Dissertations / Theses on the topic 'Au/Cu nanowire'

Дисертаційна робота присвячена вивченню закономірностей структуроутворення 3D-систем C, Cu і Zn за умов конденсації слабопересичених парів і при використанні як класичного методу магнетронного розпилення, так і накопичувальної системи плазма-конденсат (НСПК). При використанні НСПК установлені технологічні умови формування на основі вуглецю наносфер і мікросфер, на яких у подальшому зароджуються нановолокна. Створено математичну модель, яка адекватно описує процес дозрівання за Оствальдом приблизно однакових за розміром кулястих острівців міді. На прикладі трьох серій експериментів з осадження пористих структур міді за допомогою магнетронного розпилення було показано, що основу формування пористих систем становлять малі значення пересичення осаджуваних парів, що тягнуть за собою різні швидкості нарощування конденсату в близько розміщених точках ростової поверхні. Вивчені механізми структуроутворення 3D-систем цинку при використанні як класичного методу магнетронного розпилення, так і НСПК. Установлено, що окиснені пористі конденсати цинку можуть бути використані як газові сенсори.
Диссертационная работа посвящена изучению закономерностей структурообразования 3D-систем веществ существенно различной летучести (C, Cu и Zn) в условиях околоравновесной стационарной конденсации. Осаждая конденсаты углерода в условиях, близких к термодинамическому равновесию, с помощью накопительной системы плазма-конденсат (НСПК), на начальном этапе селективного роста (в течение 6 мин) при давлении аргона 6 Па и мощности разряда 50 Вт были получены шарообразные слабосвязанные графитоподобные наноструктуры. При более продолжительной конденсации в течении нескольких часов происходит формирование графитоподобных шарообразных включений. Повышение давления рабочего газа от 6 до 10 Па при слабом изменении всех прочих технологических параметров способствует реализации более стационарного технологического процесса и зарождению на графитоподобных шарообразных включениях нановолокон. Сделано предположение о том, что в качестве активных центров зарождения углеродных нановолокон выступают изогнутые графеновые плоскости шаровидных структур. Установлено, что процесс зарождения и роста различных нановолокон разнесен во времени и определяется наличием шарообразных графитоподобных включений. Создана математическая модель массопереноса распыленного вещества в промежутке между мишенью и подложкой, адекватно описывающая процесс созревания по Оствальду островков меди приблизительно одинакового размера. На примере трех серий экспериментов по осаждению пористых структур меди при помощи магнетронного распыления было показано, что основу процесса образования пор составляют малые значения пересыщения осаждаемых паров, влекущие за собой различные скорости наращивания конденсата в близлежащих точках ростовой поверхности. Подобный селективный рост кристаллов возможен вследствие флуктуаций в распределении активных центров, при избирательной застройке кристаллографических плоскостей с максимальной энергией десорбции адатомов, а также при наличии отрицательного смещения и соответствующей фокусировке осаждаемых ионов на выступающие части ростовой поверхности. В последующем неполное сращивание кристаллов приводит к образованию пор и к появлению активных центров, необходимых для зарождения новых кристаллов. На основании анализа экспериментальных данных по получению конденсатов цинка в НСПК было выявлено существование трех зон (на диаграмме параметров «давление рабочего газа – мощность разряда») в пределах которых формируются одинаковые по характеру пористые структуры. Широкий спектр значений технологических параметров зоны 1 подтверждает процесс самоорганизации малых значений пересыщений и позволяет получать наносистемы цинка с высокой воспроизводимостью структурно-морфологических характеристик при среднем диаметре нанонитей 60 нм. При переходе в зону 2, а затем в зону 3 наблюдается постепенное увеличение пересыщения, которое подтверждается постепенным переходом к формированию структур в виде слабо связанных друг с другом системы ограненных кристаллов. Показано, что сопротивление окисленных систем цинка сильно зависит от газовой среды, в которой они находятся. Так для концентрации 0,7% пропана в воздухе, сопротивление образца снижается в 159 раз по сравнению с сопротивлением в чистом воздухе. Таким образом, полученные структуры могут найти применение в качестве газовых сенсоров, по крайней мере, к смеси пропан-бутан.
Dissertation is devoted to the investigation of the structure formation regularities of the C, Cu and Zn 3D-systems under the condensation conditions of the weakly saturated vapors and by using both the classical method of magnetron sputtering and the plasma-condensate accumulation system (PCAS). Technological conditions of the nanospheres and microspheres formation on the basis of C, on which hereafter the nanowires arise, are determined. A mathematical model that adequately describes the process of Ostwald ripening of the rounded Cu islands of the approximately equal size was created. On the example of three series of experiments on Cu porous structures deposition by using magnetron sputtering it has been shown that the small values of supersaturation of the deposited vapors, which cause different speeds of the condensate’s increase in the nearby situated growth surface points constitute the basis of the porous structures formation. Mechanisms of Zn 3D-systems structure formation by using both classical method of magnetron sputtering and PCAS are studied. It is determined that the oxidized porous zinc condensates can be used as gas sensors.

碩士
國立清華大學
電子工程研究所
91
We developed the electrochemical displacement method for Cu nanowire formed by replacing the silicon and the amorphous-silicon on SiO2/Si structure with electron beam lithography. The various line width from 0.1μm to 0.2μm were patterned by e-beam resist DSE1010 exposed with dose 6mC/cm2. Oxygen-plasma treatment is used to transfer the surfaces of the e-beam resist DSE1010 from hydrophobia to hydrophilia. The width of the e-beam resist DSE1010 diluted with tolene (1:1) after 30w oxygen-plasma treatment with time 30 sec was 0.18μm. The resist flow process can reduce the line width to 78nm. Then, The copper nanowire can be fabricated by immerse the silicon and amorphous- silicon into solution mixed with cupric sulphate (CuSO4˙5H2O)with 4g/L and various HF atomic percent. We successfully fabricated Cu nanowire with a width/height of 78nm/53 nm and 98nm/68nm by replacing silicon atoms from crystal silicon wafer and amorphous-silicon, respectively.

