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Graphene Aerogels for Capacitive Energy Storage

Casano Carnicer, Gabriel

[Thesis]. Manchester, UK: The University of Manchester; 2019.

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Abstract

Graphene is a promising material for supercapacitor electrodes, both in electric double layer capacitors and as a conductive support for incorporating materials with large pseudocapacitance, yet further development is still needed. Aerogels represent an attractive way to fabricate 3D grapehene structures with large and accessible surface areas and therefore useful for supercapacitor electrodes. Among the different methods available for aerogel production, freeze casting is a versatile technique, allowing good control of morphology. Freeze casting has therefore been applied to graphene-based materials, however most examples reported so far focus on using graphene oxide (GO) as the precursor material dispersed in water, which carries some inherent disadvantages in terms crystalline quality and processing conditions available. Using non-aqueous solvents which are solid at room temperature but can be easily melted upon heating enables sublimation under ambient conditions, making the process simpler and potentially more scalable. They also enable the use of other forms of graphene-based materials, e.g. pristine graphene sheets, which are difficult to disperse in water and reduce the need for further processing after solvent sublimation. This thesis therefore explores the fabrication of graphene-based aerogels using non-aqueous solvents and room temperature sublimation. Formation of aerogels utilising camphene as solvent and using different sources of graphene-related materials is presented, including six different commercial products and in-house produced GO. Aerogels utilising commercial graphene nanoplatelets, XG C750, as the graphene source achieved the highest specific capacitance, thanks to the source material's high starting surface area and ability to be effectively dispersed in the solvent. Successful fabrication of graphene-based aerogels is also demonstrated in five different solvent systems: camphene, menthol and phenol as single solvents, as well as mixtures of camphor with camphene and naphthalene. Menthol-based aerogels achieved the best overall performance in terms of surface area and capacitance, presenting a promising route for further exploration thanks to menthol's low toxicity and cost.