Special microwave‐assisted one‐pot synthesis of low loading Pt–Ru alloy nanoparticles on reduced graphene oxide for methanol oxidation

Abstract

Published in Micro & Nano Letters; Received on 5th September 2013; Revised on 27th November 2013; Accepted on 10th December 2013In this reported work, low loading Pt–Ru alloy nanoparticles (PtRu NPs) have been highly dispersed on reduced graphene oxide (PtRu/RGO)via an auto-power adjusting microwave-assisted one-pot reaction process. The transmission electron microscopy result shows that PtRu NPswith a mean size of ∼2.99 nm decorated uniformlyon RGO. The prepared PtRu/RGO is used as an electrocatalyst for the methanol oxidationreaction (MOR). Compared with the commercial carbon-supported Pt–Ru alloy electrocatalyst, the PtRu/RGO composites demonstrate higherelectrochemical active surface area and excellent electrocatalytic activity towards the MOR, such as higher peak current density, lower onsetpotential and long-term stability. It is deduced that the good performance of the PtRu/RGO towards methanol oxidation could be attributed tothe characterised RGO support which provides more effective support and enhances the utilisation of the PtRu clusters, and to the highlydispersed small Pt–Ru alloy NPs resulting from the special microwave heating mode and lower synthesis temperature, which subsequentlyleads to a valid bifunctional mechanism between Pt and Ru. The present study proves that the PtRu/RGO composites could be apromising alternative catalyst for direct methanol fuel cells and this effective preparation method can be widely applied to other metal/bimetal NPs.1. Introduction: Fuel cells, one of the most promising alternativeenergies for the near future, have been receiving increasedattention recently because of the depletion of fossil fuels and theincrease in environmental pollution. Among them, directmethanol fuel cells (DMFCs) which have greater potentialapplication in power electric vehicles and portable electronicdevices, are excellent green power sources because of their highenergy density, low pollutant emission, low operating temperatureand ease of handling liquid methanol fuel [1–5]. However, thelack of highly efficient and inexpensive anodic catalysts is alwaysone of the most important reasons to block the commercialapplication of the DMFC. At present, platinum-based (Pt-based)electrocatalysts are still the most commonly used electrocatalystsfor both the anode and the cathode in the DMFC towards oxygenreduction and the methanol oxidation reaction (MOR), but thehigh cost, the poor utilisation and the easy-poisoning of the Ptcatalysts seriously limit their practical application in the DMFC.To solve these problems, significant efforts are currently under-way to find alternative DMFC electrocatalysts with low cost andhigh efficiency. On the one hand, to reduce the cost and enhancetheutilisation,allkindsofsupportsareused todispersethePtnano-particles (NPs), especially the carbon allotropes because of theirdifferent structures and properties from each other, such as single-walled carbon nanotubes [6], multiwalled carbon nanotubes [7],cup-stacked-type carbon nanotubes [8], mesoporous carbon [9]and graphitic carbon nanofibres [10]. Among these carbon mater-ials, graphene has attracted great attention in the nanosciencebecauseofitsoutstandingproperties[11–14].Thismaterialexhibitspromising potential application in the electrochemistry field, suchas nanoeletronics, sensors, composites, batteries, supercapacitorsand hydrogen storage [15, 16], especially as a new considerablecatalyst support to enhance electrocatalytic activity [17–20].Although many reports provide their methods to load the Pt NPson the graphene sheets, the facile preparation of the size-controland the low loading of the Pt NPs is still challenging.On the other hand, the Pt catalysts are readily poisoned by theCO