Electrocatalytic methanol oxidation with nanoporous gold: microstructure and selectivity

Abstract

The properties of Nanoporous Gold (NPG) obtained by the selective dissolution of Ag from an Au-Ag alloy can be tuned by the details of its fabrication, and specifically the residual Ag content is correlated to the ligament size of the material. We link this correlation to methanol electro-oxidation. Specifically, two different NPG types (obtained by potentiostatic dealloying) are compared with one obtained by free corrosion. They show remarkable differences in activity. Quantitative product analysis reveals that NPG shows nearly selective oxidation of CHOH to HCOO when NPG is used as an active electrode in contrast to planar Au. This trend can further be enhanced when applying finer nanoporous structures that are linked to a higher Ag content. X-ray photoelectron spectroscopy (XPS) reveals changes in the nature of residual Ag from which we conclude that Ag is not a passive component in the methanol oxidation process.

Mass Transport in Porous Electrodes Studied by Scanning Electrochemical Microscopy: Example of Nanoporous Gold

“…NPG standard was prepared by a standard dealloying protocol in perchloric acid . There is quite a large deviation between the ligament and pore diameter on the top of the disk and the bulk (Figure , left panels vs. right panels) as had been observed before for samples prepared by potentiostatic dealloying . For brevity we call the approximately 100 nm thick outer part “skin layer” .…”

“…The pore and ligament size of NPG can be tuned during the preparation by following different dealloying procedures or by heat treatment enabling the controlled adjustment of pore and ligament sizes while maintaining the unique morphology . This controlled variation of characteristic length scale provides excellent opportunities to systematically outline relationships between structure and performance …”

“…[4] An important application of NPG is the electrooxidation of small organic molecules either for sensing [5] or electrocatalysis. [4,6] Monolithic NPG samples are created via selective etching of the Ag component from a Ag-rich alloy via dealloying. Its major advantages comprise an easy preparation, high surface-tovolume ratio, high electrical and thermal conductivities and high chemical and structural flexibility.…”

Dealloyed Nanoporous Gold Catalysts: From Macroscopic Foams to Nanoparticulate Architectures

“…First, the catalytically active sites on the ligament surfaces are easily accessible by the reactant molecules when the nanoscale porosity is created inside a nanoparticle with a finite size, whereas the molecules must overcome long diffusion distances and convoluted paths to reach the active sites buried inside the interior of a macroscopic nanoporous membrane. Second, the pore and ligament dimensions of a macroscopic nanoporous membrane vary significantly from location to location, with narrower pore channels and finer ligaments on the outer surfaces than those in the interior regions . Such intrinsic structural heterogeneity significantly complicates the energy landscapes and overall kinetics of the surface‐catalyzed molecular transformations.…”

Facile Synthesis of PdCu Echinus‐Like Nanocrystals as Robust Electrocatalysts for Methanol Oxidation Reaction

“…Whereas, some drawbacks such as high price, low reserves and unsatisfactory stability severely impede the practical application of Pt‐based catalysts . Thus, a variety of non‐Pt nanomaterials such as pure Ni, NiO/Ni, Au nanoporous, NiCo 2 O 4 and Pd‐based materials have been reported . Among them, Pd‐based nanomaterials were regarded as prospective substitutes for Pt in virtue of the low cost, excellent resistance to CO‐poisoning and comparable electrocatalytic properties for MOR relative to Pt‐based catalysts …”