Photodeposited IrO2 on TiO2 support as a catalyst for oxygen evolution reaction

A simple, alternative, catalyst preparation method was proposed in order to combine the properties of photoactive and stable TiO2 with state-of-the art of IrO2 for the oxygen evolution reaction (OER). IrO2 nanoparticles were obtained in the process of photodeposition on the surface of TiO2 powder by UV illumination from appropriate Ir salt aqueous solution. Physicochemical characterization of the resulting IrO2/TiO2 composite, containing 25% w/w Ir, was carried out by transmission electron microscopy (TEM), energy-dispersive spectrometry (EDS), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The electrochemical behaviour of the prepared IrO2/TiO2 catalyst was compared with that of commercial unsupported IrO2. Cyclic voltammetry (CV), linear sweep voltammetry (LSV) and chronoamperometry (CA) were performed to identify the surface electrochemistry and OER of the IrO2/TiO2 catalyst. Electrochemical impedance spectroscopy (EIS) was used to determine uncompensated and charge transfer resistance. CA experiments were carried out in order to evaluate the stability of the IrO2/TiO2 composite during OER in the dark and under UV light irradiation. The photodeposition method on a TiO2 support resulted in 1-2 nm Ir nanoparticles, very well dispersed on the surface and in their oxidized state (IrO2). Electrochemical results indicated that despite its lower conductivity, the IrO2/TiO2 composite exhibits comparable intrinsic electrocatalytic activity for OER with that of the commercial IrO2 catalyst. It was found that under UV light irradiation there has been improvement of the stability of the IrO2/TiO2 performance during oxygen evolution (presumably due to sustained activation of reactive species via photogenerated holes or OH radicals) as well as current enhancement (due to the interaction between the photogenerated holes in TiO2 support and IrO2 nanoparticles). These would be beneficial effects in prolonged water photo-electrolysis.