The Interface Between Metallic Corrosion and Nanoscience

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SUMMARY OF PROPOSAL Metallic nanomaterials come in various forms. Many researchers are studying nanoparticles, which are critical to catalysis of chemical and electrochemical reactions, for example in fuel cells. Our group in Toronto specializes in another category : nanoporous metals. Historically these have been made in various ways, but the dominant approach nowadays involves dealloying – the selective electrolytic dissolution of one or less-noble alloying elements from a metallic alloy. The remaining, more-noble atoms rearrange to form the nanoporous structure. Usually some less-noble element(s) are trapped within this structure and may alter its properties – for example, its catalytic activity. The porosity is almost entirely continuous, not a Swiss cheese structure, so reactants and products can freely enter and leave the pores. Recently we carried out a substantial study of the nanoporous alloys created by dealloying of ternary silver-gold-platinum alloys, with small contents of platinum : 1, 2 or 3 atomic percent. The presence of platinum refines the porosity of the product, to a few nanometres, and stabilizes it against growth of the pores when heated. The most exciting result was that heating in air greatly increased the amount of platinum on the internal surface of the porous structure, while heating in vacuum had the opposite effect. This ability to tune the surface coverage of platinum (and, by extension, other desirable elements in future alloys) creates a very flexible system for many future activities - and not only catalysis. The proposed activities include, but are not restricted to, the following : • High resolution analytical transmission electron microscopy of the nanoporous structures, to better understand the distribution of alloying elements and the effect of heating. • Studies of electrocatalysis of various reactions such as oxidation of alcohols (preliminary results are extremely promising). • Studies of gas-phase catalysis in suitable systems. • Investigation of the structure and properties of nanoporous metals synthesized using unusual conditions such as high-temperature, high-pressure aqueous solutions. • Manufacture and testing of analogous alloys with much lower contents of noble metal, using the concepts developed for the silver-gold-platinum system. • Improvement of presently available atomistic computer simulation codes for dealloying, and correlation with experimental behaviour. • Use of nanoporous metals as testbeds for studying electrochemical behaviour in highly confined spaces, with potential practical applications such as tunable separation of substances.