American scientists simulated the process of photosynthesis using a cobalt-based artificial catalyst and found that water splitting on oxygen and hydrogen occurs in the same way as in plants. The results published in the Chem Catalysis magazine bring humanity to the creation of effective ways to produce pure energy from sunlight. Briefly talks about this in a press release on techxplore.com.
For photosynthesis of plants, chloroplasts are used – cellular organelles, in which protein complexes and other molecules, carrying out the conversion of the energy of sunlight into the energy of chemical bonds. One of the main complexes is the photosystem II, which absorbs the quanta of light through photochemical reactions and forms a strong oxidizing agent – a double (dimeric) chlorophyll molecule A (P680), which in the excited state contributes to the splitting of water to oxygen and hydrogen. Direct oxidation of water is carried out by a manganese complex – a complex molecule from manganese atoms, oxygen and calcium (MN4CAO).
The most structurally and functionally close to the manganese complex of the photosystem II are water oxidation catalysts (WOC) based on cobalt – CO4O4. A further increase in the efficiency of WOC faces the problem: the reaction of the splitting of water is so complicated that scientists still do not know exactly how it flows. It is known that before the release of molecular oxygen (o = o) in the complex there is a connection of O-O. To understand how this happens, the researchers used X-ray absorption spectroscopy and XAFS-spectroscopy of the complex.
In the photo system II, one of the atoms of manganese binds to the water molecule, as a result of which the key intermediate fragment Mn = O occurs. The second water molecule produces a nucleophilic attack on this fragment, which leads to the formation of O = O. It is believed that in the cobalt WoC should have a similar fragment of CO = O, however, this was not previously observed. Scientists managed to confirm that CO = O is indeed formed and activates water through a nucleophilic attack, as it occurs in plants.
The results of the study prove that the cobalt complex is valid similar to the manganese complex, which increases the understanding of water oxidation mechanisms for both systems. As the authors conclude, their work serves as the basis for the rational design of multi-core water oxidation catalysts based on 3D transition metals.