Oxygen-Evolution Reaction Performance of Nickel (Hydr)Oxide in Alkaline Media: Iron and Nickel Impurities

This study explores the mysteries of the oxygen-evolution reaction (OER) in the presence of Ni(Fe) (hydr)oxides and examines the effects of Ni and Fe impurities on the reaction. The current methods for removing Fe impurities could complicate the study of OER. A crucial aspect of this study is the reinvestigation of Ni (hydr)oxides in a Ni/Fe-free electrolyte during the OER. It is widely recognized that a Ni (hydr)oxide phase, possessing an active phase for the OER, forms on the surface of Ni foil in the presence of air, even in the absence of any applied potential. It is observed that after Fe saturation on the electrode surface, additional Fe has no significant impact on the OER when Ni foil is present. Furthermore, the presence of additional Ni(II) (hydr)oxide does not significantly influence the OER of the Ni foil. However, the OER activity is enhanced when Fe impurities are introduced into the Ni foil. In the Ni/Fe-free electrolyte, the OER current decreases due to the conversion of Ni(II) (hydr)oxide, and the activity of Ni foil results in reduced OER activity due to increased Ni(II) hydroxide thickness and electrode resistance. Furthermore, Ni and Fe ion impurities in the solution can precipitate on the Ni foil surface, leading to changes in redox-active sites. These findings have significant implications for the advancement of the OER catalysts and the comprehension of efficient water-splitting mechanisms for energy storage applications in the presence of Fe-Ni (hydr)oxides.