The active site behaviour of electrochemically synthesised gold nanomaterials

Abstract

Even though gold is the noblest of metals, a weak chemisorber and is regarded as being quite inert, it demonstrates significant electrocatalytic activity in its nanostructured form. It is demonstrated here that nanostructured and even evaporated thin films of gold are covered with active sites which are responsible for such activity. The identification of these sites is demonstrated with conventional electrochemical techniques such as cyclic voltammetry as well as a large amplitude Fourier transformed alternating current (FT-ac) method under acidic and alkaline conditions. The latter technique is beneficial in determining if an electrode process is either Faradaic or capacitive in nature. The observed behaviour is analogous to that observed for activated gold electrodes whose surfaces have been severely disrupted by cathodic polarisation in the hydrogen evolution region. It is shown that significant electrochemical oxidation responses occur at discrete potential values well below that for the formation of the compact monolayer oxide of bulk gold and are attributed to the facile oxidation of surface active sites. Several electrocatalytic reactions are explored in which the onset potential is determined by the presence of such sites on the surface. Significantly, the facile oxidation of active sites is used to drive the electroless deposition of metals such as platinum, palladium and silver from their aqueous salts on the surface of gold nanostructures. The resultant surface decoration of gold with secondary metal nanoparticles not only indicates regions on the surface which are rich in active sites but also provides a method to form interesting bimetallic surfaces.

Electrocatalytic Oxidation of Cellulose to Gluconate on Carbon Aerogel Supported Gold Nanoparticles Anode in Alkaline Medium

“…This might be ascribed to the presence of low lattice stabilized gold atoms or clusters of atoms. As we known, the atoms or atoms clusters with low lattice stability are usually considered active sites or hot spots, which afford good electrocatalytic activity [27]. According to the equation of Debye-Scherrer, a rough estimate based on the {111} peak indicates that the average size of Au nanoparticles along to the {111} lattice face is about 7.3 nm, in comparable with the result of the SEM measurement.…”

Probing the surface oxidation of chemically synthesised gold nanospheres and nanorods

“…1. However, numerous studies have shown that gold is not as inert as its d 10 configuration suggests which accounts for its pronounced catalytic and electrocatalytic activity [6,[17][18][19][20][21][22][23][24]. This has been attributed to active sites on the surface that consists of atoms or clusters of atoms that have low co-ordination number and have the ability to partake in electrocatalytic reactions [21,22,25,26].…”

The mechanism of oxygen evolution at superactivated gold electrodes in aqueous alkaline solution

“…In the case of metal surfaces, it is established that solid metals can trap and store energy and exist in metastable or non-equilibrium superactivated states [24][25][26][27][28][29][30]. These active states may be generated via potential cycling, thermal treatment, abrasion or cathodisation, and metals such as Au, Pt, Cu, Ag and Pd may be readily superactivated [31][32][33][34][35]. While a clear understanding of the nature and especially the mode of operation of such sites is not available, the metastable states are generally assumed to involve lattice defects.…”

“…Since the metal atoms involved in such a reaction are of low lattice coordination number, on oxidation, they acquire a relatively large ligand coordination sphere to form an assembly of hydrated metal surfaquo clusters [31,32]. This process is associated with a number of anomalous redox characteristics: Oxidation of the metal surface at low potentials in the premonolayer region of a cyclic voltammogram is often observed, a phenomenon which is particularly well exemplified by Au, and super-Nernstian shifts in redox potential with changes in solution pH, arising from the anionic nature of the incipient hydrous oxides [24][25][26][27][28][29][30].…”

“…Building on the work of Burke and coworkers [24][25][26][27][28][29][30][31][32][33][34][35][38][39][40][41][42][43], this paper focuses on the influence of the superactivation treatment on the electrocatalytic properties of Au surfaces, with particular attention being paid to the commercially important oxygen evolution reaction. Here, we examine the kinetics of oxygen evolution at superactivated Au electrodes using a combination of steady-state polarisation techniques and electrochemical impedance spectroscopy.…”