Defective blue titanium oxide induces high valence of NiFe-(oxy)hydroxides over heterogeneous interfaces towards high OER catalytic activity

Abstract

Nickel–iron (oxy)hydroxides (NiFeO_xH_y) have been validated to speed up sluggish kinetics of the oxygen evolution reaction (OER) but still lack satisfactory substrates to support them. Here, non-stoichiometric blue titanium oxide (B-TiO_x) was directly derived from Ti metal by alkaline anodization and used as a substrate for electrodeposition of amorphous NiFeO_xH_y (NiFe/B-TiO_x). The performed X-ray absorption spectroscopy (XAS) and density functional theory (DFT) calculations evidenced that there is a charge transfer between B-TiO_x and NiFeO_xH_y, which gives rise to an elevated valence at the Ni sites (average oxidation state ∼ 2.37). The synthesized NiFe/B-TiO_x delivers a current density of 10 mA cm⁻² and 100 mA cm⁻² at an overpotential of 227 mV and 268 mV, respectively, which are better than that of pure Ti and stainless steel. It also shows outstanding activity and stability under industrial conditions of 6 M KOH. The post-OER characterization studies revealed that the surface morphology and valence states have no significant change after 24 h of operation at 500 mA cm⁻², and also can effectively inhibit the leaching of Fe. We illustrate that surface modification of Ti which has high corrosion resistance and mechanical strength, to generate strong interactions with NiFeO_xH_y is a simple and effective strategy to improve the OER activity and stability of non-precious metal electrodes.