Charge Density Modulated Shape-Dependent Electrocatalytic Activity of Gold Nanoparticles for the Oxidation of Ascorbic Acid

The electrocatalytic performance of noble metal nanoparticles depends upon their size, shape, composition, and crystalline facets. Here we demonstrate the shape-dependent electrocatalytic activity of Au nanoparticles toward ascorbic acid oxidation in acidic medium, wherein the catalysis is strongly influenced by the shape of the nanoparticles. The synthesis of (popcorn, tetrapod, and bipod shaped) Au nanoparticles was carried out using a systematic variation of the surfactant concentrations based on the seed-mediated growth technique at room temperature. Due to the facile electrostatic interaction of the positively charged Au nanoparticles with glassy carbon electrode, the modification of the surface with variable-shaped Au nanoparticles is accomplished without involving any binding agents. Among variable-shaped face-centered cubic (fcc) crystalline AuNPs, bipod-shaped Au nanoparticles (GNBipd) exhibit a superior electrocatalytic performance over tetrapod-shaped (GNTepd) and popcorn-shaped (GNPop) nanoparticles as inferred from the differential pulse voltammetry and electrochemical impedance spectroscopy. The results have been explained by invoking the relative surface free energy (γ) with preferentially exposed crystal planes, relative surface area (<i>A</i>), zeta potential (ξ), and the curvature-induced charge density (σ_q) at the apex for individual variable-shaped gold nanoparticles