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).
Uri Vool was awarded a starting grant from the European Research Council (ERC). He is an independent group leader at the MPI-CPfS, and will use the grant to explore novel superconductors by integrating them into hybrid quantum circuits.
IMPRS-CPQM student Chia-Chi Yu won a poster Prize at the 21st GDCh Conference on Inorganic Chemistry, Solid-State Chemistry, and Materials Research in Marburg (September 27-28, 2022).
Maia G. Vergniory, a researcher in our department of Solid State Chemistry, has recently been elected as APS Fellow by the American Physical Society (APS) for her pioneering work developing a new theory known as Topological Quantum Chemistry that has allowed to identify thousands of new topological materials.
A team of researchers from MPI for Chemical Physics of Solids and the MPI for the Structure and Dynamics of Matter in collaboration with researchers from Switzerland and Spain has reported the first observation in a structurally achiral crystal, the Kagome superconductor CsV3Sb5. Their work has been published in the current issue of Nature.
We offer our warm congratulations to our Max Planck Fellow Professor J.C. Séamus Davis of the University of Oxford and University College Cork, who has been awarded the prestigious 2023 Oliver E. Buckley Prize of the American Physical Society.
Dr. Eteri Svanidze was honored with this year's award within the L'Oréal-UNESCO funding program "For Women in Science". We warmly congratulate Dr. Svanidze on this award.
A team of scientists from the MPI CPFS and Stockholm, Tsukuba, Oxford, Toronto, St Andrews and Birmingham combined focused ion beam microstructuring and uniaxial pressure to achieve a record value of uniaxial pressure for the unconventional superconductor Sr2RuO4 and found that the superconducting state of Sr2RuO4 evolved surprisingly.
Working with a new experimental technique called the ac elastocaloric effect, a team of scientists from Dresden, Karlsruhe, St Andrews, Cornell, Tsukuba and Stanford has mapped out the so-called phase diagram of the unconventional superconductor Sr2RuO4. The results narrow down the on-going, 25 years quest to understand the superconductivity of Sr2RuO4 and set a benchmark for future work.
Observations reveal the angle dependence of the magnetic field needed to suppress superconductivity in CeRh2As2. Uniquely, the behavior of “odd parity” superconductors is revealed.
