Mechanistic Studies Of Small C1 Molecular Oxidation At Platinum And Iridium Single Crystals

The electrocatalytic reaction often involves multiple parallel reaction channels,which always contain a multi-step continuous process and the electron transfer at each step can also be accompanied by the breaking and generation of chemical bonds.The reaction intermediate in the reaction channel,which plays an important contribution to the total reaction current,is very difficult to directly detect on the surface of catalyst because of its short life and low coverage.It's one of the important problems in the field of electrochemistry to reveal the mechanism of each critical channel and find out the key factors which determine its dynamics.These information can guide the design of efficient electrocatalyst and optimize the the electrochemical energy and material conversion technology and its operating conditions.In order to solve the above problems,we mainly focused on two simple oxidation reactions:formic acid oxidation and CO oxidation and studied the following two aspects.1?The pH effect and H/D kinetic isotope effect of HCOOH/HCOO-oxidation on Pt(111)The pH effect and the H/D kinetic isotope effect(KIE)for the oxidation of formic acid/formate anions(FOR)on Pt(111)have been studied using rotating disk technique combined with cyclic voltammetry and potential step tools.The pH-dependent FOR activity displays a volcano shape with a maximum at a pH close to the pKa of HCOOH.The H/D KIE factors for HCOOH/DCOOH or HCOO-/DCOO-are ca.5-6,2-3,and 1 in solutions with pH=1.1,3.6,and 13,respectively.These findings reveal that HCOOH?COOad-+2H++e is the rate-determining step(RDS)for FOR in acid.With increasing pH,the precursor to be discharged changes from HCOOH to HCOO-,and the latter goes through HCOO-?HCOOad+e as the RDS.This model can well explain the volcano-type pH effect and H/D kinetic isotope effect.The origin of the appearance of the volcano-type pH dependent FOR activity is the pH-induced change from excess HCOOH to excess HCOO" at pH = pKa and the change in overpotential for the RDS of FOR.2?The migration of COad on platinum and iridium stepped single crystals and its effect on the oxidation activity.The preparation and treatment conditions of Ir(111)and Ir(332)single crystals were investigated,and the basic CO oxidation performance on Pt and Ir single crystals was studied.The initial potential of the CO oxidation on Ir single crystal is lower than that of the Pt single crystal,but it takes longer time to complete the oxidation.And similar with Pt,the step position on Ir is the active site,and the slow scan rate of oxidation is beneficial to the migration of COad to the step position so the initial oxidation potential become lower too.We also studied the influence of the COad mobility on Pt(332)and Pt(997)using chronoamperometry and multi-step oxidation.The experiment data confirmed the COad can migrate on the electrode surface.And this mobility shows a two-sidedness.If the rate of COad diffusion is lower than the rate of OHad generate,it will promote the oxidation of COad,and vice versa,it will inhibit the oxidation.