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A special membrane electrode assembly to measure operando X‐ray absorption spectra and resonant photoemission spectra of mesoporous templated iridium oxide films is used. These films are calcined to different temperatures to mediate the catalyst activity. By combining operando resonant photoemission measurements of different films with ab initio simulations these are able to unambiguously distinguish µ2‐O (bridging oxygen) and µ1‐O (terminal oxygen) in the near‐surface regions of the catalysts. The intrinsic activity of iridium oxide scales with the formation of µ1‐O (terminal oxygen) is found. Importantly, it is shown that the peroxo species do not accumulate under reaction conditions. Rather, the formation of µ1‐O species, which are active in O−O bond formation during the OER, is the most oxidized oxygen species observed, which is consistent with an O−O rate‐limiting step. Thus, the oxygen species taking part in the electrochemical oxidation of water on iridium electrodes are more involved and complex than previously stated. This result highlights the importance of employing theory together with true and complementary operando measurements capable of probing different aspects of catalysts surfaces during operation. [ABSTRACT FROM AUTHOR]

Abstract: Maghemite and magnetite show superparamagnetic behavior when synthesized in a nanostructured form. The material's inducible magnetization enables applications ranging from contrast enhancing agents for magnetic resonance imaging to drug delivery systems, magnetic hyperthermia, and separation. Superparamagnetic iron oxides with templated porosity have been synthesized so far only in the form of hard‐templated powders, where silicon retained from the template severely degrades the material's magnetic properties. Here, for the first time, the synthesis of superparamagnetic iron oxides with soft‐templated mesopore structure is reported. The synthesis of nanostructured maghemite and magnetite films succeeds using micelles of amphiphilic block‐copolymers as templates. A thermal treatment of the initially formed mesoporous ferrihydrite in nitrogen produces maghemite, which can be partly reduced to magnetite via thermal treatment in hydrogen while retaining the templated mesopore structure. The resulting materials feature a unique combination of high surface area, controlled pore diameter, and tunable magnetic properties. [ABSTRACT FROM AUTHOR]