Nanoporous palladium fabricated from an amorphous Pd42.5Cu30Ni7.5P20 precursor and its ethanol electro-oxidation performance

Enhanced electro-catalytic performance of Pd-based hierarchical nanoporous structures fabricated by micropatterning and dealloying of Pd-Ni-P metallic glass

Pd-based catalysts are of significance for their application in direct alcohol fuel cells, due to the superior electro-catalytic performance and CO poisoning resistance. In this work, using Pd₃₂Ni₄₈P₂₀ metallic glassy ribbon as precursor, micro/nano hierarchical nanoporous structure was constructed by the hybrid approach of thermal plastic micropatterning and subsequently electrochemical dealloying at 0.88 V for 120 min in 0.5 M H₂SO₄ and 0.5 M H₃PO₄. This hierarchical structure was composed of the periodical micro-rods and nanoporous structure, where the chemical constituent was 80.33 at% Pd, 4.87 at% Ni, 4.96 at% P, and 9.84 at% O. The nanoporous structures showed an enhanced methanol electro-oxidation performance in alkaline medium, owing to their enlarged specific surface area. Compared to single nanoporous structure, the hierarchical nanoporous structure exhibited much better electro-catalysis, mainly attributed to the large surface area and high mass transfer efficiency, indicating a promising perspective for the application in alkaline direct alcohol fuel cells.

Asynchronous Evolution of Nanoporous Silver on Dual-Phase Ag⁻Sn Alloys by Potentiostatic Dealloying in Hydrochloric Acid Solution

Evolution behavior of the nanoporous architectures has been investigated via potentiostatic electrochemical dealloying of dual-phase Ag_xSn_100-x (x = 20, 30, 40 at.%) alloys, which consist of β-Sn and ε-Ag₃Sn phases with different volume fractions in 1.2 M HCl solution. The results show that the open-circuit potentials and corrosion potentials of dual-phase Ag-Sn alloys are determined by the less noble β-Sn phases rather than chemical compositions of the Ag-Sn precursor alloys. The potentiodynamic polarization curves show that the anodic dissolution of Ag-Sn alloys is divided into two stages including the first preferential dissolution of β-Sn phases and secondary dealloying of ε-Ag₃Sn phases, which is associated with the order of the nanoporous evolution. Nanoporous silver (NPS) can be fabricated by potentiostatic dealloying of dual-phase Ag-Sn alloys in HCl solution. The dealloying of two phases is asynchronous: The less noble β-Sn phases are preferentially etched to generate the larger pores, and then the more noble ε-Ag₃Sn phases are dealloyed to form the finer nanoporous structure. The significant surface diffusion of Ag adatoms at the applied potential higher than the pitting potential of ε-Ag₃Sn phases during the dealloying results in the coarsening of nanoporous ligaments with a time dependence of d(t) ∝ t^0.1. The fractions and the difference in electrochemical stabilities of the β-Sn and ε-Ag₃Sn phases in dual-phase Ag_xSn_100-x (x = 20, 30, 40 at.%) precursor alloys determines the final nanoporous structure.

Ethanol-Mediated 2D Growth of Cu₂O Nanoarchitectures on Nanoporous Cu Templates in Anhydrous Ethanol

Two types of cupric oxide (Cu₂O) nanoarchitectures (nanobelts and nanopetal networks) have been achieved via immersion nanoporous copper (NPC) templates in anhydrous ethanol. NPC templates with different defect densities have been prepared by dealloying amorphous Ti₆₀Cu₄₀ ribbons in a mixture solution of hydrofluoric acid and polyvinylpyrrolidone (PVP) with different ratios of HF/PVP. Both a water molecule reactant acting as OH⁻ reservoir and the ethanol molecule serving as stabilizing or capping reagent for inhibiting the random growth of Cu₂Oplayed a role of the formation of 2-dimensional Cu₂O nanoarchitectures. Cu₂O nanobelts are preferred to form in anhydrous ethanol on the NPC templates from Ti₆₀Cu₄₀ ribbons dealloying in the solution with low HF concentration and small addition of PVP; and Cu₂O nanopetals are tended to grow in anhydrous ethanol from the NPC templates from Ti₆₀Cu₄₀ ribbons dealloying in the solution with high HF concentration and large addition of PVP. With increasing the immersion time in anhydrous ethanol, Cu₂O nanopetals united together to create porous networks about 300 nm in thickness. The defect sites (i.e., twin boundary) on nanoporous Cu ligaments preferentially served as nucleation sites for Cu₂O nanocrystals, and the higher defect density leads to the formation of uniform Cu₂O layer. Synergistic effect of initial microstructure of NPC templates and stabilizing agent of ethanol molecule results in different Cu₂O nanoarchitectures.

Nanocatalysts Fabricated by a Dealloying Method

Two types of nanomaterials with different morphologies are described in this article: nanoporous metals and titanate nanowires. Both materials are fabricated by a dealloying method. In the former case, the catalytic properties of nanoporous gold and palladium are exemplified by many chemical transformations. The reactions proceed without any support, stabilizer, or ligands. The catalyst can be easily recovered by a simple separation process and reused many times without significant loss of catalytic activity. In the latter case, the dealloying of Ti-Al alloy is described as a new fabrication method for producing ultrafine titanate nanowires. This method does not require high-temperature conditions, which is advantageous for the construction of fine structures. The key to this process is achieving a fine dispersion of intermetallic TiAl3 nanocrystals in the Al matrix in the mother alloy. The resulting nanowires exhibit remarkable Sr(2+) ion-exchange properties.