Ti-Based Precursor Synthesized from Ball Milling as a Starting Material to Design an Active and Stable Ti₂O₃@Ni_xFe_yTi_z Nanoheterostructure for the Oxygen Evolution Reaction in an Alkaline Medium

Ball milling, an eco-friendly material synthesis route, was used to produce a Ti-based precursor from a mixture of metallic Ti and TiO₂ powders to obtain a corrosion-resistant and conductive support for the oxygen evolution reaction in an alkaline medium. The obtained materials were subsequently impregnated with Ni and Fe salts before being thermally treated under hydrogen. Thanks to this synthesis route, composite materials consisting of a Ni- and Fe-containing active phase deposited onto a Ti_yO_x substrate were obtained. The chemical nature of phases composing this precursor material directly depends on the Ti/TiO₂ mass ratio. For a mass ratio of 50%, the Ti-based precursor (sample labeled Ti₅₀), initially composed of TiO₂ and Ti hydride phases, is transformed, after impregnation with Fe and Ni salts and heat treatment under H₂, into a highly electron conductive Ti₂O₃ phase, leading to a high oxygen evolution reaction (OER) activity. The influence of active phase loading and the Ni/Fe atomic ratio on the OER activity was subsequently investigated by performing electrochemical experiments. Different physicochemical techniques (X-ray diffraction (XRD), transmission electron microscopy (TEM), and inductively coupled plasma-optical emission spectrometry (ICP-OES)) were performed to characterize the composition, structure, and morphology of the different composite catalysts in order to evidence a correlation between materials’ properties and their electroactivity toward OER. The sample labeled 30 atom % NiFe (50–50)-Ti₅₀ sample (i.e, Ni/Fe isoatomic ratio and atomic percent of the Ni- and Fe-containing active phase of 30%) appears as the most efficient material, since an overpotential of only 310 mV is required to drive a current density of 10 mA cm^–2. A chronopotentiometry test was carried out to ensure the stability of electrochemical performances after a long-term use of 7 days. Finally, post-mortem Raman spectroscopy and TEM measurements were performed to inquire into surface restructuring phenomena affecting the nanoheterostructured catalyst under working conditions.