This thesis is an attempt to understand ways to improve thermo-mechanical and structural properties of nano-structured materials. A detailed study on computational design and analysis of metallic nanowires is carried out. Molecular dynamic simulation method is applied. In particular, FCC metallic nanowires, NiAl, and CuZr nanowires are studied. Various bottom-up approaches are suggested with improved structural and thermo¬mechanical properties. In the first part of the thesis, Cu nanowires are considered. Existence of a novel and stable pentagonal multi-shell nanobridge structure of Cu under high strain rate tensile loading is reported. Such a structure shows enhanced mechanical properties. A three-fold pseudo-elastic-plastic shape recovery mechanism in such nanowires is established. This study also shows that the length of the pentagonal nanobridge structures can be characterized by its inelastic strain. It is also reported that an initial FCC structure is transformed into a new HCP structure. The evidence of HCP structure is confirmed with the help of experimental data published in the literature. Subsequent to the above study, a novel mechanism involving coupled temperature-stress dependent reorientation in FCC nanowires is investigated. A detailed map is generated for size dependent stress-temperature induced solid-solid reorientation in Cu nanowires. In the second part of the thesis, deformation mechanisms in NiAl based intermetallic nanowires are studied. A novel mechanism of temperature and cross-section dependent pseudo-elastic/pseudo-plastic shape and strain recovery by an initial B2 phase of NiAl nanowire is reported. Such a recoverable strain, which is as high as ~ 30%, can potentially be utilized to realize various types of shape memory and strain sensing phenomena in nano-scale devices. An asymmetry in tensile and compressive yield strength behavior is also observed, which is due to the softening and hardening of the nanowires under tensile and compressive loadings, respectively. Two different deformation mechanisms dominated by twinning under tension and slip under compression are found. Most interestingly, a superplastic behavior with a failure strain of up to 700% in the intermetallic NiAl nanowires is found to exist at a temperature of 0.36Tm. Such superplastic behavior is attributed to the transformation of the nanowire from a crystalline phase to an amorphous phase after yielding of the nanowire. In the last part the work, another type of nanowires having Cu-Zr system is considered. A novel stress induced martensitic phase transformation from an initial B2 phase to BCT phase in a CuZr nanowire under tensile loading is reported. It is further shown that such a stress induced martenistic phase transformation can be achieved under both tensile as well as compressive loadings. Tensile-compressive asymmetry in the stress-strain behavior is observed due to two different phase transformation mechanisms having maximum transformation strains of ~ 5% under compressive loading and ~ 20% under tensile loading. A size and temperature dependent tensile phase transformation in the nanowire is also observed. Small nanowires show a single step tensile phase transformation whereas the nanowires with larger size show a two step deformation mechanism via an intermediate R-phase hardening followed by R-phase yielding. A study of energetic behavior of these nanowires reveals uniform distribution of stress over the nanowire cross-section and such stress distribution can lead to a significant improvement in its thermo-mechanical properties. Similar improvement is demonstrated by designing the nanowires via manipulating the surface configuration of B2-CuZr system. It is found that the CuZr nanowires with Zr atoms at the surface sites are energetically more stable and also give a uniform distribution of stresses across the cross-section. This leads to the improvement in yield strength as well as failure strain. An approach to design energetically stable nano-structured materials via manipulating the surface configurations with improved thermo-mechanical properties is demonstrated which can help in fundamental understanding and development of similar structures with more stability and enhanced structural properties. Further ab-initio and experimental studies on the confirmation of the stability of the nanowires via manipulating the surface site is an open area of research and related future scopes are highlighted in the closure.

碩士
國立清華大學
化學工程學系
104
At present, due to the development of portable device and electric vehicles, high energy density isn’t the only purpose required. Possessing high power density is another issue which needs to be considered. An electrical device containing both high energy density and high power density will be the most wanted result. As a result, a lithium ion capacitor has been designed by using pre-lithiated germanium/copper and silicon/copper nanowire fabric for negative electrodes with activated carbon for positive electrodes. For germanium, the performance is 200 F g-1 at 0.1 A g-1. And at high current density of 100 A g-1, the capacitance can still hold about 50 F g-1. The LIC have 108 W kg-1, when the energy density is 180 W h kg-1. While low energy density, the LIC would have ultrahigh power density of 110kW kg-1. For silicon, the performance of this LIC at 0.1 g-1 is 220 F g-1, which is approximated twice of capacitance of AC in EDLCs. Even at high current density of 50 A g-1, the capacitance can still hold about 80 F g-1. At a low power density of 170 W kg-1, the energy density is as high as 208 W h kg-1. The power density increases to 75 kW kg-1, which is much higher than most results in lithium ion capacitors, while the energy density still remains at 43 W h kg-1. As a result, we believe that this device can be used in numerous applications such as electrical vehicles (EVs) and hybrid electrical vehicles (HEVs).

碩士
南台科技大學
化學工程與材枓工程系
97
In this study, the multilayered CoNi/Cu nanowire arrays is prepared by using the arrays nanoporous of anodic aluminum oxide membrane as a template (AAO template ) with electrodeposition method. The diameter of AAO pores is about 250nm, 90nm and 70nm, respectively. The CoNi/Cu nanowire arrays were deposited at various electrolytic condition. The optimum electrolytic conditions had been investigated. Furthermore, we changed in non-ferromagnetic layer thickness, Co/Ni ions concentration and pore diameter of AAO, and its microcrystalline structure and magnetic properties were investigated.. The deposition rates is increased with the increasing of the electrolytic potential. CoNi alloy layers almost not be obtained as the electrolytic potential less then -0.9 V. The CoNi/Cu nanowires were deposited successfully in the electrolytic potential range of -0.9 V to -1.2 V. On the other hand, the multilayered CoNi/Cu nanowires were not grown uniformly as the electrolytic potential above -1.0 V. Therefore, the optimum electrolytic potential was determined of -1.0 V. Crystalline structure of multilayered CoNi/Cu nanowires was always fcc structure with any deposited potential for Co-Ni alloy and Cu. On the other hand, the thickness of Cu layer affect significantly on the magnetization of Co-Ni alloy layers. When the thickness of layer was above 1.5μm and had a bed magnetization. Different Co-Ni deposition potential affects not only the deposition rate of the nanowire, but also the impact of Co-Ni layers of the proportion of elements. In addition, in the control of various Co-Ni ion concentration can also adjust the ratio of elements of Co-Ni alloy layer. In the TEM analysis of the elements also proved for the continuous multilayered nanowires compose of the Co-Ni layers and Cu layers. From VSM pattern the saturate magnetization can be 11000 Oe., the easy magnetization axis are all perpendicular the nanowires, and the coercivity of multilayered CoNi/Cu nanowires are in the soft and hard magnet range. The multilayered CoNi/Cu nanowires with different Cu layer thickness, as well as Co-Ni ratio of ion concentration changes on the magnetic properties also change. Looked in the coercive, because the magnetism crystal make multilayered CoNi/Cu nanowires deviation hard magnetism the material, to this us may know in multilayered CoNi/Cu nanowires may do for outside the magnetically soft material good application, may depend on the demand affiliation in the hard magnetism aspect by the different atom content ratio alloy nanowire, synthesizes must material, regarding future on magnetic recording media its application value.

碩士
國立交通大學
物理研究所
101
The material of our experiment is Si nanowires containing copper silicide nanoparticles, and the nanoparticles are randomly distributed in nanowires. We measured the correlation of resistivity and temperature. We found that for samples containing higher resistivity, electronic diffusion follows activated laws. For having lower resistivity samples, the transport properties follow Efros-Shklovskii T^(-1/2) variable range hopping (VRH) laws. This feature may verify electrons cotunneling in nanowires. For sample having the lowest resistivity, we further found the Mott T^(-1/4) VRH laws. As a future work, we can analyse I-V curves and perhaps we would get more definite conclusion.

