Nanostructure materials fabricated by electrochemical methods have many kinds of applications in energy storage, batteries, fuel cells, catalysis, sensors, and so on. This thesis is mainly focused on nanostructure materials by electrochemical ways for applications in supercapacitors, photocatalysts and Surface Enhanced Raman Spectroscopy (SERS) substrates. The key electrochemical fabrication techniques studied in this thesis include multi-compoent electrodeposition and dealloy, both being facile solution-based and suitable for large-scale production.
In Chapter 2, the nanoporous silver double-layers were fabricated by dealloying an electrodeposited AgCu double-layer possessing different composition in each layer. The pore and ligament size and porosity of each layer can be conveniently tailored by controlling the electrodeposition voltage profile used for fabricating the AgCu double-layer precursors. Therefore, nanoporous Ag double-layers with tailor-made porous profile along the film thickness can be easily fabricated. The Ag nanostructures thus obtained prove to be particularly attractive for surface enhanced Raman spectroscopy (SERS) applications by serving as novel multi-functional SERS substrates. When a higher porosity is created in the top layer, the double layer can trap more light due to the anti-reflection effect, enabling stronger SERS enhancement. On the other hand, with smaller pores formed in the top layer, the double layer readily works as a size-screening SERS substrate that can help distinguish SERS signals from a mixture of reagents of different sizes. Theoretical simulation has also been carried out and it shows good agreement with the experimental observations.
In Chapter 3, an approach to break the low surface area limits of metal foam has been demonstrated. The relatively low surface area of conventional metal foams largely limits their performance (e.g., in charge storage devices). Here, taking Cu foams as an example, a convenient electrochemical method for addressing this problem has been presented. High surface area Cu foams are fabricated in a one-pot one-step manner by repetitive electrodeposition and dealloy treatments. The thus obtained Cu foams enable greatly improved performance for different applications, e.g., as Surface Enhanced Raman Spectroscopy (SERS) substrates and 3-D bulk supercapacitor electrodes.
In Chapter 4, roughened copper foams fabricated using the method reported in chapter 3 are further investigated for the photocatalysis application. The roughened Cu foams serve as host for octahedral Cu2O nanoparticles, enabling enhanced photocatalytic performance. The photocatalytic performance of octahedral Cu2O on pristine Cu foams and roughened Cu foams under simulated solar and visible light is studied. It is found that the Cu2O@roughened Cu foams possess better photocatalytic activity than Cu2O@pristine Cu foams due to the high surface area of Cu foam. The formation of CuO-Cu2O heterostuctures also benefits the photocatalytic performance of the composites.
In Chapter 5, a novel electrochemical method to fabricate ultralight porous metallic materials is introduced. Ultralight metallic aerogels are desirable for thermal insulation, battery electrodes, catalyst support and shock energy damping. However, the complex and costly physical production methods limit their practical applications. Here, a novel type of metallic aerogel, featuring a network of hollow tubular ligands is successfully fabricated by electrodepositing the Cu foam with a NiCu coating followed by electrochemically dealloying of Cu from the entire structure. The thus obtained metallic aerogel exhibits a density of 9 milligrams per cubic centimeter. Compared with the conventional nanoporous structures, this novel type of metallic aerogel possesses higher surface area, ultralight weight, and good electrical and thermal conductivity. Moreover, supercapacitor electrodes fabricated of the metallic aerogel (NiIIIO(OH)@Ni aerogel) show great improved performance.
In Chapter 6, nanoporous Ni@NiCo2O4 particles are fabricated by using the nanoporous Ni particle generated as a byproduct of the electrochemical method reported in chapter 3. The nanoporous Ni particles feature an extraordinarily large surface area, potentially desirable for catalysis and electrode applications. The nanoporous Ni@NiCo2O4 particles produced using the nanoporous Ni particles as the template are found to exhibit higher capacitance than NiCo2O4 particles owing to their high surface area and conductivity.