Electrodeposition of a Rare‐Earth Iron Alloy from an Ionic‐Liquid Electrolyte

Rare earth element (REE)‐based metals and alloys are generally synthesized by molten‐salt electrolysis which is an energy‐intensive approach. Previous attempts to deposit alloys of rare earths from solutions at mild temperatures have met with little success. Excitingly, in this investigation we were able to electrodeposit Nd−Fe from the 1‐ethyl‐3‐methylimidizolium dicyanamide ([EMIM][DCA]) ionic liquid (IL) at 110 °C. We observed that Nd III cannot be reduced independently, although it can be co‐deposited inductively on a Cu substrate with the addition of Fe II . The transmission electron microscopy (TEM) analysis combined with electron‐energy‐loss spectroscopy (EELS) verified that Nd III is reduced to Nd 0 during the electrodeposition process. The TEM/EELS was also able to confirm that the deposition of the Nd−Fe starts with the sole deposition of Fe, followed by the co‐deposition of Nd−Fe. This is in agreement with transition‐state theory, which has the iron initially reduced to an activated state ( Fe * ), where it is able to catalyse the reduction of the rare earth from Nd III to Nd 0 . This new insight into the electrodeposition process brings us a very important step closer to being able to recycle rare earths efficiently and even to realise electrodeposited rare‐earth‐based permanent‐magnet thin films at a mild temperature, thus giving us a sustainable, green‐chemistry approach that provides a genuine alternative to high‐temperature molten‐salt electrolysis.