Towards a more environmentally sustainable production of graphene-based materials Building on current knowledge to offer recommendations

Purpose This study compares prior life cycle assessment (LCA) studies on graphene-based materials (GBMs) with new results from original data on ball milling of few-layer graphene. The analysis thus offers an overview of the current state of knowledge on the environmental sustainability of GBM production. Possible future development pathways and knowledge gaps are identified and explained to provide guidance for the future development of GBMs. Methods Comparable scopes, aggregation levels, and impact assessment methods are used to analyse diverse GBMs with three different functional units for graphene oxide, pristine graphene, and other GBMs with different carbon/oxygen ratios or thickness. The ecoinvent v3.4 cut-off database is used for background data in all models to provide a common basis of comparison. Furthermore, uncertainty calculations are carried out to give insights on the current level of knowledge and to check if GBM production methods can be differentiated. Finally, a sensitivity analysis is performed on the energy inputs with a detailed description of three future scenarios for the European electricity mix. Results and discussion The general analysis of all results highlights three key strategies to improve the environmental sustainability of GBM production. (1) The use of decarbonised energy sources reduces substantially the impacts of GBMs. This benefit is decreased, however, when conservative forecasts of the future European electricity mix are considered. (2) Increased energy efficiency of production is useful mainly for the processes of electrochemical exfoliation and chemical vapour deposition. (3) The principles of green chemistry provide relevant ideas to reduce the impacts of GBMs mainly for the processes of chemical and thermal reduction and for the production of graphene oxide. Furthermore, the analysis of new data on ball milling production reveals that transforming GBM solutions into dry-mass can substantially increase the environmental impacts because of the energy-intensive nature of this conversion. The uncertainty analysis then shows that it is still difficult to differentiate all production methods with the current knowledge on this emerging technology. Conclusions With our current level of knowledge on GBMs, it is clear that more accurate data is needed on different production methods to identify frontrunners. Nevertheless, it seems that unknowns, like the state of future electricity mixes, might not often hinder such comparisons because conservative forecasts bring similar changes on many production options. Additionally, functional properties and toxicity for GBMs will require further attention to improve our confidence in the comparison of production methods in the future.