A density functional theory study on oxygen reduction reaction on nitrogen-doped graphene
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ORIGINAL PAPER
A density functional theory study on oxygen reduction reaction on nitrogen-doped graphene Jing Zhang & Zhijian Wang & Zhenping Zhu
Received: 19 August 2013 / Accepted: 21 October 2013 / Published online: 17 November 2013 # Springer-Verlag Berlin Heidelberg 2013
Abstract Nitrogen (N)-doped carbons reportedly exhibit good electrocatalytic activity for the oxygen reduction reaction (ORR) of fuel cells. This work provides theoretical insights into the ORR mechanism of N-doped graphene by using density functional theory calculations. All possible reaction pathways were investigated, and the transition state of each elementary step was identified. The results showed that OOH reduction was easier than O–OH breaking. OOH reduction followed a direct Eley–Rideal mechanism (the OOH species was in gas phase, but H was chemisorbed on the surface) with a significantly low reaction barrier of 0.09 eV. Pathways for both fourelectron and two-electron reductions were possible. The ratedetermining step of the two-electron pathway was the reduction of O2 (formation of OOH), whereas that of the four-electron pathway was the reduction of OH into H2O. After comparing the barriers of the rate-determining steps of the two pathways, we found that the two-electron pathway was more energetically favored than the four-electron pathway. Keywords Density functional theory . Nitrogen-doped carbon . Oxygen reduction reaction . Reaction mechanism
Introduction Fuel cells are an efficient power generation source with high efficiency and low emission. They are expected to have a J. Zhang : Z. Wang : Z. Zhu (*) State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan, Shanxi 030001, China e-mail: [email protected] J. Zhang School of Chemical and Biological Engineering, Taiyuan University of Science and Technology, Taiyuan, Shanxi 030021, China J. Zhang University of Chinese Academy of Sciences, Beijing 100039, China
significant contribution in the efficient use of energy in the near future [1, 2]. In this system, the cathodic half-reaction or the reduction of oxygen into water limits the performance of fuel cells because of its multi-electron reaction character and low reaction rate [3]. The development of efficient catalysts for oxygen reduction reaction (ORR) is crucial in the practical applications of fuel cells. Platinum (Pt)-based materials are the most widely used catalysts for ORR [4, 5]. However, the commercial application of fuel cells is limited by the low durability, scarcity, and high cost of Pt [6]. In the past few decades, intensive efforts have been performed to reduce Pt usage or replace it completely. Researchers [7–20] have recently found that nitrogen (N)-doped carbons, including N-doped carbon nanotubes, graphene sheets, and graphitic arrays, exhibit excellent electrocatalytic performance. These materials have become promising candidates to replace Pt-based catalysts. However, the detailed ORR mechanisms of these N-doped carbons remain unclear, and several issues remai
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