Kinetics Of Electrocatalytic Oxidation Of Ethanol Mediated By Chemisorbed Active Oxygen Species

The effect of oxygen species chemisorbed on the surface of platinum electrode in alkaline medium on the electrocatalytic oxidation of ethanol was studied by conventional electrochemical methods（mainly cyclic voltammetry and chronoamperometry）,including the mediation role of hydroxide（OH^-）on the electrocatalytic oxidation of ethanol.The effect of potential value on species distribution was analyzed through the combination of electrochemistry and high performance liquid chromatography（EC-HPLC）,where online sampling and off-line detection were executed.The mechanism of electrocatalytic oxidation of ethanol in alkaline medium was analyzed.（1）The comparing results of the cyclic voltammetry（CV）scanning curves of the blank solution with the solutions containing ethanol in different concentrations of potassium hydroxide solutions indicated that the oxidation peak potential corresponding to the species of reactive oxygen（such as OH^*and PtO₂^*species）in the background solution was induced by the anodic oxidation peak potential of ethanol,which means that the chemisorbed oxygen species on the platinum electrode plays a key role in the electrooxidation of ethanol.（2）Herein,the effects of OH^-in solution on the electrocatalytic oxidation of ethanol were explored respectively in different concentrations of KOH solutions.The results showed that OH^-had a modulation effect on the electro-oxidation reaction of ethanol.As[KOH]<0.05 M,the chemisorbed OH^<sup>*promoted the electro-oxidation of ethanol,i.e.Increasing the concentration of OH^-in the medium could increase the corresponding anodic peak current density of ethanol.The results of[KOH]>0.05 M inhibited the reaction,and the corresponding anodic peak decreases as the concentration of OH^-,where anodic current density of the peak at-0.10 V（peak A）is dependent on the concentration of hydroxide,whereas the peak at 0.20 V（peak B）is independent off the conccentation of hydroxide.Experiments with different scanning rates indicated that both anodic peaks in positive scanning are controlled by the diffusion mass transfer process.Experiments with different initial ethanol concentrations showed that peak A is more dependent on ethanol concentration than peak B.By changing the temperature of ethanol electrooxidation process,it is found that increasing the temperature is beneficial to the electrooxidation reaction,and the apparent activation energy Ea corresponding to each oxidation peak is obtained.（3）The potential dependence of the concentration distribution of the intermediate product of electrocatalytic oxidation of ethanol,acetaldehyde and the final product of acetic acid,was studied by means of the EC-HPLC.The distribution of products is roughly consistent with the cyclic voltammetry curve of the ethanol electrooxidation process,which indicated that the electrooxidation from ethanol to acetaldehyde and acetic acid is closely related to the adsorption species formed on the surface of the platinum electrode.In addition,as the concentration of potassium hydroxide increases,the product ratio(C_CH3CHO/C_CH3COOH)gradually decreased,indicating that OH^-promoted the oxidation of intermediate acetaldehyde to acetic acid,indirectly indicating that the active oxygen species played a key role in the electro-oxidation reaction of ethanol.The kinetics of electrocatalytic oxidation of ethanol mediated by the active oxygen species on the platinum electrode and the potential distribution of the products were studied by cyclic voltammetry combined with EC-HPLC.The results showed that active oxygen species play a double-sided role in the electrocatalytic reaction of ethanol.This dissertation has 55 graphs,3 tables,and 124 references.