Addressing the surface coverage of Au nano-agglomerates and the electrochemical properties of modified carbon paste electrodes: Experimental and theoretical studies on ascorbic acid oxidation.

This article shows the formation of Au nano-agglomerates when increasing amounts of gold nanoparticles (AuNP) are incorporated into carbon paste electrodes. The surface coverage by this agglomerates is related to the electro-oxidation of a widely studied redox compound, ascorbic acid (AA); by analyzing the effect on the oxidation peak potential (E _p,a ) and oxidation peak current (i _p,a ). The effects of pH and scan rate on the E _p,a and i _p , _a were investigated by cyclic voltammetry, and enabled to estimate the transfer coefficient and the number of electrons involved in the rate determining step (αn _α ), the standard heterogeneous rate constant (k _s ), and the diffusion coefficient of the redox compound, being 0.52 and 3.5 × 10 ^-3 cm s ^-1 and 6.3 × 10 ^-6 cm ² s ^-1 , respectively. On the other hand, the sensing ability of the modified electrode was evaluated, obtaining a sensitivity of (63.2 ± 2.5) μA mM ^-1 , a detection limit of 2.7 μM and a quantification limit of 8.9 μM. Additionally, a computational model based on lattice-gas model and Monte Carlo simulations in the Grand Canonical Ensemble was proposed in order to reproduce the behavior of the system, in terms of i _p,a and E _p,a shift with increasing surface coverage by Au nano-agglomerates.
(Copyright © 2021 Elsevier B.V. All rights reserved.)