Artificial photosynthesis (AP) is one of the scientific challenges that could help us achieving a global “carbon neutral” society. Photocatalytic water splitting is considered as the first... Show moreArtificial photosynthesis (AP) is one of the scientific challenges that could help us achieving a global “carbon neutral” society. Photocatalytic water splitting is considered as the first challenge of AP, which contains two half reactions: water oxidation and hydrogen evolution. It is widely accepted that a photocatalytic system needs a minimum of three components: a photosensitizer (PS), a catalyst (Cat) and a sacrificial electron donor or acceptor (SE). In such a photocatalytic system, at least three electron-transfer steps can be identified: one between the SE and the excited PS (PS*), one between the photo-reduced or photo-oxidized PS and the Cat, and one between the Cat and its substrate. This thesis on the one hand focused on developing improved molecular components for the two half reactions of water splitting in purely homogeneous systems. On the other hand optimized photocatalytic systems with balances between the driving force of electron transfer from the SE to the PS*, and that of electron transfer between the catalyst and the oxidized or reduced photosensitizer (PS+ or PS–). Show less
Electrocatalysis allows for storing electricity or converting it into chemical bonds, producing chemical building blocks and fuels using renewable resources. Therefore, it plays an important role... Show moreElectrocatalysis allows for storing electricity or converting it into chemical bonds, producing chemical building blocks and fuels using renewable resources. Therefore, it plays an important role in the transition towards a more sustainable future for our society through electrification. Still, to bring electrochemical technologies to industrial scale and make them competitive, optimization of various aspects of electrocatalytic reactions are needed. Many fundamental studies focus on understanding the catalyst surface, however, different components of the electrolyte, as pH and cations, have also shown to significantly affect the reaction activity and selectivity. In view of that, in this thesis, various aspects of the electrode-electrolyte interface are studied at different scales, using Scanning Electrochemical Microscopy (SECM), stationary and rotating-disc electrode voltammetry techniques, and bulk electrolysis. Show less
Cecilio de Oliveira Monteiro, M.; Koper, M.T.M. 2019
In this work we show how the contamination of gold electrodes with alumina particles by electrode polishing leads to an enhancement in activity for hydrogen evolution (HER). Polishing is one of the... Show moreIn this work we show how the contamination of gold electrodes with alumina particles by electrode polishing leads to an enhancement in activity for hydrogen evolution (HER). Polishing is one of the most used electrode treatments, however, we show that particles from the polishing media cannot be easily removed from the electrode surface by standard cleaning procedures. Comparing the HER activity of gold disc electrodes polished with either diamond suspension or alumina paste, we show that the latter leads to higher current densities, specifically for the water reduction to hydrogen. A similar enhancement in HER activity was observed by the addition of Al3+ cations to the electrolyte, demonstrating that the particles are not catalytically active, but that the Al3+ species released in solution due to corrosion promote the water reduction reaction. Due to an increase in the local OH− concentration during HER, the contaminating Al3+ cations precipitate and may deposit at the electrode surface as Al(OH)3. In the presence of a high enough Al3+ concentration, layered Al(OH)3 plates cover the whole electrode surface. The plates are composed of Al(OH)3 sheets intercalated by sulphate anions. Surprisingly, the Al(OH)3 sheets do not affect the gold blank voltammetry, and therefore remain undetected by simple electrochemical characterization methods. Show less
The PhD project was aimed to understand the role of the solvent in the hydrogen oxidation and evolution reactions on platinum and gold. This approach sheds light on the molecular origins... Show more The PhD project was aimed to understand the role of the solvent in the hydrogen oxidation and evolution reactions on platinum and gold. This approach sheds light on the molecular origins affecting the kinetics of the hydrogen evolution reaction, as a promising source of energy in the era of sustainable energy production and storage. Ultimately, this work demonstrates the importance of the solvent in the hydrogen electrocatalysis, specifically, water, by settling its role as a solvent, as a proton donor, and by preferential proton solvation, clarifying a long-existing debate regarding the pH dependence of the hydrogen evolution, and setting a path for future exploration of solvent-electrode interfaces for the tailoring of electrocatalytic reactions. Show less
