Albert-Ludwigs-Universität Freiburg

AG Kurz/ AG Hillebrecht:

Syntheserouten und in-situ Studien zu optimierten Manganoxid-Katalysatoren für die elektrochemische Wasseroxidation

Synthesis routes and in-situ investigations on optimized manganese oxides for the electrochemical water oxidation

The subproject “synthesis routes and in-situ investigations on optimized manganese oxides for the electrochemical water oxidation” within the MANGAN-cluster project consists of the groups from Malte Behrens (University Duisburg/Essen), Saskia Heumann (Max-Planck Institute for Chemical Energy Conversion in Mülheim an der Ruhr), Harald Hillebrecht and Philipp Kurz (both Albert-Ludwigs-University Freiburg). One central task of the subproject is to synthesize different manganese oxide polymorphs possessing variations within their structural motive (e.g. crystalline, layered, tunneled oxides), their elemental composition (e.g. doping with transition metals) and/or their particle size (e.g. nano-structuring). In addition, the materials will be made available for other groups within the MANGAN cluster project for further characterizations and investigations.

The project groups of Prof. Kurz and Prof. Hillebrecht from the Institute of Inorganic and Analytical Chemistry of the Albert-Ludwigs-University of Freiburg are responsible for the synthesis and characterization of crystalline, nanoparticulate and highly amorphous manganese oxides and oxyhydroxides. A special focus lies on the enhancement of the catalytic activities and stabilities of manganese oxides with a layered structure (so-called birnessites); a material class that already showed promising activities in water oxidation catalysis. This will be achieved by doping other transition metals into the catalysts, e.g. Co, Ni, Fe. Furthermore, the synthesis of nanoparticles will be attempted in order to increase the reactive surface area and to improve the contact between the catalyst and conductive electrode materials.

As outcome, the synthesis and characterization of manganese oxides exhibiting different structural motifs in combination with detailed investigations of their electrochemical water oxidation activities and stabilities at different conditions (pH, current densities, overpotentials,…) could lead to a deeper fundamental understanding of the water oxidation process on manganese oxides. Furthermore, it will hopefully enable the team to identify the most suitable operating conditions for manganese

Fritz-Haber-Institut der Max-Planck-Gesellschaft

AG Knop-Gericke:

Entwicklung ortsspezifischer Spektroskopiemethoden zur Charakterisierung homogener und heterogener manganhaltiger Wasserspaltungskatalysatoren

Development of site-specific spectroscopy methods for the characterization of homogeneous and heterogeneous manganese-containing water splitting catalysts

Department: Inorganic Chemistry, Electronic Structure Group

The main goal of our group consists of in-situ spectroscopy studies of manganese oxides under oxygen evolution reaction (OER). We are working mainly in a soft X-ray regime using synchrotron radiation for X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS).

Our endstation (Innovative Station for In Situ Spectroscopy - ISISS) is located at the Bessy II synchrotron in Berlin. We are also performing in-situ measurements within our collaborations. The main focus lies on the near edge X-ray absorption fine structure (NEXAFS), recording Mn L-edges and O K-edge for manganese oxides under electrochemical conditioning with simultaneous catalytic products detection.

Probing of unoccupied Mn 3d states results in Mn L-edges enabling the evaluation of the manganese oxidation state. These unoccupied Mn 3d states tend to hybridize with the O 2p states. The latter can be probed directly by the O K-edge, which is used as a measure of the unoccupied O 2p density of states.

We obtain our spectra in the electron- and fluorescence yield as well as in a transmission mode. Combination of results coming from the different detection methods brings us closer to a complete picture of the studied system. The figure below presents the electrochemical cells used for those three approaches.

The purpose of our research is to identify an active phase or the phases present during the OER, which may give us hints concerning the mechanism of OER on manganese oxides.

