Gold/silver bimetal nanoparticles incorporated graphitic carbon nitride nanohybrid materials for oxygen reduction reaction

Abstract

A facile method for the preparation of bimetal AuAg (gold/silver) alloy nanoparticles (NPs) incorporated graphitic carbon nitride (g-C3N4) nanohybrids (NHs) materials embedded in Nafion matrix (Nf/g-C3N4/AuAg NHs) and its application towards electrocatalytic reduction of oxygen in alkaline medium are reported. The prepared Nf/g-C3N4/AuAg NHs were characterized by using X-ray diffraction (XRD), absorption spectroscopy, high resolution transmission electron spectroscopy (HRTEM), scanning electron microscopy-energy dispersive X-ray spectrophotometer (SEM-EDX), SEM-EDX elemental mapping, SEM-EDX lines scan spectra and cyclic voltammetry (CV) techniques. The absorption spectra of Nf/g-C3N4/AuAg NHs showed the characteristic surface plasmon resonance (SPR) absorption band for AuAg alloy NPs and was found in between the wavelength regions of the monometal NPs (Au and Ag NPs). The bimetal alloy formation was confirmed from the observation of single SPR absorption band and further a blue shifting in the SPR band was observed with increasing Ag content in the g-C3N4/AuAg NHs. The HRTEM images explicitly demonstrated the formation of Au, Ag and alloy AuAg NPs on g-C3N4 surface where the size of the bimetal AuAg NPs are found to be smaller than the corresponding monometals (Au and Ag NPs). The electrochemical characteristics of bimetal AuAg NPs at the Nf/g-C3N4/Au, Nf/g-C3N4/Ag and Nf/g-C3N4/AuAg NHs modified electrodes were studied using cyclic voltammetry. The combination of Nf/g-C3N4 and bimetal AuAg alloy NPs enhanced the electrocatalytic oxygen reduction reaction at the modified electrode. The GC/Nf/g-C3N4/Au75Ag25 modified electrode showed the highest catalytic current among the other controlled NHs materials towards the electrocatalytic oxygen reduction in alkaline medium. The Koutecky-Levich (K-L) plots obtained from the modified RDE studies showed four-electron transfer of oxygen reduction reaction (ORR) at the GC/Nf/g-C3N4/Au75Ag25 modified electrode.