271215 Electrocatalytic Oxidation of Ethylene Glycol (EG) On Supported Pt and Au Catalysts in High pH Media: Reaction Pathway Investigation in Both Three-Electrode Cell and Single Cell Reactors
A modified solution-phase reduction method was used to prepare Pt/C (2.6 nm) and Au/C (3.5 nm), which served as working catalysts for investigation of electro-catalytic oxidation pathway of ethylene glycol (EG) in alkaline media. The three-electrode cell with on-line sample collection system showed that glycolic acid, oxalic acid and formic acid were sequentially produced from EG oxidation on Pt/C with increasing linear staircase scan voltammetry, while only glycolic acid and formic acid were examined on Au/C. We clarified that formic acid was produced dominantly from direct C-C bond cleavage of EG on both Pt/C and Au/C. Further oxidation of glycolic acid to oxalic acid occurs only on Pt/C but not on Au/C at the specified test conditions. Electrocatalytic oxidation of EG in single anion exchange membrane-direct EG fuel cells (AEM-DEGFCs) with Pt/C and Au/C anode catalysts showed consistent results with the three-electrode cell tests. The AEM-DEGFCs with Pt/C anode demonstrated a peak power density of 71.0 mW cm-2, which is much higher than that with Au/C anode (only 7.3 mW cm-2) at 50 ˚C. This is in agreement with more negative onset potential and higher generated current density for electro-oxidation of EG on Pt/C than on Au/C obtained in the three-electrode cell reactor. With fuel cell operation voltage decreasing (anode over-potential increasing), deeper-oxidized products oxalic acid and formic acid were generated in the Pt/C anode AEM-DEGFC with increased selectivity, and no formic acid was examined when glycolic acid was independently employed as fuel. On Au/C anode catalyst, very high selectivity of >98% to glycolic acid was achieved. The AEM-DEGFC results confirmed the EG electro-oxidation pathway proposed in light of the on-line sample collection system, which is anticipated to be of useful and significant to explore the reaction sequences for electro-oxidation of other polyols.
Scheme 1. The proposed pathway for electro-catalytic oxidation of EG on Au/C and Pt/C in high pH media, the starting potentials for observed reaction paths are marked