An Exceptionally Fast Homogeneous Carbon-Free Cobalt-Based Water Oxidation Catalyst

Abstract

An all-inorganic, oxidatively and thermally stable, homogeneous water oxidation catalyst based on redox-active (vanadate(V)-centered) polyoxometalate ligands, Na10[Co4(H2O)2(VW9O34)2]·35H2O (Na101-V2, sodium salt of the polyanion 1-V2), was synthesized, thoroughly characterized and shown to catalyze water oxidation in dark and visible-light-driven conditions. This synthetic catalyst is exceptionally fast under mild conditions (TOF > 1 × 10(3) s(-1)). Under light-driven conditions using [Ru(bpy)3](2+) as a photosensitizer and persulfate as a sacrificial electron acceptor, 1-V2 exhibits higher selectivity for water oxidation versus bpy ligand oxidation, the final O2 yield by 1-V2 is twice as high as that of using [Co4(H2O)2(PW9O34)2](10-) (1-P2), and the quantum efficiency of O2 formation at 6.0 μM 1-V2 reaches ∼68%. Multiple experimental results (e.g., UV-vis absorption, FT-IR, (51)V NMR, dynamic light scattering, tetra-n-heptylammonium nitrate-toluene extraction, effect of pH, buffer, and buffer concentration, etc.) confirm that the polyanion unit (1-V2) itself is the dominant active catalyst and not Co(2+)(aq) or cobalt oxide.

Understanding the Regioselective Hydrolysis of Human Serum Albumin by Zr(IV)-Substituted Polyoxotungstates Using Tryptophan Fluorescence Spectroscopy

“…As shown in Figure 3, there is no shift in the peak positions of the characteristic Zr1-WD2 resonances (at −9.33 and −13.94 ppm) in the presence of HSA, indicating the stability of the POM upon interaction with the protein. It should not be surprising that these polyoxotungstates are stable as this was already previously demonstrated by various techniques [63][64][65]. In addition, the slight decrease in the intensity of the POM peaks can be correlated with the formation of a large molecular complex with HSA which has a longer correlation time and thus a faster relaxation.…”

Kinetic Analysis of an Efficient Molecular Light-Driven Water Oxidation System

“…In recent years, substantial progress has been reported on molecular water oxidation catalysts 1,2 although light driven water oxidation activity has been demonstrated in only a small number of cases. 3,4,5,6,7,8,9,10,11 Furthermore for these photoactivated systems, analyses of the different kinetics processes that determine system efficiency have been very limited to date and in several cases the molecular catalyst has been reported to degrade to the corresponding oxide. 3,6b,7,8,9a .…”

A cobalt-based polyoxometalate catalyst for efficient visible-light-driven H2 evolution from water splitting

“…Recently, Hill and co-workers have reported that cobalt-based polyoxometalates can be used as efficient light-driven carbon-free molecular catalysts for water oxidation [13,14]. As far as we known, very few reports describe the visible-light-driven H 2 evolution from water splitting using carbon-free homogeneous catalysts based on earth-abundant elements [12,15].…”