title: Identification of catalytic sites for oxygen reduction and oxygen evolution in N-doped graphene materials: Development of highly efficient metal-free bifunctional electrocatalyst.
abstract: Oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are critical to renewable energy conversion and storage technologies. Heteroatom-doped carbon nanomaterials have been reported to be efficient metal-free electrocatalysts for ORR in fuel cells for energy conversion, as well as ORR and OER in metal-air batteries for energy storage. We reported that metal-free three-dimensional (3D) graphene nanoribbon networks (N-GRW) doped with nitrogen exhibited superb bifunctional electrocatalytic activities for both ORR and OER, with an excellent stability in alkaline electrolytes (for example, KOH). For the first time, it was experimentally demonstrated that the electron-donating quaternary N sites were responsible for ORR, whereas the electron-withdrawing pyridinic N moieties in N-GRW served as active sites for OER. The unique 3D nanoarchitecture provided a high density of the ORR and OER active sites and facilitated the electrolyte and electron transports. As a result, the as-prepared N-GRW holds great potential as a low-cost, highly efficient air cathode in rechargeable metal-air batteries. Rechargeable zinc-air batteries with the N-GRW air electrode in a two-electrode configuration exhibited an open-circuit voltage of 1.46 V, a specific capacity of 873 mAh g(-1), and a peak power density of 65 mW cm(-2), which could be continuously charged and discharged with an excellent cycling stability. Our work should open up new avenues for the development of various carbon-based metal-free bifunctional electrocatalysts of practical significance.
authors.affiliation: School of Chemical and Biomedical Engineering, Nanyang Technological University, 62 Nanyang Drive, Singapore 637459, Singapore.
authors.forename: Hong Bin
authors.initials: HB
authors.lastname: Yang
authors.affiliation: School of Chemical and Biomedical Engineering, Nanyang Technological University, 62 Nanyang Drive, Singapore 637459, Singapore.
authors.forename: Jianwei
authors.identifier: 0000-0002-0005-2949
authors.initials: J
authors.lastname: Miao
authors.affiliation: Department of Chemistry, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Taipei 10617, Taiwan.
authors.forename: Sung-Fu
authors.initials: SF
authors.lastname: Hung
authors.affiliation: School of Chemical and Biomedical Engineering, Nanyang Technological University, 62 Nanyang Drive, Singapore 637459, Singapore.
authors.forename: Jiazang
authors.initials: J
authors.lastname: Chen
authors.affiliation: School of Chemical and Biomedical Engineering, Nanyang Technological University, 62 Nanyang Drive, Singapore 637459, Singapore.
authors.forename: Hua Bing
authors.identifier: 0000-0002-3269-3812
authors.initials: HB
authors.lastname: Tao
authors.affiliation: Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (ASTAR) #08-03, 2 Fusionopolis Way, Innovis, Singapore 138634, Singapore.
authors.forename: Xizu
authors.initials: X
authors.lastname: Wang
authors.affiliation: School of Chemical and Biomedical Engineering, Nanyang Technological University, 62 Nanyang Drive, Singapore 637459, Singapore.
authors.forename: Liping
authors.initials: L
authors.lastname: Zhang
authors.affiliation: School of Chemical and Biomedical Engineering, Nanyang Technological University, 62 Nanyang Drive, Singapore 637459, Singapore.
authors.forename: Rong
authors.initials: R
authors.lastname: Chen
authors.affiliation: School of Chemical and Biomedical Engineering, Nanyang Technological University, 62 Nanyang Drive, Singapore 637459, Singapore.
authors.forename: Jiajian
authors.initials: J
authors.lastname: Gao
authors.affiliation: Department of Chemistry, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Taipei 10617, Taiwan.
authors.forename: Hao Ming
authors.initials: HM
authors.lastname: Chen
authors.affiliation: Department of Macromolecular Science and Engineering, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106, USA.
authors.forename: Liming
authors.initials: L
authors.lastname: Dai
authors.affiliation: School of Chemical and Biomedical Engineering, Nanyang Technological University, 62 Nanyang Drive, Singapore 637459, Singapore.
authors.forename: Bin
authors.initials: B
authors.lastname: Liu
mesh_terms: D002244:Carbon / Q000737:chemistry; D002384:Catalysis; D011211:Electric Power Supplies; D004573:Electrolytes / Q000737:chemistry; D006108:Graphite / Q000737:chemistry*; D049329:Nanostructures / Q000737:chemistry*; D009584:Nitrogen; D010084:Oxidation-Reduction; D010087:Oxides / Q000737:chemistry; D010100:Oxygen / Q000737:chemistry*; D015032:Zinc / Q000737:chemistry
chemical_list: D004573:Electrolytes; D010087:Oxides; D002244:Carbon; D006108:Graphite; D015032:Zinc; D009584:Nitrogen; D010100:Oxygen
keywords: Catalytic site; N-doped graphene; bifunctional electrocatalysis; oxygen evolution reaction; oxygen reduction reaction; rechargeable metal-air battery