The thermodynamic favorability of an alkaline solution for the oxidation of water suggests the need for developing hydrogen evolution reaction (HER) catalysts that can function in basic aqueous solutions so that both of the half reactions in overall water splitting can occur in mutually compatible solutions. Although photocatalytic HERs have been reported mostly in acidic solutions and a few at basic pHs in mixed organic aqueous solutions, visible-light driven HER catalyzed by molecular metal complexes in purely alkaline aqueous solutions remains largely unexplored. Here, we report a new cobalt complex with a tetrapyridylamine ligand that catalyzes photolytic HER with turnover number up to 218 000 in purely aqueous solutions at pH 9.0. Density functional theory (DFT) calculations suggested a modified electron transfer (E)–proton transfer (C)–electron transfer (E)–proton transfer (C) (mod-ECEC) pathway for hydrogen production from the protonation of Co^II–H species. The remarkable catalytic activity resulting from subtle structural changes of the ligand scaffold highlights the importance of studying structure–function relationships in molecular catalyst design. Our present work significantly advances the development of a molecular metal catalyst for visible-light driven HER in more challenging alkaline aqueous solutions that holds substantial promise in solar-driven water-splitting systems.

中文翻译：

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碱性水溶液中钴分子配合物光催化制氢

碱性溶液对水氧化的热力学有利性表明需要开发可以在碱性水溶液中发挥作用的析氢反应（HER）催化剂，以便整个水分解中的两个半反应可以在相互兼容的溶液中发生。尽管光催化HER大多在酸性溶液中报道，少数在混合有机水溶液中的碱性pH下报道，但在纯碱性水溶液中由分子金属配合物催化的可见光驱动的HER仍然很大程度上未被探索。在这里，我们报道了一种具有四吡啶胺配体的新型钴络合物，该络合物可催化光解 HER，在 pH 9.0 的纯水溶液中转换数高达 218 000。密度泛函理论 (DFT) 计算表明，Co ^II –H质子化产生氢气的改进电子转移 (E)-质子转移 (C)-电子转移 (E)-质子转移 (C) (mod-ECEC) 途径物种。配体支架的微妙结构变化所产生的显着催化活性凸显了研究分子催化剂设计中结构-功能关系的重要性。我们目前的工作显着推进了分子金属催化剂的开发，该催化剂可用于更具挑战性的碱性水溶液中的可见光驱动的析氢反应，这在太阳能驱动的水分解系统中具有巨大的前景。