Unveiling the mechanism of thorough electrocatalytic oxidation of monoethanolamine by ultramicroelectrode and fast-scan cyclic voltammetry

The electro-oxidation of monoethanolamine (MEA) is relevant from fundamental and applied, viz. sewage treatment, fuel cell and electrochemical water splitting, perspectives. Understanding mechanistic details of thorough electrocatalytic oxidation of MEA is of paramount importance for the rational design of high-performing electrocatalysts. Herein, in order to easily and quickly quantify the electro-oxidation degree of MEA and therefore assist the mechanism study, the present paper proposes an innovative strategy for determining the number of electrons transferred in the electro-oxidation of intermediates, with the aid of ultramicroelectrode (UME) and fast-scan cyclic voltammetry (CV). Deconvolutions on two fast-scan CV oxidation peaks, one of which is originated from the electro-oxidation of MEA to glycine intermediate and the other is the further electro-oxidation of intermediate, reveal that the number of electrons transferred in the electro-oxidation of glycine intermediates is merely 3.04±0.75 on pure Au catalyst, indicating the incomplete conversion of glycine to ammonia and glyoxylate ion. The introduction of trace Ni into Au electrocatalyst can remarkably boost the number of electrons transferred, an indication of more thorough electro-oxidation of glycine intermediates and thereby more bio-friendly degradation products. Theoretical calculations based on the density functional theory elucidate that such increase in electro-oxidation degree is due to the stronger adsorption of glycine intermediates on AuNi binary sites than on sole Au sites.