Sorbitol electro-oxidation reaction on sub

Abstract

Sorbitol is a highly available and functionalized polyalcohol, with vast industrial usages and with great potential for fuel cells application. However, few studies have been done regarding its electrochemical oxidation. In this work, monometallic Au, Pt and PtAu with different compositions from Pt‒rich (such as Pt85Au15) to Au‒rich (Pt10Au90) nanomaterials were synthesized. Several parameters like sorbitol and KOH concentration, scan rate, charge-transfer resistance, and temperature were tested. According with the physicochemical characterization, average particle sizes from 5.6 to 6.5 nm were found for all electrocatalysts, while Pt atomic percentages of 85, 60, 40, and 10% were obtained. X‒ray photoelectron spectroscopy revealed shifts in Pt 4f and Au 4f core‒levels related to electron density changes by the interaction between these elements and as a result, the electrocatalytic properties for the sorbitol electro‒oxidation reaction (SOR) were modified. The PtAu nanomaterials presented an increase of the current density with the raise of the KOH and sorbitol concentrations, being Pt40Au60/C the most active electrocatalyst displaying 40 mA mg−1 at 0.1 M sorbitol in 2 M KOH with an onset potential of −0.50 V vs. NHE. This onset potential value was more negative to that typically reported for other polyols like glycerol and ethylene glycol. The reaction pathway of Pt/C, Au/C and Pt40Au60/C was followed by chromatographic and spectroscopic techniques, finding that the complex surfaces of these electrocatalysts were capable to carry the SOR via several electrons (from 2 to 24 e−). In this manner, the high electrocatalytic activity of Pt40Au60/C was attributed to the electron density changes that promote a higher electron transfer forming shorter‒chain byproducts.