Activation pathways taking place at molecular copper precatalysts for the oxygen evolution reaction

\u3cp\u3eThe activation processes of [Cu\u3csup\u3eII\u3c/sup\u3e(bdmpza)\u3csub\u3e2\u3c/sub\u3e] in the water oxidation reaction were investigated using cyclic voltammetry and chronoamperometry. Two different paths wherein CuO is formed were distinguished. [Cu\u3csup\u3eII\u3c/sup\u3e(bdmpza)\u3csub\u3e2\u3c/sub\u3e] can be oxidized at high potentials to form CuO, which was observed by a slight increase in catalytic current over time. When [Cu\u3csup\u3eII\u3c/sup\u3e(bdmpza)\u3csub\u3e2\u3c/sub\u3e] is initially reduced at low potentials, a more active water oxidation catalyst is generated, yielding high catalytic currents from the moment a sufficient potential is applied. This work highlights the importance of catalyst pre-treatment and the choice of the experimental conditions in water oxidation catalysis using copper complexes.\u3c/p\u3

Detangling catalyst modification reactions from the oxygen evolution reaction by online mass spectrometry

\u3cp\u3eHere we showcase the synthesis and catalytic response of the anionic iridium(III) complex [IrCl\u3csub\u3e3\u3c/sub\u3e(pic)(MeOH)]\u3csup\u3e-\u3c/sup\u3e ([1]\u3csup\u3e-\u3c/sup\u3e, pic = picolinate) toward the evolution of oxygen. Online electrochemical mass spectrometry experiments illustrate that an initial burst of CO\u3csub\u3e2\u3c/sub\u3e due to catalyst degradation is expelled before the oxygen evolution reaction commences. Electrochemical features and XPS analysis illustrate the presence of iridium oxide, which is the true active species. (Chemical Equation Presented).\u3c/p\u3

Variation of salivary immunoglobulins in exercising and sedentary populations

When exposed to a potential exceeding 1.5 V versus RHE for several minutes the molecular iridium bishydroxide complex bearing a pentamethylcyclopentadienyl and a N-dimethylimidazolin-2-ylidene ligand spontaneously adsorbs onto the surface of glassy carbon and gold electrodes. Simultaneously with the adsorption of the material on the electrode, the evolution of dioxygen is detected and modifications of the catalyst structure are observed. XPS and XAS studies reveal that the species present at the electrode interface is best described as a partly oxidized molecular species rather than the formation of large aggregates of iridium oxide. These findings are in line with the unique kinetic profile of the parent complex in the water oxidation reaction

Relevance of chemical vs electrochemical oxidation of tunable carbene iridium complexes for catalytic water oxidation

\u3cp\u3eBased on previous work that identified iridium(III) Cp* complexes containing a C,N-bidentate chelating triazolylidene-pyridyl ligand (Cp* = pentamethylcyclopentadienyl, C \u3csub\u3e5\u3c/sub\u3eMe \u3csub\u3e5\u3c/sub\u3e \u3csup\u3e–\u3c/sup\u3e) as efficient molecular water oxidation catalysts, a series of new complexes based on this motif has been designed and synthesized in order to improve catalytic activity. Modifications include specifically the introduction of electron-donating substituents into the pyridyl unit of the chelating ligand (H, a; 5-OMe, b; 4-OMe, c; 4-tBu, d; 4-NMe \u3csub\u3e2\u3c/sub\u3e, e), as well as electronically active substituents on the triazolylidene C4 position (H, 8; COOEt, 9; OEt, 10; OH, 11; COOH, 12). Chemical oxidation using cerium ammonium nitrate (CAN) indicates a clear structure-activity relationship with electron-donating groups enhancing catalytic turnover frequency, especially when the donor substituent is positioned on the triazolylidene ligand fragment (TOF \u3csub\u3emax\u3c/sub\u3e = 2500 h \u3csup\u3e–\u3c/sup\u3e \u3csup\u3e1\u3c/sup\u3e for complex 10 with a MeO group on pyr and a OEt-substituted triazolylidene, compared to 700 h \u3csup\u3e–\u3c/sup\u3e \u3csup\u3e1\u3c/sup\u3e for the parent benchmark complex without substituents). Electrochemical water oxidation does not follow the same trend, and reveals that complex 8b without a substituent on the triazolylidene fragment outperforms complex 10 by a factor of 5, while in CAN-mediated chemical water oxidation, complex 10 is twice more active than 8b. This discrepancy in catalytic activity is remarkable and indicates that caution is needed when benchmarking iridium water oxidation catalysts with chemical oxidants, especially when considering that application in a potential device will most likely involve electrocatalytic water oxidation. \u3c/p\u3