Modelling electrooxidation of glycerol and methanol on close-packed transition metal surfaces

Doctoral thesis, 2020

Burning fossil fuels leads to excess CO2 in the atmosphere, causing global warming, threatening civilisation and ecosystems worldwide. As a step in making the society fossil-independent, we need to replace oil, coal, and gas in the transportation sector with fuels originating from sustainable energy sources. Biodiesel is one such option, from which glycerol is a byproduct. With the help of electrooxidation, glycerol can be used as a feedstock to extract hydrogen gas, which may be used for upgrading biofuels or in proton exchange membrane (PEM) fuel cells. Methanol is a possible fuel in direct methanol fuel cells (DMFCs) and can, moreover, be used as a simple model for glycerol in some respects.

The primary focus of this thesis is to study the reaction thermodynamics of glycerol electrooxidation on Au(111) and other close-packed late transition metal surfaces. This provides routes and products that are thermodynamically favourable, information on steps that are difficult to overcome, and at what theoretical limiting potential the reaction becomes spontaneous. Using scaling relations for adsorption energies, these results can be generalised to alloys and other possible electrode materials. We use density functional theory to model the system, and to some extent experimental verification by cyclic voltammetry. Long range dispersion (van der Waals), which have been neglected in computations until recently, is investigated by assessing density van der Waals functionals. This is of particular importance for an inert metal such as gold. Another aspect that has commonly been ignored is solvent effects, which we study for the model system of methanol electrooxidation on Au(111). This includes an implicit model - a continuous dielectric -and an explicit model of water molecules.