3-Dimensional Carbon Nanotube for Li-Ion Battery Anode Free Essays

3 Dimensional Carbon Nanotube for Li-Ion Battery Anode (Journal of Power Sources 219 (2012) 364-370) Chiwon Kang1†¡, Indranil Lahiri1†¡, Rangasamy Baskaran2, Won-Gi Kim2, Yang-Kook Sun2, Wonbong Choi1, 3* Nanomaterials and Device Laboratory, Department of Mechanical and Materials Engineering, Florida International University; 10555 West Flagler Street, Miami, FL 33174, USA 2Department of Energy Engineering, Hanyang University; 17 Haengdang-dong, Seongdong-gu, Seoul 133-791, Korea 3Department of Materials Science and Engineering, University of North Texas; North Texas Discovery Park 3940 North Elm St. Suite E-132, Denton, TX 76207, USA Corresponding Author *Email: choiw@fiu. edu Author Contributions †¡These authors contributed equally. We will write a custom essay sample on 3-Dimensional Carbon Nanotube for Li-Ion Battery Anode or any similar topic only for you Order Now Abstract Carbon nanotubes, in different forms and architectures, have demonstrated good promise as electrode material for Li-ion batteries, owing to large surface area, shorter Li-conduction distance and high electrical conductivity. However, practical application of such Li-ion batteries demands higher volumetric capacity, which is otherwise low for most nanomaterials, used as electrodes. In order to address this urgent issue, we have developed a novel 3-dimensional (3D) anode, based on multiwall carbon nanotubes (MWCNTs), for Li-ion batteries. The unique 3D design of the electrode allowed much higher solid loading of active anode material, MWCNTs in this case and resulted in more amount of Li+ ion intake in comparison to those of conventional 2D Cu current collector. Though one such 3D anode was demonstrated to offer 50% higher capacity, compared to its 2D counterpart, its ability to deliver much higher capacity, by geometrical modification, is presented. Furthermore, deposition of amorphous Si (a-Si) layer on the 3D electrode (a-Si/MWCNTs hybrid structure) offered enhancement in electrochemical response. Correlation between electrochemical performances and structural properties of the 3D anodes highlights the possible charge transfer mechanism. Graphical abstract Keywords Li-ion batteries, carbon nanotubes, 3D Cu current collector, anode materials, amorphous Si, a-Si/MWCNTs composite 1. Introduction Li-ion batteries (LIB) has been widely used as one of the most important energy storage devices in diverse applications such as green electric vehicles (EV), portable electronics and power tools, since it is commercialized by Sony in 1991 [1]. The commercial cell is assembled by carbonaceous anode, separator and a Li containing layered structure cathode (e. g. LiCoO2). In terms of carbonaceous anodes, graphite and soft or poorly ordered carbons (e. g. mesocarbon microbeads or spherical graphite, microcarbon fiber) have been employed. The reasons behind their commercial prominence contain the relatively low cost of carbon, the excellent mechanical sustainability for lithium insertion and desertion (having minimum volume change ) and their formation of a protective surface film with many electrolytes [2-4]. Nevertheless, fully intercalated highly crystalline graphites have relatively lower specific capacity (372 mAhg-1, the stoichiometric formulae of LiC6) and cannot meet the demands of next generation LIB with respect to high specific capacity and volumetric capacity. To address these issues, other elemental compounds have been explored such as Al, Si, Ge and Sn [5]. Among those elements, Si is known to have highest theoretical specific capacity (4,200 mAhg-1), however huge volume expansion/contraction (300–400%) during lithiation/delithiation brings about pulverization, resulting in capacity fading in a high number of cycles. To overcome such inherit limitations of bulk electrode materials, worldwide research groups have intensively focused on novel and suitable nanomaterials such as silicon nanotubes [6], silicon nanowires [7], nano sized transitional metal oxides [8-10], graphene [11] and carbon nanotubes 12-14]. Out of the many nanomaterials available, carbon nanotubes (CNTs) have attracted great attention for anode materials due to their high surface area, short diffusion length of Li+ ions and high electrical conductivity [15]. Past researches including from our group have demonstrated outstanding performance of MWCNT based binder-free anodes in terms of high specific capacity, excellent rate capability and extremely or nil capacity degradation during long cycle operation [16-17]. However, carbon nano materials are known as low-density materials, which results in low volumetric capacity and low volumetric energy/power density. Therefore higher solid loading of MWCNTs as active materials is one of the most significant issues to be realized in practice. Very recently, it argued that nanotube based active materials have a critical shortcoming in terms of their very low weight per unit electrode area [18]. Thus, their gravimetric energy density may not give a realistic picture to commercial application. The critical limitation may lead to scale-up issues for their potential application in the development of EV. To counter this issue, we propose a new geometry