Nickel and Iron complexes for electrochemical proton and Carbon dioxide reduction

Increasing population of the world has increased the demand for energy. Since contaminant and non-renewable fossil fuels are widely used as the main energy source, environment and human health problematics are currently a worldwide challenge to be addressed. Thus, shifting from fossil fuels to alternative and sustainable energy resources is inevitable. Since the renewable energy resources like sun are highly intermittent, a method to store their energy is desirable. A source of inspiration to achieve such goal is natural photosynthesis, which harvests sun light and stores it in the form of chemical bonds. Technologies that try to mimic photosynthesis not only will be highly dependent on the energy resources used but also on a viable catalytic system that makes the overall process economically viable. Considering these challenges and opportunities, this thesis is focused on developing efficient, cheap, and robust molecular catalysts for electrochemical hydrogen production and carbon dioxide reduction reactions. 

The first research chapter includes the synthesis and spectroscopic characterisation of three families of novel ꞵ-diimino (BDI) compounds as precursors to ꞵ-diketiminato (BDK) ligands with different denticity: κ2-N2, κ3-PN2, and κ4-P2N2 types. In the following chapter two of the κ4-P2N2 BDI ligands have been used to prepare two novel Ni(II) complexes that are active for electrochemical proton reduction reaction in organic media. They are also characterized by an easy conversion of the BDI group to the corresponding BDK ligand, indicative of the non-innocent nature of the ligand as proton relay. In the next chapter, three Fe(II) complexes containing BDI or BDK ligands are described. One of them possesses a dangling pyrene group that provides an anchoring point to graphitic materials towards heterogeneous electrocatalysis. It readily interacts with CO2 as demonstrated by electrochemical and spectroscopic analysis. Although preliminary tests point to a possible electrochemical CO2 reduction reaction ability both in homogenous and heterogenous phase, further experiments are necessary to detect the resulting products and confirm the catalysis. Finally, in the last chapter of this thesis, a straightforward route towards Ni(II) complexes containing tetradentate dipicolinamido ligands has been described. These complexes show promising results as potential CO2 reduction catalysts to form CO and H2, in the presence of CO2 and water/TFE as proton source. 

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