碩士
國立中正大學
化學工程研究所
105
This study is to investigate the characteristic of copper electroplating in supercritical carbon dioxide(SC-CO2) electroplating process, and to apply this technology to produce Cu-nanowires in anodic aluminum oxide template. SC-CO2 is electroplating with operation pressure form 10.2 to 20.4MPa and temperature at 35℃, fixed rotational speed 350 rpm. Experimental result reveals, that the Cu-film is polycrystalline structure, and that the grain size of the Cu-film decreases with increasing pressure under SC-CO2 electroplating. According to the reference：(i) pressure can enhance nucleation rate, (ii) the emulsified electrolyte by SC-CO2 have a periodic plating characteristic when Sc–CO2–E is applied； this acts like pulsation electroplating leading to a decrease in grain size. At 0.1MPa the grain size is 58.6nm. By increasing the pressure to 13.6MPa, the grain size is reduced to 52.1nm. It was found that the copper film hardness is highly dependent on the grain size. For example, Cu-film at generated 0.1MPa hardness of the resulting Cu-film is 0.48GPa；in contrast, the hardness is about five-time higher 2.51GPa when the Cu-film was generated at 13.6MPa. In addition, the electroplating in supercritical carbon dioxide have higher filling rate rather than in ambient condition, because SC-CO2 has extremely low surface tension.

碩士
國立清華大學
材料科學工程學系
103
Due to it’ s good conductivity and low-cost property, copper (Cu) is often used as interconnect and flexible transparent conductive film material with the introduction of nano-processing. Therefore, many studies try to analyze the properties of copper in nanoscale, such as nanowires (NWs). Twin is a common microstructure in metals. It has been demonstrated that nano-twinned copper have high mechanical strength, good conductivity, and moreover, superior electromigration resistance. In our previous study, we have successfully fabricated Cu NWs with high density of nanoscale traverse twinning structure by using pulsed electrodeposition at low temperature. The formation of nano-twinned structure can also improve the corrosion properties of Cu metallization by changing grain boundary structure. However, research report on the oxidation characteristics of nanotwinned Cu NWs is limited. Copper is prone to oxidation in nanoscale because of high surface-to-volume ratio, some researches showed that Cu-Ni NWs with core-shell structure that was prepared by coating a thin Ni layer on Cu NWs using chemical reduction method possesses good oxidation resistance. Nevertheless, these treatment were mostly done by using highly toxic reducing agent. In this study, high aspect-ratio nano-twinned Cu NWs were prepared by pulsed current (PC) electroplating, and Cu-Ni core-shell NWs were successfully prepared by the low-toxicity reducing agent, sodium borohydride. Time-and-temperature dependence of electrical resistivity for single Cu and Cu-Ni NWs prepared by micro-fabrication process has been investigated. The bamboo-like twinning structure and core-shell structure of Cu-Ni NWs have been examined by transmission electron microscopy (TEM) and UV-visible/TEM Energy Disperse X-ray analysis. According to four-probe I-V electrical measurement, the resistivity of Cu NWs with nanotwins remained almost constant after exposed in ambient air for one month, while the resistivity of Cu-Ni core-shell NWs also kept unchanged after hundreds hours of thermal aging, revealing good chemical stability.

碩士
國立臺灣科技大學
機械工程系
95
This study analyzes mechanical behaviors of defective Cu nanowires with three different orientations during uniaxial tension, using a molecular dynamic simulation. The investigation designs the various shapes and orientations of closed cracks inside nanowires and studies the influences of the cracks on the strength, deformation mechanism, dislocation emission. The embedded-atom-method (EAM) potential is employed to describe the atomic interactions. Analysis results demonstrate that if the leading dislocation are emitted from cracks, the strength of the defective nanowires occur is lower than that of defect-free nanowires. When the load direction is <111>, the difference in the influence of the crack on strength between the defective nanowires and defect-free nanowires because the amount of later elastic deformation of the <111> nanowires is less than other orientations. When the <110> nanowires are under tension, the effect of the crack on strength is the highest because the later elastic deformation in <010> is the highest. Therefore, the <110> orientation is the most sensitive to the crack under tension. For the <100> nanowires, if the cross section of the crack is circular, the dislocation mechanism easy to form the stacking fault rhombic pillar due to the symmetry of dislocation slip.

This thesis is based on research in Cu-catalyzed electrophilic trifluoromethylation and exploiting Cu/Cu2O nanowires with novel catalytic reactivity for developing of catalytic and greener synthetic methods. A large number of biological active pharmaceuticals and agrochemicals contain fluorine substituents (-F) or trifluoromethyl groups (-CF3) because these moieties often result in profound changes of their physical, chemical, and biological properties, such as metabolic stability and lipophilicity. For this reason, the introduction of fluorine or trifluoromethyl groups into organic molecules has attracted intensive attention. Among them, transition metal-catalyzed trifluoromethylation reactions has proved to be an efficient and reliable strategy to construct carbon-fluorine (C-F) and carbontrifluoromethyl (C-CF3) bond. We have developed a catalytic process for the first time for trifluoromethylation of terminal alkynes with Togni’s reagent, affording trifluoromethylated acetylenes in good to excellent yields. The reaction is conducted at room temperature and exhibits tolerance to a range of functional groups. Derived from this discovery, the extension of work of copper catalyzed electrophilic trifluoromethylation were investigated which include the electrophilic trifluoromethylation of arylsulfinate salts and electrophilic trifluoromethylation of organotrifluoroborates. Because of growing environmental concern, the development of greener synthetic methods has drawn much attention. Nano-sized catalysts are environment-friendly and an attractive green alternative to the conventional homogeneous catalysts. The nano-sized catalysts can be easily separated from the reaction mixture due to their insolubility and thus they can be used recycled. Notably, because of the high reactivities of nano-sized metal catalysts, the use of ligands can be avoided and the catalysts loadings can be reduced greatly. Moreover, the nano-sized catalysts can increase the exposed surface area of the active component, thereby enhancing the contact between reactants and catalyst dramatically. Based on the above-mentioned concepts and with the aim of achieving one “green and sustainable” approach, C-S bond formation and click reactions catalyzed by Cu/Cu2O nanowires were investigated. It was found that the recyclable core-shell structured Cu/Cu2O nanowires could be applied as a highly reactive catalysts for the cross-coupling reaction between aryl iodides and the cycloaddition of terminal alkynes and azides under ligand-free conditions. Furthermore, these results were the first report for the crosscoupling reaction and click reaction catalyzed by one-dimensional (1D) copper nanowires.

