Producing green energy has become the main goal in our society in the search of reducing or eliminating the carbon emission from fossil fuels. In this project, proteins were used as a tool to... Show moreProducing green energy has become the main goal in our society in the search of reducing or eliminating the carbon emission from fossil fuels. In this project, proteins were used as a tool to develop an artificial system capable of promoting the most demanding reaction in photosynthesis, water oxidation, as a new concept of producing energy from a green source. For this purpose, a screening study of the interaction between selected proteins and a library photocatalytic ruthenium and cobalt complexes was carried out. The results from such study allowed the production of two types of artificial metalloenzymes (ArM) which were proven to be able to perform water oxidation reaction via blue light irradiation. As well, an unusual interaction between proteins which promote the photocatalytic O2 evolution from water. These findings lead to develop ruthenium and cobalt metalloenzymes as promising candidates for artificial photosynthesis in bio-inspired systems Show less
To design the ideal water oxidation catalyst, understanding of the catalytic mechanism and decomposition pathways is essential. The aim of the research described in this thesis is to provide... Show moreTo design the ideal water oxidation catalyst, understanding of the catalytic mechanism and decomposition pathways is essential. The aim of the research described in this thesis is to provide mechanistic insight on the water oxidation reaction catalyzed by homogeneous electrocatalysts and topostulate design criteria for the ideal water oxidation catalyst. Show less
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
Molecular complexes can be used as electrocatalysts for oxygen reduction, water oxidation, and/or hydrogen peroxide production. However, in situ degradation of these catalyst is a major issue. This... Show moreMolecular complexes can be used as electrocatalysts for oxygen reduction, water oxidation, and/or hydrogen peroxide production. However, in situ degradation of these catalyst is a major issue. This dissertations describes the analysis of degradation processes as well as the performance of various molecular electrocatalysts. In addition, complexes have been structurally modified to perform structure-activity studies that could to mechanistic insight. In addition, it is described how molecular catalysts can be beneficial to heterogeneous electrocatalysis as well. Show less
In this dissertation iron-based homogeneous catalysts were synthesized, characterized and investigated for water oxidation activity. The catalysts were studied under electrochemical conditions in... Show moreIn this dissertation iron-based homogeneous catalysts were synthesized, characterized and investigated for water oxidation activity. The catalysts were studied under electrochemical conditions in order to compare the electrochemical approach to the catalysis based on the use of sacrificial oxidants. The mechanisms under which these catalysts operate have been explored with particular attention to the O−O bond formation step. The combination of electrochemical techniques and in situ characterization techniques allowed for the identification of the active intermediates responsible for catalysis. The influence of the presence of water oxidation catalysts in solution on the evolution of carbon dioxide from the surface of a pyrolytic graphite working electrode was also investigated. Overall, the results of this work demonstrate that the combination of in operando and in situ (spectro)electrochemical techniques allows for a complete investigation of the catalytic mechanism of the water oxidation reaction. Show less
Before the large scale use of renewable energy sources can be implemented in our society, the storage of electrical energy needs to be tackled. Storage the energy as hydrogen via the reduction of... Show moreBefore the large scale use of renewable energy sources can be implemented in our society, the storage of electrical energy needs to be tackled. Storage the energy as hydrogen via the reduction of protons is a good option. In order to form a closed electrochemical cycle an oxidation reaction need to be used. The water oxidation reaction is a good candidate as second reaction. When the energy is released, the oxygen reduction reaction is used to reduce the oxygen produced in the water oxidation reaction. This thesis focusses on heterogenized water oxidation and oxygen reduction catalysts. Water oxidation occurs under highly oxidizing potentials. This causes many molecular catalysts to degrade. In this thesis an example is given of two pyridyl-triazolylidene iridium precatalysts which have different rates of activation and deposition formation under reactive conditions. A copper-based catalyst has two different activation processes, an oxidative and a reductive pathway, which stress the importance of choosing the right reaction conditions before the start of catalysis. A copper complex with 1,10-phenanthroline ligands only forms an active oxygen reduction catalyst when one 1,10-phenanthroline ligand is coordinated to the copper ion. By immobilizing the 1,10-phenanthroline ligand on the electrode, an active heterogenized catalyst is formed. Show less
In this dissertation, the synthesis and characterization of a series of iron complexes based on different ligand platforms are described. The complexes are subsequently studied for their... Show moreIn this dissertation, the synthesis and characterization of a series of iron complexes based on different ligand platforms are described. The complexes are subsequently studied for their activity in catalytic water oxidation with the help of a variety of electroanalytical techniques. The results show that the catalytic activity of structurally related iron complexes correlates strongly with the electronics of the iron centre. Another potentially very important aspect in the field of homogeneous electrocatalysis which has so far received only very little attention in published literature is the influence of the nature of the electrode material on the resulting electrochemistry. The results discussed in thesis show that interactions between the working electrode and the catalyst in solution can exhibit a strong influence on the resulting electrochemistry. Overall, the results of this work demonstrate that iron-based complexes can indeed be made to work as electrocatalysts for the water oxidation reaction. Furthermore, the results show that the electronic structure of the iron centre is a promising target for the design of new and improved catalysts. Finally, the results also highlight the importance of trying out different electrode materials as part of routine tests of new potential electrocatalysts. Show less
Ham, C.J.M. van der; Isik, F.; Verhoeven, T.W.G.M.; Niemantsverdriet, J.W.; Hetterscheid, D.G.H. 2017
Current energy-sources in the form of fossil fuels are quickly being depleted, while the demand of energy by society is increasing. In order to sustain this growth in energy demand, alternatives... Show moreCurrent energy-sources in the form of fossil fuels are quickly being depleted, while the demand of energy by society is increasing. In order to sustain this growth in energy demand, alternatives for the production of energy in a usable form are needed. One of such alternatives is to employ photocatalysis in order to use sunlight for the production of chemical fuels such as for example H2 or methanol. For the production of fuels, electrons are required that can be obtained by oxidizing water, as done by nature in a process called photosynthesis. The work in this thesis was inspired by this natural process; photosensitizers and water-oxidation catalysts were bound to lipid bilayers and their ability to photocatalytically oxidize water was studied in different conditions. The anchoring of compounds to a lipid bilayer leads to large differences in reactivity compared to homogeneous systems. In some cases, even the mechanism of the photocatalytic reaction changed upon membrane-anchoring of the constituents. In general, detailed experiments are described that fully characterize photocatalytic systems, because the mechanism of a reaction involving two different catalytic species is not straight-forward, and cannot be described by a single set of turn-over numbers. Show less
