Characterisation and application of the Fe(II)/Fe(III) redox reaction in an ionic liquid analogue

In this paper we report the properties of the Fe(II)/Fe(III) reaction in a deep eutectic solvent based on choline chloride and ethylene glycol. This reaction is shown to be facile using a wall-jet electrode and rotating disc electrode. The deposition and stripping of iron exhibits equally slow kinetics as in aqueous systems. Using these two reactions an all-iron redox flow battery based on ionic liquids is reported for the first time. An energy efficiency of 37% is attained at a current density of 0.5 mA cm(-2). A Zn(II)-Fe(II) complex is shown to form when zinc is oxidized by Fe(III). When this complex is applied in a redox flow battery energy effitiencies of 78% are achieved at a current density of 0.5 mA cm(-2). (C) 2013 Elsevier Ltd. All rights reserved.