碩士
國立清華大學
材料科學工程學系
100
Copper is often used as a interconnect material with the introduction of nano-processing. Therefore, it is important to understand the properties of copper in nanoscale, such as nanowires. Properties of material are closely related to its microstructure. For example, different crystal orientation may affect mechanical and electrical properties of materials and their applicability on integrated circuits and nano-devices. Twin structure is one of the microstructure in material. Nano-twinned copper is known to have high mechanical strength, decent electrical conductivity, and better electromigration resistance. During electrodeposition, deposition parameters such as current density and deposition temperature can greatly influence the microstructure of deposited material. Current waveform is also a factor which may affect the microstructure of deposited materials. It is generally believed that pulsed electrodeposition is an appropriate method to deposit twinned copper films. However, research about the influence of deposition temperature and current density for microstructure is mostly related to copper thin film system. The studies on the electrodeposited nanowires are limited especially for the pulsed electrodeposition system. Therefore, the objective of this study is to investigate how deposition temperature and current density affect crystal orientation and formation of twinning structure of copper nanowires in pulsed electrodeposition system. X-ray diffraction (XRD) and transmission electron microscopy (TEM) are used to analyze the crystal orientation and twin structure formation of copper nanowires, respectively. Experiment results show that the (111) crystal plane diffraction intensity of copper nanowires increases, but the average twin spacing of copper nanowires decreases with the decrease of electrolyte temperature. Moreover, with increasing current density, the (111) crystal plane diffraction intensity of copper nanowires increases, while the average twin spacing of copper nanowires decrease. The relationship between electrodeposition parameters and microstructure of copper nanowires is discussed by considering the working voltage variation at different deposition conditions and the stress induction / relaxation theory.

博士
國立臺灣科技大學
機械工程系
96
This study analyzes mechanical properties and deformation behaviors of Cu nanowires with uniaxl loading states (tension and compression), different strain rates and orientations by molecular dynamics. In this work, the maximum local stress calculated method (MLS) is proposed to validly elucidate the true stress of nanowires under uniaxial loading, in order to improve the problem that that the Virial stress(VS) is easy to undervalue the flow stress during plastic deformation. In addition, the concept of the minimum response time for yielding is proposed to explain the problem that the promotion of strain rate increases the yield stress. The combination of the elastic response time and the required time for cleavage fracture are presented to elucidate the dynamic deformation behavior as the strain rate is above . Moreover, the slipping factor is proposed to evaluate the strain rate sensitivity of yield stress. Further, the effect of lattice distortion and lattice geometrical factor can be used to explain the difference in between the different orientations under tension and compression, respectively. Analysis results demonstrate that slipping factor and lattice geometrical factor can be used to reasonably predict the various behaviors of Cu nanowire with different condition at the strain rate(7*10^7~7*10^9s^-1). The analysis also studies the variation of deformation mechanisms for various orientations and strain rates. At the strain rate of 7*10^7s^-1, the zigzag distribution of partial dislocations is observed in the nanowires of the lower the strain rate sensitivity of yield stress. When the strain rate is 7*10^8s^-1 , twinning occurs in both <100> nanowires and <110>. The variations of lattice orientation caused by twinning can result in geometrical hardening or geometrical softening with distinct loading conditions and orientations. Therefore, the deformation mechanism of two orientations (<100> and <110>) is pseudo skew-symmetry of nanowires under tension and compression. However, twinning is not easy to be operated because of the restriction of rigid body layers and free surface. When the strain rate is 7*10^9s^-1 , many partial dislocations are operated simultaneously for the conditions of higher strain rate sensitivity of yield stress(<100>tension, <111>tension /compression, <110>compression). At the strain rate between 7*10^7s^-1 and 7*10^9s^-1, immediately before fracture, the crystal structure in necking zone loses FCC, so the dislocation slip can not be operated. Therefore, the primary failure mode becomes atomic bond breakage, causing that the MLS stress increases markedly. The simulation results verify the prediction of te and tc, as the pulling speed ranges from 51 to 3000 m/s. When the pulling speed is 51~800m/s, the effect of causes the accumulation of the stress that is applied at the beginning of tensile loading in . The stress rises to the maximum at , and then the stress accumulated in the both ends of nanowires propagate forward the middle of nanowires. As the pulling speed is above 1000m/s, the fracture mode of nanowire is the cleavage fracture and the fracture surface is flat. The maximum tensile stress can be considered as cleavage stress. In this case, tc is definitely smaller than te . When the pulling speed ranges from 800 to 1000m/s, the fracture mode of nanowire is still the cleavage fracture. However, the fracture surface is not flat, because a few atoms in both ends of nanowires slip during cleavage fracture. For the specific strain rate 2.2*10^10s^-1~7*10^10s^-1 (pulling speed 166~512m/s), the stress accumulated in the both ends of nanowires have distinct influnences on dynamic behaviors in different orientation nanowires during the following deformation. For the conditions of the smaller slipping factor (<100>tension, <111>tension/compression, and <110> compression), the propagation of stress waves are obviously observed. The encounter of the stress wave causes constructive interference in the middle of the nanowires, producing the second peak. However, for the conditions whose the slipping factor is larger (<110>tension), stress wave are released by the large plastic deformation in both ends of nanowires before the stress waves propagate forward the middle of nanowires. Interestingly, the phase transformation mechanism that the FCC can be transformed into HCP is observed when the <100> nanowires is under compression. Further, this phase transformation mechanism expresses the characteristic of transitional plastic wave propagation.

博士
國立清華大學
材料科學工程學系
106
Copper (Cu) is an important conductive material used in microelectronic integrated-circuit devices due to its high electrical conductivity and low cost. However, Cu also suffers some intrinsic drawbacks such as oxidation and fast atomic diffusion, which would degrade device performance and even cause reliability problems. Cu metallization with highly dense nanoscale twin boundaries (nanotwinned Cu) have received wide attention because it possesses some excellent properties such as high tensile strength, good electromigration resistance and excellent thermal stability. However, few studies have addressed the chemical property of twin-modified Cu surface, especially for the nanotwinned Cu nanowires (nt-CuNWs). In this study, we investigate the chemical reactivity and structure stability of nt-CuNWs under moistured air ambient, water and acidic solution. The microstructural evolution and oxide formation behavior of nt-CuNWs were ex-situ monitored by transmission electron microscopy. By comparing the nt-CuNWs and nanocrystalline CuNWs (nc-CuNWs), it is found that the former exhibits a zig-zag faceted structure with very low atomic step density, while the latter have an atomically rough surface with high atomic step density. The nt-CuNWs appear to have reduced chemical reactivity and enhanced resistance to chemical corrosion. On the other hand, the nc-CuNWs were gradually oxidized by forming cuprous oxide (Cu2O) under water or moisture environment, which decomposed and transformed into Cu nanoparticles when exposed to visible light. According to the photoelectrochemical reaction of Cu/Cu2O system, we found that the nt-CuNWs demonstrate high chemical stability against the photolytic reaction. A kinetic mechanism based on the low chemical reactivity of twin-modified Cu surface and effective Cu/Cu2O interfacial vacancy sinking is proposed to explain why the nt-CuNWs are resistant against Kirkendall void formation.

