Abstract Due to its simplicity, flexibility and conformity, electroless plating presents itself as an attractive route towards functional metal nanostructures. Despite the importance for creating multimetallic materials with enhanced properties, the complex interactions between the components in electroless plating baths make alloy formations a challenging objective. In this work, we outline an electroless plating strategy fabricating Pd−Pt alloy nanomaterials, which is based on arbitrarily miscible plating baths for the individual metals. To demonstrate the excellent nanoscale conformity and homogeneity of our plating system, we apply it to ion track‐etched polymer templates with large inner surfaces as ambitious substrates, resulting in the formation of 3D free‐standing PdxPt100‐x‐nanotube‐networks (NTNWs). Based on the electro‐oxidation of methanol as a model reaction, we utilize the compositional freedom provided by our syntheses for optimizing the catalytic performance of our metal NTNWs, which heavily depends on the Pd−Pt ratio. Within our system, the highest surface normalized activity was found for the Pd20Pt80 NTNW, reaching more than a two‐fold increase of the peak current density in comparison to pure Pt. Overall, our reaction system provides a versatile toolkit for fabricating intricate Pd−Pt nanostructures of arbitrary elemental composition, and constitutes a starting point for designing new electroless alloy plating baths.

Understanding the electrical and thermal transport properties of polycrystalline metallic nanostructures is of great interest for applications in microelectronics. In view of the diverse experimental results in polycrystalline metallic nanowires and nanofilms, it is a long-standing question whether their electrical and thermal properties can be well predicted by a practical model. By eliminating the effects of electrical and thermal contact resistances, we measure the electrical and thermal conductivities of three different polycrystalline Pt nanowires. The electron scattering at the surface is found to be diffusive, and the charge reflection coefficient at grain boundaries is proved to be a function of the melting point. The Lorenz number is observed to be suppressed from the free-electron value by about 30%, which can be explained by introducing a thermal reflection coefficient in calculating the thermal conductivity to account for the small angle scattering effect involving phonons at the grain boundaries. Using this model, both the electrical and thermal conductivities of the polycrystalline Pt nanowires are calculated at different diameters and temperatures.

Nano-objects are favored structures for applications such as catalysis and sensing. Although they already provide a large surface-to-volume ratio, this ratio can be further increased by shape-selective plating of the nanostructure surfaces. This process combines the conformity of autocatalytic deposition with the defined nucleation and growth characteristics of colloidal nanoparticle syntheses. However, many aspects of such reactions are still not fully understood. In this study, we investigate in detail the growth of spiky nickel nanotubes in polycarbonate template membranes. One distinctive feature of our synthesis is the simultaneous growth of nanospikes on both the inside and outside of nanotubes while the tubes are still embedded in the polymer. This is achieved by combining the plating process with locally enhanced in situ etching of the poylmer template, for which we propose a theory. Electron microscopy investigations reveal twinning defects as the driving force for the growth of crystalline nanospikes. Deposit crystallinity is ensured by the reducing agent hydrazine. Iminodiacetic acid is not only used as a complexing agent during synthesis but apparently also acts as a capping agent and limits random nucleation on the spike facets. Finally, we apply our synthesis to templates with interconnected pores to obtain free-standing spiky nickel nanotube networks, demonstrating its ability to homogeneously coat substrates with extended inner surfaces and to operate in nanoscale confinement.

Free-standing 3D metal nanostructures represent an upcoming class of electrocatalysts for fuel cell technology, combining high aging stability and activity with efficient metal utilization while abstaining from additives such as polymer binders. Until now, most fabrication routes are complex and produce disordered nanostructures. Here, we present a highly adjustable, wet-chemical synthesis route toward ordered, thin-walled Pt nanotube networks. The approach includes an optimized electroless plating procedure and enables easy regulation of structural parameters (i.e. nanotube diameter, wall thickness, density) by using ion track-etched polycarbonate templates. In comparison to individual nanotubes, the resulting nanonetworks exhibit a free-standing and robust frame, which is a great advantage for use in various electrochemical and catalytic applications. Cyclic voltammetry studies of the methanol oxidation reaction demonstrate enhanced electrocatalytic activity compared to commercially available Pt nanoparticles. The nanonetworks provide outstanding long-life stability with up to 97% of the initial active surface area after 1000 cycles, which makes them a promising material in different application fields, for example, in direct methanol fuel cells.

Pt-decorated \(\hbox {TiO}_{2}\) nanotubes Pt@TiO2 are prepared only by applying a set of facile wet-chemical redox reactions to ion track-etched polycarbonate templates. First, a homogeneous layer of Pt nanoparticles is deposited onto the complex template surface by reducing potassium tetrachloroplatinate with absorbed dimethylaminoborane. Second, the template is coated with a conformal \(\hbox {TiO}_{2}\) layer, using a chemical bath deposition reaction based on titanium(III) chloride. After the removal of the template, the rutile-type \(\hbox {TiO}_{2}\) nanotubes remain decorated with Pt nanoparticles and nanoparticle-clusters on their outside. During the process, neither vacuum techniques nor external current sources or addition of heat are employed. The crystallinity, composition, and morphology of the composite nanotubes are analysed by X-ray diffraction, scanning and transmission electron microscopy as well as by energy-dispersive X-ray spectroscopy. Finally, the obtained materials are examplarily applied in the electrooxidation of ethanol and formic acid, and their performances have been evaluated. Compared to conventional carbon black-supported Pt nanoparticles, the Pt@TiO2 nanotubes show higher reaction rates. Mass activities of 2.36 \(\hbox {A}\hbox { mg}_{\rm Pt}^{-1}\hbox { cm}^{-2}\) are reached in ethanol oxidation and 7.56 \(\hbox {A}\hbox { mg}_{\rm Pt}^{-1}\hbox { cm}^{-2}\) in the formic acid oxidation. The present structures are able to exploit the synergy of Pt and \(\hbox {TiO}_{2}\) with a bifunctional mechanism to result in powerful but easy-to-fabricate catalyst structures. They represent an easily producible type of composite nanostructures which can be applied in various fields such as in catalytics and sensor technology.

