Water splitting in acidic media is a promising way for the production of hydrogen fuel. The limiting process of such electrochemical splitting in proton exchange membrane water electrolyzers (PEMWE) is the oxygen evolution reaction (OER). Among tested materials, Ir-based electrocatalysts currently achieve the best ratio between efficiency in the acidic environment. Despite many studies, some questions regarding the splitting mechanisms still remain open [1]. This means that, in addition to the more frequently used research techniques, it is also necessary to use other approaches. Raman spectroscopy and spectroelectrochemistry can give us additional information to support or disprove the current state-of-the-art regarding the Ir-based electrocatalyst performance.  

In this work, we compared the performance of commercial IrO₂ (i) and Ir nanoparticles (ii). Their characteristics were first studied using X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDS). XRD clearly revealed the presence of rutile type IrO₂ in the first sample (i) and metallic Ir in the second one (ii). For the latter sample (ii), EDS showed that some surface oxidation of Ir nanoparticles occurred which was confirmed by Raman spectroscopy through the presence of the broad bands of amorphous IrO₂. Rutile IrO₂ is characterized by four active Raman modes, which appeared in our Raman spectra of the IrO₂ sample (i) at 548 cm^-1 (E_g), 719 cm^-1 (overlapping B_2g and A_1g modes) while the low-intensity B_1g mode at 145 cm^-1 [2] could not be identified. Our in situ Raman spectroelectrochemical studies showed the presence of broad bands that were ascribed to different phases in rare previous works [3,4]. However, these works were performed in various electrolytes and conditions and, for electrochemically deposited Ir nanoparticles. Our aim is to identify and compare changes in in situ Raman spectra in both types of samples, in different acidic electrolytes (HClO₄ and H₂SO₄) and in different potential ranges. According to current results, it is expected to obtain important insights into the mechanisms of water splitting.

Spectroelectrochemistry has just recently paved its way into the studies of electrocatalysts, although being a well-established technique in the investigation of electrochromic thin film materials. Extending the potential into the OER region was shown to offer important conclusions about the oxidized states of Ni-based electrocatalysts [5]. Such experiments have not yet been reported for Ir-based electrocatalysts but have already been made in our laboratory for drop-casted Ir-based electrocatalysts during cyclovoltammetric cycling.