The water electrolysis is an electrochemical way for production of hydrogen, which is considered as one of the future energy carrier molecules. Therefore, looking at numerous advantages of proton exchange membrane electrolysis compared to the classical alkaline variant, it’s efficiency and applicability on the large scale is of huge importance nowadays. However, the slow kinetics of the anode oxygen evolution reaction (OER) limits the overall electrolysis process and requires an active and stable electrocatalyst. Such need inspired the scientists of Chemical Metal Science and Physics of Correlated Matter departments at MPI CPfS together with the Fritz-Haber-Institut in Berlin to employ their longstanding expertise in chemistry of intermetallic compounds, electronic features of solid matter and electrocatalysis to make a step forward in this challenging direction. As a result of fruitful teamwork, the concept of cooperative phases with different stabilities under OER conditions was successfully demonstrated with the intermetallic compound Hf2B2Ir5 as a self-optimizing electrocatalyst for OER.
Based on chemical bonding analysis, the intermetallic compound Hf2B2Ir5 has a cage-like type of the crystal structure: the two-dimensional layers of B2Ir8 units are interconnected by two- and three-center Ir-Ir interactions to polyanionic framework and hafnium atoms are guesting in such anionic cages. The atomic interactions features are reflected in the electronic structure of Hf2B2Ir5 and its chemical behaviour under OER conditions. The initial electrochemical OER activity of Hf2B2Ir5 sustains during the continuous operation at elaborated current densities of 100 mA cm-2 for at least 240 h (Figure 1) and positions this material among Ir-based state-of-the-art electrocatalysts. The harsh oxidative conditions of OER activate the surface-limited changes of the pristine material and as a result the electrochemical performance is related to the cooperative work of Ir-terminated surface of the ternary compound itself and agglomerates of IrOx(OH)y(SO4)z particles (inset of Figure 1). The latter are formed mainly due to the oxidation of HfB4Ir3 secondary phase and near-surface oxidation of the investigated compound. The presence of at least two OER-active states of Ir, originated from the Hf2B2Ir5 under OER conditions, was confirmed by the XPS analysis (Figure 2). The experimental data (electrochemical results, material characterization using bulk-and surface-sensitive methods, elemental analysis of the used electrolyte) are consistent with the chemical bonding analysis. The illustrated concept of cooperative phases with different chemical stabilities under OER conditions can be explored to other systems and offers a perspective knowledge-based way for discovery of new effective OER-electrocatalysts.
Iryna Antonyshyn/IA
Figure 1. OER performance of Hf2B2Ir5 anode material, represented by linear sweep voltammograms measured during the long-term chronopotentiometry experiment (0.1 M H2SO4, j = 100 mA cm-2, t = 0 ... 240 h). Inset: morphology of Hf2B2Ir5 material afterwards.
Figure 1. OER performance of Hf2B2Ir5 anode material, represented by linear sweep voltammograms measured during the long-term chronopotentiometry experiment (0.1 M H2SO4, j = 100 mA cm-2, t = 0 ... 240 h). Inset: morphology of Hf2B2Ir5 material afterwards.
Figure 2. Ir 4f core levels in Hf2B2Ir5 material: pristine state (black) and after 240 h of chronopotentiometry at 100 mA cm-2 current density (pink). The reference lines are drawn for Ir 4f in intermetallic Hf2B2Ir5 (black dashed), elemental Ir (grey dashed) and rutile IrO2 (red dashed).
Figure 2. Ir 4f core levels in Hf2B2Ir5 material: pristine state (black) and after 240 h of chronopotentiometry at 100 mA cm-2 current density (pink). The reference lines are drawn for Ir 4f in intermetallic Hf2B2Ir5 (black dashed), elemental Ir (grey dashed) and rutile IrO2 (red dashed).
Recent research suggested that hydrodynamic electron flow in 3D conductors was possible, but exactly how it happened or how to observe it remained unknown. Until now. A team of researchers from Harvard, MIT and the Max Planck Institute Chemical Physics of Solids developed a theory to explain how hydrodynamic electron flow could occur in 3D materials and observed it for the first time using a new imaging technique.
Über 5.000 Läufer haben am Mittwochabend am ersten Tag der REWE-Team-Challenge teilgenommen. Das MPI CPfS war mit 16 Laufbegeisterten in schicken neuen Shirts in den Max-Planck Farben mit dabei! In vier Teams, einem Frauen- und drei Männerteams, ging es auf der 5 km langen Strecke vom Kulturpalast durch die historische Innenstadt Dresdens zum Rudolf-Harbig-Stadion. Alle haben die stimmungsvolle Laufstrecke genossen und unser Frauenteam hat es fast in die Top 10 geschafft (Platz 14)!
The phenomenon of superconductivity, providing current transmission without dissipation and a host of unique magnetic properties arising from macroscopic quantum coherence, was first discovered over a century ago. It was not understood until 1957, after which it quickly became clear that superconductors could in principle exist with a wide variety of the fundamental characteristic often referred to as the order parameter. Until the late 1970’s, however, all superconductors found experimentally had the same class of order parameter.
The analogy between the behaviour of different quantum particles which have the same quantum nature is one of the most fascinating aspects of science. A simple but prominent example is the analogy between the behaviour of electrons (fermions) in a one-dimensional metal and spinons (fermions) in a one-dimensional quantum magnet. But, what are spinons?
The spatially resolved determination of which of the two enantiomorphic structural variants - the left-handed or the right-handed - of a chiral phase is present in a polycrystalline material is the focus of our publication in Science Advances. With the EBSD (electron backscatter diffraction) -based technique, this is shown for the first time for the chiral element structure β-Mn for which a determination of the handedness with usual x-ray diffraction methods is not possible so far.
The electronic structure of metallic materials determines the behavior of electron transport. Magnetic Weyl semimetals have a unique topological electronic structure - the electron's motion is dynamically linked to its spin.
Dr. Guowei Li from the Solid State Chemistry Department has left our institute this month. However, he fortunately will stay in close cooperation with members of our institute.
The U.S. National Academy of Sciences (NAS) has appointed Claudia Felser as an International Member under the auspices of the Applied Physics Section in recognition of her outstanding and continuing research accomplishments.
Maja Bachmann of the Physics of Quantum Materials department has been awarded the Otto-Hahn-Medaille of the Max Planck Society for her outstanding doctoral research.
