Preparation And Electrocatalytic Performance Of Graphene-short Peptide Assembly-Platinum Nanoparticle Composites

To date,platinum nanomaterials remain the most efficient cathode electrocatalysts in fuel cells.The synthesis of highly active platinum nanocatalysts has attracted extensive attentions of researchers.In order to solve the problem of high cost and short service life of noble metals,nanostructures can be supported on carriers with high specific surface area,such as carbon black particles,graphite nanofibers and carbon nanotubes.Among them,graphene has the advantages of good electrical conductivity,high surface area and high mechanical strength,and can be used as a good two-dimensional(2D)carrier.In this thesis,one-dimensional(1D)platinum nanoparticles were synthesized by using short peptides as templates.And then,we have studied the effects of graphene species,binding mode with graphene,and peptide type on the morphology of platinum nano-assemblies.We have also studied the effects of the concentration peptide and platinum precursor and synthetic temperature on the morphology and electrochemical properties of the platinum nanomaterials.We have investigated the effects of reduction method on the morphology and electrochemical properties of graphene/peptide/platinum assemblies in aqueous phase.TEM resulsts showed that the platinum nanofibers adsorbed side by side on the surface of graphene when platinum precursor and graphene oxide were simultaneously reduced by L-ascorbic acid(one-step reduction method).And the platinum nanofibers were smaller in diameter and closely arranged.The electrocatalytic experiments showed that the activity of the graphene/peptide/platinum was lower than that of the peptide/platinum nanomaterials without graphene.In the accelerated aging test,the catalytic activity of graphene/peptide/platinum structure synthesized via one-step reduction was retained 70.8%after 250 cycles,and 45.6%after 1000 cycles,while only 32.2%was retained of the peptide/platinum nanostructure.The graphene/peptide/platinum nanostructures synthesized via one-step reduction method had alonger service life than the peptide/platinum nanostructures.It is indicated that graphene plays a positive role in stabilizing platinum nanomaterials.The carboxyl groups of the graphene oxide were reduced to hydroxyl groups and were able to bind the platinum precursor.Furthermore,the platinum precursor/peptide self-assembles were positively charged,and could adsorbed on the negatively charged reduced graphene oxide through electrostatic interaction.The effects of temperature,concentration,and ratio of peptide to platinum precursor on the morphologies of platinum/peptide self-assembly have been studied.The platinum particles in the short peptide/platinum self-assemblies after 70?water bath were heavily fused and arranged more closely.And its electrocatalytic activity and stability were significantly improved in electrochemical experiments.Increasing the concentration of the peptide and platinum precursor was beneficial to the catalytic activity,but had little effect on the catalytic stability.The I₃KY/Pt composites exhibited rather high catalytic activity and stability under the effects of increased temperature and concentration.Its activity could be almost unchanged after even 1000 cycles.The increased temperature promoted the adsorption of platinum precursor on the surface of peptide nanofibers,and the peptide nanofibers tended to intertwine into bundles at higher concentration,and thus ensured the stability during the electrochemical process.The RGO(reduced graphene oxide)/peptide/Pt nanostructures were synthesized by one-step reduction method using four short peptides(I₃K,I₃KY,I₃YK,I₃KDopa).TEM results showed that the platinum nanoparticles in RGO/peptide/Pt nanostructures adsorbed stably on RGO surface.The platinum nanoparticles in RGO/I₃K/Pt material were closely packed and had high aspect ratio.The platinum nanoparticle aggregates of RGO/I₃KY/Pt were radial and the nanoparticles were aligned evenly.The morphologies of RGO/I₃YK/Pt were similar to those of GO/I₃KY/Pt composites,but the platinum nanoparticles were slightly larger than those in RGO/I₃KY/Pt.Platinum nanoparticles in RGO/I₃KDopa/Pt nanostructures also adsorbed on the surface of graphene,but the particles were significantly smaller,with the diameter of only about 5 nm.Electrocatalytic experiments showed that the activity of RGO/I₃KY/platinum nanostructures was retained 95.0%after 250 CV cycles and 68.0%after1000 cycles.RGO/I₃KY/Pt had higher stability than RGO/I₃K/Pt.The?-?stacking interaction between benzene ring on tyrosine and RGO made the stable combination of RGO,I₃KY and platinum nanoparticles.