1Deakin University, Burwood, Australia
Key metals and resources that are vital to produce reliable and sustainable clean technologies (e.g. wind power turbines, electric vehicles, solar cells and batteries), such as Rare Earth Metals (REMs), and move away from fossil-fuel consumption are now listed as critical raw European Commission, 1 Geoscience Australia 2 and by the US Department of Energy.3
From a commercial point of view, neodymium (Nd) is one of the most important REMs due to its application in Nd-Fe-B permanent magnets that motorize EVs and wind turbines, and Ni-MH rechargeable batteries.4
The current supply cannot meet the future demand so recovery REMs from end-of-life products using sustainable methods such as electrowinning is necessary and urgent. Electrochemically stable electrolytes such as ionic liquids (ILs) are a promising alternative to recover Nd electrochemically. In our research we have reported the Nd3+ electrodeposition process using trihexyltetradecylphosphonium bis(trifluoromethylsulfonyl)imide) ([P66614][TFSI]) ILs in the presence of water as an additive, which was necessary to obtain electrodeposits.5 An in-depth study showed the importance Nd3+ solvation shell composition and conformation (e.g cis/trans and mono/bidentate) to give a favorable Nd3+ reduction process and better quality deposits.6
More recently, we published a fluorine-free and low-cost electrolyte composition based on pyrrolidinium based ionic liquids with very promising results.7 0.5 mol kg−1 neodymium nitrate (Nd(NO3)·6H2O) in N-butyl-N-methylpyrrolidinium dicyanamide ([C4mpyr][DCA]) IL electrolyte led to eight times higher current density (−38 mA cm−2) at a lower temperature (halved to 50 °C) and less controlled environment (0.15–4.6 wt% H2O) compared to parameters previously reported in the literature.
 Joint Research Centre, European Commission & Knowledge Service. Critical raw materials and the circular economy (JRC Science for Policy Report, Background Report). (2017) doi:10.2760/378123.
 Government, A. Critical Minerals. https://www.ga.gov.au/about/projects/resources/critical-minerals.
 Leslie, H. F., Nordvig, M. & Brink, S. Critical Materials Strategy 2010. 1–166 (2010).
 Periyapperuma, K., Sanchez-Cupido, L., Pringle, J. M. & Pozo-Gonzalo, C. Analysis of Sustainable Methods to Recover Neodymium. Sustain. Chem. 2, (2021) 550–563.
 Sanchez-Cupido, L. et al. Water-Facilitated Electrodeposition of Neodymium in a Phosphonium-Based Ionic Liquid. J. Phys. Chem. Lett. 10 (2019) 289–294.
 Sanchez-Cupido, L. et al. Correlating Electrochemical Behavior and Speciation in Neodymium Ionic Liquid Electrolyte Mixtures in the Presence of Water. ACS Sustain. Chem. Eng. 8, (2020) 14047–14057.
 Periyapperuma, K., Pringle, J. M., Sanchez-Cupido, L., Forsyth, M. & Pozo-Gonzalo, C. Fluorine-free ionic liquid electrolytes for sustainable neodymium recovery using an electrochemical approach. Green Chem. 23, (2021) 3410–3419.