Materials for carbon dioxide utilization

In recent years, the rise in popular awareness over climate change and the consequent attention governments have had over the matter has brought to ever-harder goals of environmental sustainability in all sectors of industry. Carbon capture and utilization schemes are one of the many routes that have been proposed to increase the environmental sustainability of the transport and chemical industries, which are two of the biggest carbon emitters on the planet. This strategy aims at closing the cycle of fossil fuel burning by using renewable energy to transform water and carbon dioxide back into fuels and chemicals. In this work, we present a computational study of the electronic structure and catalytic performances of two classes of materials, carbon nitrides and transition metal carbides. Carbon nitrides are semiconductors used for photocatalytic water splitting, a nature-mimicking process which aims at the direct conversion of H2O into H2 and O2 using solar irradiation and band gap tuned catalysts; in Chapter 3 we will explore their structural and electronic properties, providing a rationale for their experimental catalytic activity. Transition metal carbides are metallic materials which have been shown to catalyse, among other reactions, the electrochemical hydrogen evolution from water and the catalytic reduction of CO2; in Chapter 4 and 5 we will explore the catalytic activity of the low-index surfaces of these materials, identifying descriptors and proposing routes to achieve the best rates and selectivity. The present work aims at improving our understanding of the fundamental behaviour of these materials, as part of the global effort in creating a more sustainable world.