Helmholtz-Zentrum Berlin für Materialien und Energie

AG van de Krol:

Mangan- und Kobaltoxid Katalysatoren für Wasseroxidation: Dünnschicht-Modellsysteme und Effiziente Kopplung an Metalloxid Photoelektroden

Manganese and cobalt oxide catalysts for water oxidation: Thin film model systems and efficient coupling on metal oxide photoelectrodes

The generation of fuels by electrochemical splitting of water or electro-reduction of CO₂, is one of the key technologies in a sustainable energy scenario. The technical application is, however, still hampered by the high cost of electro-catalysts so that low-cost catalysts based on earth-abundant materials are required. Hence, manganese oxides are under investigation as catalyst for the electro-oxidation of water (Oxygen Evolution Reaction- “OER”) which is the necessarily counter reaction in most fuel generating electrolysis processes.

Within the HZB-subproject, we explore the fundamental limitations of cheap abundant manganese oxide as electro-catalysts for the OER. Thin film model systems, prepared via "atomic layer deposition” (ALD), are used in order to quantitatively study the structure-property relationship as a function of the layer thickness (0.2 to 10 nm) and at different stages of the growth process. To this end oxidation states, band level positions, conductivity, crystallinity and the electrochemical activity is determined with respect to the applied bias potential.  In order to vary the electronic properties manganese oxide is also alloyed with other transition metals (e.g. Ni) in a broad range of composition. The obtained results are compared with the corresponding findings of the other sub-groups on bulky(powder)- or molecular-based materials in order to find general descriptors for manganese based materials.

Finally, these catalysts are coupled to semiconducting metal oxide as model light absorbers (BiVO₄ and Ta_xO_yN_z) in order to form integrated photoelectrochemical anodes. The charge transfer processes at the interfaces during photoelectrochemical water oxidation are investigated. Specifically, the influence of the electronic structure of the absorbers and the catalysts to these processes are explored. These studies serve to provide basic insights for the development of a universal design model of efficient photoanodes.

Johannes-GutenbergJohannes-Gutenberg-Universität Mainz

AG Waldvogel:

Funktionalisierte Elektrodenmaterialien für die biomimetische Wasserspaltung

Functionalized electrode materials for the biomimetic water splitting

Subproject: Cyclic voltammetric measurements on boron-doped diamond (BDD) 

The AK Waldvogel is located in the Institute of Organic Chemistry of the Johannes Gutenberg University Mainz. One of the main tasks of the group is the application of electrochemistry as a tool for the synthesis of organic compounds. The objective is the design of new synthetic routes to a variety of substance classes with respect to atom economy and thus to establish organic electro synthesis as an important instrument in organic chemistry. Due to its inherently safe nature and generally low amounts of reagent waste organic electro synthesis can be considered as a valuable and ‘green’ method. Furthermore, the anodic dismantling of biological building blocks such as lignin or black liquor – side products/waste products of the pulping industry – in order to recover fine chemicals represents an important research field in the group with regard to sustainability.

Working on electro synthesis for almost 20 years developed a broad knowledge with respect to cell design and electrode materials, which is crucial in order to overcome limitations in organic chemistry by employing preparative scale electrochemistry. Diverse reactions and their scaling up are conducted in batch or flow cells.

Depending on the reaction and the corresponding conditions, electrode materials are required to provide individual features or properties. BDD proofed to be a valuable electrode material in electro- organic synthesis. Moreover, it exhibits a great potential window and high chemical stability properties. Therefore, BDD is investigated in, apart from glassy carbon, as a potential electrode material for the manganese-based electro catalysts for the oxygen evolution reaction (OER).

Justus-Liebig-Universität Gießen

AG Janek:

Kontrollierte Defektchemie fester Lösungen der Manganoxide für die Wasserspaltung

Controlled defect chemistry of manganese oxide solid solutions

The subproject Controlled defect chemistry of the MANGAN-cluster is located in the physical chemistry department of the Justus Liebig University Giessen. The aim of the subproject is the synthesis and characterization of ternary and multinary manganese-based oxides like La_1-xSr_xMnO_3±δ, which could be suitable catalysts for the oxygen evolution reaction (OER) due to their electronic and atomic defect structure.

