Building And Electro-catalysis Research Of One-dimensional Array Of Several Composite Nanomaterials

Interest in composite nano-structured materials arises, in part, because their unique optical, electrical, magnetic, thermal, mechanical properties constitute beneficial conditions for the development of new high-performance functional materials, which derived from their size-dependent evolution, such as quantum size effect, small size effect, surface-interface effect and macroscopic quantum tunneling effect; Furthermore, in many cases, there is an enhancement in specific properties upon compounding due to the high interface concentration, special interface structure, high surface energy, such as optimization and improvement to the mechanical behavior, corrosion resistance, wear resistance of materials were well known for the wide application in aerospace, defense, transportation, sports and other fields. Importantly, viewing from the chemical point, the chemical activity of such special composite nanostructure can be greatly extended, especially in area of catalysis, sensitivity and response, but the corresponding research work is just started. In particular, limited by the fabrication conditions and methods, most composite nanostructures generally do not exhibit regular direction, which restricted the application in the field of micro-nano devices.The current work of this thesis is based on building one -dimensional composite nanostrcutured arrays, and discuss their electro-catalysis performances, such as electro-oxidation of methanol on fuel cells and enzyme glucose sensor. The main contents include the following:1. An urchin-like Ni-Cu nanoalloy has been prepared for the first time by hydrothermal process and subsequent nanoscale decomposition related reaction within the{Ni,Cu}(OH)2CO3 nanowires. We further study the electrocatalytic activities of Ni-Cu nanoalloy towards the oxidation of methanol. (1) Our synthesis system is novel and interesting, for the different intrinsic hydrolytic and complex chemistries of Cu(Ⅱ) and Ni(Ⅱ) would restrict the synthesis of the single {Ni,Cu}(OH)2CO3 coprecipitation to very narrow conditions; (2) The complex growth mechanism of the {Ni,Cu}(OH)2CO3 precursor has been discussed in detail through analyzing the products of different reaction time. Interestingly, we find that the specific amount of Ni element plays important role in the {Ni,Cu}(OH)2CO3 nanowire formation; (3) Annealing under a flow of N2 at 700℃,the {Ni,Cu}(OH)2CO3 nanowires are converted to hierarchical Ni-Cu nanoalloy arrays. In particular, the Ni-Cu nanowires are porous and packed with 20nm nanoparticles, which are Ni rich in the core region and Cu is uniform in the whole particle; (4) Compared with the general Ni-Cu film, the electrocatalytic activity towards methanol oxidation of Ni-Cu porous nanowires has been greatly improved. It is proposed to be related to the regularly porous nanostructure. Firstly, the homogeneous distribution of Cu clusters in the alloy ensures very efficient inhibition for volume expansion of the Ni phase. On the other hand, a large surface to volume ratio in the 1D porous nanostructure is also able to improve its adsorption capability to methanol and obviously shortens the pathway of ion and electron transport, providing more active redox sites to the electrode.2. Mixed Ni-Cu-O nanowire arrays on conductive substrate have been prepared by hydrothermal process and subsequent nanoscale decomposition related reaction within the {Ni,Cu}2(OH)2CO3, and further demonstrated exhibiting excellent glucose detection performance which could be ascribed to the synergetic effect between the mixed oxide and the unique 1D array feature. (1) To obtain well organizational Ni-Cu-O array, the annealing temperatures have been controlled in the range of 350℃-～500℃. When the temperature is below 350℃, the precursor can not be decomposed completely, higher than 500℃, the array structure is easy to collapse; (2) While different annealing temperatures, the size of the secondary naoparticles of the resulted Ni-Cu-O porous array has delicate difference, which would generate performance differences. It is found that the product obtained in the 350℃, exhibit higher glucose detection performance due to the formed～2nm smaller grains; (3) Compared with previously reported Ni or Cu-contained biosensors, these mixed array electrodes, possess higher performance, like as the high sensitivity, low detection limit. Besides above, other excellent properties, such as long-term stability and anti-interferences, are demonstrated as well. All these improvements can be attributed to the synergetic effect between the mixed oxide grains and the unique 1D array feature.3. A novel hydrothermal method for the synthesis of a C@Cu nanotube array on Ti substrate f has been reported by employing the carbon coated ZnO nanorod array as an inexpensive and partially sacrificial template. Moreover, this designed C@Cu array has been demonstrated as an excellent electrode material for an enzyme-free glucose sensor; (1) In the hydrothermal reaction process, these dehydrated carbohydrates would reduce Cu2+ ions into Cu nanoparticles and simultaneously anchor them onto the carbon layer of the template, at the same time, the ZnO nanorods are gradually etched by the NH4+ existed in the solution, finally obtain the tubular structure array; (2) Attributed to its good electronic contacts and unique tubular array nanostructures, the C@Cu composite has manifested high sensitivity, fast response, and good selectivity for the determination of glucose.4. The Kirkendall effect has been utilized to form high surface area (919.63 m2 g-1) ZnO/C composite tubular arrays on a ceramic substrate. This ordered array structure because of their high surface area has great research significance on the catalyst support. (1) In a simple hydrothermal reaction system, utilizing the organic groups generated by glucose in the NH3+ environment, we can obtain aligned one-dimensional (ID) carbonaceous species-coated ZnO arraysnanostructures on various substrates (ceramic, silicon, quartz glass and metal) without any seeds or catalysts; (2) The obtained carbonaceous species-coated ZnO arrays were subsequently subjected to aheating treatment at 900℃for 120 min. When annealing at high temperature, the carbonaceous species shell would immediately be carbonized, followed by the convectional diffusion of ZnO and the generated carbon through the interface of these two phases. Since the diffusion rate of the ZnO core was faster than that of carbon, vacancy diffusion occurred to compensate for the inequality of the ZnO material flow and small Kirkendall voids were generated at the interface. With the Kirkendall voids maintaining enlargement, carbon could deoxidize the incursive ZnO into the Zn nanoparticles and CO gases, the evaporation of massive Zn combined with the release of CO produced abundant structural gaps, which would be subsequently developed into hollow caves. During the reaction between ZnO and carbon, the initial single-crystal structure of ZnO and the continuous carbon layer could be completely destroyed, producing numerous ZnO and carbon nanoparticles. Once the annealing process was suddenly stopped after sufficient Kirkendall reaction, well-defined ZnO/C tubes could be generated.In summary, this thesis develops several methods to fabricate 1D composite array, and discuss their electro-catalysis performances, such as electro-oxidation of methanol on fuel cells and enzyme glucose sensor, expanding the potential applications of this compound array structure.