Water oxidation catalysts (WOC Sample Clauses

Water oxidation catalysts (WOC. The natural PSII system has been the inspiration and the starting point for many researchers in developing a catalytic structure for efficient water oxidation. The search of a molecular catalyst capable to generate oxygen from the oxidation of two water molecules has been very active already in the eighties and nineties with the study and synthesis of several biomimetic catalysts, mainly with two manganese centres linked by oxygen bridges [22-25]. Also ruthenium has been used extensively as metallic centre in similar catalyst architectures [25, 26]. During the last decade a large effort has been devoted in the synthesis of catalysts with different kind and number of metallic centres and different ligands [27]. The most explored catalysts are the ones based on ruthenium [28, 29], cobalt [30-32] and iridium [33-35], and during the last years also iron has been explored as a possible metallic centre [36]. DFT calculations have been also performed to clarify the underlying reaction mechanism in some of these catalysts [34, 35, 37- 39]. Available computational chemistry tools have reached a predictive power which is good enough to allow not only the understanding of reaction mechanisms in existing catalysts, but even the important and crucial landmark of assisting in the design of new catalysts. An effective water oxidation catalyst must be capable of water oxidation at a potential minimally above the thermodynamic value, with a high turnover frequency and able to run during hundred thousands of cycles. However, these are characteristics needed only from an efficiency point of view. For a good catalyst it is also necessary to use an abundant material. A catalyst based on a rare and expensive metal might represent a problem when moving into a large scale production. Nowadays, the catalysts with the best performance are based on ruthenium or iridium. However, these two metals are extremely rare, leading to an economical and availability problem. This is the reason why the search for other catalysts based on more abundant metals has been a hot topic during the last years. In Figure 1.1 it is possible to observe that ruthenium is around four orders of magnitude less abundant than cobalt, and six to eight orders of magnitude less abundant than manganese and iron, respectively. Iridium is still less abundant than ruthenium. At this point is clear that a compromise between efficiency and availability is crucial in order to find the most appropriate catalysts for the w...