pH-dependent synthesis of pure-phase BiI3 and BiOI by Electrodeposition

Abstract

This study reports the electrochemical synthesis of different morphologies of bismuth iodide and bismuth oxyiodide on graphite surfaces from acidic baths containing bismuth nitrate, sodium nitrate, iodine and ethylene glycol by a simple pH control. Linear sweep voltammetry analyses determined the potential window for the reduction of iodine where bismuth ions do not get reduced. The concentration of the iodide ions in the bath is regulated by the applied potential. At pH 0.2 and 0.5, bismuth is predominantly present as free Bi3+ ions, which react with iodide to form bismuth triiodide. On the other hand, even at slightly elevated pH 1.0 and 2.0, bismuth is predominantly complexed by water, nitrates and ethylene glycol. These complexes react with the iodide ions to form bismuth oxyiodide. Pure triiodide phase comprising polygonal platelets is obtained at pH 0.2. Pure oxyiodide phase comprising novel microflower-like morphology formed from interlinked nano-disks is obtained at pH 2.0.