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

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 Fe2+-NiFe LDH/NF electrode synthesized by in situ growth of Fe2+-doped NiFe LDH nanosheets on Ni foam using a spontaneous redox reaction. Under anodic potential section, HCrO4~– anions are adsorbed on the electrode surface and reduced to Cr(Ⅲ) by Fe2+. Then, Cr(Ⅲ) ions are desorbed from the electrode surface under coulombic force. The regeneration of Fe2+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.