Refinement of nanoporous copper by dealloying MgCuY amorphous alloys in sulfuric acids containing polyvinylpyrrolidone

Nanoporous Cu was fabricated by dealloying Mg 65 Cu 25 Y 10 amorphous alloy in a mixed solution of poly-vinylpyrrolidone (PVP) and sulfuric acid. A significant change was observed in the pore and ligament size when dealloying in the mixed solution rather than in a 0.1 M H 2 SO 4 solution free of PVP: in the mixed solution containing 10 g/L PVP the mean sizes of pores and ligaments were 10 nm and 14 nm, whereas they were 66 nm and 84 nm in the PVP-free solution. With increasing concentration of PVP in the dealloying solutions, the size of nanopores and ligaments decreased in the following manner: the decrease was small in the PVP concentration range of 0 to 0.1 g/L (Type I), and large in the 0.1 to 10 g/L range (Type II). A decrease in the surface diffusivity of more than three orders of magnitude was noted with the addition of 10 g/L PVP. This can be explained by the restrictions on free diffusion of Cu adatoms due to the adsorption of PVP macromolecules which force Cu adatoms to diffuse in a relatively narrower range, and thus smaller Cu ligaments and nanopores formed. The np-Cu materials in particular have a great potential for practical applications since they are cost effective compared to np-Au, electrochemically stable, and their mechanical performance is reliable. The np-Cu materials have been typically fabricated by dealloying crystalline 14-17 or amorphous precursors. 23-27 A significant reduction in the mean pore size of the np-Cu achieved by the addition of elements with a low surface diffusivity has been demonstrated, in some cases exceeding two orders of magnitude. However, the addition of noble metals such as Au, Pd, Pt, increases the cost of producing np-Cu considerably. Furthermore, the formation of crystalline Au or Ag phases has been shown to result in heterogeneity of the microconstituents. z E-mail: [email protected]; [email protected] Chen 28 developed a process referred to as low-temperature dealloying (−20 to 25 • C) which was shown to effectively reduce the pore size of np-Au from 28 nm to 7 nm. Sieradzki et al. 31 Evolution of nanoporosity is a dynamic roughing transition attributable to competition between curvature-dependent dissolution and surface diffusion. 29 Newman and Sieradzki also made a linkage of dealloying to localized corrosion (pitting corrosion), and the formation of nanopores is regarded to be a result of acidification in pits. In this investigation, PVP macromolecules were added into the dealloying solution to determine whether they had a refining effect on the formation of nanoporous Cu from amorphou

Effects of Catalysts and Membranes on the Performance of Membrane Reactors in Steam Reforming of Ethanol at Moderate Temperature

Steam reforming of ethanol in the membrane reactor using the Pd77Ag23 membrane was evaluated in Ni/CeO2 and Co/CeO2 at atmospheric pressure. At 673 K, the H2 yield in the Pd77Ag23 membrane reactor over Co/CeO2 was found to be higher than that over Ni/CeO2, although the H2 yield over Ni/CeO2 exceeded that over Co/CeO2 at 773 K. This difference was owing to their reaction mechanism. At 773 K, the effect of H2 removal could be understood as the equilibrium shift. In contrast, the H2 removal kinetically inhibited the reverse methane steam reforming at low temperature. Thus, the low methane-forming reaction rate of Co/CeO2 was favorable at 673 K. The addition of a trace amount of Ru increased the H2 yield effectively in the membrane reactor, indicating that a reverse H2 spill over mechanism of Ru would enhance the kinetical effect of H2 separation. Finally, the effect of membrane performance on the reactor performance by using amorphous alloy membranes with different compositions was evaluated. The H2 yield was set in the order of H2 permeation flux regardless of the membrane composition

Development of glassy alloy separators for a proton exchange membrane fuel cell (PEMFC),

The Ni 60 Nb 15 Ti 15 Zr 10 glassy alloy was developed as a separator material for a proton exchange membrane fuel cell (PEMFC). The corrosion rate of the glassy alloy in sulfuric acid was approximately 3 digits lower than SUS316L. A precise groove forming of the glassy alloy can be achieved by hot-pressing in the supercooled liquid state. The result of the power generation test of the single cell assembled with the groove-formed glassy alloy sheets revealed that sufficient power was generated. Moreover, the deterioration of the morphology of the glassy separator could hardly be recognized even after the durability test for 350 h