Lessons from early assessments of production processes for the nanomaterial graphene
Paper in proceeding, 2016
Graphene is a new nanomaterial with many promising applications, including in composite materials, transparent displays, electronic components and biosensors. We have conducted a number of life cycle assessment (LCA) studies of emerging production routes for this material. The studies cover the three production routes that currently have the most patents and largest scientific interest: Exfoliation, chemical vapour deposition (CVD), and epitaxial growth on silicon carbide. From these studies, a number of results have been obtained, which provide environmental guidance towards less impacting graphene production at an early stage in technology development. Results for exfoliation show that although some processes (chemical and thermal reduction) are energy-intensive (in the order of 1000 MJ/kg), others (ultrasonication) have life cycle energy requirements below those of today’s energy-intensive materials (<100 MJ/kg). Results for CVD show that given process settings with methane precursor excess reuse, graphene can have lower life cycle energy use than indium tin oxide, which is the competitive material for transparent displays. The use of graphene instead of indium tin oxide is also beneficial from a scarce metal perspective, since indium is a very scarce material that can then be substituted. Results for epitaxial growth show that the life cycle energy use of this production process is much dependent on the silicon carbide substrate. Reducing the use of silicon carbide per unit of graphene is thus the most important action for reducing the impact of epitaxial graphene. In addition to these case study results, we have obtained some methodological learnings regarding how to best provide environmental guidance related to emerging production processes. We find that results based on specific electricity mixes provide limited guidance because they may change in the future and between different geographical locations. Different scenarios with different electricity mixes are therefore important to illustrate the future potential of an emerging production process. We also notice the importance of considering scale-up of emerging production processes, since this can have a considerable influence on their environmental performance. Here as well, different scenarios representing different production scales are helpful for illustrating the environmental potential of an emerging production process.