The Principle of Introducing Halogen Ions Into β-FeOOH: Controlling Electronic Structure and Electrochemical Performance

Halogen ion-incorporated β-FeOOH(X)s (X = F−, Cl−, Br−) were designed and fabricated successfully and showed good performance for negative electrodes of supercapacitors.The embedment of X− caused the change of Fe–O bond length and structural distortion of β-FeOOH, which resulted in the narrow band gap and good electric conductivity.The presence of unexpected high valence state (3 + δ) Fe element facilitated the adsorption for SO32− species endowing the β-FeOOH(X)s with good wettability in Na2SO3 electrolyte.