The aim of this thesis is to undertake a life cycle analysis to identify the environmental impact of using graphene to manufacture supercapacitors. It was part of a larger project to develop supercapacitors using graphene in place of activated carbon. The first part of this work focuses on production of graphene in the laboratory. Data were directly measured in different laboratories to perform a comparative life cycle analysis in order to evaluate the environmental performance of several graphene synthesis methods including graphite electrochemical exfoliation, graphite chemical oxidation with subsequent chemical or thermal reduction and chemical vapour deposition. One electrochemical exfoliation technique, one chemical oxidation followed by two different reduction routes were selected on the base of their environmental performance and their measured specific capacitance and used as electrode materials for supercapacitors. The second part of the thesis is a comparative life cycle assessment involving three supercapacitors having the electrodes made of graphene synthesised via the three shortlisted production routes and one state of the art activated carbon based supercapacitor commercially available. A commercial-scale graphene production process is simulated using a process simulation tool in order to minimise the process inefficiencies inherent to laboratory processes and to compare it with a commercial-scale activated carbon production process. The results showed a large reduction of the graphene environmental impact of around 50% in most of the environmental impact categories analysed but also proved that the activated carbon supercapacitor is currently the technology with the lowest impact for all categories. They also showed that graphene production needs more research to improve its efficiency and efficacy as it is the operation with the highest environmental impact in the supercapacitor manufacturing for most of the analysed impact categories. In the third part of this study the use-phase and end-of-life of supercapacitors is evaluated in which the supercapacitors are used to power a car door mirror and are finally recycled. The results showed that over the lifetime of a vehicle (150,000 km), the graphene based supercapacitors have a lower impact (10% less) during the use-phase as they are lighter. The recycling process is also simulated to be scaled up to a commercial-scale with minimised heat losses for both graphene and activated carbon based supercapacitors. Recycling proved to be the key to reduce the environmental impact of the graphene supercapacitor. As graphene proved to be the most problematic material for the environment and the recycled graphene proved to be of a quality similar to pristine material, its recovery generates an environmental credit that is 90% of the production burden for all categories by displacing the production of new graphene for polymer reinforcement applications. Sensitivity analysis is performed and various scenarios generated to evaluate potential variations in specific capacitance of all active materials and subsequently the impact of these variations on the manufacture of supercapacitors. The results are normalised and weighted according to the latest EU requirements. Aggregating the weighted results proved that the activated carbon and the graphene based supercapacitors could have similar impacts. This is a very encouraging result considering that the graphene synthesis process is still at its infancy while the activated carbon production is a well-established industrial process. When a more efficient graphene production can be industrialised, graphene supercapacitors will have the potential to become the future technology with the lowest environmental impact.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:692736 |
| Date | January 2016 |
| Creators | Cossutta, Matteo |
| Publisher | University of Nottingham |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://eprints.nottingham.ac.uk/33411/ |
Page generated in 0.0021 seconds