A general problem in the search for well-functioning manganese-based catalysts is the insufficient knowledge of the correlation of the electrical properties with the defect chemistry of the relevant multinary oxide phases. The defect chemistry of multinary oxides is much more complex than that of simple binary manganese oxides, since different cationic and anionic defect species can occur depending on the oxide composition and surrounding atmosphere.

By analyzing this defect chemical influence on the catalytic properties of multinary manganese oxides, the subproject contributes essentially to a deeper understanding of manganese oxides in the project cluster. The results of the subproject will help to control the electrical properties of the electrodes and thus support the development of improved electrocatalysts for the OER.

Max-Plack-Institut für Chemische Energiekonversion

AG DeBeer:

Entwicklung ortsspezifischer Spektroskopiemethoden zur Charakterisierung homogener und heterogener manganhaltiger Wasserspaltungskatalysatoren

Development of site-specific spectroscopy methods for the characterization of homogeneous and heterogeneous manganese-containing water splitting catalysts

In preparation

AG Heumann:

Entwicklung neuer, katalytisch aktiver Elektrodenmaterialien aus verfügbaren Basismaterialien unter Nutzung nachhaltiger Ressourcen

Developement of new catalytic active electrode materials from available base materials and sustainable resources

The project is located in the „Carbon Synthesis and Applications“ group at the Max Planck Institute for Chemical Energy Conversion (MPI-CEC) at the Department of Heterogeneous Reactions in Mülheim an der Ruhr. Within this project we incorporate manganese oxides in a conductive carbon matrix to enhance the material properties when they are applied as electrocatalysts for the water oxidation process. Beside an increase of activity and conductivity, the stability of the materials has to be improved as well to resist the harsh oxidizing conditions under the oxygen evolution reaction (OER). Furthermore, the electrode materials are synthesized with abundant sustainable resources to fulfill the ecofriendly requirements.

Solvothermal synthesis is applied to generate manganese oxide containing carbon based electrode materials. Systematic process variations to obtain homogeneously distributed Mn-oxides within the carbon structures are investigated to do a knowledge-based approach. Different manganese oxide precursors and different carbon sources like glucose or saccharose are investigated as well as the impact of the dosing time and temperature on the final products.

The electrocatalytic performances of the composite materials are investigated by pressing mechanically stable pellets and subsequent annealing of the powders. Large scale and long-term experiments are applied to mimic industrial relevant conditions.

Syntheserouten und in-situ Studien zu optimierten Manganoxid-Katalysatoren für die elektrochemische Wasseroxidation

Synthesis routes and in-situ investigations on optimized manganese oxides for the electrochemical water oxidation

The joint project between the groups of Philipp Kurz and Harald Hillebrecht both from University of Freiburg, the group of Malte Behrens from University of Duisburg-Essen and the group of Saskia Heumann from the Max Planck Institute for Chemical Energy Conversion (MPI-CEC) try to answer the question whether manganese oxides are potential candidates for large-scale applications as water oxidation catalysts. The project partners apply solid state chemistry for the synthesis of nanocrystalline towards macrocrystalline materials to investigate correlations between conductivity, stability and activity.

In the subproject at the MPI-CEC, nanocrystalline manganese oxides are anchored by atomic layer deposition (ALD) on conductive carbon based support materials. Covalent bonds shall be generated to prevent agglomeration and leaching of the manganese oxides on the carbon surface. Furthermore, a strong interaction between the active manganese species and the support material is intended for a favorable electron transfer to overcome the missing conductivity of manganese oxides. For this procedure, the carbon materials have to be pre-treated to generate feasible anchor groups for the deposition. Wet chemical methods and plasma treatment are therefore applied.

The electrocatalytic performances of the composite materials are tested in alkaline media applying the developed standard measurement protocol. Pre- and post-analysis of the investigated samples provides deeper insights on the stability and performance of the electrocatalysts.

