Synthesis Of Pt Nanoparticles Of Different Sizes And Their Electrocatalytic Oxidation Performance

Due to the limited storage and uneven distribution of Pt,the price of Pt based catalyst is very high,which increases the cost of alcohol fuel cell and limits its commercial development.In order to reduce the cost of catalyst fundamentally,in addition to reducing the load of Pt,Pt based catalyst with smaller particle size and higher activity should also be developed.In this paper,1～12 nanometer Pt nanoparticles were synthesized by ethylene glycol synthesis method without surfactant.The size effect of particle size on CO electro oxidation,methanol electro oxidation and ethanol electro oxidation was explored.The intermediate products of methanol oxidation and ethanol oxidation were detected by differential electrochemical mass spectrometry.Then we studied the effect of Pt particle size on the electrooxidation of methanol and ethanol.The results showed that with the increase of Pt particle size,the peak potential of methanol electrooxidation（MOR）first shifted positively and then negatively,and the peak current density first decreased and then increased.When the particle size was 12.51 nm,the peak potential and current density of MOR were the lowest and the highest,respectively.Formaldehyde,formic acid,methyl ether,and CO₂ can be qualitatively detected by DEMS during the MOR on all catalysts.CO₂ was the major product.For ethanol electrooxidation（EOR）,the peak potential first shifted positively and then negatively,and the peak current density first increased and then decreased.When the particle size was 7.06 nm,the peak potential and current density of EOR were the lowest and the highest.DEMS can detect products such as CO₂,acetaldehyde,acetic acid,and ethyl acetate on all catalysts during EOR.Acetaldehyde was the major product.The size of Pt nanoparticles directly affects the electrooxidation performance of the catalyst.The electrooxidative removal of the adsorbed CO showed that the electrochemical active surface area（ECASA）decreased with the increase of the size of Pt nanoparticles.The CO stripping peak potential shifted positively and then shifted negatively,as the particle size increased.For the peak current density,it increased and then decreased.When the diameter of Pt particle is 3 nm,the CO stripping potential and current density were the highest.For CO_adelectrooxidation,the catalytic activity was not only determined by the surface hydroxyl group,but also affected by the surface diffusion rate of CO_ad.Electrochemical experiments have confirmed that the chemical diffusion of surface adsorbed CO_ad generally existed in the electrooxidative removal of CO_adon many other noble metal nanoparticles.Combining with DFT calculation,we confirmed that the structural sensitivity of CO_ad electrooxidation not only included the reaction rate of CO_ad and OH_ad at the reactive sites,but also included the diffusion rate of CO_ad migrating to the reactive site.Finally,a simplified mathematical model was developed to qualitatively reproduce the transient current curve,revealing that the peak current and position depended on the ratio of the reaction rate constant k to the diffusion coefficient DCO.