Developing efficient ways to control the nanocluster properties and synthesize atomically precise metal nanoclusters are the foremost goals in the field of metal nanocluster research. In this article, we demonstrate that the direct synthesis of atomically precise, hydrophilic metal nanoclusters as well as tuning of their properties can be achieved by an appropriate selection of reactants, binding ligand, and their proportions. Thus, a facile, single-step method has been developed for the direct synthesis of Au(SCHCOH) nanocluster in an aqueous medium under ambient conditions. The synthesis does not require any pH or temperature control and postsynthesis size-separation step. The use of a hydrophilic, bifunctional short carbon-chain capping ligand, HSCHCOH, allows tuning of cluster properties such as the photoluminescence and stability in an aqueous medium via the variation of pH of the cluster solution. By using a phase transfer catalyst, the nanoclusters can also be transferred into toluene solvent, which further enhances the nanocluster photoluminescence. The formation, composition, and purity of the product clusters have been characterized by using a number of methods such as the polyacrylamide gel electrophoresis, UV-visible and FTIR spectroscopies, transmission electron microscopy, energy dispersive X-ray analysis, thermogravimetric analysis, X-ray photoelectron spectroscopy, and matrix-assisted laser desorption ionization-time-of-flight mass spectrometry. Gold nanoclusters with properties such as water solubility, water-to-organic phase-transfer ability, and tunable stability and photoluminescence are promising for various studies and applications. The work reveals a few principles that can be helpful in the development of a general toolbox for the rational design of size-selective synthesis and properties tuning of the metal nanoclusters.

The counter-intuitive choice of an insulating polymer for embedding electrocatalysts is shown to facilitate a simple and general strategy to fabricate catalytic electrodes for efficient oxygen evolution reaction (OER) during water splitting. The hydrogel characteristics and appreciable swelling of the polymer in aqueous medium are the key enabling factors; electrolyte absorbed in the polymer matrix is likely to be involved in the electrocatalytic process. Nanocomposite thin films of chitosan spin-cast on common conducting substrates, with an optimal content of NiO and [Ni,Fe]O nanoplates generated through a facile and simple in situ protocol, are shown to effect OER with excellent overpotentials (down to 240 mV at 10 mA/ cm 2 ), low Tafel slope, high Faradaic efficiency, appreciable turnover frequency, and extended stability with high current density. Preliminary investigations with a range of catalystpolymer combinations illustrate the general applicability of the approach.The generation of ever more efficient electrocatalysts for the fundamentally important oxygen and hydrogen evolution reactions (OER and HER) has been the prime focus in the water splitting and related energy research front. Equally important and challenging, but relatively less focused on, is the development of simple and general protocols for the fabrication of robust electrodes bearing the catalyst. Methods like electrodeposition are commonly used to fabricate catalytic electrodes, but their temporal stability under electrolysis and gas-forming conditions can be limited; prominent issues include catalyst dissolution requiring compensation by feeding the relevant ions in the electrolyte, [1] and adverse composition changes of mixed metal oxide catalysts over extended electrolytic runs. [2] The critical problem of fixing powder catalysts has been highlighted in recent studies. Mills and coworkers have discussed the relevance of 'powder-to-electrode' fabrication, in particular the utility of a mechanical, solvent-free approach. [3][4][5] The problem has also been addressed by replacing common binders like Nafion having relatively low electrical conductivity, by carbon material generated from polymer precursors; [6] the latter step requires calcination at 450°C. Enhancement of electrode surface wettability using electrochemically inert but super-hydrophilic carbon nitride that enables also wider exposure of the catalyst sites, is another interesting approach, [7] but again involves high temperature (550°C) calcination and multiple fabrication steps. New strategies to fabricate stable catalyst electrodes, avoiding multiple steps and lengthy processing are desirable. We envisioned that hydrogel polymers, even if electrically insulating, would be widely adaptable and versatile matrices for embedding electrocatalysts that carry out efficient water splitting. Swelling of the polymer in aqueous medium makes this unlikely choice of material highly relevant, and an optimal polymer-catalyst combination can ensure a robust and efficient electrode system; ...

