Research On Pd-based Nanomaterials Prepared By Cyano Gum Method And Their Catalytic Properties

The noble metal palladium(Pd)and platinum(Pt)are in the same family of the periodic table and have very similar physicochemical properties.More importantly,the content of Pd on the earth is more than 50 times that of Pt,and the price is relatively low.Therefore,many efforts have been devoted to study Pd nanomaterial catalysts with widely use in various fields.The synthesis method has great influence on the composition,morphology,particle size and distribution of the catalyst,which directly afifects the catalytic activity and stability of the catalyst Studies have shown that nanomaterials doped with one or two other metals in noble metals exhibit superior catalytic performance due to the electronic effects and synergistic effects.Up to now,the commonly used liquid phase chemical reduction method is difficult to overcome the huge difference in the reduction potential between the noble metal and the 3d transition metal precursor.Therefore,when the two are reduced,it is not easy to obtain a noble metal-3d transition metal alloy having a single homogeneous structure.Cyanogel is used as the precursor of the synthesis of noble metal nanomaterials.Two different atoms in the cyanogel can be reduced at the same time to obtain an ideal atomic arrangement because the two different atoms are placed in the same molecule to form a multinuclear metal complex.In this dissertation,Pd-based nanomaterials with different morphologies and compositions were synthesized by cyanogel method,and their electrocatalytic properties for formic acid oxidation reaction(FAOR),methanol oxidation reaction(MOR)and oxygen reduction reaction(ORR)as well as the performance of catalytic hydrogenation to reduce rhodamine B(RhB)were studied.The main results are summarized as follows:1.The Porous Pd nanosheets were synthesized by a novel coordination polymer(CP)nanosheet-engaged method.The Hofmann-type CP of Pd(H2O)2[Ni(CN)4]·xH2O with square plate-like nanostructure was synthesized through a feasible hydrothermal approach.Then the CP square nanoplates were converted into Pd-Ni oxide through a mild calcination and eventually transformed into Pd porous nanosheets after electrochemical reduction with selective dissolution of Ni species.It can be found that the synthesized product is a two-dimensional sheet-like Pd nanoparticle with abundant pores.The highly open porous structure can promote mass diffusion and transportation during the catalytic reaction.The surface rich edge and comer atoms provide a large number of active sites.So the prepared porous Pd nanosheets exhibit excellent electrocatalytic performance for the FAOR,MOR and ORR.2.The three-dimensional PdNi nanocorals were obtained through cyanogel-bridged synthetie strategy.The cyanogel was initially prepared through the reaction of K2PdCl4 and K2Ni(CN)4 aqueous solutions,which can be conveniently transformed into 3D PdNi nanocorals upon the chemical reduction by fresh NaBH4 solution.It can be found that the synthesized PdNi nanocorals have a unique three-dimensional porous network structure,and Ni forms an alloy with Pd,which changes the electronic structure of Pd.The electrochemical results show that the mass activity of PdNi nanocoral at 0.85 V in alkaline oxygen reduction reaction is 1.58 times and 1.75 times higher than those of commercial Pd black and Pd nanoparticles,respectively.And after cyclic voltammograms for 5000 cycles,it is still 96.9%of initial value,indicating the PdNi nanocorals have excellent electrochemical activity and stability for ORR.3.The ordered Pd3Fe/C intermetallic compound was synthesized through a carbon-sipported cyanogel(C@cyanogel)-derived method.It involves the formation of carbon-supported K2Pd?Cl4/K4Fe?(CN)6 cyanogels,conversion to carbon-sipported Pd hexacyanoferrate(C@PdHCF),and thermal pyrolysis of the C@PdHCF precursor.It can be found that the prepared Pd3Fe nanoparticles are ordered structures with a particle size of??11 nm and are uniformly distributed on the carbon support The electrochemical results show that the electrochemical mass activity of the ordered Pd3Fe/C for the formic acid oxidation is 1.41 times higher than that of the disordered Pd3Fe/C alloy,1.91 times higher than that of the commercial Pd/C.After soaking in the sulfuric acid solution for 72 hours,the Fe content in the ordered Pd3Fe/C catalyst was attenuated a little,indicating that the ordered Pd3Fe/C intermetallic compound has excellent electrocatalytic activity and durability for the formic acid oxidation.4.The three-dimensional PdCo/PdHCC nanoflowers were fabricated by a one-pot cyanogel-based hydrothermal approach.The K2PdCl4/K3Co(CN)6-PEG hybrid cyanogel was generated by mixing K2PdCl4-PEG and K3Co(CN)6-PEG solution.Upon a hydrothermal treatment,the hybrid cyanogel eould be readily converted to 3D PdCo/PdHCC nanoflowers.It can be found that the prepared PdCo/PdHCC is a three-dimensional flower-like metal/Prussian nanocomposite composed of a large number of two-dimensional ultra-thin nanosheets.Due to its unique three-dimensional hierarchical structure and synergistic effect between hybrid components,the synthesized PdCo/PdHCC nanoflowers have excellent catalytic activity and durability toward the reduction of RhB by NaBH4.