An increasing energy demand connected with the replacement of fossil fuels and environmental concerns has made necessary the development of advanced and next-generation technologies for energy production. Between them, in the last years, fuel cells have received much attention, however, their practical application has to overcome the request for a high overpotential for the Oxygen Reduction Reaction (ORR) at the cathode. Among the approaches pursued to enhance the ORR process, the use of catalysts revealed to be the most effective. From previous studies, it is clear that the catalyst should be able to perform a 4-electrons reduction of O2. Generally, organometallic compounds consisting of a red-ox active transition metal cation stabilized by aromatic organic ligands have been applied. Despite being efficient catalysts for the ORR, the platinum-based compounds are very expensive. Although porphyrin, corrole and phtalocyanine-based ligands can be a valid alternative, their synthesis is frequently characterized by low yields, a feature which can hamper their production on industrial scale. While the proof of concept has been demonstrated, the potentiality of tetrapyrazinoporphyrazines derivatives has still to be explored. With the aim to study systematically the influence of substituents on the ORR selectivity, this project will be focused on the preparation of different tetrapyrazinoporphyrazine derivatives, their complexation with several low cost and environmental friendly transition metals and their adsorption on a solid support (nanotubes, reduced graphene oxide, carbon material). The compounds showing the most outstanding performances will be applied in fuel cells.
To make fuel cells a valid alternative to fossil fuels, more efficient catalysts for the ORR process need to be developed. Platinum-based catalysts have been largely applied but the high cost and the shortage of this metal together with the sensitivity to hydrogen peroxide prevents their application on concrete devices. Porphyrin derivatives could represent a valid alternative but from the synthetic point of view these macrocycles are very difficult to prepare. Generally these ligands are obtained in low yield (in average 20-40%) and in most cases a not trivial purification by column chromatography on silica gel is necessary making their preparation lengthy. In contrast, a catalyst for a fuel cell device requires an easy and straightforward prepared on large scale. Tetrapyrazinoporphyrazines derivatives, which are the subject of this project, with respect to porphyrins can be obtained in high yields applying very simple synthetic procedures. Moreover, the macrocycle and the metal complex can be purified by crystallization, a desirable feature for a potential industrial scale preparation.
While the proof of concept has been demonstrated, the potentiality of tetrapyrazinoporphyrazines derivatives has still to be exploited. Tetrapyrazinoporphyrazines with simple structures proved, in fact, to be suitable catalysts for the ORR process, but a systematic study about the influence of substituents on the ORR selectivity (preference for the reduction vai 2 or 4 electrons pathway) is still missing. Aim of this project is, therefore, to study systematically the influence of non-noble transition metal and different substituents on the tetrapyrazinoporphyrazine core structure in order to develop efficient catalysts for a sustainable Oxygen Reduction Reaction which could find application in fuel cells.