WATLab and Department of Chemistry, University of Waterloo, Waterloo, Ontario N2L3G1, Canada.
Nanoscale. 2017 Oct 5;9(38):14395-14404. doi: 10.1039/c7nr04378c.
Formation of nanoclusters has attracted a lot of attention in recent years because of their distinct properties from isolated atoms and bulk solids. Here, we focus on the catalytic properties of supported transition metal oxide nanoclusters, such as TaO, with a well-defined size distribution below 10 nm. We show that their catalytic performance can be greatly enhanced by introducing a reaction promoter such as Pt. Different combinations of precisely size-selected, defect-rich TaO and Pt nanoclusters are produced by a gas-phase aggregation technique in a special DC magnetron sputtering system. Argon flow rate and aggregation length are carefully optimized to control the sizes of these ultrasmall TaO and Pt nanoclusters by using a quadrupole mass filter, and TEM studies reveal the different crystalline nature of TaO (amorphous) and Pt (crystalline) nanoclusters. We have further demonstrated the size-dependent photoanode activity of (TaO, Pt) nanocluster systems in a photoelectrochemical water splitting reaction, where the Pt nanocluster promoters are found to provide a significant enhancement in the photocurrent density, approximately tripled that was observed from just TaO nanocluster catalysts alone. The photocurrent density and photoconversion efficiency tend to reduce when Pt nanoclusters become overpopulated due to blocking of the photosensitive TaO surface. Reducing the Pt nanocluster size resolves this problem by incorporating a greater number of smaller nanocluster promoters without blocking TaO, which leads to further enhancement in the photocurrent density. The enhanced photocatalytic activity is attributed to synergetic effects introduced by the Pt nanoclusters that act as temporary charge storage sites to facilitate effective separation of a large number of electron-hole pairs, generated from a large number of active sites on the defect-rich amorphous TaO nanoclusters upon illumination.
纳米团簇的形成近年来引起了广泛关注，因为它们具有不同于孤立原子和体相固体的独特性质。在这里，我们重点研究了负载型过渡金属氧化物纳米团簇（如 TaO）的催化性质，这些纳米团簇的尺寸分布在 10nm 以下，具有良好的定义。我们表明，通过引入反应促进剂（如 Pt）可以大大增强其催化性能。通过在特殊的直流磁控溅射系统中的气相团聚技术，制备了不同组合的精确尺寸选择、富含缺陷的 TaO 和 Pt 纳米团簇。氩气流速和团聚长度被仔细优化，以通过四极质量过滤器控制这些超小 TaO 和 Pt 纳米团簇的尺寸，TEM 研究揭示了 TaO（非晶态）和 Pt（晶态）纳米团簇的不同晶体性质。我们进一步证明了（TaO、Pt）纳米团簇体系在光电化学水分解反应中的尺寸依赖性光阳极活性，其中 Pt 纳米团簇促进剂被发现显著提高了光电流密度，大约是单独使用 TaO 纳米团簇催化剂时的三倍。当由于光敏 TaO 表面被阻塞而使 Pt 纳米团簇过度聚集时，光电流密度和光电转换效率趋于降低。通过将更多的较小纳米团簇促进剂结合到 TaO 中而不阻塞 TaO，可以解决这个问题，从而进一步提高光电流密度。增强的光催化活性归因于 Pt 纳米团簇引入的协同效应，这些纳米团簇充当临时电荷存储位点，有利于有效地分离大量电子-空穴对，这些电子-空穴对是由富含缺陷的非晶态 TaO 纳米团簇上的大量活性位点在光照下产生的。