碩士
國立清華大學
材料科學工程學系
104
Transparent conductive films (TCFs) are essential components in many optoelectronic devices. Indium tin oxide (ITO) that possesses high transmittance ( > 90 T%) and low sheet resistances ( <10 Ωsq−1 ) has been widely employed in TCFs. The development of flexible electronic devices drives the need of the TCFs on flexible substrates. However, the brittleness of ITO and the low throughput of the vapor-phase sputtering process on plastic substrate restricted the applicability of ITO on the flexible electronic devices. Looking for alternatives to the next-generation TCFs becomes imperative. Cu nanowires (NWs) have become a promising alternative solution for TCFs by forming a NW network on a transparent substrate. Cu NWs have superior electrical conductivity and flexibility. Nano-twinned Cu NWs have exhibited high mechanical strength, good conductivity, and moreover, superior electromigration resistance, which can be an excellent material to the NW-based TCFs. Still, the sheet resistance of Cu NWs films can easily increase due to the formation of copper oxides and leads to a severe reliability issue. In this study, Cu NWs were synthesized by pulsed electrodeposition with porous anodic aluminum oxide (AAO) templates at low temperature. To improve their anti-oxidation property, we develop a method that can uniformly coat a thin layer of silver on the Cu NWs through a galvanic replacement reaction. The microstructure of Cu NWs and silver shell have been examined by transmission electron microscopy (TEM). The evolution of electrical resistivity for single Cu-Ag NWs was measured as a function of time by a four-point probe method. A transfer printing approach was used to fabricate the TCFs with Cu-Ag NWs. The pressure applied for the transfer printing process has been optimized to obtain a TCF with RS = 41 Ω/sq and T = 88.9 %, which gives a good figure of merit (FOM) up to 70. The Cu-Ag NWs film has demonstrated good anti-oxidation ability after thermal aging at 85 °C for 300 hours. Meanwhile, the sheet resistance of Cu-Ag NWs film remained unchanged after 1000 bending cycles, which shows the film has excellent flexibility. In summary, the Cu-Ag core-shell NWs show the good chemical stability that are able to improve the performance and reliability of the Cu NWs-based TCFs.

碩士
國立清華大學
材料科學工程學系
104
The increasing demand for flexible electronic devices drives the need for alternative materials other than indium tin oxide (ITO) as transparent conducting films (TCFs). Dispersing metallic nanowires on a polymer substrate appears to be a good solution for flexible TCFs. Among various metallic nanowires (NWs) used in TCFs, Cu based NW has been considered a potential candidate because of its cost advantage and good electrical properties. In our previous study we introduced dense nanoscale twinning structure in Cu NWs that was deposited in porous anodic aluminum oxide (AAO) templates using pulsed electroplating process. However, oxidation is the detrimental problem for the application of Cu NWs in TCFs. In this study, we have successfully synthesized Cu-Ni core-shell NWs. First, the nanotwinned Cu NWs were released from AAO templates by a wet chemical method. They were coated a thin layer of Ni using a reducing agent, sodium borohydride, in ethylene glycol solvent. We optimized the reaction temperature to achieve a smooth Ni layer coating. Next, the Cu-Ni NWs were transferred onto a PET substrate to form a TCF through vacuum filtration method and pressing process. The TCF sheet resistance is substantially reduced from 31 K/sq. to 40 /sq. at a transmittance of 88% with the optimized pressure applied during the film transfer process. The TFC sheet resistance increases 3~10 /sq. after a 1000 cycles of dynamic bending and static bending tests. Finally, the Cu-Ni TCFs had a negligible increase in sheet resistance after heating at 85 C for several hundreds of hours. It achieves the goal of improving oxidation resistance of Cu NWs by forming a Cu-Ni core-shell structure.

Oxygen and Nitrogen containing compounds are of utmost importance due to their interesting and diverse biological activities. The construction of the C-O and C–N bonds is of significance as it opens avenues for the introduction of ether and amine linkages in organic molecules. Despite significant advancements in this field, the construction of C-O and C–N bonds is still a major challenge for organic chemists, due to the involvement of harsh reaction conditions or the use of expensive catalysts or ligands in many cases. Thus, it is a challenge to develop alternative, milder, cheaper and more reproducible methodologies for the construction of these types of bonds. Herein, we introduce a new efficient ligand free catalytic system for C-O and C-N bond formation reactions.

