Electrocatalytic Efficiency of the Oxidation of Ethylene Glycol, Glycerol, and Glucose under Oscillatory Regime

Abstract

There is an increasing interest in the use of small organic molecules in the interconversion between chemical and electrical energies. Among the strategies to improve the processes of yielding electrical energy in fuel cells and the production of cleaner hydrogen in electrochemical reform, there is the use of kinetic instabilities to improve the conversion and selectivity. Herein, we report on the electrocatalytic efficiency of the oxidation of ethylene glycol, glycerol, and glucose, under regular and oscillatory regimes, on polycrystalline platinum, in sulfuric acid aqueous solution, and at 25 °C. Despite the high overpotentials for the electro-oxidation of these molecules, the electrochemical activity along quasi-stationary potentio-/galvanostatic experiments evidenced that, in all cases, relatively lower potential values, and thus higher activity, are reached during oscillations. Noticeably, higher power densities for the electro-oxidation of ethylene glycol and glycerol under the oscillatory regime were found in a hypothetical direct liquid fuel cell. The use of identical experimental conditions of that of our previous study [J. Phys. Chem. C, 2016, 120, 22365] allowed to discuss some universal trends for seven small organic molecules. We compile the results in terms of the peak current, the maximum poisoning rate found along the oscillations, and the oscillation frequency. The three parameters were found to decrease in the order: formaldehyde > formic acid > methanol > ethanol > ethylene glycol > glycerol > glucose. In addition, we discussed the increase of the voltammetric current due to the self-organized poisoning rate and reinforced the trend that high electrocatalytic activity implies high susceptibility to surface poisoning for this set of species. Finally, the analysis done for all species (formic acid, formaldehyde, methanol, ethylene glycol, ethanol, glycerol, and glucose) adds to the available thermodynamic data and is a benchmark against which the activities under the oscillatory regime at 25 °C may be compared or assessed. This point of reference permits to explore further experimental conditions that are relevant for energy-related devices, including the conversion of chemical into electrical energy and the electrochemical reform to produce clean hydrogen in electrolyzers.