A case study using spectroscopy and computational modelling for Co speciation in a deep eutectic solvent

Area of Science:

• Materials Science
• Electrochemistry
• Sustainable Energy

Background:

• Cobalt is essential for clean energy technologies, but supply deficits are projected.
• Recycling end-of-life devices is vital for sustainable cobalt sourcing.
• Electrorecovery offers a sustainable alternative to traditional cobalt extraction methods.

Purpose of the Study:

• To investigate cobalt ion (Co2+) speciation in ethylene glycol:choline chloride (EG:ChCl) ionic liquid systems.
• To understand how different cobalt sources (cobalt chloride vs. cobalt sulfate) affect Co2+ speciation.
• To correlate Co2+ speciation with electrodeposition efficiency for improved cobalt electrorecovery.

Main Methods:

• Utilized spectroscopic techniques including Nuclear Magnetic Resonance (NMR), Electron Paramagnetic Resonance (EPR), and Fourier-Transform Infrared Spectroscopy (FTIR).
• Employed molecular dynamics simulations to complement experimental spectroscopic data.
• Analyzed cobalt speciation in two distinct EG:ChCl systems based on cobalt chloride and cobalt sulfate precursors.

Main Results:

• Identified distinct Co2+ speciation based on the cobalt source in EG:ChCl.
• Observed monodentate coordination of sulfate to Co2+, forming [CoCl3(SO4)]3-, as the dominant species in the cobalt sulfate system.
• Determined a homoleptic tetrahedral [CoCl4]2- as the dominant species in the cobalt chloride system.

Conclusions:

• Gained fundamental insights into Co2+ speciation in EG:ChCl ionic liquids.
• Established a correlation between cobalt speciation and electrochemistry, crucial for optimizing electrorecovery.
• This knowledge contributes to designing safer and more efficient electrolytes for sustainable cobalt recycling.