Evaluation of reduced-graphene-oxide-supported gold nanoparticles as catalytic system for electroreduction of oxygen in alkaline electrolyte

TL;DR

This study evaluates reduced-graphene-oxide-supported gold nanoparticles as effective catalysts for oxygen reduction in alkaline solutions, highlighting their preparation, stability, and high electrocatalytic activity demonstrated through voltammetric experiments.

Contribution

It introduces a novel catalytic system using reduced graphene oxide-supported gold nanoparticles, with detailed synthesis, stabilization, and electrochemical performance analysis.

Findings

Gold nanoparticles are well-dispersed and stable on reduced graphene oxide.

The catalytic system shows high activity for oxygen reduction in alkaline medium.

Polyoxometallate ligands facilitate nanoparticle dispersion and support attachment.

Abstract

Chemically-reduced graphene-oxide-supported gold nanoparticles are considered here as catalytic materials for the reduction of oxygen in alkaline medium. Gold nanoparticles are prepared by the chemical reduction method, in which the NaBH4-prereduced Keggin-type phosphomolybdate heteropolyblue acts as the reducing agent for the precursor (HAuCl4). Polyoxmetallate (PMo12O403-) capping ligands stabilize gold nanoparticle deposits, facilitate their dispersion and attachment to carbon supports. Indeed, it is apparent from the independent diagnostic voltammetric experiments (in 0.5 mol dm-3 H2SO4) that heteropolymolybdates form readily stable adsorbates on nanostructures of both gold and carbon (reduced graphene oxide and Vulcan). It is reasonable to expect that the polyoxometallate-assisted nucleation of gold has occurred in the proximity of oxygenated defects existing on carbon substrates. Under conditions of electrochemical diagnostic experiments (performed in 0.1 mol dm-3 KOH): (i) the phosphomolybdate adsorbates are removed from the interface as they undergo dissolution in alkaline medium; and (ii) the Au nanoparticles (Au loading, 30 {\mu}g cm-2) remain well-dispersed on the carbon as evident from transmission electron microscopy. High electrocatalytic activity of the reduced-graphene oxide-supported Au nanoparticles toward reduction of oxygen in alkaline medium is demonstrated using cyclic and rotating ring-disk voltammetric experiments. Among important issues are possible activating interactions between gold and the support, as well as presence of structural defects existing on poorly organized graphitic structure of reduced graphene oxide (as evident from Raman spectroscopy).