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."
- Green hydrogen: How photoelectrochemical water splitting may become competitiveSunlight can be used to produce green hydrogen directly from water in photoelectrochemical (PEC) cells. So far, systems based on this "direct approach" have not been energetically competitive. However, the balance changes as soon as some of the hydrogen in such PEC cells is used in-situ for a catalytic hydrogenation reaction, resulting in the co-production of chemicals used in the chemical and pharmaceutical industries. The energy payback time of photoelectrochemical "green" hydrogen production can be reduced dramatically, the study shows.
- Perovskite solar cells from the slot die coater - a step towards industrial productionSolar cells made from metal halide perovskites achieve high efficiencies and their production from liquid inks requires only a small amount of energy. A team led by Prof. Dr. Eva Unger at Helmholtz-Zentrum Berlin is investigating the production process. At the X-ray source BESSY II, the group has analyzed the optimal composition of precursor inks for the production of high-quality FAPbI3 perovskite thin films by slot-die coating. The solar cells produced with these inks were tested under real life conditions in the field for a year and scaled up to mini-module size.
- Superstore MXene: New proton hydration structure determinedMXenes are able to store large amounts of electrical energy like batteries and to charge and discharge rather quickly like a supercapacitor. They combine both talents and thus are a very interesting class of materials for energy storage. The material is structured like a kind of puff pastry, with the MXene layers separated by thin water films. A team at HZB has now investigated how protons migrate in the water films confined between the layers of the material and enable charge transport. Their results have been published in the renowned journal Nature Communications and may accelerate the optimisation of these kinds of energy storage materials.