Metallo-Supramolecular and Bioinspiried Coordination Compounds for H2O Oxidation

Abstract

Ever-increasing energy demands and associated climate change issues impose imperative scientific challenges to society. Switching to an economy based on the carbon-free, high density energy carrier H2 represents a promising solution to the problems posed by fossil fuel consumption. However, current methods of H2 production are expensive and unsustainable. Solar H2O splitting presents an attractive approach for renewably generating H2 in abundance. Despite this, current technological breakthroughs in this area are hampered by a lack of efficient, cost-effective catalysts for the endergonic, proton-coupled 4 electron O2 evolution half-reaction (OER). Therefore, the development of H2O oxidation catalysts (WOCs) based on earth-abundant materials to provide low-energy pathways for the OER is of utmost importance to satisfy global energy needs in an environmentally friendly manner.

Due to the thermodynamic and kinetic barriers to the OER, current catalysts for this reaction suffer from poor activity or instability. Moreover, many state-of-the-art WOCs rely on costly rare-earth elements. Metal-organic frameworks (MOFs) are metallo supramolecular materials with well defined cavities and unprecedented surface areas which can incorporate redox active building units. Thus, MOFs represent a hopeful class of compounds to catalyse H2O oxidation. This thesis aims to prepare and use metallo-supramolecular assemblies such as MOFs, metal-oxo clusters and complexes constructed using earth abundant elements as catalysts for the challenging OER. The results presented in this thesis include the synthesis and structural characterisations of several metalloenzyme inspired materials. Moreover, the exploration of these hybrid organic inorganic systems as WOCs towards artificial photosynthetic applications is described. Ultimately, post-catalytic experiments are discussed which attribute the observed OER activities to various molecular species.