Abstract
The catalytic activity of the bimolecular reaction was affected by many parameters. Although many efforts have been dedicated to investigate the influence of secondary interactions in pre-organizing catalysts, the hydrophobic effect on Ru-bda-type water oxidation catalysts remains unclear as a result of the lack of an ideal catalytic model. In this work, four catalysts 1–4 with variable hydrophobicity have been synthesized, and cerium(IV)-driven water oxidation results showed that the hydrophobic complexes 3 and 4 outperformed the hydrophilic complex 2. Steric mapping, nuclear magnetic resonance, and differential pulse voltammogram studies indicated that the increase in activity has no correlation with electronic and steric effects but has correlation with hydrophobicity. Molecular dynamics have shown that the modifications of the hydrophobicity on the axial pyridine ligands of the Ru-bda type of catalysts can improve the water oxidation catalytic activity by stabilizing the pre-reactive catalyst dimer.
Highlights
Photosynthesis, using solar energy to convert water and carbon dioxide into oxygen and carbohydrate molecules, has powered most life forms on the Earth for billions of years
Two Ru molecules are included in a unit cell, as presented in Figure 2, where the distances between hydrophobic chains and axial aromatic rings are in the range of 3.5−
To compare the hydrophobic effects of axial ligands on catalytic activities, chemical-driven water oxidation was carried out using cerium(IV) as the oxidant in acidic aqueous solution
Summary
Photosynthesis, using solar energy to convert water and carbon dioxide into oxygen and carbohydrate molecules, has powered most life forms on the Earth for billions of years. Inspired by nature, splitting water into oxygen and hydrogen as a fuel via artificial photosynthesis has become a popular topic and potentially solves the energy shortage problem. As one of the half-reactions, water oxidation suffers uphill thermodynamics and sluggish kinetics as a result of the four proton and four electron transfer involved. To this end, the development of efficient water oxidation catalysts accompanied by a comprehensive mechanism understanding is highly needed. This limits the application at lower concentrations
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