AG Schlögl:
Projektkoordination
Project-Coordination

The coordination project of the MANGAN-cluster is located at the department “Heterogeneous Reactions” of the Max-Planck-Institute for Chemical Energy Conversion in Mülheim an der Ruhr. It is responsible for the technical coordination of all involved sub projects of the MANGAN-cluster. As one central task, the coordination project manages the acquisition and archiving of all results into a single database as well as the subsequent consolidation and evaluation of the data to create a structure-function library of Mn-based catalysts. In addition, the coordination project takes care of organizational tasks and supports networking among the project partners by organizing meetings, workshops, and conferences.

The coordination project provides all project partners with identical experimental setups and offers technical support. To ensure the reproducibly and comparability of the electrocatalytic characterization of the individual samples, the coordination project develops a standard measurement protocol for the characterization of OER catalyst in alkaline media. Beside the usage of standardized measurement parameters, this also comprises sample preparation, pretreatment, and conditioning steps.

As outcome, the coordination project in collaboration with all project partners will establish a function-structure database for Mn-bases catalyst for the OER that will be available for scientist worldwide. Moreover, the development of a standard measurements protocol will serve as a reference for establishing standardized methods to facilitate the comparability of electrochemical experiments in future large scale projects.

Ruhr-Universität Bochum

AG Muhler / AG Schuhmann:

Biomimetische Wasserspaltung – Nanoskalige Manganoxid-Kohlenstoff-Hybridmaterialien für die Wasserelektrokatalyse: Synthese, Charakterisierung und Elektrokatalyse

Biomimetic water splitting – Nanoscale manganese-oxide–carbon–hybrid-materials for water electrocatalysis: Synthesis, characterization and electrocatalysis

Substituting fossil fuels with hydrogen as a green energy carrier is of utmost urgency to advance the Energiewende. The overriding bottleneck for achieving sustainable mass production of H₂ by renewable energy driven water electrolysis is the frustratingly slow kinetics of the oxygen evolution reaction (OER). Inspired by nature’s CaMn₄O₅ oxygen-evolving complex (OEC), the prospect of exploiting manganese oxide species as OER catalysts is compellingly attractive. However, the inherently low electrical conductivity of manganese oxides hampers realization of their potential as anode materials for water electrolysis. Enhancing the electrical conductivity of manganese oxides is therefore an integral design strategy of the Ruhr University Bochum (RUB) subproject in all synthetic endeavors to realize high performance manganese oxide catalysts for the OER. 

Technische Universität Berlin

AG Drieß:

Gezielte Oxidation nanostrukturierter metaloxidischer Präkatalysatoren
Targeted oxidation of nanostructured metal-oxide pre-catalysts

The Driess group from the Technische Universität Berlin at the Department of Chemistry works within the MANGAN-cluster in the sub project of nano structures. Following the project aims to identify Mn-based catalysts and its potential for industrial application in water splitting, the Driess group develops new synthetic methodologies to make Mn-based nanomaterials for oxygen evolution reaction (OER) catalysis. With long experience in water splitting and development in catalyst materials, the group combines the experience from molecular metalorganic and solid state chemistry to explore the suitability of Mn-containing materials for water splitting. Of major interest is the access to new classes of materials and the design of nano structures for efficient and long-term stable catalytic materials. To identify the active sites of manganese catalysts, the synthesized materials are thoroughly characterized by various microscopic and spectroscopic methods such as XRD, (HR)-SEM, (HR)-TEM, IR etc. in house and in cooperation with the project partners. The materials are tested on various substrates and conditions as well as different electrochemical setups. For the MANGAN database the synthesized materials are further electrochemically tested following the project related protocol to provide reproducibility and comparability with other samples in that database. As outcome of the project, the Driess group follows the agenda to identify potential candidates for industrial application in water splitting and to help building a convenient and reliable database of Mn-based catalysts for OER.

Technische Universität Darmstadt

AG Jaegermann:

Integration neuartiger Manganoxid-Katalysatoren mit lichtabsorbierenden Halbleiter-Strukturen
Integration of novel manganese-oxide catalysts with light absorbing semiconductor-structures

Aim of this project part is the setup and characterization of new transition metal oxides based on manganese and their integration with light-absorbing semiconductor structures. An artificial leaf shall be demonstrated, that is able to convert light and water to H₂ and O₂ in a photochemical process with technologically relevant efficiencies. For this demonstrator setup only non-expensive noble metal free electrocatalysts as well as semiconductors from abundant materials shall be used.

