Insights of the efficient hydrogen evolution reaction performance in bimetallic Au4Cu2 nanoclusters.

The design of efficient electrocatalysts for improving hydrogen evolution reaction (HER) performance using atomically precise metal nanoclusters (NCs) is an emerging area of research. Here, we have studied the HER electrocatalytic performance of monometallic Cu6 and Au6 nanoclusters and bimetallic Au4Cu2 nanoclusters. A bimetallic Au4Cu2/MoS2 composite exhibits excellent HER catalytic activity with an overpotential (η10) of 155 mV vs. reversible hydrogen electrode observed at 10 mA cm-2 current density. The improved HER performance in Au4Cu2 is due to the increased electrochemically active surface area (ECSA), and Au4Cu2 NCs exhibits better stability than Cu6 and Au6 systems and bare MoS2. This augmentation offers a greater number of active sites for the favorable adsorption of reaction intermediates. Furthermore, by employing X-ray photoelectron spectroscopy (XPS) and Raman analysis, the kinetics of HER in the Au4Cu2/MoS2 composite were elucidated, attributing the favorable performance to better electronic interactions occurring at the interface between Au4Cu2 NCs and the MoS2 substrate. Theoretical analysis reveals that the inherent catalytic enhancement in Au4Cu2/MoS2 is due to favorable H atom adsorption over it and the smallest ΔGH* value. The downshift in the d-band of the Au4Cu2/MoS2 composite influences the binding energy of intermediate catalytic species. This new catalyst sheds light on the structure-property relationship for improving electrocatalytic performance at the atomic level.

Co-reactant-Free Transformation in Atomically Precise Metal Nanoclusters.

Transformation chemistry has advanced significantly in recent years as an excellent methodology for synthesizing new nanoclusters and functionalizing the existing ones. However, rational synthesis and fundamental understanding of the structural evolution among clusters have not yet been achieved in nanocluster science. A deeper understanding of the fundamental aspects of structure-property correlation is necessary for the employment of befitting nanoclusters for specific applications. Very recently, the transformation of nanoclusters without the use of conventional co-reactants has been brought to light. These co-reactant-less transformations are triggered by various conditions, such as pH, solvent, light, temperature, etc. In this perspective, we discuss how this unique method of transformation without any co-reactant benefits the basic understanding of growth patterns and the corresponding property evolution in nanoclusters.

Incorporating Au11 nanoclusters on MoS2 nanosheet edges for promoting the hydrogen evolution reaction at the interface.

The electrocatalytic hydrogen evolution reaction (HER) holds grip as a promising strategy to obtain renewable energy resources in the form of clean fuel - hydrogen (H2). However, understanding the catalytic mechanism at the atomic level for sustainable and efficient production of hydrogen remains an arduous challenge. In this regard, atomically precise nanoclusters (NCs) with their molecule-like properties can be utilized for a better understanding of the mechanism at the catalytic interface, identification of active sites, and much more. Herein, we report a strategy to enhance the HER activity of the well-known electrocatalyst MoS2 by the incorporation of atomically precise gold nanoclusters, Au11(PPh3)7I3. Interestingly, Au11(PPh3)7I3 NCs were impregnated onto MoS2 nanosheets without protecting ligands as naked Au11 clusters which have increased atom efficiency. Different loadings of Au11(PPh3)7I3 nanoclusters on MoS2 nanosheets revealed the superior HER activity of 2% loading of the NCs. Theoretical calculations have shown that the nanocomposite has the optimum hydrogen adsorption energy that is crucial for efficient H2 production. Combined experimental and theoretical results provide the atomic-level understanding of the utilization of electrochemically dormant ligand-protected NCs to accelerate the HER activity of MoS2 nanosheets.

Gold Deassembly: From Au44(SPh-tBu)28 to Au36(SPh-tBu)24 Nanocluster through Dynamic Surface Structure Reconstruction.

Molecular level understanding of the structural growth patterns and property evolution in nanoclusters (NCs) is crucial for the design and rational synthesis of clusters for specific properties and applications. In this regard, transformation has always been a versatile approach to achieve atomic precision with atomic purity and a deeper understanding of the growth mechanisms of noble metal NCs. To the latter end, we have demonstrated a structural transformation of Au44(SPh-tBu)28 to Au36(SPh-tBu)24 NC, which occurred through the deassembly of an Au8(SPh-tBu)4 fragment. Kinetic studies conducted on the transformation showed that it follows zero-order kinetics with a low activation energy pathway. Theoretical studies demonstrated that this process happens via surface restructuring of the core-ligand interface, which was found to be the rate-determining step of this transformation. Based on this, a plausible mechanistic pathway for the transformation have been proposed which we envision, will provide useful insights into NC structure evolution.

A N,N-dimethylformamide protected rhodium nanocluster with engrossing optical properties and its application.

Here, we present the synthesis and characterization of a new N,N-dimethylformamide (DMF) protected rhodium nanocluster (Rh NC) and its interesting optical properties. These small clusters are emissive and exhibit inhomogeneous broadening. The origin of the inhomogeneous broadening and emission behavior were investigated through detailed photo-physical studies. In this study, we demonstrated that the charge transfer from ligand to metal (DMF to Rh) was the source of the emission. Interactions between the polar DMF protected Rh NC and the solvent in the ground state generate inhomogeneous broadening. We probed the emission behavior for the detection of toxic metal ions. Photo-physical studies established the static mechanism of this sensing behavior.