Recent Advances in the Field of Iridium‐Catalyzed Molecular Water Oxidation

Selective Electrochemical Oxidation of Lactic Acid Using Iridium-Based Catalysts

“…10 This emphasizes approaches that maximize activity of small amounts of precious metal catalysts for cost-effective utilization, a prominent research direction in this field. 11,12 Using lessons like these, that have been learned from research in renewable fuels, we can find new value for water oxidation catalysts by applying these materials to supply protons and electrons in other fuel-generating reactions. Primarily in the waste-to-value industry, there are numerous easily oxidizable wastewater streams, 13 and many have not received as much attention as they are having impact on the environment.…”

“…Iridium-based catalysts are being used for oxidative chemical synthesis and wastewater treatment, but do not draw the same attention as when used for renewable fuels. , In these cases, the scarcity of iridium is not a major factor because its use is restricted to niche applications or, in the case of larger-scale uses, a very small amount of the material is able to suffice due to its high catalytic activity and resistance to corrosion when compared to nonprecious metals . This emphasizes approaches that maximize activity of small amounts of precious metal catalysts for cost-effective utilization, a prominent research direction in this field. , …”

Vibrational Signatures of Electronic Properties in Oxidized Water: Unraveling the Anomalous Spectrum of the Water Dimer Cation

“…One potentially fruitful avenue for renewables is the storage of solar energy in chemical bonds, , such as the electrochemical splitting of water into molecular hydrogen and oxygen. − The water-splitting process provides as many questions for the field of chemistry, however, as it provides promises for renewable-energy technologies. Many viable catalysts have been developed for the more difficult water-oxidation process, ,− for example, but unraveling the detailed, inner-sphere redox mechanisms − remains a challenge that hampers continued progress toward the development of efficient, robust catalysts …”

Extremely Active, Tunable, and pH-Responsive Iridium Water Oxidation Catalysts

“…Iridium organometallic precursors have attracted much attention because they provide extremely efficient catalysts , whose performances are strongly affected by the nature of ancillary ligands. , Among the various ligand functionalizations reported to date, it has been shown that the introduction of OH-moiety in the pyridine ring directly bonded to the iridium center causes a dramatic alteration of the nature of the active species and catalytic performances. − Particularly, Fukuzumi and co-workers showed that [Cp*Ir­(4,4′-R 2 -2,2′-bpy)­(H 2 O)] 2+ precursors (R = OH, OMe, Me, and COOH; bpy = bipyridine) generate extremely efficient catalytic species (TOF max = 45 min –1 , TOF = turnover frequency), especially when R = OH, likely due to the formation of iridium hydroxide nanoparticles, in water oxidation driven by cerium ammonium nitrate (CAN) . Later, Papish and co-workers reported [Cp*Ir­{4,4′-(OH) 2 -2,2′-bpy}­Cl] + and [Cp*Ir­{6,6′-(OH) 2 -2,2′-bpy}­Cl] + as pH-responsive precatalysts for water oxidation (WO) driven by NaIO 4 that showed high catalytic activity (TOF max = 112 min –1 ) at pH close to neutrality. , Finally, Fujita and co-workers also investigated the water oxidation catalytic activity of [Cp*Ir­{6,6′-(OH) 2 -2,2′-bpy}­(H 2 O)] 2+ and analogous tetrahydoxy-bipyrimidine mononuclear and dinuclear iridium complexes confirming their pH-responsive performances with NaIO 4 with TOF among the highest ever reported (210 min –1 ) in phosphate buffer at pH 7.2 …”

“…11−14 Generally speaking, the advantage of exploiting heterogenized catalysts stems from the possibility of preliminarily optimizing the electronic and steric features of the metal center, before the anchorage, through the appropriate selection of the ligand framework. 15,16 Iridium organometallic precursors have attracted much attention because they provide extremely efficient catalysts 17,18 whose performances are strongly affected by the nature of ancillary ligands. 19,20 Among the various ligand functionalizations reported to date, it has been shown that the introduction of OH-moiety in the pyridine ring directly bonded to the iridium center causes a dramatic alteration of the nature of the active species and catalytic performances.…”