Liu Chengyu, van den Bos Daan, den Hartog Barthold, van der Meij Dennis, Ramakrishnan Ashok, Bonnet Sylvestre
Leiden Institute of Chemistry, Leiden University, Einsteinweg 55, PO Box 9502, 2333CC, Leiden, The Netherlands.
Angew Chem Int Ed Engl. 2021 Jun 7;60(24):13463-13469. doi: 10.1002/anie.202103157. Epub 2021 May 7.
Finding photostable, first-row transition metal-based molecular systems for photocatalytic water oxidation is a step towards sustainable solar fuel production. Herein, we discovered that nickel(II) hydrophilic porphyrins are molecular catalysts for photocatalytic water oxidation in neutral to acidic aqueous solutions using [Ru(bpy) ] as photosensitizer and [S O ] as sacrificial electron acceptor. Electron-poorer Ni-porphyrins bearing 8 fluorine or 4 methylpyridinium substituents as electron-poorer porphyrins afforded 6-fold higher turnover frequencies (TOFs; ca. 0.65 min ) than electron-richer analogues. However, the electron-poorest Ni-porphyrin bearing 16 fluorine substituents was photocatalytically inactive under such conditions, because the potential at which catalytic O evolution starts was too high (+1.23 V vs. NHE) to be driven by the photochemically generated [Ru(bpy) ] . Critically, these Ni-porphyrin catalysts showed excellent stability in photocatalytic conditions, as a second photocatalytic run replenished with a new dose of photosensitizer, afforded only 1-3 % less O than during the first photocatalytic run.
寻找用于光催化水氧化的光稳定的第一行过渡金属基分子体系是迈向可持续太阳能燃料生产的一步。在此，我们发现镍（II）亲水性卟啉是以[Ru(bpy)₃]²⁺为光敏剂和[S₂O₈]²⁻为牺牲电子受体，在中性至酸性水溶液中进行光催化水氧化的分子催化剂。作为缺电子卟啉，带有8个氟或4个甲基吡啶鎓取代基的缺电子镍卟啉的周转频率（TOF；约0.65 min⁻¹）比富电子类似物高6倍。然而，带有16个氟取代基的最缺电子镍卟啉在这种条件下没有光催化活性，因为催化析氧开始时的电位过高（相对于标准氢电极+1.23 V），无法由光化学产生的[Ru(bpy)₃]²⁺驱动。至关重要的是，这些镍卟啉催化剂在光催化条件下表现出优异的稳定性，因为在第二次光催化运行中补充新剂量的光敏剂后，析氧量仅比第一次光催化运行时少1-3 %。
