Easy Accommodation of Different Oxidation States in Iridium Oxide Nanoparticles with Different Hydration Degree as Water Oxidation Electrocatalysts

Abstract

In this paper, we present a comprehensive study on low hydration Ir/IrO 2 electrodes, made of an Ir core and an IrO 2 shell, that are designed and synthesized with an innovative, green approach, in order to have a higher surface/bulk ratio of Ir−O active centers. Three materials with different hydration degrees have been deeply investigated in terms of structure and microstructure by means of transmission electron microscopy (TEM) and synchrotron radiation techniques such as high-resolution (HR) and pair distribution function (PDF) quality Xray powder diffraction (XRPD), X-ray absorption spectroscopy (XAS), and for what concerns their electrochemical properties by means of cyclic voltammetry and steady-state I/E curves. The activity of these materials is compared and discussed in the light of our most recent results on hydrous IrO x . The main conclusion of this study is that the Ir core is noninteracting with the IrO x shell, the latter being able to easily accommodate Ir in different oxidation states, as previously suggested for the hydrated form, thus explaining the activity as electrocatalysts. In addition, in operando XAS experiments assessed that the catalytic cycle involves Ir(III) and (V), as previously established for the highly hydrated IrO x material.

Oxygen evolution activity and stability of iridium in acidic media. Part 2. – Electrochemically grown hydrous iridium oxide

“…Alternatively, it can be concluded that the mechanism proposed by Kötz et al [58] is not operative. Below we present a tentative mechanism of OER on hydrous and also compact iridium oxide electrodes, similar to those reported by Minguzzi et al [40,62] for the former, which explains the observed dissolution results. Based on the results from CVs and density functional theory (DFT) calculations, Steegstra et al [41] suggested a binuclear mechanism of OER with participation of neighbor Ir(V) cites.…”

Activity and Durability of Iridium Nanoparticles in the Oxygen Evolution Reaction

“…Ir nanoparticles did not exhibit Ir oxide characteristics in cyclic voltammograms (III/IV transition) or a shoulder in OER tests (Figure 2c, IV/V transition), before or after durability. 31,[35][36][37][38] The impact on dissolutiondriven losses is also unclear, since only a small amount of dissolution occurred during accelerated stress tests at these potentials ( Figures 4e and 4f). In either case, potential cycling of Ir nanoparticles produced less severe losses than potential holds in durability tests at electrolyzer-relevant potentials (Figures 4a and 4c).…”

High‐Performance Supported Iridium Oxohydroxide Water Oxidation Electrocatalysts

“…[13] They showedt hat the highest stability under potentiostatic conditions was achieved for ATO-supported Pt electrocatalysts. [38][39][40] Such issues in preparing and characterizing amorphous Ir oxide/hydroxides might explain the lack of attention they have received so far. [14] In addition to optimized catalyst morphology by dispersion of Ir particles on as uitable support, producingt he "right" chemicals tate of Ir is no less critical to the OER performance of the catalytic system.E arly electrochemical studies showed that metallici ridium is inefficient in OER and needs to be activated under oxidative conditions.…”