Photoelectrochemical and Electrocatalytic Water Oxidation Performance of Sol-gel-derived Mesoporous High-Entropy Spinel Oxide Thin Films
Marcus Einert a, Qingyang Wu a, Arslan Waheed a, Stefan Lauterbach a, Maximilian Mellin a, Marcus Rohnke b, Lysander Wagner b, Julia Gallenberger a, Chuanmu Tian a, Bernd Smarsly b, Wolfram Jaegermann a, Franziska Hess c, Helmut Schlaad d, Jan Philipp Hofmann a
a Technical University of Darmstadt, Jovanka-Bontschits-Straße, 2, Darmstadt, Germany
b Institute for Physical Chemistry & Center for Materials Research, Justus Liebig University Giessen, Heinrich-Buff Ring 17, 35392 Giessen, Germany
c Technical University of Berlin (TU), Straße des 17. Juni, Berlin, Germany
d Institute of Chemistry, University of Potsdam, Germany, University of Potsdam, Potsdam, Germany
ECAT
Proceedings of Catalyst Design Strategies for Photo- and Electrochemical Fuel Synthesis (ECAT25)
Madrid, Spain, 2025 February 10th - 11th
Organizers: Marta Liras and Claudio Ampelli
Oral, Marcus Einert, presentation 004
Publication date: 19th December 2024

With the introduction of high-entropy oxides (HEO) as a novel class of materials, unexpected and interesting properties have emerged. A HEO consists of five or more ions occupying a single crystallographic site and inducing a high degree of configurational disorder, which increases the entropic contribution to the Gibbs free energy of formation, thus stabilizing their crystallographic structure. Significant efforts have been devoted to the development of new HEO phases; however, the large majority of synthetic approaches are based on solid-state, rather than sol-gel chemistry allowing only the preparation of micrometer-sized, low-surface-area particles. Sol-gel chemistry requires precise control of reaction kinetics in order to form uniform structures, which is most likely the reason why the preparation of ordered mesoporous HEO thin films by the soft-templating and evaporation induced self-assembly (EISA) approach has not been reported yet.

The presentation informs about sol-gel synthesis of (ordered) mesoporous (CrMnFeCoNi)3O4[1] and (CoNiCuZnMg)Fe2O4[2] high-entropy spinel oxides prepared by dip-coating and EISA process. A synthetic route was developed, utilizing the unique copolymer (poly(ethylene-co-butylene)-block-poly(ethylene oxide), known as KLE, in order to obtain periodically ordered and 15−18 nm sized mesopores within the high-entropy ferrite (HEF) framework.[2] The meso-structured HEF electrodes were found to be crack-free on the nano- and macroscale. Time-over-flight secondary ion mass spectrometry and electron microscopy verified a homogenous distribution of all elements within the structure. The fundamental impact of a nanoscale frame-work on the photoelectrochemical and electrocatalytic properties was investigated: mesoporous HEF applied as both n-type photoanode and oxygen evolution cocatalyst for solar water oxidation, showed near-metallic electric conductivity, which was related to an electron hopping mechanism induced by the interaction of 3d-states of the inserted transition metals, and was found to improve performances. The photoresponse of HEF photoanodes was limited owing to severe surface recombination as evidenced by intensity-modulated photocurrent spectroscopy. The novel high-entropy nanostructures can be considered as interesting candidate for energy conversion applications

Marcus Einert acknowledges both the Federal Ministry of Education and Research (BMBF) within the project TWOB under Award Number 033RC036 and the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation, Walter Benjamin Program to M. Einert) with project no. 469377211 for financial support. Jan Philipp Hofmann and Achim Alkemper acknowledge financial support from DFG SPP2080 under project no. 493685339. Qingyang Wu acknowledges support from China Scholarship Council (CSC) under no. 202208320036. Julia Gallenberger and Jan Philipp Hofmann acknowledge financial support from BMBF, the German Ministry for Science and Education, under project no. 03HY105H. Chuanmu Tian acknowledges financial support from China Scholarship Council (no. 202008420222).

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