Ho Xian Liang, Shao Haiyan, Ng Yik Yie, Ganguly Rakesh, Lu Yunpeng, Soo Han Sen
Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences , Nanyang Technological University , 637371 , Singapore.
Solar Fuels Laboratory , Nanyang Technological University , 50 Nanyang Avenue , 639798 , Singapore.
Inorg Chem. 2019 Jan 22;58(2):1469-1480. doi: 10.1021/acs.inorgchem.8b03003. Epub 2019 Jan 4.
Hydrogen (H) is a clean fuel that can potentially be a future solution for the storage of intermittent renewable energy. However, current H production is mainly dominated by the energy intensive steam reforming reaction, which consumes a fossil fuel, methane, and emits copious amounts of carbon dioxide as one of the byproducts. To address this challenge, we report a molecular catalyst that produces H from aqueous solutions, is composed of affordable, earth-abundant elements such as nickel, and has been incorporated into a system driven by visible light. Under optimized conditions, we observe a turnover number of 3880, among the best for photocatalytic H evolution with nickel complexes from water-methanol solutions. Through nanosecond transient absorption, electron paramagnetic resonance, and UV-vis spectroscopic measurements, and supported by density functional theory calculations, we report a detailed study of this photocatalytic H evolution cycle. We demonstrate that a one-electron reduced, predominantly ligand-centered, reactive Ni intermediate can be accessed under visible light irradiation using triethylamine as the sacrificial electron donor and reductive quencher of the initial photosensitizer excited state. In addition, the computational calculations suggest that the second coordination sphere ether arms can enhance the catalytic activity by promoting proton relay, similar to the mechanism among [FeFe] hydrogenases in nature. Our study can form the basis for future development of H evolution molecular catalysts that incorporate both ligand redox noninnocence and alternative second coordination sphere effects in artificial photosynthetic systems driven by visible light.
氢（H）是一种清洁燃料，有望成为未来间歇性可再生能源存储的解决方案。然而，目前氢气的生产主要由能源密集型的蒸汽重整反应主导，该反应消耗化石燃料甲烷，并产生大量二氧化碳作为副产物之一。为应对这一挑战，我们报道了一种分子催化剂，它能从水溶液中产生氢气，由镍等价格低廉、储量丰富的元素组成，并已被整合到一个由可见光驱动的系统中。在优化条件下，我们观察到其周转数为3880，这在从水 - 甲醇溶液中通过镍配合物进行光催化析氢中处于最佳水平之一。通过纳秒瞬态吸收、电子顺磁共振和紫外 - 可见光谱测量，并在密度泛函理论计算的支持下，我们对这个光催化析氢循环进行了详细研究。我们证明，使用三乙胺作为牺牲电子供体和初始光敏剂激发态的还原猝灭剂，在可见光照射下可以得到一种单电子还原的、主要以配体为中心的活性镍中间体。此外，计算结果表明，第二配位层的醚臂可以通过促进质子传递来增强催化活性，这类似于自然界中[FeFe]氢化酶的作用机制。我们的研究可为未来在可见光驱动的人工光合系统中开发兼具配体氧化还原非无辜性和替代第二配位层效应的析氢分子催化剂奠定基础。
