Noble metal

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

Nanoparticle conversion chemistry: Kirkendall effect, galvanic exchange, and anion exchange

Abstract: Conversion chemistry is a rapidly maturing field, where chemical conversion of template nanoparticles (NPs) into new compositions is often accompanied by morphological changes, such as void formation. The principles and examples of three major classes of conversion chemical reactions are reviewed: the Kirkendall effect for metal NPs, galvanic exchange, and anion exchange, each of which can result in void formation in NPs. These reactions can be used to obtain complex structures that may not be attainable by other methods. During each kind of conversion chemical reaction, NPs undergo distinct chemical and morphological changes, and insights into the mechanisms of these reactions will allow for improved fine control and prediction of the structures of intermediates and products. Conversion of metal NPs into oxides, phosphides, sulphides, and selenides often occurs through the Kirkendall effect, where outward diffusion of metal atoms from the core is faster than inward diffusion of reactive species, resulting in void formation. In galvanic exchange reactions, metal NPs react with noble metal salts, where a redox reaction favours reduction and deposition of the noble metal (alloying) and oxidation and dissolution of the template metal (dealloying). In anion exchange reactions, addition of certain kinds of anions to solutions containing metal compound NPs drives anion exchange, which often results in significant morphological changes due to the large size of anions compared to cations. Conversion chemistry thus allows for the formation of NPs with complex compositions and structures, for which numerous applications are anticipated arising from their novel catalytic, electronic, optical, magnetic, and electrochemical properties.

Copper Corrosion With and Without Inhibitors

Abstract: The utility of copper interconnects may ultimately depend on the ability to protect copper from corrosion. We have studied the capacity of lH-benzotriazole (1H-BTA) to provide a protective and stable surface film able to withstand harsh chemical and thermal environments. The film was characterized with electrochemical techniques, in situ ellipsometry, ex situ time-of-flight static secondary ion mass spectrometry, high-temperature mass spectrometry, and accelerated temperature and humidity tests. Several important passivating film properties (thickness, degree of polymerization, thermal stability, corrosion resistance) depend critically on the details of the film preparation conditions. The best corrosion protection is offered by the thin film formed on an oxidized Cu surface. This film has also shown the slowest growth kinetics and the highest degree of polymerization in the Cu-BTA structure. With more aggressive performance requirements for multilevel interconnections, higher conductivity metals, such as copper, are finding their way into a number of products. Copper is a relatively noble metal. Nevertheless, it reacts easily in ordinary, oxygen containing, environments (1). In view of the limited passivation offered by Cu-oxides, we have studied the effectiveness of organic azoles, such as lH-benzotriazole (1H-BTA), as a general method of controlling Cu degradation. For over 40 years 1H-BTA has been successfully used in the prevention of atmospheric Cu corrosion (2), in packaging, storage and transport, in the reduction of thermal oxidation and, in particular, in the protection of copper under immersed conditions (Ref. (3) and references within). The relevant literature is abundant but not unified in its teaching about bonding, thickness, composition and structure of the resulting film and the nature of its protection. Recent work from our laboratory, based on a combination of electrochemical, ellipsometric, and XPS data, has shown that the spontaneous reaction of Cu and 1H-BTA under a variety of conditions leads to the formation of Cu-BTA (4, 5), with copper being Cu +1 , as reported elsewhere (6-12). The formation of a Cu-N bond was clearly identified from the Cu LMM Auger lines. The film was formed both on an oxidized and an oxide-free Cu surface, in contrast to reports suggesting that the presence of Cu2O is a prerequisite for the buildup of CuBTA (8, 14). The thickness of the film was determined to be 0.5-4 nm in the pH range from 3 to 12, reaching 25 nm only under harsh conditions, i.e., in pH 2. Several recent studies of ultrahigh vacuum deposited 1H-BTA have indeed detected 1H-BTA adsorption on clean Cu metal (14-16). An electrochemical equivalent of such a film was formed in our laboratory at Cu 0 kept in

Highly Active, Nonprecious Metal Perovskite Electrocatalysts for Bifunctional Metal-Air Battery Electrodes.

Abstract: Perovskites are of great interest as replacements for precious metals and oxides used in bifunctional air electrodes involving the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). Herein, we report the synthesis and activity of a phase-pure nanocrystal perovskite catalyst that is highly active for the OER and ORR. The OER mass activity of LaNiO3, synthesized by the calcination of a rapidly dried nanoparticle dispersion and supported on nitrogen-doped carbon, is demonstrated to be nearly 3-fold that of 6 nm IrO2 and exhibits no hysteresis during oxygen evolution. Moreover, strong OER/ORR bifunctionality is shown by the low total overpotential (1.02 V) between the reactions, on par or better than that of noble metal catalysts such as Pt (1.16 V) and Ir (0.92 V). These results are examined in the context of surface hydroxylation, and a new OER cycle is proposed that unifies theory and the unique surface properties of LaNiO3.

Nickel nanoparticles in hydrogen transfer reactions

Abstract: The transfer hydrogenation of organic compounds is a much safer and more environmentally benign process than reduction reactions involving molecular hydrogen, metal hydrides, or dissolving metals. In transfer hydrogenation, 2-propanol is often preferred as the source of hydrogen because it is cheap, easy to remove, and environmentally friendly. This class of transformation has been mostly pursued through the use of expensive noble metals, such as Ru, Pd, and so forth; research involving cheaper catalytically active metals has been relatively neglected.On the other hand, alcohols have recently emerged as desirable alkylating agents, a useful alternative to organic halides, in reactions of hydrogen autotransfer, also known as the “borrowing of hydrogen” methodology. For instance, the α-alkylation of ketones with alcohols is an atom-efficient process that produces water as the only byproduct in the presence of a noble metal catalyst. Hydrogen autotransfer is also successful in the synthesis of amines through...