Accessing Molecular Dimeric Ir Water Oxidation Catalysts from Coordination Precursors

Abstract

One ongoing challenge in the field of iridium-based water oxidation catalysts is to develop a molecular precatalyst affording well-defined homogeneous active species for catalysis. Our previous work by using organometallic precatalysts Cp*Ir(pyalk)-OH and Ir(pyalk)(CO) 2 (pyalk = (2-pyridyl)-2-propanolate) suggested a μ-oxo-bridged Ir dimer as the probable resting state, although the structure of the active species remained elusive. During the activation, the ligands Cp* and CO were found to oxidatively degrade into acetic acid or other products, which coordinate to Ir centers and affect the catalytic reaction. Two related dimers bearing two pyalk ligands on each iridium were crystallized for structural analysis. However, preliminary results indicated that these crystallographically characterized dimers are not active catalysts. In this work, we accessed a mixture of dinuclear iridium species from a coordination precursor, Na[Ir(pyalk)Cl 4 ], and assayed their catalytic activity for oxygen evolution by using NaIO 4 as the oxidant. This catalyst showed comparable oxygen-evolution activity to the ones previously reported from organometallic precursors without demanding oxidative activation to remove sacrificial ligands. Future research along this direction is expected to provide insights and design principles toward a well-defined active species.

Photo-electrochemical Effect in the Amorphous Cobalt Oxide Water Oxidation Catalyst Cobalt–Phosphate (CoPi)

“…Quantitative lifetime values can be found in Table S2. The first decay lifetime (10s of seconds) is assigned to charge recombination, and the second decay lifetime (100s of seconds) is assigned to hole transfer from surface-state trap sites. ,− A detailed analysis and description of the light-induced OER behavior at potentials significantly below water-splitting (+0.9, +1.11, and +1.21 V) can be found in Figure S16.…”

Highly Active Visible Light-Promoted Ir/g-C3N4 Photocatalysts for the Water Oxidation Reaction Prepared from a Halogen-Free Iridium Precursor

“…Nowadays, iridium­(III) complexes are highlighted as superior homogeneous catalysts for the OER. − Various organic ligands were utilized ,,, to modulate activity and stabilize the iridium active centers in such compounds, but high oxidation potential of oxygen species generated along the OER causes the degradation of the ligands. ,, In this context, the reorientation to the heterogeneous Ir-based catalyst is the natural initiative. − In a view of the rarity of iridium and its high cost, the maximization of metal utilization in heterogeneous catalysts is highly essential; however, typical turnover frequency (TOF) values of iridium heterogeneous OER catalysts are rather low compared to homogeneous analogues. A correct thorough adjustment of the active species size and morphology plays a pivotal role in gaining the highest activity with adequate stability.…”

“…In agreement, the UV−vis spectrum of the carefully separated reaction solution after cycling shows a broad band in the region of 500−700 nm (Figure S14) that gives a light-blue color to the supernatant. Formation of the analogous "Ir-blue" solutions is described for the homogeneous iridium(III) water oxidation catalysts 10,11,13,19,53 and was attributed to the interaction of the Ir complexes with active oxygen, formed during the catalytic process. It is interesting to note that appearance of a very close absorption band after the addition of sodium periodate is also observed for parent Ir_ANC solutions.…”

Selective Methane Oxidation by Heterogenized Iridium Catalysts

“…Motivated by these prior results, here we report a strategy of using heterogenized Ir complexes for direct CH 4 activation. The molecular precursor we used was [Ir­(pyalc)­(H 2 O) 2 (μ-O)] 2 2+ (pyalc = 2-(2′-pyridyl)-2-propanoate), which was developed by one of the authors (Brudvig). , Upon heterogenization on SBA-15 mesoporous silica sieve support with a tunable pore diameter of 5 to 15 nm, it formed a stable catalyst. When used as-prepared in oxidative CH 4 carbonylation, the catalyst produced CH 3 COOH as the main product, with a selectivity of up to 62.1%; when subjected to a mild reduction treatment, the catalyst exhibited 6 times more selectivity of CH 3 OH than as-prepared catalysts.…”

“…which was developed by one of the authors (Brudvig). 25,26 Upon heterogenization on SBA-15 mesoporous silica sieve support with a tunable pore diameter of 5 to 15 nm, it formed a stable catalyst. When used as-prepared in oxidative CH 4 carbonylation, the catalyst produced CH 3 COOH as the main product, with a selectivity of up to 62.1%; when subjected to a mild reduction treatment, the catalyst exhibited 6 times more selectivity of CH 3 OH than as-prepared catalysts.…”