An in situ XAS study of high surface-area IrO₂ produced by the polymeric precursor synthesis

Abstract

In situ XAS measurements show that iridium oxide electrocatalysts manufactured by the polymeric precursor synthesis method contain a significant fraction of elemental iridium metal and that potential cycling only oxidises a thin layer of the elemental component of the composite.

Increased Ir–Ir Interaction in Iridium Oxide during the Oxygen Evolution Reaction at High Potentials Probed by Operando Spectroscopy

“…This redox change at higher potentials is important to note since mostly an increase of the Ir oxidation state at applied OER potentials was observed, which are also highly oxidizing conditions. [30][31][32][33]49 However, the applied potentials used here are also higher than in these previous studies.…”

“…The small reflections observable in the uncalcined sample relate to metallic Ir. This metallic Ir occurs commonly during the synthesis of rutile IrO 2 . ,− After calcination, these reflections are still observable, but comparison with the rutile IrO 2 diffraction peaks shows that metallic Ir is only present in traces. Also, the Fourier-transform EXAFS spectra of IrO 2 calcined and uncalcined at OCP (see later) show backscattering due to a metallic as well as an oxidic Ir–Ir shell, which further supports that both phases are present at the beginning of the measurement.…”

“…Prior XAS investigations on IrO 2 OER catalysts have been performed at lower OER potentials, below 1.5 V vs reversible hydrogen electrode (RHE), given the strong bubble evolution occurring at higher OER potentials, which complicates in situ XAS investigations above this potential. − All of these studies show a change of the IrO 2 electrocatalyst to higher oxidation states with increasing potential. Ex situ measurements by Abbott et al show reduction of the electrocatalyst after electrochemical cycling up to a higher potential of 1.6 V. This was hypothesized to be related to an increased number of Ir 3+ .…”

Phase- and Surface Composition-Dependent Electrochemical Stability of Ir-Ru Nanoparticles during Oxygen Evolution Reaction

“…FSP was shown in the past to be a valuable approach to manufacture highly crystalline nanoparticles in a large scale, , crucial for industrial applications . In addition, FSP enables the preparation of mixed oxide phases with specific compositions by simple mixing of the different metal precursors at different ratios. − Previous reports on Ir x Ru 1– x O y NPs are mostly based on sol–gel synthetic routes, such as the Pechini synthesis, where a metallic Ir x Ru 1– x core was still present − and could affect any OER activity–stability relationships if directly exposed to the acidic electrolyte.…”

Iridium Oxide Redox Gradient Material: Operando X-ray Absorption of Ir Gradient Oxidation States during IrOx Bipolar Electrochemistry

“…Previous XPS results on the other hand have shown no sensitivity to changes in the iridium oxidation state; neither has spatial resolution nor has the cell fulfilled the vacuum requirements for local exploration of the IrO x surface so that XPS experiments have not been considered. X-ray absorption spectroscopy (XAS) experiments have previously been carried out in homogeneous electrodeposited oxohydroxo IrO x coating samples with success, ,, evidencing the sensitivity of the absorption energy to various oxidation states, including large oxidation phases. In particular, for the potential window that aqueous systems allow, differences have been observed between electrodeposited IrO x and IrO 2 and iridium chlorides …”