Study On The Catalysis Of Polyaniline-Modified Platinum For The Oxidation Of HCOOLi

As the lightest formate,lithium formate(HCOOLi)has a feature of high energy density(per unit mass).Polyaniline(PANI),as a kind of conductive polymer with conjugated structure,exhibits many characteristics such as high conductivity,excellent environmental and electrochemical stability,cheap price,simple synthetic process,et al.Therefore,it has become a hotspot in the field of conductive polymers.This paper focuse on the electrocatalytic effect of PANI-modified Pt electrode for lithium formate oxidation,and the purpose is to lay the foundation of theorytical and experiment for the application of direct formate fuel cell.In this paper,a kind of PANI nanofiber was synthesized by chemical in-situ polymerization.The average diameter of the fibers was about 300 nm and the conductivity was 5.5 S cm-1.PANI was characterized by TG,XRD,FT-IR,SEM EDS,and other experimental methods.Pt electrode modified by the nanofiber PANI was further prepared by in-situ chemical polymerizing method.The electrochemical activity and stability of the modified electrode in 0.1 mol L-1 sulfuric acid solution were studied by CV technique.The electrochemical catalysis effect of PANI/Pt electrode were researched by CV and current time curves(j-t)in three kinds of formate(lithium formate,sodium formate,potassium formate)solution and their mixtures with 0.1mol L-1 sulfate solution,respectively.Finally,the electrochemical catalytic effect of PANI/Pt electrode to HCOOH-HCOOLi oxidation was studied in detail.Experimental results show that the prepared nanofiber PANI has a desirable modification for Pt electrode,which solves the problem that large lithium hydrate molecules bulk form on Pt surface and occupy the catalyst activity site.In three kinds of formate solution,therefore,the electrocatalytic activity of PANI/Pt electrode shows the best in acid solution of lithium formate.The peak current density of formic acid-formate through the direct oxidation path is improved in 2.5 mol L-1 lithium formate,which is about 64 mA cm-2.Furthermore,the oxidation peak current density j is proportional to the square root v1/2 of the scanning rate.It indicates that,under the concentration,the electrode reaction is controlled by diffusion.If make ratio of the integral area through the direct oxidation to the total oxidation greater than 85%as the standard,the suitable working concentration of lithium formate should be among 2.0?4.0 mol L-1 under the experimental conditions.The j-t curves show that the current density of PANI/Pt catalyzing for HCOOLi decays slowly and keeps a better level in 1200 s in this range of concentrations.On the other hand,based on the dual-path mechanism of formic acid reaction,this paper provides some direct electrochemical evidences for the third oxidation pathway of formic acid.The third important oxidation path is the direct oxidation of formate.The results show the electrochemical oxidation of HCOOH—HCOOLi system on PANI/Pt is obvious in a wide range of formate concentration,and show an obvious oxidation peak in low potential range.The oxidation peak at low potential mainly comes from the third oxidation pathway of formate.Meanwhile,the oxidation through indirect pathway is strongly inhibited.