(553e) 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