Turning free-standing three-dimensional graphene into electrochemically active by nitrogen doping during chemical vapor
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Turning free-standing three-dimensional graphene into electrochemically active by nitrogen doping during chemical vapor deposition process Yuxiao Ma1 · Xueke Wu1 · Mei Yu1 · Songmei Li1 · Jianhua Liu1 Received: 30 September 2019 / Accepted: 10 December 2019 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract By chemical vapor deposition on nanometer-size copper nanopowder sinter template with ammonia as nitrogen source, a free-standing N-doped three-dimensional graphene (N3DG) with macro–meso–micro-hierarchical porous structure was prepared. The existence of nitrogen-containing groups in N3DG turned inert graphene into electrochemically active. The flow ratio between methane and ammonia significantly influences the chemical environment of as-doped nitrogen atoms, the structure of defects in graphene, as well as the electrochemical performance. With the flow ratio between methane and ammonia of 1:4, the specific capacitance of N3DG could be as high as 558.9 F g− 1. The areal capacitance is 4.26 F m− 2.
1 Introduction Tremendous efforts have been made for supercapacitor electrode materials with excellent electrochemical performance. Among all electrode materials, graphene is an excellent candidate due to its high-specific capacitance, high-electron conductivity, as well as light weight [1–3]. However, due to the lack of electrochemical active dots, inert carbon materials such as carbon nanotubes or graphene only have electrical double-layer capacitance [4, 5]. Pure electrical double-layer capacitance mechanism leads to lowspecific capacitance [6]. Even at a very large-specific surface area of 2630 m2 g− 1 (theoretical surface area of single-layer graphene), the specific capacitance would reach ~ 550 F g − 1. In practice, it is difficult to get the theoretical surface area due to the stacking and agglomeration of graphene. Thus, the specific capacitance of graphene materials are usually about 200–300 F g− 1 [7]. To increase the specific capacitance of carbon-based materials, it is vital to introduce electroactive dots which
* Mei Yu [email protected] * Jianhua Liu [email protected] 1
School of Materials Science and Engineering, Beihang University, No. 37 Xueyuan Road, Haidian District, Beijing 100191, China
could conduct pseudocapacitance redox reactions [8–10]. Materials such as polypyrrole and polyaniline could be protonated and have pseudocapacitance properties. In previous literatures, numerous kinds of such materials have been developed to hybridize with carbon materials [11–14]. To achieve high capacitance without extra weight and difficulties caused by hybridizing with other materials, efforts have been made to turn inert graphene into electrochemically active substance. Among all these methods, nitrogen doping is the most favorable one due to its reliability. By alternating some carbon atoms in graphene with nitrogen atoms, N-based function groups with pseudocapacitance activity were formed [15–17]. Previously, nitrogen doping of graphene is mainly conducted on reduced
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