Ethylene Glycol Electrooxidation on Smooth and Nanostructured Pd Electrodes in Alkaline Media

Abstract

The electrooxidation of ethylene glycol (EG) has been studied either in situ on a smooth Pd electrode by FTIR spectroscopy or on nanostructured Pd‐based catalysts by cyclic voltammetry. The electrooxidation on the Pd electrode is dramatically influenced by the pH. Below pH 12, CO2 is formed and detected in the thin layer by FTIR, while at higher pH values glycolate, carbonate and oxalate are formed almost simultaneously at a potential of ca. 0.4 V versus RHE. Above 0.9 V glycolate is oxidised to oxalate and carbonate. The nanostructured electrocatalysts Pd–(Ni–Zn)/C, Pd–(Ni–Zn–P)/C and Pd/C are much more active than the smooth Pd electrode (up to 3,300 A g(Pd)–1) and give different distributions of the oxidation products. Pd/C is the most selective catalyst yielding glycolate, while mixtures of glycolate (major>60%), oxalate and carbonate are obtained with Pd–(Ni–Zn)/C or Pd–(Ni–Zn–P)/C. Carbonate is produced by oxidation of both glycolate (major contribution) and oxalate, while the major part of oxalate seems to be produced by the direct oxidation of EG.

Electro-oxidation of ethylene glycol and glycerol at palladium-decorated FeCo@Fe core–shell nanocatalysts for alkaline direct alcohol fuel cells: functionalized MWCNT supports and impact on product selectivity

“…In fact, according to literature, adsorbed hydroxyl species are required to release the carboxylic acid upon coupling with Pd-acyl species. 30,53 −2 ) and 2.7 times higher than Pd/MWCNT-SO 3 H. The J f /J b values for the four catalysts are above 2 for EG but above 3 for the GLY. This indicates excellent tolerance of the catalysts to the presence of the carbonaceous products from alcohol oxidation.…”

“…Indeed, at high potential, are formed surface palladium oxides that are inactive for the electrooxidation of alcohols. 30,52 The backward scan peak can be associated with the oxidation of freshly chemisorbed EG or GLY. In fact, previous CV studies of ethanol oxidation on Pd showed that the decrease in current at high voltages was mainly due to the formation of a PdO layer, which blocked the adsorption of the substrate.…”

“…Both FeCo@Fe@Pd/MWCNT-COOH and Pd/MWCNT-COOH electrocatalysts showed a preference towards the oxidation of one hydroxyl group of EG (path a), whereas a small amount of oxalate seems to be produced mainly by the direct oxidation of EG (path b) rather from the further oxidation of the glycolate (path d). 30 While the Pd/MWCNT-COOH showed a weak ability towards the C-C bond, the FeCo@Fe@Pd/MWCNT-COOH seems very efficient in the further oxidation of EG producing formate and a large amount of carbonate (route c). The oxidation of GLY gave a plethora of oxidation products as shown in Fig.…”

A Bird’s Eye View of Energy-Related Electrochemistry

“…Glycerate is further oxidized to tartronate and, by cleavage of C-C bond, into glycolate and formate. The latter species lead to carbonate and glycolate is oxidized to oxalate [25][26][27][28]. G is also oxidized directly to tartronate (path b) by chelating adsorption on catalytic surfaces.…”

“…However, the oxidation of G yields significant amounts of carbonate. Since oxalate is very slowly oxidized on Pd-based electrodes [25,26,29,30] CO 2 is prevalently a by-product of the oxidation of either glycerate or glycolate.…”