Metal Nanoparticles/Mesoporous Carbon Composite Electrode Materials: Preparation And Electro-synthesis Application

Electrochemical synthesis,as a green synthesis technology that conforms to"atomic economy",has the ultimate goal of achieving high-efficiency production by consuming the lowest energy.However,there are still defects such as small electrode active area and low product selectivity.Therefore,it is necessary to develop better electrode materials to improve the catalytic performance of the electrosynthesis reaction.Mesoporous carbon material is a class of porous carbon material with high specific surface area,good chemical stability and excellent conductivity.Excellent conductivity and open pore structure are conducive to the transmission of substances during the reaction process;high specific surface area can provide more active sites;the fixation of the carbon substrate can prevent the agglomeration of metal nanoparticles in the reaction.Therefore,the combination of metal nanoparticles with good catalytic activity and mesoporous carbon material to prepare a novel electrocatalyst may have better electrocatalytic performance in electrosynthesis.In this thesis,mesoporous carbon was used as support,by combining with high activity metals,to prepare metal nanoparticles/mesoporous carbon composite electrode materials.The electrocatalytic properties of the composites were investigated towards electrocatalytic hydrogenation of aromatic ketone,electroreduction of halogenated and electroreduction of CO₂.The relationship between material structure and electrocatalytic properties was explored.The main research contents of this thesis are as follows:?1?Using the synthesis principle of mesoporous carbon material,a high dispersion Ni nanoparticles/ordered mesoporous carbon composites were synthesized by soft template method.The stable block structure can be obtained simply and conveniently by firstly compressing the precursor material?polymer film?and then calcining.The composite material maintains the body center cubic ordered structure,and the Ni nanoparticles are partially embedded in the carbon pore wall and uniformly dispersed,and the particle size is small?7-15 nm?.The effects of stirring time,calcination temperature and pressure on precursor on the phase structure of the material were investigated.The results show that the prepared materials show very high performance in selective?⁸3%?electrocatalytic reduction of aromatic ketones into alcohols?⁷9%?when the electrolysis was carried out in the 0.1 mol·L^-1 TEABr-DMF/EtOH at a current density of 1.0 mA·cm^-2 until 4 F·mol^-1 charge passed through.Moreover,the composite materials has good universality to other aromatic ketone substrates.By analyzing the relationship between material structure and electrocatalytic performance,it is speculated that the pores of OMC may have spatial restrictive effect on the reaction.?2?In order to further study the confinement effect of the orifice on the electrocatalytic hydrogenation of aromatic ketone,a novel microporous C/Ti composite with smaller pore size was designed and synthesized for the electrocatalytic hydrogenation of propiophenone.Mesopores and micropores coexist in the obtained composites,and the TiO₂ nanoparticles of uniform size?7 nm?are highly dispersed and single non-overlapping in the carbon layer.Experiments show that the microporous C/Ti composites show better selectivity?84%?for electrocatalytic hydrogenation of propiophenone into phenylpropanol?81%?after optimizing the reaction conditions.The result further verifying the restrictive effect of pore structure for the reaction.?3?The metal Ag with good catalytic effect on the electroreduction of halide is introduced into mesoporous carbon to synthesize a series of nano-Ag/ordered mesoporous carbon composites with different Ag content,the same mesoporous size and pore volume.The phase structure and catalytic performance of Ag/OMC electrode materials with different Ag content were characterized by various characterization techniques,cyclic voltammetry and potentiostatic electrolysis.The results show that the composites has excellent electrocatalytic properties to the electroreduction reaction of benzyl bromide,the highest yield of bibenzyl can be up to 98%after optimizing the reaction conditions.By analyzing the relationship between material structure and electrocatalytic performance,it is speculated that the carbon pore wall has shielding effect on smaller nanoparticles.The appropriate content and nanoparticles size are the key factors in determining the catalytic performance of composite materials.?4?A new method for synthesis of N-doped functional mesoporous carbon material was designed.Based on nano-Ag/ordered mesoporous carbon composites,N and Ag co-doping composite functional mesoporous carbon electrode materials were synthesized in one step.The structure of the composites was detailedly characterized by a variety of characterization methods and the synthesis mechanism was speculated.The effects of N amount and Ag content on the adsorption performance of CO₂ and catalytic activity were studied by CO₂ adsorption-desorption test,cyclic voltammetry and potentiostatic electrolysis.The results show that the introduction of N improves CO₂ adsorption performance of composites and promotes the uniform dispersion of Ag nanoparticles.Compared with nano-Ag/ordered mesoporous carbon materials,N and Ag co-doped composite functional mesoporous carbon materials exhibit excellent electrocatalytic properties for the electrocarboxylation of benzyl bromide.Under the optimized reaction conditions,the highest carboxylation product yield was 62%,much higher than that on Ag and Ag/OMC electrode.?5?Combining N-doped ordered mesoporous carbon with excellent CO₂adsorption performance and Cu nanoparticles,N-doped mesoporous carbon material supported Cu was synthesized.The composite material maintains body-centered cubic ordered structure,and the Cu nanoparticles are highly dispersed in the carbon substrate.Under mild reaction conditions,the Cu/NOMC modified electrode can reduce CO₂ in aqueous solution to alcohol.The effects of low temperature calcination and Cu content on the catalytic performance of directly electroreduction CO₂ were studied by linear voltammetry and potentiostatic electrolysis.The results show that the composite exhibits good electrocatalytic performance for electroreduction of CO₂.After optimizing the reaction conditions,the total current efficiency of ethanol and n-propanol reached 30%.