Upcycling process of transforming waste coffee into spherical graphene by flash pyrolysis for sustainable supercapacitor manufacturing with virgin graphene electrodes and its comparative life cycle assessment

In the present study, the fabrication of scalable and eco-friendly supercapacitor electrodes by upcycling process of transforming waste coffee into spherical graphene by applying flash and spinning pyrolysis with low energy consumption was reported, and two different supercapacitor configurations with virgin graphene electrodes obtained from graphite source were developed in a custom-designed system. Initially, waste coffee was directly converted into spherical graphene structures in the rotary furnace without applying any post-treatment. Extensive characterization indicated the formation of spherical graphene with an average particle diameter of 200 nm by flash pyrolysis with a significant increase in the C/O ratio from 8.45 to 19.78 and a high density of sp 2 bondings. This upcycled graphene was assembled with functionalized graphene and graphene oxide obtained from graphite acted as counter electrodes by using glass fiber as a separator and liquid electrolyte of KOH. The supercapacitor with upcycled graphene and reduced graphene electrodes has shown high capacitance retention of 93%, and Coulombic efficiency of 99% with a higher charge transfer resistance of 58 Ω. Furthermore, a comparative life cycle assessment study was carried out to investigate the carbon footprint and ecological impact of different graphene types received from virgin and recycled sources. The process of upcycling waste coffee was much more desirable from an ecological aspect and the release of CO 2 emissions to obtain sustainable supercapacitor electrodes compared to conventional graphene manufacturing techniques. Graphical abstract