Preparation Of Novel Noble Metallic (Pd/Au/Ag)Nanocomposites And Their Electrocatalytic Performance

Noble metallic nanoparticles have been widely used in the field of catalysis,energy, biosensor and photics, due to their unique catalytic and photonic properties.The research about the noble metal based nanocomposite could be beneficial for theenhancement of electrocatalytic performance and service efficiency. The knowledgebetween noble metallic nanostructure and their electrocatalytic behavior could behelpful to design and prepare the noble metallic catalyst with superior performance.The unique property of Surface Plasmon Resonance (SPR) on noble metalnanoparticles has recently facilitated the rapid progress of Plasmonic Materials (PM)in photoelectric converse, biosensing and catalyst. Now, how to effectively control thesynthesis of noble metallic nano-materials, the research about the relationshipbetween the structure, composition and the performance, how to combine the catalyticand photonic properties of the noble metals, are still the research highlights in thefield of nanomaterials.Considering above research background, we choose the noble noble metallicnanostructures with excellent catalytic and photonic properties in this thesis, and theelectrocatalytic properties of noble metallic nanostructures were researched and tunedby controlling their structure, composition and hetero-structure. The main contentsand results of this thesis are summarized as following:1. We constructed mono-dispersed Pd nanoparticles with uniform size ongraphene oxide by using a simple and environmentally friendly method of ultrasonic,in which graphene oxide was used as reductant and stabilizer. Comparing with magnetic stirring, the dispersion of Pd nanoparticles can be improved by treating withultrasonic. The morphology and electrocatalytic performance of Pd nanoparticles areinfluenced by both the ultrasonic time and by the composition ratios of GO and Pd. Inalkaline solution, the sensor based on the as-prepared nanocomposite (the ultrasonictime is15min, and the volume ratios of GO and Pd is20:1) showed high sensitivity,selectivity and linear relation response to glucose in concentration range of0.2~10mM with a correlation coefficient of0.9897at a detection potential of0.4V. Thissimple and effective composite platform could potentially be extended to othermetal/graphene nanomaterials, and have broad applications in biosensing, fuel cell,and other fields.2. Based on the well-dispersed Pd NPs/GO nanohybrid prepared by ultrasonicmethod, we have successfully synthesized well-dispersed flower-shaped AuPd alloyon graphene oxide using a facile method with displacement and co-reduction reaction.During the preparation progress, the decrease of oxygen-group on the surface of GOwould result in lower density of AuPd alloy NPs, and the pre-synthesis of Pd NPscould provide the site for nucleation of AuPd alloy. The electrocatalytic activity of theAuPd/GO nanocomposites for ethanol oxidation is examined with electrochemicalcyclic voltammetry and chronoamperometric methods. The results show that theas-prepared flower-shaped AuPd alloy supported on graphene oxide performsexcellent eletrocatalytic activity (13.16mA/cm2at a working potential of-0.12V) andlong-time stability than the other catalysts. The enhanced electrocatalytic activities ofthe AuPd/GO nanohybrids could be contributed to the complementation andcooperation of Au and Pd catalytic activities and well dispersion of AuPd alloy on theGO nanosheets. This simple method can be extended to other alloy orbimetal/graphene nanomaterials. The material will have broad potential applicationsin biosensing, fuel cell, and other fields.3. We chose two kinds of silver nanostructures, namely nanodecahedra andnanocubes, for investigating the shape effect on ORR. Nanodecahedra are surroundedby ten Ag (111) facets, while nanocubes are surrounded by six Ag (100) facets. Theirelectrocatalytic performances in alkaline solution are investigated by cyclic androtating disk voltammetry. We found that the oxygen reduction on nanodecahedraprecedes the most efficient four electron reduction, where as on nanocubes precedes atwo-step pathway. That means nanodecahedra have higher activity than nanocubes for ORR in alkaline solution. We employed the simulation data to elucidate the differentcatalytic activity of ORR on silver nanostructure surfaces. It was demonstrated thatthe weaker adsorption of OH*on silver (111) facet provides more active sites, leadingto the higher catalytic activity of ORR on silver nanodecahedra than that on silvernanocubes. This finding will give a deep insight for designing silver nanostructures asan effective catalyst in alkaline based fuel cells.4. We synthesize mushroom-shaped AgPd bimetallic nanostructures with a hollowspace via combining of galvanic replacement reaction and co-reduction reaction. Thestructure and morphology were characterized to be mushroom shaped alloynanostructure by UV-vis, XRD, XPS and TEM. We also research the structure,morphology and electrochemical performance with different molar ratio between thesacrificial template (Ag nanocube) and the precursor of Pd. The results indicate thatthe AgPd alloy with molar ratio of1:1shows the best electrocatalytic performance forORR due to the synergistic effect of the alloyed AgPd crystalline phase and a superiortolerance to methanol crossover at high concentrations. This kind of catalyst could beused in the cathode of direct methanol fuel cells.5. We designed and implemented a Pd-Au bimetallic heterostructure(raspberries-like) that merge the plasmonics property with catalysis performances.This heterostructure carries the SPR property of Au nano-core and well-definedcatalytic properties of Pd and Au (different applied potential). With excellentmorphology control, we provide chances of tuning their catalytic properties withrespect to the Pd antenniform nanoislands and the incorporated Au cores. The Pd-Aunanoraspberries (NRs) with more interfaces between Pd and Au show the highestcatalytic activity. That is because the interaction of the two metals at interface couldlower the d-bond center and change the bond strengths of Pd and the adsorbedintermediate that may kinetically favor the ethanol oxidation. We employ thewell-defined SPR property of Au NPs that used as the core to tune the electrocatalyticperformance on the hetero-nanostructures’ surface. We also demonstrate that, withvisible-light irradiation, the electron resonated with the photons, could transfer to thePd nanopetals from Au, resulting in the enhancement of electrocatalytic performanceon Au and inhibition on Pd. Besides, the anti-poisoning property and stability ofas-prepared samples can also be enhanced by the visible-light-irradiation.