Synthesis And Catalytic Performance Of Conductive Polymers-noble Metal Nanocomposites

The conductive polymer-noble metal nanoparticle composites are materials obtained by conductive polymer and noble metal nanoparticles by chemical method,physical method and so on.Such materials can not only exert the respective advantages of the conductive polymer and noble metal nanoparticles,but also increase the related activity through the synergistic effect between each other.On the one hand,the support and protection of the conductive polymer ensure the catalytic activity and stability of the noble metal nanoparticles.On the other hand,the noble metal nanoparticles enhance the conductive ability of the conductive polymers and make the electron transfer more efficient.In this paper,polyaniline,polypyrrole gold and silver as the research object,were carried out related experiments.The details are as follows:1.Ammonium persulfate as an oxidant was used to oxidize aniline to prepare polyaniline fibres,and then,polyaniline was used to reduce silver ions in the silver nitrate solution to prepare dendrites silver and form polyaniline-dendritites silver composites.We believe that the formation mechanism of dendritites silver conforms to the diffusion-limited aggregation model:In the initial stage of reaction,the silver nanoparticles which reduced by polyaniline are directly anchored on the polyaniline fiber.As the reaction proceeds,both the silver ion concentration and the diffusion rate decrease.At this point,the newly formed silver nanoparticles adhered to the existing silver nanoparticles and growed in orientation to form dendritites silver.We used this composites as a catalyst for cathode oxygen reduction of fuel cells and conducted relevant catalytic tests.The linear sweep voltammetry curve shows that the onset potential is 0.846 V with respect to the reversible hydrogen electrode?RHE?,the half-wave potential is 0.651 V?vs.RHE?,and the current density is 5.209 mA cm^-22 at a potential of 0.265 V?vs.RHE?.The catalytic activity retention rate was 74%after 20,000 s cycle,and the ability to resist methanol poisoning was better than pure dendritites silver.2.Oxidation reduction reaction between pyrrole and silver nitrate with sodium lauryl sulfate as surfactant was used to prepare core-shell polypyrrole coated silver?silver@polypyrrole?with good dispersion and uniform size.We found that the degree of eccentricity of silver nuclei was controlled by reaction time,reaction temperature,and sodium dodecyl sulfate concentration.By means of the galvanic replacement reaction,we chose silver@polypyrrole of suitable eccentricity as the seed and chloroauric acid solution to prepare mushroom-like gold/silver-polypyrrole ternary composites.Then,Ag@polypyrrole and mushroom gold/silver-polypyrrole as catalysts were used to catalyze reduction of p-nitrophenol by sodium borohydride.The catalytic processes of the two catalysts conformed to the first-order kinetic equation.The k_m of silver@polypyrrole was only 40400 min^-1 g^-1,while the k_m of mushroom-like gold/silver-polypyrrole reached 836,000 min^-1 g^-1.Because gold/silver in mushroom-like gold/silver-polypyrrole is sufficient contact with the solution compared to silver@polypyrrole,due to exposing more active sites,which is beneficial to increase the catalytic efficiency.Moreover,after 5 cycles of experiments,the Au/Ag-PPy catalytic activity was maintained at 84%,exhibiting good cycle stability.