Robust Fe^(2+)-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 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.