City Research Online

Abstract

Investigating advanced materials and their applications in energy storage/conversion devices is the key to meet the increase in global demand for energy. Graphene, with promising properties has proved itself to be a potential candidate in energy applica- tions. Since its discovery, it has been investigated for its use in computer chips, flexible transparent screens and desalination membranes. Researchers globally are exploring its use in transparent batteries, smaller capacitors, quick charging devices with high capacity due to its impressive ability to store high amounts of energy (Zhang et al., 2013). Graphene possesses high electrical and thermal conductivities, a unique electronic structure in which charge carriers behave as particles and every atom in graphene can be considered as a surface atom (Novoselov et al., 2004). Graphene can be produced from many methods, some of the popular methods include mechanical exfoliation (Lu et al., 1999), epitaxial growth (Yu et al., 2011), chemical vapor deposition (An et al., 2011) and reduction of graphene oxide (GO) (Pei and Cheng, 2012). Out of these methods, the most economical method for large-scale production of graphene is through reduction of GO which can be done either thermally or chemically, or a combi- nation of both (Bak et al., 2011; Ding et al., 2010; Yang et al., 2012; Zhu et al., 2012). It can be noted from the literature that, the reduction process might affect the band structure of graphene which might affect the electrical properties of the end product. The chemical reduction of GO involves hydrazine, a reduction compound that does not react with water. Hydrazine and its derivatives are used to reduce GO nanolayers whilst water is still present in the mixture, electrical conductivity of 99.6 S cm—1 can be obtained through this method (Fernández-Merino et al., 2010). Unfortunately, hydrazine is highly toxic and not recommended in many applications which limits its use as a reducing agent. Ascorbic acid is one of the potential replacements for the use of hydrazine which resulted in improved electrical conductivity. Thermal reduction of GO to obtain rGO is used by many researchers to remove oxide functionalities, which is temperature and time sensitive (Wang et al., 2008, 2012b). For instance, heat treating GO in Ar/H2 atmosphere will improve electrical conductivity but prolonged heating at 350ºC in air will reduce electrical conductivity. Most common methods used in production of graphene and its derivatives are shown in Fig. 1 (Raccichini et al., 2015).

Publication Type:	Book Section
Additional Information:	Copyright © 2020 Elsevier Inc. All rights reserved.
Publisher Keywords:	Electrochemical properties, Electrodes, Graphene, Lithium-ion batteries and sodium-ion batteries
Subjects:	Q Science > QC Physics T Technology > TK Electrical engineering. Electronics Nuclear engineering
Departments:	School of Science & Technology > Engineering

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