How will large-scale manufacturing of MXenes impact the environment?

Conference poster, 2023

MXenes are two-dimensional advanced materials that have become an important focus of nanomaterials research since they were first created in 2011. MXenes can have a wide range of compositions – their formula is Mn+1Xn, where M is a transition metal (e.g., titanium or vanadium) and X is either carbon or nitrogen. The most widely studied MXene is Ti3C2, which has a high electric conductivity that enables a variety of potential applications, for instance as electrode material in batteries. However, Ti3C2 production is still restricted to laboratory syntheses, mainly by etching with hydrofluoric acid (HF). To date, no environmental assessment of its potential future production has been performed, neither at laboratory scale nor large scale. In this study, a prospective life cycle assessment (LCA) of large-scale manufacturing of Ti3C2 is performed in order to fill this knowledge gap. The goal of the study is to assess different Ti3C2 synthesis routes and pinpoint their environmental impacts with a particular emphasis on climate change, energy use, and mineral resource scarcity. This analysis also identifies the manufacturing process steps that have the largest environmental impacts and provides recommendations on how environmental impacts of large-scale production of Ti3C2 can be reduced. The LCA is a cradle-to-gate study with a functional unit of 1 kg of Ti3C2. Two routes for producing Ti3C2 are considered: the HF etching and the in-situ HF synthesis. The distinction between these two routes is that the first adds HF as an etching chemical, whereas the second does not add HF but instead forms it through reactions involving other chemicals. Data on synthesis procedures, material inputs and energy requirements are obtained from state-of-the-art synthesis descriptions of Ti3C2 MXenes in the scientific literature as verified by technology experts in the field. These procedures are then scaled up using process calculations. The sensitivity to different parameters is tested in terms of future scenarios, including varying amounts of HF input and different future electricity mixes. Preliminary findings indicate that impacts are dominated by the production of the titanium powder, which constitutes the titanium input to the Ti3C2 production. This implies the need to investigate less impacting production routes for titanium in order to considerably reduce impacts of Ti3C2 MXenes.