Robust Fe2+-doped nickel-iron layered double hydroxide electrode for electrocatalytic reduction of hexavalent chromium by pulsed potential method

Abstract

• A 3D porous Fe 2+ -NiFe LDH/NF was synthesized using a spontaneous redox reaction. • Pulsed potential remarkably improved electrocatalytic Cr(VI) reduction performance. • Anodic potential accelerated the adsorption of Cr(VI) and desorption of Cr(III). • Cathodic potential can regenerate Fe 2+ and reduced. • Bare Ni foam can reduce Cr(VI) directly under cathodic potential. Electrocatalytic reduction of Cr(VI) to less toxic Cr(III) is deemed as a promising technique. Conventional electrocatalytic reduction is always driven by a constant cathodic potential, which exhibits a repelling action to Cr(VI) oxyanions in wastewater and consequently suppresses reduction kinetics. In order to remarkably accelerate Cr(VI) electrocatalytic reduction, we applied a pulsed potential on an Fe 2+ -NiFe LDH/NF electrode synthesized by in situ growth of Fe 2+ -doped NiFe LDH nanosheets on Ni foam using a spontaneous redox reaction. Under anodic potential section, HCrO 4 – anions are adsorbed on the electrode surface and reduced to Cr(III) by Fe 2+ . Then, Cr(III) ions are desorbed from the electrode surface under coulombic force. The regeneration of Fe 2+ and direct reduction of Cr(VI) are achieved under cathodic potential section. The pulsed potential can achieve complete elimination of Cr(VI) within 60 min at an initial concentration of 10 mg L −1 , and the removal efficiency shows a 60% increase with respect to that under constant cathodic potential.