How electron spin coupling affects catalytic oxygen activation
A team at the EPR4Energy joint lab of HZB and MPI CEC has developed a new THz EPR spectroscopy method to study the catalytic activation of molecular oxygen by copper complexes. © T. Lohmiller/HZB
A team at the EPR4Energy joint lab of HZB and MPI CEC has developed a new THz EPR spectroscopy method to study the catalytic activation of molecular oxygen by copper complexes. The method allows insights into previously inaccessible spin-spin interactions and the function of novel catalytic and magnetic materials.
Molecular oxygen (O2) is a preferred oxidant in green chemistry. However, activation of O2 and control of its reactivity requires precise adjustment of the spin states in the reactive intermediates. In nature, this is achieved by metalloenzymes that bind O2 at iron or copper ions, and spin-flip processes are enabled through metal-mediated spin-orbit couplings allowing for mixing of states. In the case of type III dicopper metalloproteins involved in oxygen transport and oxygenation of phenolic substrates, little was known about the pathway leading to a dicopper peroxo key species with a stabilized singlet ground state after triplet oxygen binding.
Through a sophisticated ligand design, the research group led by Prof. Franc Meyer at the University of Göttingen has now succeeded in isolating a series of model complexes that mimic the initial stage of oxygen binding at dicopper sites and exhibit a triplet ground state. Researchers from the EPR4Energy joint lab of HZB and MPI CEC complemented this breakthrough in chemical synthesis with a new approach of THz-EPR spectroscopy. This method, developed in Alexander Schnegg's group at MPI CEC, was applied for the first time to study the function-determining antisymmetric exchange in coupled dicopper(II) complexes.
The new method allowed for detection of the entirety of spin state transitions in the system, which leads to propose antisymmetric exchange as an efficient mixing mechanism for the triplet-to-singlet intersystem crossing in biorelevant peroxodicopper(II) intermediates. Thomas Lohmiller, one of the first authors of the study, explains, "In addition to the knowledge gained about this important system, our method opens up the possibility of studying previously inaccessible spin-spin interactions in a variety of novel catalytic and magnetic materials."
- BESSY II: How intrinsic oxygen shortens the lifespan of solid-state batteriesAlthough solid-state batteries (SSBs) demonstrate high performance and are intrinsically safe, their capacity currently declines rapidly. A team from the TU Wien, Humboldt-University Berlin and HZB has now analysed a TiS₂|Li₃YCl₆ solid-state half-cell in operando at BESSY II using a special sample environment that allows for non-destructive investigation under real operating conditions. Data obtained by combination of soft and hard X-ray photoelectron spectroscopy (XPS and HAXPES) revealed a new degradation mechanism that had not previously been identified in solid-state batteries. They have gained some surprising insights, particularly regarding the harmful role played by intrinsic oxygen. This study provides valuable information for improving design and handling of such batteries.
- Spintronics at BESSY II: Real-time analysis of magnetic bilayer systemsSpintronic devices enable data processing with significantly lower energy consumption. They are based on the interaction between ferromagnetic and antiferromagnetic layers. Now, a team from Freie Universität Berlin, HZB and Uppsala University has succeeded in tracking, for each layer separately, how the magnetic order changes after a short laser pulse has excited the system. They were also able to identify the main cause of the loss of antiferromagnetic order in the oxide layer: the excitation is transported from the hot electrons in the ferromagnetic metal to the spins in the antiferromagnet.
- Electrocatalysts: New model for charge separation at the solid-liquid interfaceHydrogen is at the heart of the transition to carbon neutrality, as both an energy carrier and a reagent for green chemistry. However, large-scale production of hydrogen via electrolysis, as well as the production of many other chemical products, requires significantly cheaper and more efficient catalysts. A precise understanding of the electrochemical processes that take place at the interface between the solid catalyst and the liquid medium is highly useful for developing better electrocatalysts. In the journal Nature Communications, an European team has now presented a powerful model that determines charge separation at the interface, the formation of the electric double layer and local electric potential variations, and the resulting influence on the catalytic activity.