Noble metal

About: Noble metal is a research topic. Over the lifetime, 15113 publications have been published within this topic receiving 337947 citations.

Gold dissolution: towards understanding of noble metal corrosion

Abstract: The electrochemical dissolution of gold is an intricate topic and even though it has been studied for more than 50 years, its understanding remains rather limited. In the current work, we obtain unique information on gold dissolution by using a setup composed of a micro-electrochemical scanning flow cell (SFC) and inductively coupled plasma mass spectrometry (ICP-MS). Thus, comprehensive online gold dissolution profiles during the initial stage of oxidation as a function of the potential, time and pH are presented. A microscopic model explaining the experimental findings is proposed. According to this model, two dissolution mechanisms take place in two different potential regions: at low anodic potentials the dissolution is driven by the place-exchange between metal and adsorbed hydroxyl/oxygen ions, while at higher potentials the oxygen evolution reaction taking place on the surface of gold oxide initiates concomitant gold loss.

Area Relationships in Galvanic Corrosion

Abstract: The effect of variations of the area of two metals in a galvanic couple is discussed for three common cases. In Case 1, it is assumed that the only significant process on the more active metal (A) at the galvanic potential (ϕg) is metal oxidation (dissolution), while the only significant process on the more noble metal (C) is reduction of the oxidizer (H+, H2O, O2) and Tafel behavior is observed. Various possibilities to present the galvanic current as a function of electrode areas, which might have lead to some confusion in the literature, are discussed. In Case 2, it is assumed that metal (A), the anode in the galvanic couple, is polarized only slightly from its corrosion potential. It is shown that in this case the galvanic current density (igA) is not equal to the dissolution rate (idA) of the anode. A correlation between these two values is given. In Case 3, it is assumed that the cathodic process on both metals is entirely diffusion controlled. In this case, the dissolution rate of the anod...

Molybdenum Carbide-Decorated Metallic Cobalt@Nitrogen-Doped Carbon Polyhedrons for Enhanced Electrocatalytic Hydrogen Evolution.

Abstract: Electrocatalytic hydrogen evolution reaction (HER) based on water splitting holds great promise for clean energy technologies, in which the key issue is exploring cost-effective materials to replace noble metal catalysts. Here, a sequential chemical etching and pyrolysis strategy are developed to prepare molybdenum carbide-decorated metallic cobalt@nitrogen-doped porous carbon polyhedrons (denoted as Mo/Co@N-C) hybrids for enhanced electrocatalytic hydrogen evolution. The obtained metallic Co nanoparticles are coated by N-doped carbon thin layers while the formed molybdenum carbide nanoparticles are well-dispersed in the whole Co@N-C frames. Benefiting from the additionally implanted molybdenum carbide active sites, the HER performance of Mo/Co@N-C hybrids is significantly promoted compared with the single Co@N-C that is derived from the pristine ZIF-67 both in alkaline and acidic media. As a result, the as-synthesized Mo/Co@N-C hybrids exhibit superior HER electrocatalytic activity, and only very low overpotentials of 157 and 187 mV are needed at 10 mA cm-2 in 1 m KOH and 0.5 m H2 SO4 , respectively, opening a door for rational design and fabrication of novel low-cost electrocatalysts with hierarchical structures toward electrochemical energy storage and conversion.

Physico-chemical and antimicrobial properties of co-sputtered Ag–Au/PTFE nanocomposite coatings

Abstract: In this work, we used co-sputtering of noble metals together with polytetrafluorethylene (PTFE) as a method for producing antibacterial metal/polymer nanocomposite coatings, where the precious metals are only incorporated in a thin surface layer. Moreover, they are finely dispersed as nanoparticles, thus saving additional material and providing a very large effective surface for metal ion release. Nanocomposite films with thickness between 100 and 300 nm were prepared with a wide range of metal filling between 10 and 40%. The antimicrobial effect of the nanocomposite coatings was evaluated by means of two different assays. The bactericidal activity due to silver release from the surface was determined by a modification of conventional disc diffusion methods. Inhibition of bacterial growth on the coated surface was investigated through a modified proliferation assay. Staphylococcus aureus and S. epidermidis were used as test bacteria, as these species commonly cause infections associated with medical polymer devices. The antibacterial efficiency of the coatings against different bacteria was demonstrated at extremely small noble metal consumption: Au: ~1 mg m−2 and Ag: ~0.1 g m−2. The maximum ability for having an antibacterial effect was shown by the Ag–Au/PTFE nanocomposite, followed by the Ag/PTFE nanocomposite.