IrO₂-Based Disperse-Phase Electrocatalysts: A Complementary Study by Means of the Cavity-Microelectrode and Ex-Situ X-ray Absorption Spectroscopy

Abstract

In this work, IrO(2)-based powders are screened by cyclic voltammetry for the determination of the electrochemical active sites and for the qualitative evaluation of the iridium atoms speciation. All results are obtained using a cavity-microelectrode as powder holder, thus exploiting the features of this innovative tool, whose best potentialities have been recently introduced by our group. All the studied materials have been prepared by the sol-gel technique and differ in calcination temperature and method of mixing the metal oxide precursors. The electrochemical results are complemented with the information obtained by X-ray absorption spectroscopy (XAS), that give insights on the local structure of each selected sample, confirming the trends found by cyclic voltammetry and give new and unexpected insights on the powder structural features.

Water Oxidation with Molecularly Defined Iridium Complexes: Insights into Homogeneous versus Heterogeneous Catalysis

“…The second is the weaker signal after the white line, which is rather intense for Ir 0 , [30] of lower intensity for Ir III , and finally disappears for Ir IV . [31] As can be seen in all the XANES spectra ( Figure 3), the white line increases, whereas the second resonance, observed in all Ir III pre-catalysts, is reduced in intensity during water oxidation reaction. A significant contribution of an Ir IV species is therefore suspected in all spectra recorded under water oxidation conditions.…”

“…Whereas the XANES part of XAS is mainly sensitive to the oxidation state of an X-ray-absorbing atom by the shape and position of the white line (first resonance after the edge jump), the EXAFS (extended X-ray absorption fine structure) part yields type, number, and distance of coordinating atoms to the X-ray absorber. [30][31][32][33] Figure 3 shows the XANES spectra at the Ir L 3 -edge of the pre-catalysts IrO 2 , IrCl 3 ·xH 2 O, IrA C H T U N G T R E N N U N G (acac) 3 , 1 and 4 in comparison to the spectra under water oxidation conditions. The corresponding EXAFS spectra are given in Figure 4.…”

Oxide-supported Ir nanodendrites with high activity and durability for the oxygen evolution reaction in acid PEM water electrolyzers

“…The two redox waves can be associated with the Ir( iii )/Ir( iv ) and Ir( iv )/Ir(> iv ) redox couples, respectively. 62 In particular, Ir(0) is first oxidized to Ir( iii ) at low potentials (region II) and subsequently to a hydrous Ir( iv ) oxide species in potential region III. Further anodic above +1.2 V (region IV), the redox features involve the oxidation of Ir( iv ) to a higher valence, most likely to Ir( vi ) and Ir( v ).…”

Designing materials by means of the cavity-microelectrode: the introduction of the quantitative rapid screening toward a highly efficient catalyst for water oxidation

“…under real operative conditions. Moreover, and quite recently, 42 we have evaluated, by CV and by X-ray absorption measurements, the fine structure of most of the materials treated in the present work.…”