Influence of Fe(III) doping on the crystal structure and properties of hydrothermally prepared β-Ni(OH)2 nanostructures

S. Krehula a, *, M. Risti_c a, C. Wu b, e, X. Li b, d, e, L. Jiang b, c, J.Wang b, d, G. Sun b, T. Zhang d, e, M. Perovi_c f, M. Bo_skovi_c f, B. Anti_c f, L. Kratofil Krehula g, B. Kobzi h, S. Kubuki h, S. Musi_c a

a Division of Materials Chemistry and Center of Excellence for Advanced Materials and Sensing Devices, RuCer Bo_skovi_c Institute, P.O. Box 180, HR-10002, Zagreb, Croatia

b Dalian National Laboratory for Clean Energy, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, 116023, China

c College of Material Science and Engineering, Qingdao University of Science and Technology, Qingdao, 266042, China

d Mossbauer Effect Data Center, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, 116023, China

e University of the Chinese Academy of Sciences, Beijing, 100039, China

f Condensed Matter Physics Laboratory, Vin_ca Institute of Nuclear Sciences, University of Belgrade, P. O. Box 522, 11001 Belgrade, Serbia

g Faculty of Chemical Engineering and Technology, University of Zagreb, Maruli_cev Trg 19, P. O. Box 177, HR-10000, Zagreb, Croatia

h Department of Chemistry Graduate School of Science and Engineering, Tokyo Metropolitan University, 1-1 Minamiosawa, Hachioji, Tokyo, 192-0397, Japan

Abstract

This paper systematically examines the influence of the level of Fe(III) doping on the crystal structure and other properties of Ni(OH)2. Reference β-Ni(OH)2 and Fe-doped Ni(OH)2 samples were synthesized by hydrothermal precipitation of mixed Ni(II) and Fe(III) nitrate aqueous solutions in a highly alkaline medium. The samples were investigated using X-ray powder diffraction (XRPD), scanning and transmission electron microscopy (FE-SEM and TEM), energy dispersive X-ray spectroscopy (EDS), Mossbauer spectroscopy, magnetic measurements, Fourier transform infrared (FT-IR) spectroscopy, ultraviolet evisibleenear infrared (UV-Vis-NIR) spectroscopy, thermogravimetric analysis (TGA) and electrochemical measurements. Incorporation of Fe in β-Ni(OH)2 by cation substitution was confirmed from the shifts in position of XRPD lines due to the difference in the ionic radius of Fe3+ and Ni2+. The Fe3+-for-Ni2+ substitution in b-Ni(OH)2 caused formation of an interstratified structure withβ-Ni(OH)2 andα-Ni(OH)2 structural units interconnected within the same structural layers and crystallites. M€ossbauer spectra revealed the presence of Fe3+ ions in highly distorted octahedral sites, presumably at the boundary between the α-Ni(OH)2 and β-Ni(OH)2 structural units within the same structural layer. Electrochemical measurements showed significant increase in oxygen evolution reaction (OER) catalytic activity of Fe-doped Ni(OH)2 compared to pure phase.