For this project it is necessary to develop suitable deposition techniques, which allow the controlled formation of thin catalyst layers with controlled composition and structure based on Mn_xO_y on light absorbing silicon based multi junction absorbers. The decisive scientific question is here to understand and apply the successful coupling between catalyst and absorber without current (charge carrier recombination) and potential losses (reduction of the electrochemical potential).

Finally, device structures shall be setup as model systems for an artificial leaf and their performance data shall be evaluated. From these results in combination with the knowledge of the physical and chemical properties of these subsystems design principles will be derived for the realization of technologically competitive systems.

Max-Planck-Institut für Eisenforschung

AG Erbe:

Mechanistische Untersuchungen der elektrochemischen Sauerstoffentwicklung auf Modellelektroden - Natur der Oxide und Intermediate

Mechanistic investigation of electrochemical oxygen evolution on model electrodes – Nature of oxides and intermediates

The Interface Spectroscopy Group at the Max-Planck-Institut für Eisenforschung GmbH, Düsseldorf, Germany, is carrying out spectroscopic investigations of manganese surfaces at the transition into potential regions in which oxygen evolution occurs. The main working experiments are Raman spectroscopy and spectroscopic ellipsometry, all coupled in situ and operando to electrochemical experiments. In this manner, we can follow the formation of surface oxides and other surface species, can follow their structural evolution with time or with potential, can estimate their quantities, and correlate this structural data with electrochemical data obtained from the same surface at the same time.
As an outcome, we obtain detailed information on the oxide formation and stability on manganese.

AG Mayrhofer:

Mechanistische Untersuchungen der elektrochemischen Sauerstoffentwicklung auf Modellelektroden - Natur der Oxide und Intermediate

Mechanistic investigation of electrochemical oxygen evolution on model electrodes – Nature of oxides and intermediates

Subproject: Stability of the catalysts

The Elecrocatalysis group headed by Prof. Karl Mayrhofer is located at the department “Interface Chemistry and Surface Engineering” of the Max-Planck-Institute for Eisenforschung GmbH in Düsseldorf. The group is responsible for the stability tests of the catalytic materials during OER provided by other partners involved in the MANGAN-cluster. The main task is establishing correlation between composition, electronic structure of the catalysts and their activity and stability towards the OER. This is achieved by a versatile combination of electrochemistry with complementary analytic techniques for determination of reaction products, as well as by the investigation and comparison of the behavior between well-defined model thin film electrodes and catalysts of nanoparticles utilized in real applications. In particular, a home developed setup coupling the electrochemical scanning flow cell (SFC) with an inductively coupled plasma mass spectrometer (ICP-MS) is used to address the problem. The advantage of using such setup is that various catalysts provided by different groups can be tested in the identical conditions, which gives a good basis for direct comparison of activity-stability trends.

Rheinisch-Westfälische Technische Hochschule Aachen

AG Palkovits:

Elektroden-Design und Charakterisierung

Electrode design and characterization

The group of Prof. Regina Palkovits is located in the institute of technical and macromolecular chemistry at RWTH Aachen University. The group aims to identify electrode material properties in addition with a deep understanding of the relationships between catalyst architecture, intrinsic activity and catalyst stability.

This subproject includes the preparation and characterization of novel manganese-based solid electrode materials for OER. With respect to the electrolysis cell, cost and long-term stable catalyst materials should be synthesized, and in particular examined according to their activity and stability. The novel electrode materials were physically and chemically characterized using N₂-Physisorption analysis, X-Ray diffraction spectroscopy and thermogravimetric analysis. In addition, electrochemical impedance spectroscopy is used to get an insight into OER kinetic, electron transfer processes and material porosity.

