Ultrafine Pt–Ru bimetallic nanoparticles anchored on reduced graphene oxide sheets as highly active electrocatalysts for methanol oxidation

Abstract

The controlled fabrication of bimetallic nanocatalysts with a suitable size, structure and morphology is extremely important to realize direct methanol fuel cells (DMFCs) as promising energy-generating sources. In this paper, a facile approach for depositing platinum–ruthenium (Pt–Ru) bimetallic nanoparticles on a reduced graphene oxide (RGO) support has been demonstrated. Two electrocatalysts denoted as Pt–Ru/RGO-AA and Pt–Ru/RGO-AB were synthesized by synchronously reducing H₂PtCl₆ and RuCl₃ on the graphene oxide (GO) support with reducing agents ascorbic acid and methyl ammonia borane, respectively. For comparison of methanol electrooxidation activity, monometallic Pt nanoparticles supported on RGO sheets (Pt/RGO) were also synthesized. All the catalysts were conveniently synthesized under ambient conditions without using any surfactants. The Pt/RGO, Pt–Ru/RGO-AA and Pt–Ru/RGO-AB electrocatalysts were characterized using X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), selected area electron diffraction (SAED) and energy dispersive X-ray spectroscopy (EDS). Among all the catalysts, the Pt–Ru/RGO-AB catalyst with an average particle size of 2.8 nm possessed remarkable uniformity on the RGO sheets. The electrochemical performance of RGO-supported Pt and Pt–Ru catalysts towards methanol oxidation was systematically studied using cyclic voltammetry and chronoamperometry. The results demonstrate that the Pt–Ru/RGO-AB catalyst with a high electrochemical active surface area (ECSA) of 130.46 m² g⁻¹ exhibits a higher mass and ECSA normalized activities towards methanol oxidation. Furthermore, the Pt–Ru/RGO-AB catalyst has a better tolerance towards accumulated CO-like species as realized from its higher ratio of forward peak current density to reverse peak current density (I_f/I_b) of 3.21. The facile fabrication strategy described here is convenient and could be used for the fabrication of other multi-component nanostructured electrocatalysts for fuel cell reactions.