Oxygen Evolution Reaction on Porous Iridium Oxide / Titanium Dioxide Electrodes Obtained by Plasma Electrolytic Oxidation

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In recent years, research on Proton Exchange Membrane Water Electrolysis (PEMWE) has emphasized the development of iridium oxide catalysts with large electrochemical surface areas and reduced metal content. Titanium dioxide nanostructures can be promising support materials for electrode fabrication because of their (i) excellent stability under anodic polarization, (ii) potentially adequate electronic conductivity, and (iii) ability to promote synergistic interactions with metal catalysts (1,2). In this work, Plasma Electrolytic Oxidation (PEO) of titanium is introduced as a single-step, industrially scalable approach for producing crystalline TiO₂ submicrometric architectures to be used as support materials for iridium oxide deposition. The PEO process was carried out on titanium substrates in refrigerated H₂SO₄ electrolytes under DC potentiostatic conditions (3,4). IrO 2 was deposited by combining wet impregnation under UV light irradiation and subsequent thermal treatments. The so-obtained electrodes were characterized by Scanning Electron Microscopy (SEM), Glow Discharge Optical Emission Spectroscopy (GDOES), X-Ray Fluorescence (XRF), and X-Ray Diffraction (XRD). Electrochemical Surface Area (ECSA) measurements were performed through cyclic voltammetry, and OER mass activity was assessed through Linear Sweep Voltammetry (LSV) between 1.3 and 1.8V RHE at a scan rate of 2 mV/s. Long-term electrochemical stability was evaluated by Cyclic Voltammetry (CV), cycling between 1 V RHE and 1.8 V RHE with a potential hold of five seconds at each vertex potential. The TiO₂ supports displayed a porous, sponge-like morphology typical of PEO processes, with surface porosity values between 12% and 15%, enabling significant electrochemical surface areas. The oxide films had thicknesses of approximately 4–5 µm, and their crystalline structure consisted of tunable mixtures of anatase and rutile polymorphs, depending on the applied PEO parameters. Various IrO₂ loadings were deposited on the samples with the goal of maximizing mass activity. The resulting electrode surfaces preserved the morphology of the support and exhibited a homogeneous distribution of IrO₂ both on the surface and within the porous structure of the PEO-derived TiO₂ films. (Figure 1). Based on the support composition and IrO 2 loadings, it was possible to overcome the mass activity toward OER of pure, commercially available IrO 2 TKK, with the most active sample reaching 186 A/g(IrO 2 ) at 1.55V RHE in 0.1M HClO 4 . This sample consisted of rutile TiO₂ doped with 10 wt.% Nb and loaded with 4 wt.% IrO₂ (0.065 mg cm⁻²). Remarkably high capacitance values of 839.93 F g⁻¹(IrO₂) were achieved. The influence of the substrate crystalline structure, surface area, support thickness, electrical properties, and iridium oxide loading on OER activity was systematically investigated, with the dual objective of minimizing iridium content and developing a single-step, easily scalable approach for the fabrication of large-area anodes for PEMWE. Lavacchi A., Bellini M., Berretti E., Chen Y., Marchionni A., Miller H.A., Vizza F., Current Opinion in Electrochemistry (28) 100720 (2021). Zargarian S., Roiron C., Ferro G., Atanassov P., ChemElectroChem, e202400625 (2025). Franz S. , Arab H., Chiarello G.L., Bestetti M., Selli E., Advanced Energy Materials 10 (23), 2000652 (2020). Franz S., Arab H., Lucotti A., Castiglioni C., Vicenzo A., Morini F., Bestetti M., Catalysts 10 (3) 325 (2020). Figure 1

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