Electrochemical preparation of crystalline γ-CuI thin films through potential-controlled anodization of copper and its photoelectrochemical investigations

Abstract

Copper iodide (CuI) thin film has been fabricated by controlled potential anodization of copper (Cu) in the potassium iodide (KI) electrolyte. Thin film X-ray diffraction investigations confirm the growth of highly crystalline and pristine γ-CuI thin films at lower anodization potentials. In contrast, the films prepared at higher anodization potentials show the mixed phase with iodine and less crystalline nature. The simultaneous rapid electrooxidation of the Cu and iodide at higher positive potentials results in the growth of iodine crystals with CuI thin films. In particular, the surface morphology of the thin film micro/nanocrystals is tuned by the anodization potentials and the extent of iodine formation at the anode. The CuI thin film deposited at lower potentials exhibits a stable cathodic photocurrent response (−36 to −40 μA cm⁻²) in 0.5 M Na₂SO₄ medium. The photoelectrochemical hydrogen evolution studies illustrate the enhanced activity of p-type γ-CuI than the bare Cu electrode in acidic conditions. The systematic anodic shift in the onset hydrogen evolution potential depends on the film deposition potentials.