Synthesis of reduced graphene oxideeTiO 2 nanoparticle composite systems and its application in hydrogen production Pawan Kumar Dubey a,* , Prashant Tripathi a , R.S. Tiwari a , A.S.K. Sinha b , O.N. Srivastava a,* a Department of Physics, Banaras Hindu University, Varanasi 221005, India b Department of Chemical Engineering and Technology, Indian Institute of Technology, Banaras Hindu University, Varanasi 221005, India article info Article history: Received 19 July 2013 Received in revised form 25 February 2014 Accepted 16 March 2014 Keywords: TiO 2 nanoparticles Hydrogen production Water electrolysis Graphene Nanocomposite abstract The utilization of solar energy for the conversion of water to hydrogen and oxygen has been considered to be an efficient strategy to solve crisis of energy and environment. Here, we report the synthesis of reduced graphene oxideeTiO 2 nanoparticle composite system through the photocatalytic reduction of graphite oxide using TiO 2 nanoparticles. Photo- electrochemical characterizations and hydrogen evolution measurements of these nano- composites reveal that the presence of graphene enhances the photocurrent density and hydrogen generation rate. The optimum photocurrent density and hydrogen generation rate has been found to be 3.4 mA cm 2 and 127.5 mmole cm 2 h 1 in 0.5 M Na 2 SO 4 electrolyte solution under 1.5AM solar irradiance of white light with illumination intensity of 100 mW cm 2 . In grapheneeTiO 2 nanocomposite, photogenerated electrons in TiO 2 are scavenged by graphene sheets and percolate to counter electrode to reduce H þ to molec- ular hydrogen thus increasing the performance of water-splitting reaction. Copyright © 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. Introduction The utilization of solar energy for the conversion of water to hydrogen is the crucial component for harvesting hydrogen energy. It is now generally agreed that hydrogen may be the best option for tackling the triple issues of, depletion, pollu- tion and climate change effects. Photoelectrolysis of water is considered to be one of the most promising methods to generate hydrogen (and oxygen) through the cleavage of water utilizing solar energy. Many photocatalysts have been reported to catalyse the evolution of hydrogen from aqueous solutions. Among these photocatalysts, TiO 2 is one of the most promising because of its superior photocatalytic per- formance, easy availability, long-term stability, and non- toxicity [1e3] However, TiO 2 suffers from the limited absorption of solar light due to its large bandgap (3 eV) and fast recombination of charge carriers [4]. Typically, photoexcited electronehole pairs can be generated under the irradiation with wavelength lower than that corresponding to the band gap energy of TiO 2 (3.20 eV for anatase phase). The photogenerated electrons * Corresponding authors. Tel.: þ91 542 2368468; fax: þ91 542 2369889. E-mail addresses: dubey.pawan@yahoo.com (P.K. Dubey), heponsphy@gmail.com (O.N. Srivastava). Available online at www.sciencedirect.com ScienceDirect journal homepage: www.elsevier.com/locate/he international journal of hydrogen energy 39 (2014) 16282 e16292 http://dx.doi.org/10.1016/j.ijhydene.2014.03.104 0360-3199/Copyright © 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.