Nanocatalysts can potentially harmonize the advantages of homogeneous and heterogeneous catalysts, provided they are sequestered in a suitable host matrix that not only enables convenient introduction into repeated reaction cycles, but also allows facile access for the reaction system. Polymer-metal/semiconductor nanocomposite thin films fabricated through an in situ protocol offer a promising solution involving eco-friendly synthesis and sustainable application. Salient features of the approach include (i) the simple, softchemical fabrication methodology that also allows real-time observation of the catalyst formation, (ii) efficient nano-catalyst action through the facile movement of the reactants and products to and from the catalyst site enabled by the swelling of the polymer matrix, and (iii) realization of the 'dip catalyst' concept that emphasizes the ease of insertion and retrieval of the thin film into and from the reaction system, coupled with the feasibility of effective catalyst monitoring through multiple uses. An overview of the nanocomposite thin film fabrication, types of nanostructures that have been reported in this context, deployment of the thin film 'dip catalysts' in several reactions, and emerging new directions in the field and open problems are presented.[a] U.

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Development of simple and facile protocols for the fabrication of highly efficient and robust catalytic electrodes for water splitting reactions is of paramount interest in establishing clean energy generation strategies. We show that hydrogel polymer thin films, in spite of their insulating character, enable a unique solution of wide scope, combining the ease of in situ fabrication of the electrocatalyst and efficient application. RuO 2 nanoplates are generated within thin films of poly(hydroxyethyl methacrylate) (PHEMA) spincast on Ni foam, through mild thermal annealing. RuO 2 -PHEMA affects efficient hydrogen evolution reaction (HER) in an alkaline medium, with a very low overpotential of 30 mV at a current density of 10 mA cm −2 and stability for 24 h at 40 mA cm −2 ; Faradaic efficiency is 99.6%, and the turnover frequency is 24.2 s −1 at 100 mV overpotential. Experiments with a range of polymers establish a clear correlation between the swelling characteristic of the polymer and the overpotential for HER. Efficient water splitting using a cell with both electrodes based on polymer-semiconductor nanocomposite thin films is also demonstrated. The novel catalytic electrode design offers abundant scope for developing costeffective and scalable strategies for the generation of hydrogen fuel.

Fabrication of gold nanoclusters (GNCs) with tunable fluorescence characteristics inside polymer thin films is attractive from the device application perspective. In this study, GNCs are generated in situ in poly(methyl methacrylate) films exploiting their weak reducing capability with no additional reducing agent, and by short and mild thermal annealing; the chemistry involved is probed through control experiments. The nanoclusters formed with ∼0.5 weight percent of gold are very stable and show appreciable fluorescence emission with a small Stokes shift (∼40 nm); interestingly, blending polystyrene enhances the fluorescence. The Au clusters formed in situ are characterized by using mass spectrometry, microscopy and computational modeling. Composite thin films fabricated with a gold content of ∼9 weight percent showed an unusually distinct absorption peak and enhanced fluorescence emission. Gradual coalescence of the nanoclusters in these films could be arrested by incorporating thiourea; the mechanistic aspects of the thiourea interaction are probed. The resulting films showed strong, stable and visible red emission, with very large Stokes shift (∼320 nm) and quantum yield (∼30%), attributable to ligand effects and nanocluster aggregation in the film. The study presents a novel and facile route to the in situ generation of GNCs in polymer thin films, exhibiting fluorescence emission with variable energy, intensity and Stokes shift. Preliminary experiments show that Au cluster embedded thin films can be used for the detection of POCl, an important precursor for nerve agents.

The Cover Feature shows an insulating polymer–semiconductor nanocomposite thin film used as an electrocatalyst for water oxidation. The critical role of polymer swelling in aqueous electrolyte is highlighted. More information can be found in the Communication by U. Divya Madhuri and T. P. Radhakrishnan on page 1984 in Issue 7, 2019 (DOI: 10.1002/celc.201801659).