Nitrogen doped graphene supported palladium-cobalt as a promising catalyst for methanol oxidation reaction: Synthesis, characterization and electrocatalytic performance Roya Kiyani a , Soosan Rowshanzamir a, b, * , Mohammad Javad Parnian a, b a School of Chemical Engineering, Iran University of Science and Technology, Iran b Fuel Cell Laboratory, Green Research Center, Iran University of Science and Technology, Iran article info Article history: Received 23 December 2015 Received in revised form 25 July 2016 Accepted 26 July 2016 Keywords: Nitrogen doped graphene Solvothermal method Palladium-cobalt nanoparticles Methanol oxidation reaction Direct methanol fuel cells abstract In this work, palladium and palladium-cobalt supported on nitrogen doped graphene as anode materials in direct methanol fuel cells is reported. A simple and low temperature solvothermal method is used to directly prepare nanoflower-like NG and then, Pd and PdeCo nanoparticles are precipitated onto the surface of NG using a modified polyol reduction method. The synthesized electrocatalysts are charac- terized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). Cyclic voltammetry (CV), linear sweep voltammetry (LSV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS) are used to measure electrocatalytic methanol oxidation activity and the durability of electrocatalysts. The results show that PdeCo/NG has better electrocatalytic activity than Pd/NG toward methanol oxidation reaction (MOR) in alkaline media that is related at the presence of cobalt atoms. In addition, chronoamperometric results indicate that PdeCo/NG is more stable than commercial Pt/C for MOR. © 2016 Elsevier Ltd. All rights reserved. 1. Introduction In recent years, direct methanol fuel cells (DMFCs) have been noticed due to its high energy efficiency, low operating tempera- ture, fuel availability, easy handling and transportation, low pollution emission, and elimination of fuel reformers [1e3]. It is considered as one of the most suitable and promising power sources for vehicles and portable electronic devices [2,4]. Despite the inherent advantages, there still exist several critical problems that hinder the widespread commercialization of DMFCs. The first problem is the relatively low kinetics of methanol oxidation reac- tion (MOR) at the anode and low kinetics of the oxygen reduction reaction (ORR) at the cathode, which significantly limit the DMFC performance. In comparison to ORR, the electro-oxidation kinetics of methanol is a much lower and complicated process; also the poisoning of the anode catalysts by residual species is another problem [5e8]. Hence, significant efforts should be made to improve the activity of the catalyst at the anode electrode [9e11]. Also, more researchers have focused on ORR and pursued different approaches such as using different metals as an active phase for replacing with platinum, use of different support materials such as NG, MWCNT, and alloying of metals for increasing the activity and stability of catalysts [8,12e17]. The second problem is related to the standard membrane used in DMFC. Currently, perfluorosulfonic acid membranes, such as Nafion, leads to permeate methanol and water from the anode to the cathode side, that is referred to methanol crossover, which can decrease cell performance [18,19]. So, researchers used some new membranes such as hydrocarbon membranes [20e24]. Methanol decomposition and oxidation re- action is one of the most investigated reactions in fuel cells due to its significance in the development of direct methanol fuel cells (DMFCs) technology. Pt and Pt-based alloys due to excellent elec- trocatalytic activity, are the most promising catalysts for methanol oxidation in acidic media [25,26]. However, some challenges such as the high cost of Pt-based catalysts, low abundance, and electrode poisoning by CO-like intermediates that are formed during the methanol oxidation, still remain as serious obstacles to use of Pt at a commercial level [27,28]. Using an alkaline electrolyte in DMFCs rather than acidic media, leads to significant improvement in * Corresponding author. Iran University of Science and Technology, P.O. Box: 16846-13114, Tehran, Iran. E-mail address: Rowshanzamir@iust.ac.ir (S. Rowshanzamir). Contents lists available at ScienceDirect Energy journal homepage: www.elsevier.com/locate/energy http://dx.doi.org/10.1016/j.energy.2016.07.143 0360-5442/© 2016 Elsevier Ltd. All rights reserved. Energy 113 (2016) 1162e1173