Double-Walled Ag–Pt Nanotubes Fabricated by Galvanic Replacement and Dealloying: Effect of Composition on the Methanol Oxidation Activity

Abstract

The synthesis of bimetallic nanostructures using galvanic replacement displays a versatile route toward e±cient catalysts for fuel cell reactions. We show that electrolessly plated Ag nanotubes (NTs) are a unique template for the synthesis of double-walled Ag-Pt NTs. After replacement reaction, di®erent dealloying protocols are applied to adjust the residual Ag content. The structures were thoroughly characterized by scanning electron microscopy, transmission electron microscopy, X-ray di®raction and X-ray photoelectron spectroscopy, providing evidence of a hollow tube structure composed of Ag-Pt alloy. Experiments under harsh conditions reveal, that a signi¯cant amount of Ag remain in the NTs, which strongly a®ects the methanol oxidation performance. With optimized Ag-Pt ratio, the speci¯c activity of Pt/C catalysts can be outperformed. From the obtained results, we emphasize that each e®ort using galvanic replacement should be accompanied by detailed compositional analysis.

Electroless Plating of Metal Nanomaterials

“…[184] 1D nanostructures of limitless aspect ratio are invaluable for metal-based transparent conductors, [182,184] which achieve percolation at ultralow coverages through the crossing of continuous, extended, and narrow conduction paths. [185] By combining electroless plating and galvanic displacement steps, multiwalled metal nanotubes can be created from 1D precursors, [186,187] providing a route towards extended nanoscale gaps. Nanowires can be overcoated to obtain core-shell architectures.…”

Metal Nanotube/Nanowire-Based Unsupported Network Electrocatalysts

“…Galvanic replacement of colloidal silver, copper, or tellurium nanowires with a more noble metal (e.g., Pt [11,[55][56][57], Pd [56,58], Au [58]) or metal combinations (e.g., Au-Pt [59], Pd-Pt [11,56], Pt-Ru [60]) is a common approach. It should be considered that even in the case of replacement with a single metal, the commonly occurring incompleteness of the exchange reaction-and/or accompanying purification steps intended to remove the residual educt metal-will result in bimetallic systems, in which a considerable impact of the composition on the catalytic performance is to be expected [61]. By applying galvanic replacement reactions or Kirkendall transformations on metal nanotubes instead of nanowires, double-walled or porous nanotubes can be created [61][62][63].…”

“…In the future, it is necessary that these promising initial studies, which mostly remain limited to individual half reactions performed on model working electrodes, will be more frequently complemented by experiments which properly integrate such catalysts into membrane electrode assemblies [74]. The unsupported, extended, and hollow nature of nanotubes lends itself to the production of catalysts with high surface area and activity, which can be enhanced, e.g., by multi-element synergy [11,56,61,64], the presence of defects such as grain boundaries [64], or pores [65,66]. Nevertheless, it is challenging to outperform conventional catalysts on the basis of noble metal mass or cost, which can be realized with careful tuning of the nanotube structure and composition [11,56,59].…”

“…(C) Ag nanotubes, electrolessly deposited in ion-track etched polycarbonate templates, prepared according to [67]. (D) Double-walled Ag-Pt nanotube, prepared by galvanic replacement, according to [61]. (E) Ag nanotubes, which have been subjected to galvanic replacement with Au to create porous Ag-Au nanotubes, prepared according to [67].…”

Electroless Synthesis of Highly Stable and Free‐Standing Porous Pt Nanotube Networks and their Application in Methanol Oxidation

“…As a result of their remarkable chemical and physical properties, 1D nanostructures have attained considerable attention over the past decades . Especially the large specific surface area in combination with high stability are basis for an excellent performance in a wide range of applications (e. g. catalysis,, energy conversion,, sensing,). Furthermore, 1D nanostructures have an anisotropic morphology with continuous conduction pathways, resulting in an increased suitability for electrochemical and electronic applications ,,.…”