Alla luce del recente allarmante tasso di esaurimento delle riserve di combustibili fossili e al contemporaneo drastico aumento dei livelli di CO2 nell'atmosfera, principale gas serra responsabile del riscaldamento globale e di cambiamenti climatici molto gravi, una delle priorità assolute nella ricerca a livello mondiale è quella di sfruttare il più possibile le fonti di energia rinnovabile. Una possibilità molto interessante è quella di realizzare un processo di riduzione della CO2 a combustibili liquidi che sfrutti energie rinnovabili, quale quella solare, mediante dispositivi più comunemente noti come celle fotosintetiche artificiali o foglie artificiali o celle foto-elettro-catalitiche (PEC). L'obiettivo principale di questo lavoro, è stato pertanto quello di condurre uno studio approfondito su due diversi sistemi elettrocatalitici di riduzione della CO2 a prodotti liquidi con un più alto valore aggiunto, uno operante in fase gassosa (cioè in assenza di elettrolita al catodo) e uno operante in fase liquida. In particolare, è stata progettata e utilizzata nel processo di conversione della CO2, un’innovativa cella in fase liquida operante su scala di laboratorio, sulla falsariga della cella in fase gas precedentemente sviluppata all’Università di Messina. Il lavoro è stato svolto principalmente presso il laboratorio CASPE/INSTM dell’Università degli Studi di Messina (Dipartimento di Ingegneria Elettronica, Chimica e Ingegneria Industriale). Un periodo di sei mesi è stato svolto invece, nel corso del secondo anno di dottorato, presso l’École supérieure de chimie, physique, électronique de Lyon (CPE Lyon). In tale periodo sono stati sintetizzati, mediante innovative tecniche di sintesi organometallica, materiali compositi da utilizzare come elettrocatalizzatori nel processo di riduzione della CO2. Sono state effettuate molteplici prove sperimentali utilizzando svariate tipologie di catalizzatori, sia in fase gas che in fase liquida, al fine di indagare la differente selettività, produttività e varietà di prodotti ottenuti. Il processo in fase liquida è infatti quello maggiormente studiato in letteratura, ma esistono alcune problematiche che devono essere superate per consentire un successivo semplice scale up. quali ad esempio, la scarsa solubilità della CO2 e la tipologia di prodotti ottenuti (principalmente acido formico). Lo scopo principale di questo lavoro è stato quello di preparare nuovi materiali a base di carboni dopati con metalli, catalizzatori questi molto diversi da quelli comunemente utilizzati nel processo di riduzione della CO2 (generalmente metalli in bulk), e di testarli sia in fase gas (per sfruttare i vantaggi di questa condizione, quali ad esempio facile recupero dei prodotti e alta qualità dei prodotti stessi) sia in fase liquida (per avere un miglior confronto con i dati ampiamente presenti in letteratura). Per gli studi sulla riduzione elettrocatalitica della CO2 nella cella operante in fase gassosa, sono stati preparati una serie di elettrodi (basati su nano particelle –NP- di Cu, Fe, Pt e Cu/Fe depositate su nanotubi di carbonio o carbon black e successivamente poste all'interfaccia tra una membrana di Nafion e uno strato a diffusione di gas –GDL-). I risultati ottenuti sono stati molto promettenti, sia in termini di tipologia di prodotti formati che di produttività. In fase gas (senza elettrolita) è stata osservata la formazione di prodotti ≥C1 quali etanolo, acetone e isopropanolo, in particolare utilizzando il Fe (seguito dal Pt), evidenziando che anche metalli non nobili possono essere usati in maniera efficiente in questo processo. Per migliorare la produttività nella reazione di riduzione della CO2, sono stati preparati elettrodi differenti, basati su coating con sostituti zeolitici imidazolici (SIM-1) tipo MOF. In particolare, i catalizzatori testati sono stati MOF modificati con Fe-CNT, Pt-CNT, e CuFe-CNT. E’ stato osservato un cambiamento significativo in termini di produttività e anche di selettività verso i prodotti finali. Nel dettaglio, in particolare per il catalizzatore a base di MOF modificato con Pt, è stato osservato un aumento nei prodotti carboniosi e anche una selettività più alta verso prodotti con un più elevato numero di atomi di C. Per quanto riguarda lo studio del processo di riduzione elettrocatalitica della CO2 utilizzando la cella operante in fase liquida, sono state preparate tipologie di elettrodi simili ai precedenti. Inizialmente infatti, sono stati studiati elettrodi a base di nanoparticelle metalliche (Cu, Fe, Pt, Ru, Co) depositate su nanotubi di carbonio o carbon black. L'ordine relativo della produttività nella riduzione elettrocatalitica della CO2 in questa serie di elettrodi, è però risultato essere diverso rispetto alla fase gassosa, indicando quindi un differente percorso di reazione. In termini di produttività totale, gli elettrodi a base di Pt hanno consentito di ottenere le migliori performance, seguiti da Ru e Cu, mentre il Fe ha dato risultati peggiori. Sulla base dei risultati sperimentali ottenuti, è stato inoltre ipotizzato un possibile meccanismo di reazione. Successivamente, per cercare di migliorare ulteriormente le prestazioni nel processo di riduzione della CO2 in fase liquida, è stato effettuato uno studio approfondito, volto ad indagare la dipendenza di tale processo dalle dimensioni delle nanoparticelle metalliche. A tale scopo sono stati utilizzati elettrodi a base di nanoparticelle metalliche (Ru, Fe, Pt e Cu) su nanotubi di carbonio (CNT) depositati su GDL. Sono state sintetizzate nanoparticelle metalliche di diverse dimensioni utilizzando molteplici tecniche di sintesi: (i) impregnazione che ha consentito di ottenere NP di dimensioni comprese tra 10-50 nm; (ii) sintesi organometallica che ha consentito di ottenere NP uniformi e ultrafine con dimensioni comprese tra 1-5 nm. (ad esempio sono state sintetizzate NP di Fe di 1-3 P nm) (iii) sintesi mediante nanowires che ha consentito di ottenere NP di rame ultrafine con dimensioni comprese tra 2-3,8 nm. In particolare, la novità dell’approccio mediante nanowires sta nella possibilità di ottenere particelle di dimensioni molto piccole sintetizzando inizialmente i Cu NWs, mettendoli poi a contatto con il supporto carbonioso e facilitandone il suo trasferimento, ciò grazie alle forze intermolecolari di attrazione dei gruppi funzionali presenti sui CNT parzialmente ossidati. Inoltre, a differenza della sintesi organometallica, tale approccio permette di condurre le reazioni in aria e non in atmosfera inerte. I valori di produttività ottenuti sono stati 5-30 volte più alti utilizzando nanoparticelle metalliche più piccole (ottenute via nanowires o mediante sintesi organometallica) rispetto alle nanoparticelle metalliche più grandi (ottenute per impregnazione). I risultati sperimentali indicano pertanto che le NP di dimensioni più piccole hanno un ruolo fondamentale nelle performance catalitiche. Inoltre, il carico di NP metalliche è stato significativamente ridotto dal 10% al 1-2% in peso consentendo di ottenere, per le NP più piccole, una produttività equivalente o addirittura superiore rispetto alle nanoparticelle più grandi. In seguito, è stato effettuato anche uno studio sul possibile riutilizzo degli elettrodi di lavoro e sulla disattivazione per tempi di reazione più lunghi. E’ stata infine preparata una diversa tipologia di elettrodi a base di nano-foams su lastrine metalliche, al fine di ottenere un ulteriore miglioramento nel processo di riduzione elettrocatalitica della CO2. Le nano-foams o dendriti, sono state preparate mediante la tecnica di deposizione elettrochimica ed è stato effettuato uno studio preliminare di ottimizzazione, al fine di determinare le condizioni di sintesi più adatte. In aggiunta, è stato eseguito uno studio specifico per ottimizzare il valore di Voltaggio da utilizzare nelle prove catalitiche, mediante sia test di voltammetria ciclica che test completi di riduzione della CO2. Sono stati testati nano-foams a base di Cu e Fe depositati su fogli di Cu Fe, Al, di Inconel e su una griglia di Al. L’aumento nella produttività usando queste tipologie di elettrodi, è stata nell’ordine di 2-10 volte rispetto alla massima produttività ottenuta utilizzando NP metalliche su materiali carboniosi. Svariate tecniche analitiche sono state poi utilizzate per caratterizzare in modo approfondito i materiali preparati tra cui, microscopia elettronica a trasmissione (TEM), microscopia elettronica a scansione (SEM), spettroscopia ad assorbimento atomico (AAS), diffrazione a raggi X (XRD), spettroscopia fotoelettronica a raggi X (XPS), determinazione dell’area superficiale mediante metodo Brunauer-Emmett-Teller (BET). La determinazione dei prodotti di reazione è stata effettuata invece mediante cromatografia ionica (IC), gas cromatografia con rivelatore a spettrometria di massa (GC-MS), gas cromatografia (GC) con rivelatore a termo conducibilità (TCD).