During the project first materials were synthesized that were inspired by common carbon type materials and characterized (for example: structured Manganese phthalocyanine) to understand the influence of electrochemical conductivity and the structure on OER performance. The OER activity of metal-based catalysts compared to metal free catalysts was also studied. In addition, the aim is to get structure activity relationships of mesoporous structured catalysts and bulk catalysts during the OER process. Due to the low electrochemical stability of carbon-based electrode materials in alkaline media the focus was shifted towards nanostructured transition metal-based spinel catalysts (MnCo₂O₄, NiCo₂O₄). Here the influence of the MnCo₂O₄ nanoparticle size and morphology on OER activity, as well as the number of active sides is studied.

AG Leitner:

The group of Prof. Dr. Walter Leitner is part of the subproject No. 3 of the MANGAN-Cluster which is located at the “Institute for Technical and Macromolecular Chemistry” at RWTH Aachen University. The core expertise of the group comprises the whole development process of new molecular catalysts, namely the design, synthesis, characterization and evaluation of transition-metal complexes.

Within the MANGAN project, the group uses this experience to synthesize various mononuclear manganese complexes and investigate their potential as molecular water oxidation catalysts. Systematic ligand modifications allow the group to identify the main factors that influence the catalytic activity.

The experimental work is supported by computational investigations to achieve a detailed mechanistic understanding of the catalytic process. Based on these information computational simulations enable a fast screening of different ligands to rationally improve the catalyst’s design which then can be tested in the lab.

In the last stage of the project, incorporation of linker-units into the ligand system will open the possibility to immobilize the catalyst on a carrier material to apply it in water electrolysis.

Universität Bielefeld

AG Glaser /AG Hütten/ AG Kruse:

Wasseroxidation mit biomimetischen Mangankomplexen gekoppelt mit artifiziellen und biologischen Lichtsammelantennen

Water oxidation with biomimetic manganese complexes coupled to artificial and biological light harvesting antennas

            Subproject: Biomimetic water splitting in a microfluidic system

The project “Biomimetic water splitting in a microfluidic system” of the MANGAN-Cluster is a collaboration between the three disciplines biology, physics and chemistry. It is located at the Bielefeld University in the department for “Algae Biotechnology and Bioenergy”, “Thin Layer and Physics of Nanostructures” and “Inorganic Chemistry I”.

The aim is to combine heterologous expressed light harvesting proteins from microalgae for capturing solar energy with dinucleating Manganese-complexes for efficiency water splitting on a titaniumdioxid semiconductor surface.

The generation of this photoelectrochemical cell, mimicking photosynthesis, reflects the fundamental aspects of the global project, the conversion of solar energy into chemically usable energy.

Universität Duisburg Essen

AG Behrens:

Syntheserouten und in-situ Studien zu optimierten Manganoxid-Katalysatoren für die elektrochemische Wasseroxidation

Synthesis routes and in-situ investigations on optimized manganese oxides for the electrochemical water oxidation

The development of an efficient non-precious metal based electrocatalyst for the oxygen evolution reaction (OER) can be seen as a milestone to a sustainable energy scenario. Manganese oxides, which are discussed as promising OER electrocatalysts, are in the focus of our work with a particular emphasis on correlation of materials and catalytic properties. Several different manganese oxide compounds were synthesized in phase pure bulk form, characterized and analyzed regarding their electrocatalytic activity in the OER. By comparison of the electrocatalytic data, clear differences in catalytic activity and stability depending on the manganese oxide species can be observed. Thus, the most active catalysts can be found within the hollandite-type oxides, like Cryptomelane which reaches a current density of about 30 mA cm^-2 at a potential of 1.8 V. An in-depth examination of Cryptomelane was carried out for a determination of influencing factors independent of the structure type. Thereby, the sample conductivity and the morphology were identified as important impact factors. A detailed study on pure α-MnO₂ showed that potassium is readily incorporated in the tunnels of the crystal structure under electrochemical operation. Finally, the evaluation of manganese oxides as OER electrocatalysts is complemented by an investigation of the stability and material changes during catalysis.