Nitrogen-doped reduced graphene oxide electrodes for electrochemical supercapacitors

Abstract

Herein we use Nitrogen-doped reduced Graphene Oxide (N-rGO) as the active material in supercapacitor electrodes. Building on a previous work detailing the synthesis of this material, electrodes were fabricated via spray-deposition of aqueous dispersions and the electrochemical charge storage mechanism was investigated. Results indicate that the functionalised graphene displays improved performance compared to non-functionalised graphene. The simplicity of fabrication suggests ease of up-scaling of such electrodes for commercial applications.Recent research has shown that the unique physical, chemical and electronic properties of graphene may be exploited in a wide range of applications; namely sensing, 1,2 electronics 3,4 and energy. 5,6 In particular, energy conversion and storage technologies that take advantage of graphene's excellent mechanical strength, chemical stability and high surface area may be developed. Indeed, many research publications detail the use of graphene and related materials in lithium ion battery electrodes, 7 solar energy conversion, 8 supercapacitors 9 and as electrode materials in other electrochemical energy devices. 10 For many of these applications it has been shown that the presence of heteroatoms in the graphene lattice improves material performance. Chemical modification allows for tuning of graphene properties such as surface chemistry and electronic properties; 11 which renders them more suited to certain applications than pristine graphene. Nitrogen-doped (N-doped) graphene has been demonstrated to be of use as an electrocatalytic material for oxygen reduction in hydrogen fuel cells, 12 improves biocompatibility of carbon devices in biosensing 13 and enhances the performance of graphene-based supercapacitors. 14 Graphene may be synthesised via mechanical cleavage of graphite flakes, 15 Chemical Vapour Deposition (CVD) 16 or the decomposition of silicon carbide (SiC). 17 However, while the latter two have great potential in electronics fabrication, it is not feasible to produce gram-scale quantities using these methods. Liquid phase exfoliation and processing of graphene is one method which shows great potential as a means of producing large quantities of material. 18,19 Reduction of graphene oxide (GO) is one method which shows promise as a means of producing large quantities of material suited for energy applications. [20][21][22] Graphite oxide is easily exfoliated and the oxygen functional groups can be removed via thermal or chemical means. While the reduction of GO produces a graphene material with structural defects and residual heteroatoms, these issues may not be problematic for applications such as catalysis and energy storage, where crystallinity and structural integrity of the graphene material is not a priority. In fact, the presence of a few oxygen-containing groups at the surface can advantageously influence the interfacial activity between graphene electrodes and the electrolyte.Much work has been carried out towards production of N-doped graphene via several m...

Graphene oxide: A promising nanomaterial for energy and environmental applications

“…In principle, GO cannot be directly used in SCs due to its intrinsically poor electrical conductivity, although there have been some investigations that demonstrated feasible usage of GO in SCs [150,151]. To improve the electrical conductivity of GO and to retain the pseudo-capacitive behavior, partially reduced GO has been widely adopted [152][153][154][155][156][157][158][159][160][161][162]. The residual oxygenated groups on RGO can induce large pseudocapacitance in SCs [152].…”

“…RGO sheets in the acidic and neutral media, which display both electrochemical double-layer (EDL) and pseudocapacitive behavior, have more oxygenated groups and lower surface areas but broader pore size distributions compared with those in the basic medium (mainly EDL). Meanwhile, chemically nitrogen doping of RGO can also tune the electronic properties to enhance the supercapacitor performance [131,[157][158][159]. For instance, the nitrogen doped RGO exhibited much higher specific capacitance than pure RGO [159].…”

Chlorine-doped reduced graphene oxide nanosheets as an efficient and stable electrode for supercapacitor in acidic medium

“…Graphene-doped with various heteroatoms such as oxygen, boron, nitrogen, phosphor, sulfur and their mixtures have been investigated in order to study their capacitive performance [19,20]. Among the dopants, nitrogen-doped graphene has attracted a great deal of attention because experimental studies showed that doping with nitrogen can improve capacitance performance of graphene [21,22]. However, the agglomeration due to intensive p-p interaction is dramatically reduces the surface area, resulting in a lower capacitance [23].…”

Electrochemical stability of the polymer-derived nitrogen-doped carbon: an elusive goal?

“…5a) can be resolved into four components with maxima at 284.9, 286.2, 288.4 and 289.7 eV, representing sp 2 C-sp 2 C graphite bonds, N-sp 2 C (N substitution in graphite-like configuration), C-O and C=O functionalities and N-sp 3 C (pyrrolic), respectively [43][44][45]. Also, a small peak at 292.5 eV of the C-F 2 bonding is localized and associated with Nafion binder [46] and the intensity of C-F peaks for the fresh and degraded samples depends on the effectiveness of the washing step and do not affect the C-C, C-O and the C-N signals.…”