In view of the recent alarming rate of depletion of fossil fuel reserves and the drastic rise in the CO2 levels in the atmosphere leading to global warming and severe climate changes, tapping into all kinds of renewable energy sources has been among the top priorities in the research fields across the globe. One of the many such pathways is CO2 reduction to fuels using renewable energies, more commonly referred as artificial photosynthetic cells or artificial leaves or photo-electro-catalytic (PEC) cells. The key objective of the present PhD work was to conduct in-depth studies on two different electro-catalytic CO2 reduction systems: electrolyte-less cell (gas phase) and electrolytic cell (liquid phase). In particular, a novel lab scale liquid phase cell, on the similar lines of the previously realized gas phase cell at the University of Messina, was developed and used to convert electro-catalytically CO2 to more value-added products. The work was carried out at the Laboratory CASPE/INSTM of the University of Messina (Department of Electronic Engineering, Industrial Chemistry and Engineering). During the second year, a six-month period was spent at the École supérieure de chimie, physique, électronique de Lyon (CPE Lyon), where organometallic routes were explored for the synthesis of novel composite materials to be used as electrocatalysts in the CO2 reduction process. Experimental tests were carried out on various types of catalysts in both the gas and liquid phase cells to understand the different selectivity, productivity and the reaction products obtained. Liquid phase, in fact, has been the most studied process in literature, but some issues mainly related to CO2 solubility and types of products formed (i.e. mainly formic acid), have never be allowed to pass the lab scale stage. The general aim of this PhD was to prepare novel metal doped nanocarbon substrates, which are very different with respect to the conventional metal bulk layers used as electrocatalysts in CO2 reduction, and test them both in gas phase (to take advantage of these conditions, i.e easy recovery and improved quality of the products) and in liquid phase (to have a better comparison with conditions typically adopted in literature). For the studies on the electro-catalytic reduction of CO2 in gas phase cell, a series of electrodes (based on Cu, Fe, Pt and Cu/Fe metal nanoparticles – NPs - deposited on carbon nanotubes – CNTs - or carbon black and then placed at the interface between a Nafion membrane and a gas diffusion-layer) were prepared. The results, evidencing the various types of products formed and their different productivities, are very promising. Under electrolyte-less conditions, the formation of ≥C1 products (such as ethanol, acetone and isopropanol) were observed, the highest being for Fe and closely followed by Pt, evidencing that also non-noble metals can be used as efficient catalysts under these conditions. To enhance the productivities of the CO2 reduction, a different set of electrodes were also prepared based on substituted Zeolitic Imidazolate (SIM-1) type MOF coatings during a stay at CPE Lyon and Institut de recherches sur la catalyse et l'environnement de Lyon (IRCELYON). Particularly, the catalysts tested were MOF-based Fe-CNTs, Pt-CNTs and Cu/Fe-CNTs. There was a significant change in the reaction products and in the selectivity towards the end-products. Particularly, especially for the MOF modified Pt based catalyst, there was an increase in the C-products and also a better selectivity towards higher C-products. Moving to the studies on the electro-catalytic reduction of CO2 in liquid phase cell, a similar set of electrodes were prepared. Initially, electrodes based on metal NPs of Cu, Fe, Pt, Ru and Co deposited on CNTs or carbon black were studied for their CO2 reduction capability. The relative order of productivity in CO2 electro-catalytic reduction in these series of electrodes was found to be different between the gas and liquid phase cells indicating the different reaction pathways. For liquid phase conditions, in terms of net C-products, catalytic electrodes based on Pt topped the class, closely followed by Ru and Cu, while Fe got the lowest position. The probable underlying reaction mechanism was also provided. In order to improve further the performances of the CO2 reduction in liquid phase conditions, a metal NPs size dependant study on the electro-catalytic reduction of CO2 to fuels was carried out. This study was performed using electrodes based on metal NPs of Ru, Fe, Pt and Cu loaded on CNTs and then transferred on a gas diffusion layers (GDL). Varied sized metal NPs have been synthesized using different techniques: (i) impregnation route to achieve NPs in the size range of 10-50 nm; (ii) organometallic approach to synthesize uniform and ultrafine NPs in the size range of 1-5 nm (i.e., Fe NPs were synthesized through a novel synthesis route to attain 13 nm NPs);(iii) Nanowire (NW) top-down approach to obtain ultrafine copper metal NPs in the size range of 2-3.8 nm. Particularly, the novelty of nanowire approach is the ability to obtain very small metal NPs starting from the synthesis of Cu NWs and then transferring the Cu onto the carbon surface, taking advantage of the different inter-forces of between Cu NWs and the functional groups present on the partially oxidized CNT surface. Furthermore, unlike the case of organo-metallic approach, this approach allows a preparation under air avoiding the use of potentially demanding inert atmospheric conditions. The enhancements in the fuel productivity were found to be 5-30 times higher for the smaller metal NPs obtained via organo-metallic route or nanowire route as compared to the larger metal NPs obtained via impregnation route. The results signify that the smaller sized metal NPs loading on the CNTs have a prevailing role in the catalytic performance and the selectivity towards different products. Moreover, the percentage of metal NPs loading was significantly reduced from 10 to 1-2 wt. % producing higher or equivalent fuels for small NPs as compared to the larger NPs. The reusability of the working electrodes and long reaction times (until 24 hours) were also probed. A different set of electrodes based on nano-foams on metal foils, were also investigated to achieve further improvements in the electro-reduction of CO2 to fuels. These nano-foams or dendrites were prepared by electrochemical deposition technique. Optimization studies on the deposition of these foams were performed initially to fix the set of preparation conditions. Moreover, voltage optimization study was performed using cyclic voltammetry and full CO2 reduction tests to find the optimum voltage for the process. The nano-foam electrodes tested include Cu and Fe foams on Cu foil, Fe foil, Al foil, Inconel foil and Al grid/mesh. The enhancements in the fuel productivity for various foams were in the range of 2-10 times greater as compared to the highest net fuel productivity achieved using metal NPs doped carbon catalytic electrodes, from all the previous studies. Various characterizations and analysis tools were used to analyse the catalysts qualitatively and quantitatively, which include Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), Atomic Absorption Spectroscopy (AAS), X-ray diffraction (XRD), X-ray Photo-electron spectroscopy (XPS), and Brunauer-Emmett-Teller (BET). To determine the fuel productivities, Ion Chromatography (IC), Gas Chromatography-Mass Spectrometer (GC-MS), Gas Chromatography (GC) were used.
