A pentanuclear iron catalyst designed for water oxidation
A pentanuclear iron catalyst designed for water oxidation
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DOI：
10.1038/nature16529
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发表时间：
2016-02-25
期刊：
影响因子：
64.8
通讯作者：
Masaoka, Shigeyuki
中科院分区：
文献类型：
--
作者：
Okamura, Masaya;Kondo, Mio;Masaoka, Shigeyuki
尽管光系统II(参考文献1和2)中的放氧复合体有效地催化了水的氧化，但它仍然是以阳光或电力为动力的合成化学燃料生产的主要瓶颈之一。因此，开发活性和稳定的水氧化催化剂至关重要，多相体系(3，4)被认为更适合实际使用，而它们的均相体系更适合于在机理理解的指导下进行有针对性的分子水平设计(5-19)。对水氧化机理的研究产生了一系列合成分子催化剂，但人们对使用丰富、廉价和环境友好的金属的系统仍然很感兴趣，例如铁(地壳中含量最丰富的过渡金属，存在于天然(20，21)和合成(22)氧化催化剂中)。基于单核铁络合物(9，12，16，18)的水氧化催化剂已被开发出来，但它们往往失活迅速，表现出相对较低的活性。在这里，我们报道了一种五核铁络合物，它高效而有力地催化水氧化，其周转频率为1900次/秒，比其他铁基催化剂高出约三个数量级。电化学分析证实了该体系的氧化还原柔性，表现为Fe-5(II)和Fe-5(III)之间存在六种不同的氧化状态，Fe-5(III)状态对氧化水具有活性。量子化学计算表明，相邻活性中心的存在促进了O-O键的形成，反应势垒小于每摩尔10千卡。尽管对高过电位的需要和不能在富水溶液中运行限制了本系统的实用性，但我们的研究结果清楚地表明，通过确保该系统具有氧化还原灵活性并包含相邻的水活化中心，可以创建基于铁络合物的高效水氧化催化剂。
Although the oxidation of water is efficiently catalysed by the oxygen-evolving complex in photosystem II (refs 1 and 2), it remains one of the main bottlenecks when aiming for synthetic chemical fuel production powered by sunlight or electricity. Consequently, the development of active and stable water oxidation catalysts is crucial, with heterogeneous systems(3,4) considered more suitable for practical use and their homogeneous counterparts more suitable for targeted, molecular-level design guided by mechanistic understanding(5-19). Research into the mechanism of water oxidation has resulted in a range of synthetic molecular catalysts, yet there remains much interest in systems that use abundant, inexpensive and environmentally benign metals such as iron (the most abundant transition metal in the Earth's crust and found in natural(20,21) and synthetic(22) oxidation catalysts). Water oxidation catalysts based on mononuclear iron complexes have been explored(9,12,16,18), but they often deactivate rapidly and exhibit relatively low activities. Here we report a pentanuclear iron complex that efficiently and robustly catalyses water oxidation with a turnover frequency of 1,900 per second, which is about three orders of magnitude larger than that of other iron-based catalysts. Electrochemical analysis confirms the redox flexibility of the system, characterized by six different oxidation states between Fe-5(II) and Fe-5(III); the Fe-5(III) state is active for oxidizing water. Quantum chemistry calculations indicate that the presence of adjacent active sites facilitates O-O bond formation with a reaction barrier of less than ten kilocalories per mole. Although the need for a high overpotential and the inability to operate in water-rich solutions limit the practicality of the present system, our findings clearly indicate that efficient water oxidation catalysts based on iron complexes can be created by ensuring that the system has redox flexibility and contains adjacent water-activation sites.