of 3D Cu current collectors, which can play a crucial role in creating higher surface area to accommodate more solid loading of MWCNTs on the uniformly arrayed patterns in the 3D structure, leading to higher specific capacity and C-rate capability. Until now, efforts have been dedicated to employ a number of 3D structured current collectors including carbon papers [19], a self-assembled 3D bicontinuous nanoarchitecture [20], aluminum nanorods [21], and nanoporous nickel [22]. The previous research proved that a self-assembled 3D bicontinuous nanoarchitecture could be one of the ideal electrode architectures in order to realize not only high volume fraction of nanostructured electrolytically active materials (NiOOH/Nickel and MnO2 cathodes) but also their efficient ion and electron transport [20]. In addition, ALD coated TiO2 anodes on 3D aluminum nanorod current collectors showed the 10 times increase in their theoretical area and total capacity (0. 0112 mAhcm-2), compared to those resulted from the same anodes on 2D flat aluminum plate and high rate capability (the capacity ratios at 10 C/0. 5 C and 20 C/0. 5 C of the 3D anode were 0. 4 and 0. 35, respectively. ) [21]. Currently, the diverse types of hybrid anode structures have been designed and synthesized in order to expect the synergetic combination of two different types of nanomaterials for the igher electrochemical performances. As one of the most preferable combinations, MWCNTs/Si hybrid structure can be chosen due to the better mechanical accommodation of MWCNTs of the large volume expansion/constriction of Si during lithiation/delithiation process and the higher bonding strength between MWCNTs and Si. There were some selected reports on MWCNTs/Si composite structures, employing either SiH4 CVD method [23] or sputte r deposition [24]. In this study, we present a novel concept 3D anode system, comprising of MWCNTs directly grown on 3D Cu mesh using catalytic thermal CVD method [25]. Electrochemical performances of this 3D anode structure are compared with those of MWCNTs directly grown on 2D Cu foil. Furthermore, enhanced electrochemical properties of a-Si/MWCNTs hybrid structure, synthesized on 3D Cu mesh using a two step process of CVD and sputtering deposition, are presented. Morphology and structure of as-grown MWCNTs and a-Si/MWCNTs hybrid anode structures and their role in the electrochemical performance are discussed. 2. Experimental A Cu mesh (TWP Inc. with average dimensions of 50  µm thickness and 65  µm hole size was prepared. In parallel, a 50  µm thick pure Cu foil (Nimrod Hall Copper, 99. 9% purity) was also employed. Both types of samples were used as substrates for depositing Ti (underlayer)/Ni (catalyst) thin film through a RF and DC magnetron sputtering system. These Ti/Ni thin film deposited samples were cut to 14 mm diameter disc shape for 2032 button cell assembly, before inserting into a thermal CVD system for direct MWCNT growth. During CVD, samples were heated very rapidly, under an inert Ar gas environment, to the growth temperature of 750 °C, and MWCNT growth began with flow of a mixture of ethylene (C2H4) and hydrogen (H2) gas (1:2 volume ratio) in the chamber. After 50 minutes of growth, the samples were cooled to room temperature within the furnace under an Ar gas envelope. Amorphous Si (a-Si) was deposited further on the as-grown MWCNT samples using the sputtering system with the incorporation of Ti adhesion layer in order to enhance bonding strength between a-Si and MWCNTs. Weights of samples were measured before and after CVD growth to exactly identify weights of the active materials (i. e. MWCNTs and a-Si thin layer). Morphology and structural properties of the prepared anode structures were carefully investigated using field emission scanning electron microscopes (FESEM) (JEOL, JSM-7000F), an energy dispersive spectroscope (EDS) (Thermo Electron Corporation, NORAN System SIX), a Raman spectrometer (Ar+ laser with ? = 514 nm, 33 mW power) and a field emission transmission electron microscope (FETEM) (FEI, TECHNAI F20). Electrochemical performance for these anodic materials was conducted in a typical coin cell (half cell). The cells were assembled in a CR2032 press. The complete cell assembly was carried out in an argon glovebox under extremely low levels of oxygen and humidity (both individually 0. 1 ppm). A pure Li (purity, 99. 9%) metal foil (150  µm thickness) was used as both the reference electrode and counter electrode, while the MWCNTs on 3D Cu mesh, the MWCNTs on 2D Cu foil and the a-Si/MWCNTs composite on 3D Cu mesh were used as the working electrodes. All the coin cells employed a solution 1. 0 M LiPF6 in EC-DEC (ethylene carbonate : diethyl carbonate, 1:1 in volume ratio) as the electrolyte and a typical polypropylene-polyethylene material (Celgard 3401) as the separator. The charge-discharge tests of the cells were performed in TOSCAT 3100U multichannel battery testing unit, at a constant temperature of 30 °C, in galvanostatic (constant current density) mode. The cells were cycled in the voltage range 3. 0 – 0. 01 V, recording a current value in each 10 mV step, at a slow rate (0. C) during the initial formation process and at various C-rates in the following cycles. 