Mechanism Study On The Effect Of Pt Nanoparticle Spacing On Oxygen Reduction And Methanol Oxidation Reactions

Platinum nanoparticles on carbon are the classical catalysts for direct methanol fuel cells,which are used for the electrooxidation of methanol at the anode and oxygen reduction at the cathode.Although the morphology and size of Pt particles as well as the selection of support for Pt catalysts have been extensively studied,the effect of the distance between Pt nanoparticles on electrocatalysis has not received enough attention and intensive investigation.In this work,we first prepared Pt nanoparticles sol with particle size of about 2 nm by ethylene glycol reduction method,and then loaded them on conductive carbon black.By controlling Pt loading,the inter-nanoparticle distance was adjusted based on similar physical and chemical properties of Pt nanoparticles.Finally,the mechanistic insights of the effect of interparticle distance on the oxygen reduction(ORR)and the methanol electrooxidation(MOR)were quantitatively studied.The main research contents and results are as follows:(1)Surface clean Pt nanoparticles of about 2 nm were prepared by ethylene glycol reduction method and loaded on carbon black to obtain 10 catalysts with different Pt interparticle distance.Physical characterization shows that the size and valence state of Pt particles were almost unchanged in a wide range of interparticle distance from 10 nm to 117 nm,which provides a guarantee for exploring the effect of interparticle distance.The dimensionless distance ?(the ratio of interparticle distance d to particle diameter D)was used as a quantitative descriptor of interparticle distance in order to reduce the influence of small particle size changes.(2)Interparticle distance not only affects the activity of ORR,but also the selectivity of ORR.When the interparticle distance is small(?<12),ORR tends to occur with 4 electrons forming water;when ??12,the ORR process tends to occur with 2 electrons producing hydrogen peroxide.(3)Through ORR electrochemical impedance system study,it is confirmed that there are two kinds of reactions of 2-electrons and 4-electrons on Pt catalyst.By adjusting the interparticle distance,the two reactions can be distinguished and the possibility of the two reactions can be regulated.(4)Interparticle distance of Pt nanoparticle has a significant effect on MOR activity.When??3.3,The intrinsic activities of Pt/C catalyst were almost the same,but the mass-based activity were increased with the increase of Pt interparticle distance.When ??3.3,MOR intrinsic activity and mass-based activity are decreased with the increase of Pt interparticle distance.For CO electrooxidation,interparticle distance affects the mass transfer-adsorption-reaction of CO.This fundamental study has an important scientific significance and practical value for the design and optimization of Pt catalysts for direct alcohol fuel cells.