Probing the surface oxidation of chemically synthesised gold nanospheres and nanorods

Abstract

In this study, the electrochemical behaviour of commercially available gold spheres and rods stabilised by carboxylic acid and cetyl trimethyl ammonium bromide (CTAB) moieties, respectively, are investigated. The cyclic voltammetric behaviour in acidic electrolyte is distinctly different with the nanorods exhibiting unusual oxidative behaviour due to an electrodissolution process. The nanospheres exhibited responses typical of a highly defective surface which significantly impacted on electrocatalytic activity. A repetitive potential cycling cleaning procedure was also investigated which did not improve the activity of the nanorods and resulted in deactivating the gold spheres due to decreasing the level of surface defects.

Electrodissolution Inhibition of Gold Nanorods with Oxoanions

“…Halide ions are common in both environmental and physiological conditions, but additional ions are often present . Investigations into the oxidation mechanisms of bulk gold have observed oxoanion inhibition of chloridation and electrodissolution. ,, Research groups studying gold nanoparticle electrochemistry have primarily examined anodic processes in electrolyte solutions containing single anion species. ,− Gold nanoparticle oxidation in the presence of halide-oxoanion electrolytes has been demonstrated, but the role of the oxoanions was not examined. − …”

Activation Effect of Electrochemical Cycling on Gold Nanoparticles towards the Hydrogen Evolution Reaction in Sulfuric Acid

“…The formation of this OA1 peak is complicated. Some reports [18,34,35] have associated it with an increase of the surface defects [36,37] while others suggest the electrodeposition of OH and O species on the anion free surface of the electrode [30,38]. In a paper by Compton [18], decreased electroactivity of the ORR was observed on gold nanoparticles with an increased intensity of this peak.…”

“…Application of a potential larger than 1.74 V vs RHE is avoided to prevent detachment of gold nanoparticles [31] from the electrode and aggressive growth of multi-oxide layers on the surface [28,32]. In the reverse scan, a major cathodic peak appears at 1.14 V vs. RHE corresponding to the reduction of gold oxide to metallic gold [18,30,[33][34][35].…”

“…To explore the origins of this catalytic effect could be able to shed some lights on how to design catalysts for the HER in the future. It might be correlated with the complicated gold oxidation process in sulfuric acid which involves chemical adsorption, electro-oxidation, possible gold dissolution and a potential induced surface reconstruction process [18,28,30,31,[33][34][35][36][37][45][46][47][48][49][50]. Based on the studies on the bulk gold electrode [46,51], under the condition A, a step like structure is believed to be formed with the "lifting" effect of some surface gold atoms from the change of surface energy due to specific adsorbed anions on the gold surface [52].…”

Capping agent promoted oxidation of gold nanoparticles: cetyl trimethylammonium bromide

“…0.48 V). This is instead attributed to the reduction of gold species which formed through dissolution during the forward scan, [16][17][18] indicating that the oxidative signal is due to both the oxidation of bromide as well as the dissolution of gold through either a one electron (eqn (3)) or a three electron oxidation (eqn ( 4)). 19,20 Au + 2Br À $ AuBr 2…”