Electroless plating of magnetic materials on catalytically active noble metal seeds is a powerful tool to design highly efficient recyclable catalysts. For the electroless plating procedure of metallic nanotubes in porous polymer templates, a sensitisation and activation process of the template is necessary. Therefore, metallic seeds are created on the surface of the polymer, which then enable the selective heterogeneous nucleation of a metal film on the template's surface. By choosing the metals for seeds and structures wisely, different functional materials can be purposefully combined. In this work magnetically recoverable catalysts were designed, which consist of magnetic NiCo nanotubes as carrier for catalytically active Pd seeds. The synthesised catalyst structures were thoroughly characterised by SEM, TEM, EDX, XRD, XPS, ICP-OES, VSM and then tested in the 4-nitrophenol reduction reaction, which was monitored by UV-Vis spectroscopy. After the reaction the structures were recycled and reused without a decrease in activity.

The fabrication of ordered superstructures composed of nano-and microscale building blocks is of tremendous interest. In this work, we present a versatile approach for the synthesis of hierarchical and free-standing metal architectures of high structural complexity. Using the ion-track etching technique, hierarchically porous polycarbonate membranes are obtained, which are employed as nanocasting templates. Pore filling is accomplished by the two complementary wet-chemical techniques electrodeposition and electroless plating. Depending on the pore filling mechanism and the template structure, a wide range of novel metal nano-/micro-architectures can be realized. The products can be characterized as hierarchical assemblies of 1D structures (nanotubes, nanowires, microwires, nanorods). With electrodeposition, complete pore filling is achieved, which results in the formation of wire-based morphologies. Special attention is dedicated to the controlled partial filling of the pores with electroless plating, which allows the simultaneous deposition of tubes and - depending on the conformity of the plating reaction and the deposition time - narrower arrays of tubes, wires or rods. To demonstrate the favorable functional properties of the obtainable products, a silver-based wire-tube assembly is employed in the enzyme-free and selective electrochemical detection of hydrogen peroxide. An excellent sensitivity of 1340 mu A mM(-1)cm(-2) and a fast response time of <2 s is achieved, which is explained by the absence of binders, the well-accessible, open-pored structure, the presence of continuous conduction pathways and the high surface area of the material. (C) 2016 Elsevier Ltd. All rights reserved.

Nanotube assemblies represent an emerging class of advanced functional materials, whose utility is however hampered by intricate production processes. In this work, three classes of nanotube networks (monometallic, bimetallic, and metal oxide) are synthesized solely using facile redox reactions and commercially available ion track membranes. First, the disordered pores of an ion track membrane are widened by chemical etching, resulting in the formation of a strongly interconnected pore network. Replicating this template structure with electroless copper plating yields a monolithic film composed of crossing metal nanotubes. We show that the parent material can be easily transformed into bimetallic or oxidic derivatives by applying a second electroless plating or thermal oxidation step. These treatments retain the monolithic network structure but result in the formation of core-shell nanotubes of altered composition (thermal oxidation: Cu2O-CuO; electroless nickel coating: Cu-Ni). The obtained nanomaterials are applied in the enzyme-free electrochemical detection of glucose, showing very high sensitivities between 2.27 and 2.83 A M-1 cm-2. Depending on the material composition, varying reactivities were observed: While copper oxidation reduces the response to glucose, it is increased in the case of nickel modification, albeit at the cost of decreased selectivity. The performance of the materials is explained by the network architecture, which combines the advantages of one-dimensional nano-objects (continuous conduction pathways, high surface area) with those of a self-supporting, open-porous superstructure (binder-free catalyst layer, efficient diffusion). In summary, this novel synthetic approach provides a fast, scalable, and flexible route toward free-standing nanotube arrays of high compositional complexity.

The method of electroless plating offers a facile synthesis route to high-aspect ratio metal nanotubes. Despite the simplicity of the method, the traditional approach involves hazardous and toxic chemicals; to change this Green Chemistry has come into play. Since both, nanotechnology and Green Chemistry, have become important research topics, the combination of these offers new opportunities. According to the concept of Green Chemistry, Pd nanotubes were produced by using nonhazardous chemicals. The challenge was to rebuild the sensitisation and activation process of electroless plating and to find green reaction parameters for controlling the auto-catalysed heterogeneous nucleation of Pd. The produced Pd nanotubes were characterised by SEM and EDX. Furthermore TEM characterisation was done for determining the structural properties of Pd NTs. The efficiency of the reaction was quantified by ICP-OES and XPS measurements. To illustrate that green synthesized nanomaterials can be compared with conventionally prepared catalysts, the Pd nanotubes were tested in a model reaction to determine their catalytic activity. For this purpose the reduction of 4-nitrophenol to 4-aminophenol with NaBH4 was chosen, which also finds application in the synthesis of acetaminophen.