Controlling Synthesis Of Noble Metal Nanocomposites And Their Electrocatalytic Properties

In this thesis,a series of noble metal nanocomposites with unique morphologies,including noble metal heterostructures,noble metal/non-noble metal heterostructures,and noble metal-based alloy structures,were controllably prepared by seed-mediated growth method,chemical reduction method,and galvanic replacement reaction method.Effectively combining the desirable optical?localized surface plasmon resonance?properties and catalytic activities,to achieve the goal of modifying noble metal nanocomposites through three main modulation methods,"photoelectric effect","photothermal effect"and"structural effect",is the main guideline.The prepared samples were applied to the field of photo-assisted electrocatalytic hydrogen production and methanol oxidation reaction,which revealed the remarkably enhanced photoelectric performance.The formation mechanism and electrocatalytic reaction mechanism of the catalysts were studied in detail.The specific research contents are listed as follows:1.Preparation and properties of noble metal heterostructures.?1?Plasmonic bimetallic structures have been wildly used in photocatalysis,owing to their tunable optical properties and desirable catalytic activities.However,it is still a challenge to realize the enhanced electrocatalytic hydrogen evolution reaction?HER?using these structures with electric,photo-,and thermal effects.Herein,we report that Pd-tipped Au nanorods?NRs?were prepared for electrochemical water splitting in the visible and near-infrared region.The NRs exhibited a lower onset overpotential?40 mV?and high exchange current density(1.585mA cm^-2),which was largely ascribed to the increased carrier density in Pd induced by photo-excited Au NRs,and further enhancement of Pd catalytic activity resulted from the photothermal effect of Au NRs.As the hot electron transport channel was hindered by excess Pd nanoparticles,the HER performance of tipped NRs was much higher than that of fully covered ones.?2?According to the research ideas of the previous part,the multibranched Au nanostars with stronger local electromagnetic field effect were designed and synthesized as the matrix materials.Then,the unique AgPt alloy-modified multibranched Au nanostar heterostructures with wider tunable optical properties and desirable activities are precisely fabricated via selective deposition of Ag and Pt,through adjusting the amounts of KI and metal precursors.AgPt-tipped Au nanostars have the most remarkable performance in electrocatalytic hydrogen evolution and methanol oxidation reaction driven by visible and near-infrared light irradiation,which are mainly ascribed to the effective transfer of plasmon-excited electron-hole pairs.Additionally,the increased system temperature generated by the photothermal effect of Au,larger active area,and modified electronic state also contribute to the enhancement of activity,stability,and tolerance of CO poisoning.As the adverse charge transport pathway,the electrocatalytic performances of AgPt-edged and-covered Au nanostars are inhibited.The experimental results reveal that rationally designed bifunctional plasmonic electrocatalysts which make full use of the synergy of photoelectric,photothermal,and structural effect have promising potential in photoelectric catalytic conversion fields.2.Preparation and properties of noble metal/non-noble metal heterostructures.Taking advantage of localized surface plasmon resonance?LSPR?properties of Ag nanoparticles,Ag-MoS₂/C nanocomposites were synthesized,to investigate the roles of photoelectric effect and structure effect on the electrocatalytic properties of noble metal/non-noble metal heterostructures.Due to the weak conductivity of MoS₂ itself and the less in-plane active sites,the pre-modification study was first carried out by doping with heteroatoms and combining with carbon materials.In order to construct the MoS₂ hybrid nanostructure with enhanced conductivity and more active sites towards electrocatalytic HER,hierarchical P-doped MoS₂ nanosheets decorated N-doped hollow carbon spheres?N-C@P-MoS₂?core-shell structures were synthesized via calcination and hydrothermal methods.N-C@P-MoS₂ with optimized loadings exhibited favorable HER activities and fine stability compared with pure MoS₂ nanosheets and all undoped samples.This is largely ascribed to the synergy of MoS₂ and carbon in the rational hierarchical structures,as well as the modified electronic structure with improved conductivity,increased active sites by virtue of N and P doping.Furthermore,P-doped MoS₂ nanosheets were encapsulated in carbon spheres?N-C/P-MoS₂?inside??by controlling the dropping rate of adding MoS₂ precursors.As the active sites were hampered,the N-C/P-MoS₂?inside?revealed poor HER performance compared with the core-shell counterparts.The results demonstrate that the fabrication of hierarchical MoS₂/carbon composites with the synergy of structural?morphology and content?and electronic?active sites and conductivity?effects induced by various nonmetal doping pave the way for enhanced electrocatalytic HER activities.Then,the Ag nanoparticles were modified on the MoS₂ based composites with the best doping and loading amounts via chemical reduction method.The plasmon-induced electron transfer effect of Ag greatly promoted the electrocatalytic performance under visible light irradiation.3.Preparation and properties of noble metal-based alloy structures.The noble metal-based alloy structure contributes to the activity enhancement of the catalytic reaction,due to the shift of the d-band energy caused by the stronger interaction involving metals.The nano-cubic self-assembled structures of ternary PtNiCu and binary PtCu alloy was synthesized via a one-pot high-temperature chemical reduction method,and applied to the fields of visible light-assisted electrocatalytic hydrogen production and methanol oxidation reaction.The ternary PtNiCu alloy exhibits superior catalytic performance,mainly due to its regular morphology,more surface active sites?structural effect?,the shift of d-band energy of Pt induced by strong interaction involving metals and lattice stress makes it more conducive to the absorption and desorption of hydrogen and the ability to resist CO poisoning?electronic effect?.In addition,under visible light irradiation,the accelerating efficiency of electron transfer between Cu and Pt further promotes the photo-assisted hydrogen production and methanol oxidation performance.