Tuning arylation of gold nanoparticles for the electrocatalyzed oxidation of ethanol

Abstract

Alcohol oxidation is important for food industry and pharmaceuticals to name but a few. In this regard, precious metals such as gold operate in various shapes and sizes as effective catalysts for the oxidation of alcohols. In this work, 20‐nm‐sized gold nanoparticles (NPs) were synthesized and modified with either 4‐carboxybenzenediazonium tetrafluoroborate (AB) (single‐salt catalyst) or a mixture of the latter with 3,5‐dimethylbenzenediazonium tetrafluoroborate (AB‐DMB, double‐salt catalyst). The relative concentrations of the diazonium salts were tuned in order to maintain the electrocatalytic property of the arylated gold NPs in the electro‐oxidation of ethanol. The physicochemical properties (size, aryl layer thickness, and composition) and electrocatalytic performances of the capped gold NPs (in single‐ and double‐salt catalyst systems) were investigated by means of TEM, XPS, UV–visible, TGA/DTA, and electrochemistry. The aryl capping layer thickness is below 1 nm when the total salt concentration was 5 × 10−5 M, without any significant loss of current compared with pure gold NPs. For 1 μl of pristine or arylated Au NPs, coated on 0.07 cm2 glassy carbon electrode disk, we achieved a low oxidation potential of 200 mV and high current ethanol oxidation peak intensity leveling off at ~80 μA for the single diazonium arylation. It is demonstrated that dilution of the carboxylic acid‐functionalized diazonium is more important than mixing this compound with 3,5‐dimethylbenzenediazonium salt at equal total concentration. The dual arylation strategy induced lower ethanol oxidation intensity likely due to hydrophic effect imparted by the 3,5‐dimethylphenyl groups, thus hindering access of ethanol to the nanocatalyst surface. This work demonstrates that arylated gold NPs are unique nanocatalysts for ethanol oxidation reaction, with remarkable performances. This electrocatalytic performance of the NPs was maintained through the use of finely tuned aryl capping layer. The strategy opens avenues for other arylated electrocatalysts and uses thereof.