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: CuO-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 cm. 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.
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.
The tailored structure of a bifunctional, semi-homogeneous NiCo-nanotube catalyst system with embedded Pd nanoparticles, is synthesised by electroless plating.
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