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."
- CIGS-perovskite tandem cell achieves record efficiency of 25.5 %A Berlin-based team from HZB and Center for the Science of Materials Berlin (CSMB) at the Humboldt-Universität zu Berlin has set a new record for a tandem solar cell. Using a combination of a CIGS semiconductor layer and perovskite, along with several optimised intermediate layers, they were able to convert 25.5% of sunlight into electrical energy. The previous record for this combination of materials and this size of cell stood at 24.6%. The new record has been certified and is visible in the prestigious Solar Cell Efficiency Tables (the "Green Tables"), which serve as the definitive ledger for the global photovoltaic community.
- Disorder creates new properties in compound semiconductorsAn international research team has demonstrated that the intrinsic disorder of the compound semiconductor CuInSnS₄ can be exploited to influence its optical properties. While the atomic vibrations also sense the local disorder, their response is averaged over many different local environments and therefore appear isotropic, as expected for a cubic crystal. In contrast, the optical excitations, known as excitons, are much more sensitive to the local arrangement of atoms. Surprisingly, they show a direction-dependent optical response even though the average crystal structure is cubic. These findings shed new light on the relationship between disorder and material properties, opening up new options for targeted 'disorder engineering' in optoelectronic and photocatalytic devices.
- Perovskite solar cells: Predictions of long-term stabilityReliable statements about the long-term stability of perovskite solar cells are still difficult to make. However, a new study by Dr Carolin Ulbrich’s team, published in the renowned journal Joule, highlights which methods are useful for this purpose and identifies areas where further research is needed.