| With the massive consumption of energy,the search for clean and renewable energy has become one of the biggest challenges for the sustainable development of society.The key to solving this problem is to find advanced energy conversion systems such as electrolyzed water,fuel cells and metal-air batteries.In these systems,the electrocatalytic hydrogen evolution reaction and ethanol oxidation reaction play an extremely important role,and provide an effective way for clean energy utilization and energy conversion.Noble metal catalysts such as Pt and Pd show excellent performance in these reaction systems.However,these noble metal catalysts are expensive and have small reserves,thereby inhibiting their large-scale industrial applications.In order to solve the above problems,in this paper we use graphene with high conductivity and large surface area as a carrier,and modify it to load precious metals so that they are distributed on graphene with high dispersion and fully expose their active sites,thereby improving catalytic activity.At the same time,we conduct a systematic and in-depth study of the structure-activity relationship between the electronic structure,physical and chemical properties of noble metal/graphene composites and the activity of electrocatalysis（hydrogen evolution reaction and ethanol oxidation reaction）.The research content and important conclusions are as follows:1.In this part of the work,hydrogenated graphene（HG-60,HG-300,HG-800）with different degrees of hydrogenation were prepared by a simple electrochemical cathode exfoliation method,and then a simple impregnation method was used to load Pd nanoparticles.A new class of ethanol electrooxidation catalyst was developed,with was based on Pd nanoparticles supported by hydrogenated graphene（HG）.The catalytic activities of Pd/HG with different hydrogenation degree（annealed at 60,300,800℃respectively）were also carefully studied.Test results suggested that Pd/HG-60exhibited super activity for electrocatalytic ethanol oxidation to Pd/HG-300 and Pd/HG-800.Moreover,Pd/HG-60 showed the highest electrochemically active surface area（EASA）among these obtained catalysts.The characterization data indicated that hydrogenated graphene with high hydrogenation degree was more favorable to promote the formation and dispersion of small Pd nanoparticles.In turn,the highly dispersed Pd nanoparticles have strong electronic interaction with graphene support,which contributes to high EASA resulting in better electrocatalytic activity for ethanol oxidation reaction in alkaline media.2.In this part of the work,firstly graphite exfoliate into graphene using an electrochemical cathode exfoliation method,while carbon quantum dots（CQDs）and Pt nanoparticles（NPs）are in-situ generated in the electrolyte simultaneously.CQDs are evolved from propylene carbonate solvent and Pt NPs are derived from reduction of Pt intermediate species generated from anodic dissolution of Pt counter electrode during electrolysis process.Then Pt NPs and CQDs are well dispersed on graphene at subsequent solvothermal process.In this study,we controlled the concentration of carbon quantum dots and the loading of Pt nanoparticles by adjusting the working voltage and the type of electrolyte,and adjusted the electrochemically active surface area and hydrogen evolution reaction activity of the obtained catalyst through two conditions.Research results surface that the mass activity of the high-efficiency catalyst loaded with trace Pt（0.145 wt%）in acidic medium is 37.5 A mg-1 at-50 m V,which is 68.2 times that of Pt/C activity.Among them,the synergistic effect of Pt nanoparticles and carbon quantum dots on graphene contributes to the hydrogen evolution performance of this catalyst.The carbon quantum dots formed on graphene are not only beneficial for supporting Pt nanoparticles but also for the construction of3D conductive materials to enhance electrochemical performance.This study provides a universal and promising methodology for synthesizing Pt,CQDs coloaded hybrid with the assistance of electric field as cost-effective catalysts for fuel cells. |
