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Wen Zhang, Ph.D., P.E., BCEE
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Dr. Wen Zhang’s group in New Jersey Institute of Technology reported a novel AFM-SECM technique which can examine facet/shape-dependent electronic and electrochemical properties in nanoscale. Cuprous oxide (Cu2O) has extensively been studied owing to its excellent optical, magnetic, and catalytic properties. Many of these properties are facet-dependent and have not been well elucidated. This work synthesized cubic, cuboctahedral, octahedral, and rhombic dodecahedral shaped Cu2O nanocrystals of ∼300 nm in size to evaluate the facet-dependent electrochemical activities. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were firstly used to reveal the average electrochemical activities at the ensemble level. Atomic force microscopy-scanning electrochemical microscopy (AFM-SECM) was further used to assess the electrochemical activities of different Cu2O nanocrystals at the facet level. Hexaammineruthenium (III) chloride ({Ru(NH3)6}Cl3) was employed as the probe molecules that reacted with four different Cu2O nanocrystals under ‒400 mV and yielded ∼300 pA current between the probing tip and the nanocrystal surface. The tip-current mapping results indicate that rhombic dodecahedral Cu2O exhibits higher electrocatalytic activity than other shaped Cu2O, due to the presence of dominant exposed facet of {110} as indicated by the high current. Density-functional theory (DFT) calculations confirmed the facet dependence of local surface energy and electronic structure of Cu2O nanocrystals. Besides electrochemical activity, the surface work function and adsorptive properties were both observed to vary with the shape and dominant exposed facets of Cu2O. This study presented a unique experimental and computational chemistry approach to analyze surface electrochemical properties of Cu2O crystals at a crystalline facet level. This study is supported by the US National Science Foundation (Award#: 1756444), NSF INTERN grant (Award number: 1836036) and the New Jersey Water Resources Research Institute (NJWRRI) Grant (Project Number: 2020NJ025B).
Mr. Qingquan Ma is a Ph.D. candidate in Environmental Engineering at NJIT. He received his B.S. in 2016 and M.S. in 2018 from Beihang University. Mr. Ma’s research focuses on the synthesis and characterization of facet-dependent nano-catalysis, electrocatalysis, density functional theory (DFT) and multidisciplinary research in material characterization and electrochemical membrane processes.
Elucidating Facet Dependent Electronic and Electrochemical Properties of Cu2O Nanocrystals using AFM/SCEM and DFT
第一作者：马清泉
通讯作者：张文
通讯单位：新泽西理工学院
https://doi.org/10.1016/j.nantod.2022.101538
文章摘要
新泽西理工大学土木与环境工程系张文教授课题组近期于Nano today发表研究论文, 报道了利用扫描电化学原子力显微镜, 表面电位显微镜以及结合密度泛函理论(DFT) 阐明不同氧化亚铜晶面的电子能带结构和电化学响应特性。氧化亚铜具有出色的光学、磁学和催化性能，然而这些与晶面相关的性质并没有得到很好的阐释。该项研究合成了立方体、立方八面体、八面体和菱形十二面体形状的氧化亚铜纳米材料，用以评估不同晶面的电化学活性。首先，利用循环伏安法（CV）和电化学阻抗法（EIS）揭示大尺度水平上不同形貌/晶面的平均电化学活性。进一步使用扫描电化学原子力显微镜（AFM-SECM）来评估不同氧化亚铜纳米材料在纳米尺度上的电化学活性。实验用氯化六氨合钌作为探针分子，施加-400 mV电压来测试四种不同的氧化亚铜纳米材料的电化学响应。扫描电化学结果表明，由于菱形十二面体主要为{110}面，菱形十二面体氧化亚铜比其他形状的氧化亚铜表现出更高的电流信号。密度函数理论（DFT）模拟计算进一步证实了氧化亚铜纳米材料的表面能和电子结构与晶面的相关性。除了电化学活性，氧化亚铜纳米材料表面电位和吸附性能都随着其形貌/晶面发生变化。这项研究提出了一种纳米尺度测试和计算化学相结合，能够在晶面水平上分析纳米材料的表面电化学特性的方法。该研究基于扫描电化学平台，可用于理解表面或界面电化学反应的异质性。
扫描电化学原子力显微镜(AFM-SECM)结合密度泛函理论(DFT) 阐明氧化亚铜不同晶面的电子和电化学特性