Preparation and characterization of a gold nanoparticle/graphene composite for the electrocatalytic oxidation of glucose

Abstract

Over the past few years there has been a shift towards sustainably producing chemicals. The valorization of biomass into value-added chemicals has been thoroughly investigated as a means of production for several carbon containing compounds. Through the use of lignocellulose waste materials, glucose can be obtained and electrochemically oxidized to gluconic acid. Oxidation is enhanced using graphene/gold nanoparticle (AuNPs) electrocatalyst. Electrocatalysts offer an advantage over the current industrial process of fermentation. The waste associated with fermentation requires proper disposal in order to be compliant with environmental safety. The use of an electrocatalyst also holds an advantage over chemical oxidation as it provides a less harsh chemical environment and can be ran under ambient conditions. In order for the catalyst to be viable for industrial use it must have high activity, be selective towards the formation of gluconic acid and be stable. In this research, a stable water-based graphene dispersion fabricated by high shear exfoliation method was used as a support for AuNPs prepared by the pH- controlled addition of a hydrogen tetrachloroaurate (III) hydrate precursor and was spray-coated on a glassy carbon (GC) electrode and drop-casted onto a carbon felt (CF) electrode. Carbonous electrode materials were used in this work as they provide are a high surface area substrate. AuNPs were used over other noble metal catalysts as they have been shown in literature to selectively oxidize glucose at lower potentials than both copper and platinum catalysts. The graphene/AuNPs composite and films were physico-chemically, electrochemically and microscopically characterized. Following the electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) experiments the graphene/AuNPs film on the GC electrode degraded. Thus, for the determination of the activity and stability of the graphene/AuNPs catalyst, a CF substrate was used. Electrolysis of glucose on the graphene/AuNPs CF electrode produced gluconic acid as confirmed by high performance liquid chromatography (HPLC). The stability of the electrode was analyzed over four, three-hour electrolysis by looking at the resulting chronoamperogram, the glucose conversion efficiency and the turnover frequency. As the electrolysis was carried out using the same electrode the stability could be analyzed. The average glucose conversion efficiency of the four electrolysis was 18 % and the average TOF was 1.97 ·103 h-1. The graphene/AuNPs CF electrode was determined to be stable and a viable option for the electrochemical oxidation of glucose to gluconic acid.