Electrochemical preparation of photoelectrochemically active Cul thin films from room temperature ionic liquid

Cuprous iodide (Cul) thin films with photoelectrochemical activity were prepared by anodizing copper wire or copper-electrodeposited tungsten wire in the room temperature ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (BMI-PF6 RTIL) containing N-butyl-N-methylpyrrolidinium iodide (BMP-I). A copper coating was formed on the tungsten wire by potentiostatic electrodeposition in BMP-dicyanamide (BMP-DCA) RTIL containing copper chloride (CuCI). The CuI films formed using this method were compact, fine-grained and exhibited good adhesion. The characteristic diffraction signals of Cul were observed by powder X-ray diffractometry (XRD). X-ray photoelectron spectroscopy (XPS) also confirmed the formation of a Cul compound semiconductor. The Cul films demonstrated an apparent and stable photocurrent under white light illumination in aqueous solutions and in a RTIL. This method has enabled the electrochemical formation of Cul from a RTIL for the first time, and the first observation of a photocurrent produced from Cul in a RTIL. The coordinating strength of the anions of the RTIL is the key to the successful formation of the Cul thin film. If the coordinating strength of the anions of the RTIL is too strong, no CuI formation is observed.