6 research outputs found
Evaluation of iron-based electrocatalysts for water oxidation: an on-line mass spectrometry approach
Metals in Catalysis, Biomimetics & Inorganic MaterialsCatalysis and Surface Chemistr
Iron complexes as electrocatalysts for the water oxidation reaction
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 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.
Metals in Catalysis, Biomimetics & Inorganic Material
Electrocatalytic water oxidation with alpha-[Fe(mcp)(OTf)(2)] and analogues
The complex alpha-[Fe(mcp)(OTf)(2)] (mcp = N,N'-dimethyl-N,N'-bis(pyridin-2-ylmethyl)-cyclohexane-1,2-diamine and OTf = trifluoromethanesulfonate anion) was reported in 2011 by some of us as an active water oxidation (WO) catalyst in the presence of sacrificial oxidants. However, because chemical oxidants are likely to take part in the reaction mechanism, mechanistic electrochemical studies are critical in establishing to what extent previous studies with sacrificial reagents have actually been meaningful. In this study, the complex alpha-[Fe(mcp)(OTf)(2)] and its analogues were investigated electrochemically under both acidic and neutral conditions. All the systems under investigation proved to be electrochemically active toward the WO reaction, with no major differences in activity despite the structural changes. Our findings show that WO-catalyzed by mcp-iron complexes proceeds via homogeneous species, whereas the analogous manganese complex forms a heterogeneous deposit on the electrode surface. Mechanistic studies show that the reaction proceeds with a different rate-determining step (rds) than what was previously proposed in the presence of chemical oxidants. Moreover, the different kinetic isotope effect (KIE) values obtained electrochemically at pH 7 (KIE similar to 10) and at pH 1 (KIE = 1) show that the reaction conditions have a remarkable effect on the rds and on the mechanism. We suggest a proton-coupled electron transfer (PCET) as the rds under neutral conditions, whereas at pH 1 the rds is most likely an electron transfer (ET).Catalysis and Surface ChemistryMetals in Catalysis, Biomimetics & Inorganic Material