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Updated: Sep 27, 2026

Photochemical Oxidative Growth of Iridium Oxide Nanoparticles on CdSe@CdS Nanorods
Published on: February 11, 2016
Benchmarking Water Oxidation Catalysts Based on Iridium Complexes: Clues and Doubts on the Nature of Active Species
Gabriel Menendez Rodriguez1, Giordano Gatto1, Cristiano Zuccaccia1
1Department of Chemistry, Biology and Biotechnology, University of Perugia, Via Elce di Sotto 8, 06123, Perugia, Italy.
Abstract:
Water oxidation (WO) is a central reaction in the photo- and electro-synthesis of fuels. Iridium complexes have been successfully exploited as water oxidation catalysts (WOCs) with remarkable performances. Herein, we report a systematic study aimed at benchmarking well-known Ir WOCs, when NaIO4 is used to drive the reaction. In particular, the following complexes were studied: cis-[Ir(ppy)2 (H2 O)2 ]OTf (ppy=2-phenylpyridine) (1), [Cp*Ir(H2 O)3 ]NO3 (Cp*=1,2,3,4,5-pentamethyl-cyclopentadienyl anion) (2), [Cp*Ir(bzpy)Cl] (bzpy=2-benzoylpyridine) (3), [Cp*IrCl2 (Me2 -NHC)] (NHC=N-heterocyclic carbene) (4), [Cp*Ir(pyalk)Cl] (pyalk=2-pyridine-isopropanoate) (5), [Cp*Ir(pic)NO3 ] (pic=2-pyridine-carboxylate) (6), [Cp*Ir{(P(O)(OH)2 }3 ]Na (7), and mer-[IrCl3 (pic)(HOMe)]K (8). Their reactivity was compared with that of IrCl3 ⋅n H2 O (9) and [Ir(OH)6 ]2- (10). Most measurements were performed in phosphate buffer (0.2 m), in which 2, 4, 5, 6, 7, and 10 showed very high activity (yield close to 100 %, turnover frequency up to 554 min-1 with 10, the highest ever observed for a WO-driven by NaIO4 ). The found order of activity is: 10>2≈4>6>5>7>1>9>3>8. Clues concerning the molecular nature of the active species were obtained, whereas its exact nature remains doubtfully.
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