Fabrication Of Nanoporous Copper Based Electrocatalysts And Study Of Their Microstructure And Catalytic Properties

Nanoporous metals (NPMs), a representative type of nanostructured materials, have attracted a huge interest during the past several decades. Extensive attentions have been paid to NPMs for a broad variety of potential applications in catalysis, fuel cells, sensors, bio-detection and actuators due to their intriguing extraordinary properties such as large surface to volume ratio, unique surface structure, and high thermal and electrical conductivities.Nanoporous copper (NPC), a symbolic category of nanoporous materials, has been widely studied due to its extensive ability to generate propitious potentials for a broad range of highly promising potential applications. Especially, with the advancement in fabrication techniques, nanoporous copper with numerous special and superior properties, such as unique pore structure, large surface to volume ratio, enlarged specific surface area, high electrical and thermal conductivities and low cost have boosted the interest to explore its electrochemical properties and extend its promising applications in energy and catalytic systems.Herein, we focus on the fabrication of NPC based electrocatalysts through various advanced strategies for numerous industrial scale applications in catalysis and energy systems. Meanwhile, we investigated the influence of microstructure and pore-size distribution on the catalytic activity of NPC and developed a series of catalyst for the elimination of organic dyes from waste water, electroreduction of CO2 into hydrocarbons and improved surface enhanced Raman spectroscopy. We have demonstrated that, compared with normal planer polycrystalline copper, NPC exhibits superior electrochemical activity, which results from the easy pathways for electron/proton transfer, leading to faster reaction kinetics, more efficient electrolyte ions contact, and increased active sites for the catalytic processes. Results are described as follows:1. Facile fabrication of nanoporous copper and its application in ultrafast degradation of the methylene blue dyeMaterials optimized at nanoscale that generate active oxygen species from hydrogen peroxide (H2O2) are highly desired to maximize the rate of cationic dye degradation. In this study, NPC has been successfully utilized for the ultrafast oxidative degradation of methylene blue (MB) for the first time. The NPC was fabricated by an alloy-de-alloy process of Ti/Cu with 30-40 at.% Ti under free corrosion conditions. The uniform NPC with homogeneous and interpenetrating pore-to-ligament structure played a crucial role in the dissociation of H2O2 into active oxygen species, resulting in the ultrafast oxidative degradation of MB. Results suggested that for NPC with uniform bicontinuous structure morphology acquired by dealloying Ti4oCu60 alloy, the degradation of MB followed first-order rate kinetics with a rate constant of k=44×10-3 min-1 that was 30 times higher than that of a bulk copper foil. The large-scale active sites present in the bicontinuous porous network of NPC could account for its excellent degradation capability. The ultrafast degradation of MB over NPC suggests its extensive catalytic ability for numerous applications based on its enlarged specific surface area,3-dimensional bicontinuous nanoporous structure and increased electron and mass transfer capabilities.2. Fabrication and characterization of 3-d bicontinuous bulk nanoporous copper and its application in SERSThree dimensional bicontinuous bulk nanoporous copper (NPC) was successfully prepared by chemical dealloying 1mm thick slices of TixCu100-x (x= 50,60 at.%) alloys in the hydrofluoric acid (HF) solution under ambient conditions. Influences of initial alloy compositions and acid concentrations on the fabrication of nanoporous structure were systematically investigated. Results indicated that Ti6oCu4o alloy was the paramount precursor for fabricating a uniform 3-D bicontinuous NPC. By optimizing the dealloying solution concentration and dealloying time, a pore size of-50-200 nm has been fabricated. It was found that crackles bulk nanoporous structure with tunable pore size results in the significant improvement in the surface enhanced Raman spectroscopy (SERS) of NPC. This work develops a promising approach to fabricate non-fragile, crackless, and easy to handle bulk NPC for SERS and other industrial scale applications.3. The electrochemical reduction of CO2 into hydrocarbons and fuels at nanoporous copper catalystA uniform bicontinuous NPC was fabricated by chemical dealloying to examine its catalytic ability for the electroreduction of CO2 into hydrocarbons. The interpenetrating 3-D bicontinuous uniform nanoporous copper has been obtained by dealloying the binary amorphous TixCu100-x (x= 30,40 at.%) alloy ribbons obtained from melt-spun method. Different pore sizes were obtained after dealloying for different periods, with different HF concentrations and with different initial alloy compositions. The electrochemical reduction of CO2 over NPC was investigated systematically. The 3-D nanoporous copper has shown enhanced catalytic activity toward the electroreduction of CO2 to alcohols. Electrochemical analysis showed that NPC can catalyze not only CO2 but can reduce CO as well. The surprising multifunctional NPC catalyst has greatly contributed to the conversion of CO to alcohols. This NPC is believed to be the promising catalyst for electroreduction of carbon dioxide into hydrocarbons and fuels.