Compte tenu du récent taux alarmant d'épuisement des réserves de combustibles fossiles et de l'augmentation drastique des niveaux de CO2 dans l'atmosphère qui a conduit au réchauffement de la planète et à des changements climatiques sévères, l'exploitation de toutes sortes d'énergies renouvelables a été la Parmi les principales priorités de la recherche Champs à travers le monde. L'une des nombreuses voies de ce genre est la réduction du CO2 aux combustibles utilisant des énergies renouvelables, plus communément appelées cellules photosynthétiques artificielles ou feuilles artificielles ou cellules photoélectro-catalytiques (PEC). L'objectif principal de ce travail était de réaliser des études approfondies sur les différents systèmes de réduction électro-catalytique du CO2, à savoir les cellules sans électrolyte (phase gazeuse) et les cellules électrolytiques (phase liquide). Dans ce processus, nous avons conçu une nouvelle cellule en phase liquide à échelle de laboratoire sur les lignes similaires de la cellule de phase gazeuse de modèle précédemment modélisée. Des essais expérimentaux sur la réduction du CO2 ont été réalisés sur différents types de catalyseurs dans les deux cellules afin de comprendre la sélectivité, la productivité et les produits de réaction obtenus. L'obtention de résultats de test dans les deux cellules nous a permis d'effectuer une comparaison décente avec les résultats de réduction électro-catalytique de CO2 existants dans la littérature. Des essais expérimentaux ont été réalisés sur différents types de catalyseurs à la fois dans les cellules en phase gazeuse et en phase liquide pour comprendre la sélectivité, la productivité et les produits de réaction obtenus. La phase liquide, en fait, a été le processus le plus étudié dans la littérature, mais certaines questions liées principalement à la solubilité du CO2 et aux types de produits formés (c'est-à-dire principalement l'acide formique) n'ont jamais été autorisées à franchir le stade de l'échelle du laboratoire. L'objectif général de ce doctorat était de préparer de nouveaux substrats de nanocarbone dopés par des métaux, qui sont très différents par rapport aux couches en vrac métalliques conventionnelles utilisées comme électrocatalyseurs dans la réduction de CO2, et de les tester en phase gazeuse (pour profiter de ces conditions, Une récupération facile et une qualité améliorée des produits) et en phase liquide (pour une meilleure comparaison avec les conditions typiquement adoptées dans la littérature). Pour les études sur la réduction électro-catalytique du CO2 en phase gazeuse, une série d'électrodes (à base de nanoparticules de Cu, Fe, Pt et CuFe déposées sur des nanotubes de carbone ou de noir de carbone puis placées à l'interface entre une membrane Nafion et Une électrode à couche de diffusion de gaz). Les résultats démontrent le type divers de produits formés et leurs productivités. Dans des conditions sans électrolyte, la formation de produits ≥C1 tels que l'éthanol, l'acétone et l'isopropanol a été observée la plus élevée étant pour Fe et suivie de près par Pt. Pour améliorer les productivités de la réduction du CO2, un ensemble différent d'électrodes a été préparé sur la base de revêtements MOF de type imidazolate de type zéolitique substitué (SIM-1) lors d'un séjour au CPE Lyon et à l'Institut de recherches sur la catalyse et l'environnement de Lyon (IRCELYON). Les catalyseurs testés étaient Fe-CNT, Pt-CNT et CuFe-CNT basés sur MOF. Il y a eu un changement significatif dans les produits de réaction et aussi, la sélectivité vis-à-vis des produits finaux. Pour le catalyseur à base de Pt modifié, MOF, il y avait une augmentation des produits C et également une sélectivité différente tandis que pour le catalyseur à base de Fe, il y avait une légère diminution des produits C. En se reportant aux études sur la réduction électro-catalytique du CO2 dans une cellule en phase liquide, un ensemble similaire d'électrodes a été préparé afin d'obtenir une bonne comparaison des résultats dans les expériences en phase gazeuse. Initialement, des électrodes à base de nanoparticules métalliques (Cu, Fe, Pt, Ru, Co) déposées sur des nanotubes de carbone ou du noir de carbone ont été étudiées pour leur capacité de réduction du CO2. L'ordre relatif de productivité dans la réduction électrocatalytique de CO2 dans ces séries d'électrodes a été trouvé différent entre les cellules en phase gazeuse et en phase liquide indiquant les différentes voies de réaction. Pour les conditions de phase liquide, en termes de produits C nets, les électrodes catalytiques à base de Pt sont en tête de la catégorie, suivies de près par Ru et Cu, tandis que Fe a obtenu la position la plus basse. Le mécanisme réactionnel sous-jacent probable a également été fourni. Afin d'améliorer encore les performances de la réduction du CO2 dans les conditions de phase liquide, une étude de la nanoparticules métalliques (NPs) dépendant de la taille de la réduction électro-catalytique du CO2 aux combustibles a été réalisée. Ceci a été réalisé à l'aide d'électrodes à base de nanoparticules métalliques (Ru, Fe, Pt et Cu) chargées sur les nanotubes de carbone (CNT) transférés sur les couches de diffusion gazeuse (GDL). On a synthétisé des nanoparticules de métal de différentes tailles en utilisant différentes techniques de synthèse: (i) l'itinéraire d'imprégnation pour obtenir des NP dans la plage de tailles de 10 à 50 nm; (Ii) Approche organométallique pour synthétiser des NPs uniformes et ultrafines dans la plage de tailles de 1-5 nm. Fe ont été synthétisés par une nouvelle voie de synthèse et des conditions pour atteindre des NP de 1 à 3 nm. (Iii) Approche de haut en bas de Nanowire pour obtenir des NP métalliques de cuivre ultrafin dans la plage de taille de 2-3,8 nm. En particulier, la nouveauté de l'aide de nanofils est la capacité à obtenir des particules de très petite taille d'abord la synthèse du Cu NFs, puis de les mettre en contact avec le support carboné et de faciliter son transfert, cela grâce à des forces d'attraction intermoléculaires des groupes fonctionnels présent sur le CNT partiellement oxydée. En outre, contrairement à la synthèse organométallique, cette approche permet d'effectuer les réactions dans l'air et non pas dans une atmosphère inerte. Les améliorations de la productivité du combustible ont été trouvées être au moins 5 à 30 fois plus élevées pour les NP métalliques de plus petite taille obtenus par voie organo-métallique ou par nanofil, par rapport aux NP métalliques plus grands obtenus par voie d'imprégnation. Les résultats indiquent que les NP métalliques de plus petite taille chargés sur les CNT jouent un rôle prédominant dans la performance catalytique et la sélectivité vis-à-vis de différents produits. En outre, le pourcentage de charge de NP métalliques a été réduit de façon significative de 10% à 1-2% en poids, produisant des carburants plus élevés ou équivalents pour de petites NP en comparaison avec les NP plus grandes. De plus, comme on a observé clairement la productivité en H2 qui a augmenté de nombreux facteurs pour les NP plus petits sur les plus grandes NP. La réutilisabilité des électrodes de travail et les longs temps de réaction ont également été sondés. Un ensemble différent d'électrodes à base de nano-mousses sur des feuilles métalliques a également été étudié afin d'obtenir des améliorations beaucoup plus importantes de l'électro-réduction de CO2 aux carburants. Ces nano-mousses ou dendrites ont été préparées par une technique de dépôt électrochimique. Des études d'optimisation sur le dépôt de ces mousses ont été effectuées initialement pour fixer l'ensemble des conditions de préparation. De plus, une étude d'optimisation de la tension a été réalisée en utilisant la voltamétrie cyclique et des tests de réduction de CO2 complets pour fixer une tension optimale pour les réactions. Les électrodes nano-mousses testées incluent (mousses Cu, Fe sur feuille Cu, feuille Fe, feuille Al, feuille Inconel et grille Al). Les améliorations de la productivité du combustible pour diverses mousses se situaient dans la plage de 2 à 10 fois par rapport à la productivité nette de combustible la plus élevée obtenue en utilisant des électrodes catalytiques en carbone dopé par des NP métalliques. Différentes caractérisations et outils d'analyse ont été utilisés pour analyser les catalyseurs qualitativement et quantitativement qui incluent la microscopie électronique à transmission (TEM), la microscopie électronique à balayage (SEM), la spectroscopie d'absorption atomique (AAS), la diffraction des rayons X (XRD) La spectroscopie électronique (XPS) et Brunauer-Emmett-Teller (BET) et pour déterminer les productivités des combustibles, chromatographie ionique (IC), chromatographie gazeuse-spectromètre de masse (GC-MS), chromatographie gazeuse.