Synthesis and characterization of graphene nanosheets supported platinum nanocomposite as catalyst for methanol oxidation

Abstract

Platinum (Pt) is a noble metal catalyst that is most frequently used as the anode catalyst in direct methanol fuel cell (DMFC) because of its superior catalytic activity performance as compared to other metal catalysts. Besides the merit, Pt catalyst is expensive and also contributes to the problem of Pt poisoning by carbon monoxide (CO) during the methanol oxidation which can reduce the performance of DMFC. The use of carbonaceous material which is graphene nanosheets (GNS) as catalyst support for Pt catalyst can reduce the cost and enhance the catalytic property. Since the GNS have large surface area, the Pt nanoparticles can be dispersed uniformly onto the surface of GNS. Therefore, the main objective of this research is to synthesis and characterize the GNS supported Pt catalyst nanocomposite for methanol oxidation in DMFC. The nanocomposite from GNS and Pt catalyst precursor was fabricated by chemical reduction method using sodium borohydride as reducing agent. The physiochemical properties of the prepared graphene oxide nanosheets, GNS and the catalytic activity performance of GNS/Pt nanocomposite catalyst were successfully studied. Extensive characterization of the produced GNS as catalyst support in terms of morphology, structure, thermal stability and electrical conductivity property were conducted. The results showed that the prepared GNS possess high electrical conductivity of 7.65 S cm-1 thus indicated a highly potential catalyst support. HRTEM and FESEM analysis showed well-dispersed Pt nanoparticles on the surface of GNS with small average particle size around 3.33 nm obtained. The findings were consistent with the XRD data (~4.47 nm) obtained. The catalytic activities of GNS/Pt nanocomposites were measured by cyclic voltammogram. The electrochemical surface area (ECSA) of GNS/Pt nanocomposite catalyst was 0.36 cm2 larger than Vulcan XC-72/Pt (0.25 cm2) and graphite/Pt (0.14 cm2) catalysts. It has been found that GNS/Pt nanocomposite catalyst has better catalytic activity and high stability than Vulcan XC-72/Pt and graphite/Pt catalysts for methanol oxidation reaction. As a conclusion, the GNS/Pt nanocomposite catalyst fabricated in this study possesses appropriate characteristics to be used as anode catalyst in DMFC system.