组合掺杂引入新型、多种镉配位方式增强金纳米团簇的电催化性能

Introducing Novel,Multiple Cd Coordination Modes into Gold Nanoclusters by Combined Doping for Enhancing Electrocatalytic Performance

为提高金纳米团簇电催化还原二氧化碳生成一氧化碳的电流密度,本文引入了一种组合掺杂法(同时掺入硫和镉),合成一种新型Au-Cd纳米团簇—Au41Cd6S2(SCH2Ph)33,并对其组成结构进行了精确表征。单晶结构表明,它包含一个双二十面体的Au23内核,所有的镉原子都掺杂在外壳层中且具有多种配位环境,外层staple(类订书针结构)除两个常见的Au3(SR)4三聚体外,还有两条独特的Au5Cd2(SR)9S长staple交叉覆盖在内核顶部,此外还发现了(S-Au-S)2(CdS-S-CdS)四聚体,这种两个Cd原子通过S原子直接相连的结构也为首次报道。与“同核异壳”的Au38(SCH2Ph)24团簇相比,Au41Cd6S2(SCH2Ph)33表现出更高的法拉第效率(−0.7 V电位时达99.3%)和更高的CO分电流密度(−0.9 V电位时为120 mA∙cm^(−2))。利用理论计算结果对Au41Cd6S2(SCH2Ph)33的高催化活性进行了解释,揭示Cd-Cd是最高活性位点,离内核最远的Au-Cd位点在同时考虑活性和选择性的情况下是最优的活性位点。本工作提供了一种提高金纳米团簇催化性能的策略,对金纳米团簇的合成、结构及构效关系研究具有重要的启发意义,有望推动相关研究的开展。

In recent years,gold nanoclusters have been widely used in catalysis,and alloying has become one of the most important methods for improving the catalytic performance of gold nanoclusters.As for the electrocatalytic reduction of CO_(2)(CO_(2)RR),although many gold nanoclusters show fairly good Faraday efficiencies through Cd-doping,they still exhibit low current density.Furthermore,as an increasing number of Au-Cd alloy nanoclusters are reported,there is a growing interest in understanding the correlation between Cd coordination and catalysis performance.In most cases,Cd atoms are typically doped in the outer staples and connect with Au atoms through S coordinations.Are there any other unreported Cd coordination modes?Can novel or numerous Cd coordination modes be introduced into gold nanoclusters to increase the current density in the CO_(2)RR?This study investigates these questions.Inspired by our previous work on surface sulfur doping,we employed a combined doping(S+Cd doping)strategy,developed a two-step synthesis method,and successfully synthesized a novel Au-Cd nanocluster—Au41Cd6S2(SCH2Ph)33.Precise formula and structure were determined by electrospray ionization mass spectrometry(ESI-MS),thermalgravimetric analysis(TGA),X-ray photoelectron spectroscopy(XPS),and single-crystal X-ray crystallography(SCXC).SCXC shows that the nanocluster contains a biicosahedral Au23 kernel,and all the Cd atoms are doped in the outer staples,providing a variety of coordination environments for Cd atoms.In addition to two common Au3(SR)4 trimers in the outer staples,two unusual Au5Cd2(SR)9S long staples were discovered cross-covering the top of the kernel,and a(S-Au-S)2(CdS-S-CdS)tetramer staple with two Cd atoms directly linked through S was also discovered for the first time.This alloy cluster shows robust stability in both high-temperature and oxidation environments.Compared with the“homo-kernel-hetero-staples”nanocluster Au38(SCH2Ph)24,Au41Cd6S2(SCH2Ph)33 exhibits distinct UV-Vis/NIR absorption and differential pulse voltammetry(DPV)results,indicating that the differences in the outer staples have a significant effect on the optical and electronic properties of gold nanoclusters.When used as an electrocatalyst,the Au41Cd6S2(SCH2Ph)33 exhibits a higher Faradaic efficiency for the CO_(2)RR(99.3%at−0.7 V)and a higher CO partial current density(120 mA∙cm^(−2) at−0.9 V)than Au38(SCH2Ph)24,providing an ideal platform for investigating the roles of different Cd coordination modes in outer staples on CO_(2)RR.DFT calculations interpret the experimental finding that Cd doping improves the catalytic performance and reveal that the Cd-Cd site is the most active site and the Au-Cd site furthest away from the kernel is the best-performing catalytic site given the consideration of both selectivity and activity.This work introduces a novel strategy to enhance the catalytic performance of gold nanoclusters,having important implications for future research on the syntheses and structural properties of metal nanoclusters,and is expected to inspire more work in related areas.