The chemistry of transition metal complexes related to solar energy storage : H₂ production and small molecule (CO₂ and HX; X = Cl, Br) chemistry.

Abstract

The studies in this thesis have focused on the chemistry of transition metal complexes related to solar energy storage: electrochemical H₂ production, HX splitting and CO₂ activation mediated by transition metal complexes. Transition metal complexes, for example with macrocyclic ligands, can catalyze electrochemical proton reduction, a half reaction of water splitting to H₂/O₂ by electricity generated by sunlight. The strategy for designing efficient molecular catalysts were explored by introducing a Hangman scaffold into metallomacrocyles. The study exhibits synthesis and electrochemistry of metallomacrocyles, and an example of Hangman effect for electrochemical H2 production. Thermodynamically demanding HX splitting to H₂/X₂ by sunlight can be a promising method for solar energy storage. To date, most HX splitting chemistry was studied with metal complexes based on 2"d or 3 rd row transition metals. Hence, the usage of cheaper first row metals is an imperative to discover economically viable catalytic systems. HX chemistry of Ni complexes and photoelimination of H₂ from Ni hydride complexes, and photoactivation of Ni-Cl bonds were studied. CO₂ can be utilized as a carrier of H₂ by the syntheses of liquid fuels from CO₂ and H₂. The challenge of using CO₂ as a precursor for organic molecules is the activation of strong O=CO bonds. The reaction with metal complexes is one of the methods to break or weaken the bonds. The CO₂ chemistry of Ni complexes was explored, and generation of a new binding mode of CO₂ and activation of CO₂ to CO were studied.