Fabrication processes and electrochemical properties of nanoporous metal foam and metal/oxide core-shell nanocomposite

Abstract

Nanoporous materials have many advantages, including high surface areas, low densities, and high strength-to-weight ratios. Nanoporous materials have been the focus of much research related to catalytic, gassensing, optical, and mechanical applications. Nanoporous metal foams combine a number of useful properties of metals, such as good electrical and thermal conductivities, selective catalytic activities, and ductilities. Additionally, nanostructured metals can have enhanced properties because of their very small sizes, further distinguishing the potential of nanoporous metal foams from bulk metals. Nanoporous metal foams have been fabricated using various approaches, including the dealloying of metal alloys, the self-organization of nanowires and by deposition onto porous templates by physical or chemical vapor deposition (CVD) methods. Iron aerogels have been synthesized by a nanosmelting process, and transition metal foams of nickel, copper, cobalt, and Ni-Cu and Ni-Co alloys have been synthesized by a controlled-combustion method. These nanoporous metal foams are expected to be used in the development of new nanostructured catalysts, three-dimensional electrochemical energy-storage structures, hydrogen-storage materials, electromagnetic composites, and lightweight structural materials. Much of the previous work has focused on the synthesis and fundamental properties of nanoporous metal foams, rather than on practical applications. A potential application of nanoporous metal foam is as an electrode for a supercapacitor, which requires a large surface area and high electrical conductivity. Faradic pseudocapacitor electrodes have been widely studied because of their high specific capacitances deriving from redox reactions. Some transitionmetal oxides (e.g., Mn, Fe, Co, Ni) have emerged as candidates to replace RuO. Of these, the cobalt oxides and hydroxides are particularly attractive because of their high redox activities and excellent reversibilities. In ...