of Pd NAs catalysts for FAOR is-0.154 V,which is lower than most catalysts reported in recent year,indicating the fast electrode kinetics.