Highly enhanced electrochemical water oxidation reaction over hyperfine ß-FeOOH(Cl):Ni Nanorod electrode by modification with amorphous Ni(OH)2

Abstract

A highly crystalline, 10 nm-sized red rust water oxidation catalyst composed of pure ß-phase FeOOH(Cl) nanorods (ca. 3 © 13 nm) doped with Ni ions (ß-FeOOH(Cl):Ni) and surfacemodified with amorphous Ni(OH)2 (a-Ni(OH)2, at a Ni to Fe ratio of 22 at.%) was synthesized by a facile one-pot process at room temperature. The overpotential during the electrochemical oxygen evolution reaction (OER) over the ß-FeOOH:Ni/a-Ni(OH)2 stacked nanorod anodes was 170mV, and an OER current of 10mA/cm2 was obtained at an overpotential of 430 mV in a 0.1M KOH solution. X-ray absorption fine structure analysis, Mssbauer spectroscopy, X-ray photoelectron spectroscopy, field emission scanning electron microscopy, X-ray diffraction and impedance spectroscopy suggested that surface modification with the a-Ni(OH)2 lowered the OER overpotential of ß-FeOOH(Cl):Ni, resulting in the very high current density at low potential compared with Fe-rich oxide and oxyhydroxide electrodes reported previously. Mössbauer spectroscopy suggested interaction between Fe and Ni species, which may be crucial evidence for the enhanced activity in the Fe-rich OER system.