Facile synthesis of polypyrrole/graphene nanosheet-based nanocomposites as catalyst support for fuel cells
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Facile synthesis of polypyrrole/graphene nanosheet-based nanocomposites as catalyst support for fuel cells Burcu Saner, Selmiye Alkan Gürsel and Yuda Yürüm Faculty of Engineering and Natural Sciences, Sabanci University Orhanli, Tuzla, Istanbul 34956, Turkey ABSTRACT The integration of catalyst metals into the graphene-based composites can be a new way to ensure thermal and electronic conductivities of the catalyst support materials in polymer electrolyte membrane fuel cells. In this work, graphene nanosheets were synthesized via a mild and safer chemical route including three major steps: graphite oxidation, ultrasonic treatment and chemical reduction. Then, polypyrrole was coated on graphene nanosheets by in-situ polymerization to fabricate polypyrrole/graphene nanosheet-based nanocomposites as the catalyst supports. Pt nanoparticles were uniformly dispersed on the surface of nanocomposites by sonication technique. INTRODUCTION Polymer nanocomposites incorporating carbon black, carbon nanotubes, and carbon nanofibers have been utilized for improved mechanical, thermal, electrical and gas barrier properties of polymers especially in the field of energy storage and electronics [1]. Recently, graphene sheets are promising materials to be used as nanofillers in the polymer matrices due to their high electrical conductivity, excellent mechanical strength, high surface area and high chemical stability [2]. Graphene is a single flat monolayer of sp2-carbon atoms in 2D crystal structure. With the proper surface modifications, single graphene sheets can be separated from the graphite material and the layer-to-layer distance can be extended [3]. Chemical exfoliation is one of the extensively used methods to break van der Waals forces between graphene sheets in graphite and to receive monolayer graphene sheet. In fuel cells, the catalyst layer must be very effective at breaking molecules into protons and electrons have high surface area, adequate porosity, high electronic conductivity, and it should be chemically and mechanically stable [4]. Catalyst has a great effect on both the cost and durability of polymer electrolyte membrane fuel cells (PEMFCs). In PEMFCs, platinum (Pt) can be considered as the best electrocatalyst in acidic media since it serves the lowest overpotentials and the highest activity [5]. Conducting polymers, especially polypyrrole (PPy), are widely preferred for fuel cell operations because of good electronic and proton conductivity, and dispensability [6]. PPy-modification can increase the electrochemical surface area and enhance the electrocatalysis ability of Pt/carbon catalyst [7]. In present work, graphene nanosheets as nanofillers were reinforced in polypyrrole by in situ polymerization to be used as the catalyst support material. In these nanocomposites, graphene sheets act as electron acceptors while PPy serves as an electron donor. Graphene nanosheets were exfoliated from graphite flakes in large amounts by applying a mild and safer
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method. The distribution and the size of Pt nanoparticle
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