Heterogenized Iridium Water-Oxidation Catalyst from a Silatrane Precursor

Abstract

A pentamethylcyclopentadienyl (Cp*) iridium water-oxidation precatalyst was modified to include a silatrane functional group for covalent attachment to metal oxide semiconductor surfaces. The heterogenized catalyst was found to perform electrochemically driven water oxidation at an overpotential of 462 mV with a turnover number of 304 and turnover frequency of 0.035 s–1 in a 0.1 M KNO3 electrolyte at pH 5.8. Computational modeling of the experimental IR spectra suggests that the catalyst retains its Cp* group during the first hour of catalysis and likely remains monomeric.

Rational Design Rules for Molecular Water Oxidation Catalysts based on Scaling Relationships

“…The dimeric nature of this type of iridium catalysts is also supported by kinetic analysis of the reaction progress . When mononuclear iridium catalyst 4 was anchored to an ITO surface, with no freedom to come in close proximity to a second iridium center, preventing ROC, indeed a much higher overpotential of 462 mV was found at the onset of water oxidation (Figure , 4@MO x ) …”

A full set of iridium(iv) pyridine-alkoxide stereoisomers: highly geometry-dependent redox properties

“…With reactions selective for the tris-pyalk species, yields of mono- and bis-chelate species were low to trace. Complex 8 was prepared in this manner, as reported previously, 27 in poor yield (8%, Scheme 3). The same reported reaction also produced very small amounts of 3–7 (below 1% for most), which was unfeasible for bulk preparation.…”

The Middle‐Earth between Homogeneous and Heterogeneous Catalysis in Water Oxidation with Iridium

“…More recently, Brudvig and Wang showed that the same molecular Ir WOC can be successfully heterogenized onto hematite . The functionalization in the periphery of 4 with a silatrane functional group allowed for a covalent attachment to metal oxide semiconductor surface (ITO and TiO 2 ) and the assembly of photoanodes from a SnO 2 film, sensitized with a combination of a high‐potential CF 3 ‐substituted porphyrin dye …”

“…The strategies to minimize the contents of iridium foresee the exploitation of molecular Ir WOCs (Figure A), under the assumption that all Ir‐centers are catalytically active, differently from what happens in heterogeneous IrO 2 . Otherwise, it is conceivable to anchor a well‐defined molecular Ir WOC onto a suitable support, thus obtaining a heterogenized WOC (Figure B), combining the positive aspects of homogeneous and heterogeneous catalysis. Finally, the minimization of Ir‐atoms can be achieved by diluting them in a proper material (Figure C), having features that maximize Ir‐accessibility and performance .…”