Synergistic Effect of Urea on Vitamin C Electro-Oxidation at NiOx/CoOx Binary Catalysts Supported on Graphene Nanosheets

The electro-oxidation of ascorbate (AAO) in the presence of urea at NiOx/CoOx/GNs/GC electrode is investigated. Cyclic voltammetry measurements show that the peak current (I (p)) of AAO at NiOx/CoOx/GNs/GC electrode is ten times that of GNs/GC electrode. This highlights the role of catalyst composition and order of deposition on the activity of AAO. Interestingly, blending ascorbate (AH(- )) with urea caused a significant promotion of AAO. Both the I (p) of AAO and the fuel utilization in the AH(-) /urea fuel blend solution are doubled when compared to those obtained at the same electrode in pure AH(-) solution (in addition to a favorable negative shift in the onset potential, E (onset) = 150 mV). Urea molecules are believed to act as anchoring molecules for AH(-) molecules at the NiOx/CoOx/GNs/GC surface with a favorable geometry facilitating its oxidation (by two-electron transfer process) to dehydroascorbate (DHA). Four interaction geometries are proposed, and comparative DFT calculations are conducted, displaying the relative stability and dipole moments of AH(-) in such a way that facilitates its adsorption and oxidation. These findings demonstrate the crucial role of the catalysts tailoring together with the selection of a smart blending fuel with AH(-).

Automated summary

The electro-oxidation of ascorbate (AAO) in the presence of urea at NiOx/CoOx/GNs/GC electrode is investigated. The study highlights the crucial role of catalyst composition and order of deposition on the activity of AAO. Blending ascorbate with urea significantly promotes the AAO reaction and increases fuel utilization.