Glucose electro-oxidation on Pt(100) in phosphate buffer solution (pH 7): A mechanistic study

Glucose is an important biomolecule that participates as a main source of energy in living organism reactions. Considering its biological importance, the electrochemical investigation about glucose electro-oxidation has attracted attention with the aim to develop non-enzymatic catalysts able to achieve the complete oxidation of glucose to be used as fuel in Direct Glucose Fuel Cells (DGFC). However, there are some challenges related to the oxidation of this relatively large, complex molecule, such as product distributions, adsorbed species, surface poisoning and structure sensitivity that must be understood. The use of well-defined surfaces, as single crystals, is a helpful tool to progress in this knowledge. In this context, the goal of this manuscript is the elucidation of the glucose electro-oxidation reaction in phosphate buffered solution (pH 7) on Pt(100) using cyclic voltammetry and in situ FTIR techniques at room temperature. It was observed that the reaction product distribution depends on glucose concentration. The maximum current density was reached with 2 × 10−2 mol dm−3 glucose (~2.04 mA cm−2) and then decreases with the increase of glucose concentration, because the reaction becomes dominated by the formation of strongly adsorbed species. In situ FITR experiments on Pt(100) show that the reaction proceeds through a complex mechanism, involving CO2, COL, COB, cyclic carbonate, γ-lactone, δ-lactone and carboxylic acids as intermediates and/or oxidation products. CO2 is generated mainly from COB and cyclic carbonate. Adsorbed CO seems to be the poisoning species responsible of the decrease of the catalytic activity on Pt(100), especially in the linear configuration, at higher glucose concentration.