Katalysmaterial för en effektivare vattenklyvning -att möjliggöra lagring av förnyelsebar energi
Examensarbete för kandidatexamen
Engineering Physics (300 hp)
This work presents a broad study of the catalytic activity of possible metal oxide cata- lysts for the oxygen evolution reaction (OER) in the electrolysis of water. Experiments are conducted in a three-electrode cell with 0,1 M KOH base electrolyte in order to rank the following metal oxides according to their catalytic ability for this reaction: IrO2, PtO2, ITO, Fe2O3, TiO2, FTO, SnO2, HfO2, Nb2O5, all of which are on an ITO-on-glass substrate. FTO on glass is also tested, as well as Fe2O3 on an FTO-on-glass substrate. Indicators for catalytic ability are taken to be overpotential and exchange current den- sity. Parallell, in-depth studies of the literature lead to suggestions as to which surface properties and material parameters are important in this process. The practical and the- oretical approaches are then combined as the following possible relevant parameters are related to the performance of the metal oxides as catalysts: binding energy of OH to the catalytic surface, total number of d electrons, number of valence d electrons, enthalpy of formation of the next oxidation state, and the number of so-called outer electrons. Relationships are set up with the aim of identifying which parameters best predict ca- talytic activity. Of these parameters, called descriptors for the OER, binding energy of OH to the catalyst surface as calculated by computational physics methods appears the most successful. In an attempt to grasp these methods, which are the prevalent form of research in the field, they are applied for a surface of PtO2. A relaxation of this surface as well as its binding energy for O is presented, which according to the literature scales linearly to the binding energy for OH. In order to tie this work to technological advan- ces in society and to renewable energy systems where hydrogen can be used either to store energy or to create biofuels such as methane, calculations are made for the actual efficiency of hydrogen production of the most economically sound catalyst identified in this work. IrO2 was identified as the best catalyst for the OER, and Nb2O5 as the worst. This was confirmed by the best descriptor for catalytic ability which was shown to be binding energy between catalyst surface and intermediate OH. Other descriptors were at best moderately predictive, or too complex to be included in a study on this level. The performance of a catalyst for the OER is shown to be critical for the economical viability of an industrial hydrogen production based on electrolysis.
Hållbar utveckling , Kemisk fysik , Elektronstruktur , Elektrokemi , Sustainable Development , Chemical physics , Electronic structure , Electrochemistry