Effects of temperature on electrodeposition of Al coating in AlCl3-N-methylformamide system

The electrochemical Al metal extraction in the room-temperature electrolyte is considered a green and sustainable approach, where temperature serves as a critical parameter that significantly influences the process. This study systematically investigates effects of the temperature on the thermal behavior of AlCl 3 - N -methylformamide (NMF) system and corresponding electrochemical process. Firstly, the thermogravimetric analysis and the in-situ temperature-rising Raman spectroscopy are combined to reveal the thermal behavior of AlCl 3 -NMF system. The results show that AlCl 2 NMF 2 + fractures to produce NMF and AlCl 3 at 360 K, while NMF decomposes at 360 K and AlCl 3 volatilizes at 440 K. Secondly, cyclic voltammetry and chronoamperometry illustrate that increasing temperature enhances the limiting diffusion current density of Al(III) and reduces the electro-crystallization nucleation induction time. Thirdly, XRD, SEM and non-contact optical microscope analyses indicate that the crystal orientation, the grain size, the micro-morphology, the surface roughness and the thickness of Al coatings electrodeposited in AlCl 3 -NMF system change with the rising temperature. The changes are related to the competition for the nucleation-growth of Al grains and the thermal stability of AlCl 3 -NMF system. Al coatings electrodeposited at 333 K possess the grain size of 24.8 nm, the thickness of 12.6 ± 0.5 μm and the absolute value of average roughness of 6.1 μm.