Quantized Double‐Layer Charging of Rhodium₂₀₅₇(Tridecylamine)₃₂₁ Clusters Using Differential Pulse and Cyclic Voltammetry

Abstract

Metallic and semiconducting nanoclusters stabilized by a variety of organic monolayers of thiols, amines, and carboxylic acids have received considerable attention in the past decade because of their size-and shape-dependent electronic, chemical, and electrochemical properties, especially because of the ease with which they show discrete single-electron-transfer behavior, also known as quantized double-layer (QDL) charging. [1][2][3][4] This phenomenon has been extensively studied for some systems, using techniques such as scanning tunneling microscopy (STM), cyclic voltammetry (CV), and differential pulse voltammetry (DPV), within a narrow size domain (ca. 1-2 nm). [1][2][3][4] In addition, earlier reports have demonstrated QDL-charging behavior of larger-core clusters (e.g., Au 1400 , Au 2869 ), where surface adsorption plays an important role. [5][6][7] Also, much of the effort aimed at observing the QDL charging of smaller monolayer-protected clusters (MPCs) (1-2 nm) has involved the use of gold particles, with a few exceptions such as Ag, [8] Pd, [9] and Cu, [10] and semiconducting systems such as Si [11] and CdTe.[12]Most of the reports have discussed the synthesis of smaller metal particles and their electrochemical properties, suggesting a tiny-capacitor model for metal nanoclusters that show multiple peaks in voltammetric experiments, corresponding to QDL charging (a single-electron-transfer phenomenon in this size regime). STM studies under high vacuum at 83 K also reveal a reversible "Coulomb blockade" (CB) phenomenon, with multiple equidistant charging steps with different bias. [1] However, so far no report is available that shows both solution phase and solid-state CB effects in the case of transition metal nanoclusters such as Pt and Rh, despite their significance. Consequently, there is an urgent need to explore synthetic procedures in order to obtain monodispersed nanoclusters of Rh: being able to tune their size-and shape-dependent properties is important. More significantly, soluble Rh catalysts would be especially useful for many industrial catalytic processes. For example, polyoxo-anion-stabilized Rh(0) clusters have shown excellent performance, as illustrated by a total turnover (TTO) of 193 000 and 2600 for the hydrogenation of olefin and arenes, respectively.[13] However, their stability is limited because the capping agent is not robust and, more significantly, none of them have indicated a singleelectron-transfer phenomenon.To fill this lacuna, we report here for the first time discrete single-electron-transfer behavior of Rh MPCs stabilized by tridecylamine (TDA) in the (4.9 ± 0.2) nm size regime. A series of evenly spaced redox peaks have been observed at room temperature (298 K), which correspond to the limiting currents controlled by the diffusion of smaller particles towards the electrode surface, thus also facilitating the adsorption of Rh MPCs.The core diameter of the MPCs was calculated by using transmission electron microscopy (TEM) and also confirmed by using DPV, utilizing the...

Highly monodisperse cubic and octahedral rhodium nanocrystals: Their evolutions from sharp polyhedrons into branched nanostructures and surface-enhanced Raman scattering

“…However, this resulted in Rh nanoparticles of 2-10 and 6-20 nm with variable, poorly defined shapes at 120 1C, especially the formation of Rh nanoparticles in the heterogeneous growth and more than 90% of branched Rh nanoparticles (such as tripods and tetrapods). Recently, the phenomenon of intriguing quantized double-layer charging of Rh 2057 (tridecylamine) 321 clusters of metal core $ 4.9 nm has been studied by using differential pulses and cyclic voltammetry [33]. Most researches on the synthesis of Rh nanoparticles by polyol method have led to tailor their size and shape just simply by varying the experimental conditions [29][30][31][32][33][34], such as using H 2 , Ar, N 2 , and other gases for the reduction of Rh salt, even at high temperatures and high pressures [32].…”

Enhanced electrocatalytic performance of interconnected Rh nano-chains towards formic acid oxidation

“…[11][12][13] Despite its high cost, Rh is an attractive material which needs to be exploited properly for fuel cell applications in view of its higher tolerance for CO (present inadvertently in the fuel stream or formed as intermediates in some cases, such as when methanol is used) with respect to Pt and more significantly due to its better sizedependant electrocatalytic properties. 14,15 Moreover, it has several unique capabilities like chemical inertness towards mineral acids and its specific catalytic activity for a variety of organic transformations 13 on single crystals, 16 multivalent redox capability 17 and ability to act as a supported catalyst on a variety of flat oxide substrates. 18,19 However, the dependence of the rate of formic acid oxidation on the Rh nanoparticles is not entirely understood.…”

Electrodeposition of Rhodium Nanowires Arrays and Their Morphology-Dependent Hydrogen Evolution Activity

“…Rhodium (Rh) is a well-known metal belonging to the platinum group and exhibiting outstanding catalytic properties in many important applications [ 1 , 2 , 3 ]. Despite its high cost, Rh is still attractive because it has specific chemical properties which allow the catalyzation of specific chemical reactions [ 4 , 5 , 6 , 7 , 8 ]. Moreover, Rh has several superior properties like chemical inertness towards mineral acids, low electrical resistance for electrical device applications and reflective properties for ornamental use.…”