Exploring the Possibility of Aluminum Plating/Stripping from a Non-Corrosive Al(OTf)3-Based Electrolyte

Abstract

Rechargeable aluminum batteries offer a promising candidate for energy storage systems, due to the aluminum (Al) abundance source. However, the development of non-corrosive electrolytes, facilitating reversible Al plating/stripping, is a critical challenge to overcome. This study investigates the feasibility of Al plating on a platinum (Pt) substrate using a non-corrosive trifluoromethanesulfonate (Al(OTf)₃)/N-methylacetamide (NMA)/urea electrolyte. This electrolyte was proposed earlier as an alternative chloroaluminate-based ionic liquid, but Al plating/stripping was not proved. In this work, various techniques, including cyclic voltammetry, scanning electron microscope/energy-dispersive X-ray spectroscopy, operando optical microscopy and electrochemical quartz crystal microbalance (EQCM), gas chromatography (GC), and X-ray photoelectron spectroscopy were employed to understand the Al plating/stripping behavior. While cyclic voltammetry indicates redox activity on Pt, further analysis reveals no significant plating. Instead, hydrogen evolution reaction, promoted by the water-residue, dominates the observed current, confirmed by operando microscopy and GC measurements. EQCM studies suggest the concurrent adsorption/desorption of Al(OH)²⁺ and Al³⁺ ions on the Pt electrode. Further drying the electrolyte reduces the hydrogen evolution, but plating of metallic Al remains elusive. These findings highlight the need for further optimization of the electrolyte composition to achieve efficient Al plating/stripping.