Darstellung, Charakterisierung und Eigenschaften oxidischer Mischphasen

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Monitoring the hydrothermal growth of cobalt spinel water oxidation catalysts - from preparative history to catalytic activity

The hydrothermal growth of cobalt oxide spinel (Co₃O₄) nanocrystals from cobalt acetate precursors was monitored with in situ powder X‐ray diffraction (PXRD) in combination with ex situ electron microscopy and vibrational spectroscopy. Kinetic data from in situ PXRD monitoring were analyzed using Sharp‐Hancock and Gualtieri approaches, which both clearly indicate a change of the growth mechanism for reaction temperatures above 185°C. This mechanistic transition goes hand in hand with morphology changes that notably influence the photocatalytic oxygen evolution activity. Complementary quenching investigations of conventional hydrothermal Co₃O₄ growth demonstrate that these insights derived from in situ PXRD data provide valuable synthetic guidelines for water oxidation catalyst production. Furthermore, the ex situ analyses of hydrothermal quenching experiments were essential to assess the influence of amorphous cobalt‐containing phases arising from the acetate precursor on the catalytic activity. Thereby, we illustrate how the efficient combination of a single in situ technique with ex situ analyses paves the way to optimize parameter‐sensitive hydrothermal production processes of key energy materials

Reactive stability of promising scalable doped ceria materials for thermochemical two-step CO2 dissociation

ISSN:2050-7488ISSN:2050-749

Isothermal relaxation kinetics for the reduction and oxidation of SrFeO3 based perovskites

The perovskite oxide SrFeO3 has favourable redox properties for oxygen exchange applications, including oxygen separation and oxygen production chemical looping cycles. For such applications, lower temperature operation can improve the energy demand and feasibility of the process, but can also lead to kinetic limitations. Here we investigate the oxidation and reduction reaction kinetics of SrFeO3 in the temperature range 450–750 K. Isothermal relaxation techniques are used to observe the reaction rates across this temperature range, using a thermogravimetric analysis system. Experimental data are analysed according to an isoconversional method and fit with a simple power law model to extract activation energies. The apparent activation energy of oxidation and reduction was found to be 92 ± 16 and 144 ± 17 kJ mol−1 respectively. Comparison of oxidation and reduction kinetics together with considerations of particle size indicate that the oxidation reaction rate may be limited by diffusion in the bulk, while the reduction reaction rate is limited by the surface reaction. Furthermore, we also investigated the mixed perovskite Sr0.93Ca0.07Fe0.9Co0.1O3, which exhibited a 4-fold increase in the oxidation rate.ISSN:1463-9084ISSN:1463-907