Synthesis, Structural, and Morphological Characterizations of Reduced Graphene Oxide-Supported Polypyrrole Anode Catalysts for Improved Microbial Fuel Cell Performances G. Gnana kumar,* ,† C. Joseph Kirubaharan, † S. Udhayakumar, † K. Ramachandran, † C. Karthikeyan, † R. Renganathan, ‡ and Kee Suk Nahm* ,§ † Department of Physical Chemistry, Madurai Kamaraj University, Madurai-625 021, Tamilnadu, India ‡ School of Chemistry, Bharadhidasan University, Trichy-620 024, India § School of Chemical Engineering and Department of Hydrogen Fuel Cell Engineering, Chonbuk National University, Jeonju-561-756, Republic of Korea ABSTRACT: The conductive polypyrrole (PPy)/reduced graphene oxide (rGO) composites were synthesized through simple, environmentally benign, time and cost efficient, in situ polymerization and bioreduction techniques. The pyrrole monomer effectively adsorbed over the negatively charged GO sheets through electrostatic and π-π interactions was polymerized into polypyrrole in its adsorbed state. The obtained morphological images of the rGO/PPy composite ensured that the entire surface of the active carbon support was covered by PPy. The removal of oxygen functionalities from GO with the aid of Ocimum tenuiflorum extract was ascertained through FT-IR and UV-vis absorption spectroscopic studies. The rGO/PPy composite exhibited higher electrocatalytic oxidation current as evidenced from the cyclic voltammetric analysis. The number of actives sites and continuous carrier channels of the rGO/ PPy composite exhibited a maximum MFC power density of 1068 mW/m 2 , which is almost two-fold higher than that of bare PPy. The strong active carbon support prohibited the swelling and shrinkage of the conductive polymer PPy and provided the strong physico and electrochemical robustness of the rGO/PPy composite, which increased the MFC durability performances up to 300 h. These findings have not only provided fundamental knowledge on the preparation rGO-based composites through a green approach but also have found possible applications in large-scale green energy devices. KEYWORDS: Carbon support, Conduction paths, Electrical conductivity, Oxidation current ■ INTRODUCTION Microbial fuel cells (MFCs) are emerging green energy devices that can use bacterial metabolism for the generation of electrical current from a broad range of organic substrates. 1-3 In MFCs, biomass energy is directly converted into electrical energy via an electron transfer process under an ambient temperature. The development of efficient anode catalysts that could improve the power production of MFCs is highly significant. 4,2 An MFC anode amendment has been extensively developed to increase the bacterial adhesion and electron transfer from bacteria to the electrode surface. 5 A number of electrode materials such as carbon cloth, carbon paper, carbon felt, carbon mesh, stainless steel, graphite, titanium, silver, stainless steel, aluminum, and nickel have been exploited for the green power generation of MFCs. 6-10 Among the studied electrode materials, carbon cloth is well known for its elevated chemical and physical stabilities under an aqueous environment, prompt electrical conductivity, stability, high specific surface area, and porosity. However, the improvement of electron transfer efficiency of carbon cloth is essential in which electrode modification by the conducting polymers is significant. 2 Conducting polymers such as polypyrrole (PPy), 11 polyaniline, 12 polythiophene, 13 poly- (aniline-co-o-aminophenol), 14 PPy/anthraquinone-2,6-disul- fonic disodium salt, 15 poly(3-hydroxy butyrate-co-3-hydroxyval- erate), 16 etc. have been exploited for the anode modification process for effectual MFC performances. Among the studied conducting polymers, PPy has been specifically preferred for anode modi fication, owing to its easier synthesis and processability, elevated electrical conductivity, redox properties, high specific capacitance, low charge transfer resistance, chemical stability, and biocompatibility. 11,15 The high electrical conductivity and electrocatalytic activity of PPy even under neutral solution favors the entrapment of biocatalysts, which increases its viable applications in MFCs. Hence, few research efforts have been devoted to the modification of anodes by PPy for the application of MFCs. 11,15,17 The conductive polymer PPy-equipped photo- synthetic MFC exhibited a power density of 3.4 mW/m 2 , and the obtained performance was ascribed to the physical interaction or intercalation of PPy chains into the cell membranes, enabling direct and fast transfer of electrons. 11 The conductive PPy modified with anthraquinone-2,6-disul- Received: April 10, 2014 Revised: August 18, 2014 Published: September 5, 2014 Research Article pubs.acs.org/journal/ascecg © 2014 American Chemical Society 2283 dx.doi.org/10.1021/sc500244f | ACS Sustainable Chem. Eng. 2014, 2, 2283-2290