Controllable Construction Of Pd Nanostructures With Different Dimensions Based On Self-assembly And Their Electrocatalytic Performance

Pd and Pd-based catalysts have been widely used in direct alcohol fuel cells,direct formic acid fuel cells,oxygen reduction reaction,organic coupling synthesis,hydrogen detection,purification and storage due to lower price(vs.Pt)and good catalytic performance.In the synthetic methods of nanomaterials,the soft template method provides infinite possibilities for preparing nanometerials with novel morphology.However,the choices of amphiphilic molecules,inorganic precursors and temperature are crucial.Based on the current researches for the synthesis and properties of Pd and Pd-based nanomaterials,in this dissertation,we adopted the self-assembly process of some novel surfactants and prepared Pd nanomaterials with three kinds of different dimensionals and desired morphology,such as one-dimensional(1D)Pd nanowires,two-dimensional(2D)Pd nanosheets,two-dimensional(2D)PdPt dendritic alloy nanosheets with various feeding ratio and three-dimensional(3D)hollow-like porous Pd nanospheres through choosing suitable surfactants,temperature and reducing agents.Additionally,we also studied the catalytic activities of formic acid oxidation for Pd nanowires and hollow-like porous Pd nanospheres,glycerol oxidation for Pd nanosheets and PdPt dendritic alloy nanosheets with various feeding ratio.We have obtained some satisfactory electrocatalytic results.Specific works are as follows:(1)In the mixing solution of surfactant dioctadecyldimethylammonium chloride(DODAC),n-heptane,H2O and Na2PdCl4,hollow-like porous Pd nanospheres with mesoporous and macroporous structure were skillfully prepared though reduce of L-ascorbic acid and synergistic effect between DODAC and n-heptane.Due to the characteristic of porous structure,in the formic acid oxidation reaction,electrochemical current density of hollow-like porous Pd nanospheres(Pd NSPs)is 3.5 times as much as commercial Pd black(Pd B),and after 2500 s,the current density of hollow-like porous Pd NSPs is still bigger than Pd B.The results demonstrate that,hollow-like porous Pd NSPs exhibit better performance in electrocatalysis towards formic acid oxidation reaction(FOR)than commercial Pd B.(2)Ultrathin single-crystalline Pd nanowires(Pd NWs)based on the self-assembly of surfactant DODAC was obtained in the synthetic system simply consisting of DODAC,H2PdCl4 and H2O.The Pd NWs can be obtained simply and immediately after the addition of L-ascorbic acid(AA)under the temperature of 95℃.Due to the ultrafine structural characteristics,with regard to formic acid oxidation reaction,the peak current density of Pd NWs is 2.8 times as much as the commercial Pd B,moreover,after 3000 s,the residual current of Pd NWs is 16.4 times as much as commercial Pd B.It shows that Pd NWs exhibit better performance in electrocatalysis towards FOR than commercial Pd B.(3)Novel surfactants with different hydrophobic carbon chains and carboxyl groupfnctional head group have been designed and synthesized,surfactants with different hydrophobic carbon chains and without carboxyl groupfunctional head group also have been synthesized,in which C22N-COOH and C22N are mainly studied.Ultrathin Pd nanosheets-1(Pd NSHs-1)and Pd nanosheets-2(Pd NSHs-2)have been easily obtained from the synthesis system(only consisting of surfactants,H2O and H2PdCl4)with AA as the reduction agent when surfactants are C22N-COOH and C22N respectively.We also studied the different synthetic effects of surfactants C22N-COOH and C22N for Pd nanosheets.For the first time,ultrathin(100)-oriented PdNSHs-1 could be produced via the confined growth among the organic lamellar micelles.Owning to the ultrathin 2D nanostructure,the obtained Pd NSHs exhibited superior electrocatalytic kinetics,electrocatalytic activity and stability toward glycerol oxidation compared to the commercial Pd B,especially the performance of Pd NSHs-1 is superior to Pd NSHs-2.(4)Pt dendritic nanosheets have been successfully obtained through using novel surfactant C22N-COOH as the soft template,H2PtCl6 solution instead of H2PdCl4 solution.Furthermore,mixed solutions with different molar ration of H2PtCl6 and H2PdCl4 and C22N-COOH,under the reduction of AA,PdPt alloy nanosheeets with different feeding ratios have also been prepared.The tests of glycerol oxidation performance show that,Pt-incorporated Pd nanostructures can effectively improve the catalytic activity.When the feeding ratio of Pd and Pt precursor reached to 1:1,the obtained product displayed better glycerol oxidation performance and stability than others.