Study Of The Electrocatalysis Of Polypyrrole-Modified Platinum On Formic Acid/Formate Oxidation

A chemical method,with p-toluenesulfonic acid(p-TSA)as doping agent and ammonium persulfate as oxidizing agent,was applied to polymerize pyrrole monomers.We explored the synthesis conditions of polypyrrole(PPy)and prepared polypyrrole-modified platinum electrode(PPy/Pt)by in-situ self-assembly method.SEM,XRD,FT-IR,EDS and standard four-probe methods were used to characterize the PPy.Cyclic voltammetry(CV)and current-time curve methods were used to research the electrochemical properties of PPy/Pt.The results show that the synthesized PPy was spherical particle aggregated into coralline cluster in small part.The particle is about 100 nm in diameter.The average conductivity(± standard deviation)of PPy is 39.8(±1.0)S·cm-1.The electrochemical experimental results indicate that,comparing with pure Pt electrode,the PPy modification of Pt increases the electrocatalysis of Pt to HCOOH-HCOOoxidation obviously.In addition,the oxidation current density of PPy/Pt can be up to 33.3 mA·cm-2 in pure sodium formate aqueous solutions.Comparing with pure Pt electrode,the current value increases by 60%.If mixture solution of sodium formate and sulfuric acid substitute for the pure solium formate solutions,the current value of PPy/Pt can be up to 18 mA-cm-2,which also increases by 40%comparing with pure Pt electrode.The comparative results indicate that,in sodium formate solutions,the electrocatalysis of PPy/Pt on HCOOH-HCOO-oxidation is the best,as well as the anti-CO species poison performance.It is generally accepted that the electrooxidation of HCOOH-HCOO-on Pt catalyst follows a dual-path mechanism:(1)direct oxidation of Pt-HCOOH to CO2 at low potential;(2)indirect oxidation of Pt-HCOOH mediated by a poison adsorbed Pt-CO(COads)and then to CO2 at high potential.Nearly,a third path was also pointed:direct oxidation of Pt-HCOO-to CO2 at low potential.It is well known that there are plenty of formate anions in the solution if a sodium formate solution or a mixture of sodium formate and sulfuric acid substitutes for a formic acid solution or a mixture of formic acid and sulfuric acid.Meanwhile,our experimental results indicate that the oxidation current density increases with the concentration of formate.Therefore,we consider that the main path of HCOOH-HCOO-oxidation is the third path,namely direct oxidation of Pt-HCOO-.Meanwhile,the direct oxidation and indirect oxidation of Pt-HCOOH also exist in the system.The results mentioned above also indicate that the electrocatalytic activity of PPy/Pt electrode in formate solution is much higher than that in formic acid solution.The conclusion provides experimental evidence to substitute formate for formic acid in fuel cells.