3. Results and Discussion 3. 1. Theoretical calculation of the surface area of 3D Cu mesh The purpose to introduce 3D Cu mesh as current collector was to increase in surface area for the growth of MWCNTs, thus leading to more amount of Li+ intake into them, as compared to 2D Cu foil. 3D Cu mesh was an interlaced structure of numerous Cu wires (Appendix A. F igure 1(a) and Figure 1(b). ). Simple geometrical model was followed to calculate the total surface area of this 3D structure, since the calculation of the actual surface area of the assembled 3D Cu mesh was very difficult. For easier calculation, the cylindrical Cu wires were simplified to rectangular wires of equivalent surface area, creating a cuboid array (Appendix A. Figure 1(c). ). In this study, MWCNTs were synthesized on the top and lateral surface areas of the 3D Cu mesh only, hence only these areas were considered for calculation. Figure 1(a) was a schematic view of an anode stack built up of 4 layers of MWCNTs on 3D Cu mesh. As a real example, we implemented an anode stack system using 9 individual MWCNTs on 3D Cu mesh, in which MWCNTs were coated over the entire area of the Cu meshes as illustrated in Figure 1(b). The assembled anodes were physically bonded by adhesion force between the entangled MWCNTs. This phenomenon may be thought of as being in some way analogous to â€Å"Velcro† effect of scales on wool fibers [26]. A simple geometrical relationship was established to calculate the total surface area of 3D Cu mesh and 2D Cu foil (no hole). Variation of the surface ratio of 3D Cu mesh to 2D Cu foil as a function of the thickness (T) and the size of holes (L) of 3D Cu mesh is presented in Figure 1(c) (The detail calculation procedure is shown in the Appendix A. ). Surface area increased with the thickness of the structure, though its relation with hole size was not straight forward owing to contribution from a fixed Cu wire diameter. It may be recalled here that the present study used a Cu mesh with its dimension 50  µm thickness and 65  µm hole size, which showed surface area improvement (almost 60%) as compared to 2D Cu foil. Empirically, the average weight of MWCNTs on 3D Cu mesh was 4. 37 mg for a cell with 14 mm diameter and 50  µm thickness dimension, which represented solid loading increase by 400%. Thus, it was found that the theoretical calculation was inconsistent with the experimental results since it did not include the influence of control parameters on the properties of MWCNTs such as their diameters, lengths and densities during the CVD growth. From an anode system assembled using 9 individual MWCNTs on 3D Cu mesh (The size of a cell is 15 mm diameter and 50  µm thickness. , the average maximum loading amount and packing density of MWCNTs were higher than 50 mg and 0. 248 g/cm3, respectively. The weight of stacked anodes proportionally increased with the number of individual one, which is in a good agreement with the calculation results. 3. 2. Morphology and structural properties of MWCNTs and a-Si/MWCNTs on 3D Cu mesh Unique 3D structure of the proposed anode is expected to influence the electrochemical performance. Structural characterization, involving SEM and Raman spectroscopic analysis, has been conducted on these 3D anodes (See Figure 2. . As presented in Figure 2(a), MWCNTs were homogeneously and densely grown over the whole top and lateral Cu mesh area. In addition, the high magnification SEM image showed the randomly entangled MWCNTs with their length around 30  µm and diameter in the range of 200 – 300 nm (See Figure 2(b)). Compared to the 2D Cu foil, the surface areas of the Cu wires surrounding the hole spaces could be available sites for the MWCNT growth, which is structural advantage of the 3D Cu mesh to increase the weight of the MWCNTs as active materials. In Figure 2(c), the sketch of the cross section view of MWCNTs grown on a single Cu wire exhibited the densely grown larger diameter MWCNTs on the top surface area and relatively smaller diameter MWCNTs on the lateral side area. Along with the structural characteristic, the interfacial control between active material and current collector significantly influences the electrochemical performance of the anode system. It is highlighted that the strong bonding between MWCNTs and Cu making it possible to directly grow MWCNTs on Cu mainly stemmed from TiC underlayer [16, 27]. The TiC underlayer was formed by the reaction of Ti thin film sputter deposited onto 3D Cu mesh with carbon precursor gas at high temperature about 750 °C during CVD processing. High ratio of ID/IG (around 1) in Raman spectra (Figure 2(d)) of the MWCNT structure also revealed high defect density in the structure. It is reported that the MWCNTs containing more defects showed the better electrochemical performance since the higher presence of defects provided with more available sites for Li+ ion intakes into the MWCNTs structure and shortened the diffusion length of Li+ ion [28-29]. MWCNTs possessing more defects, generated by mechanical breakage and chemical etching, resulted in an increase in specific capacity compared to untreated MWCNTs. In the case of a-Si/MWCNTs hybrid structure, the broad intensity peak around 480 cm-1 (in Raman spectra) showed amorphous Si [30]. It was subsequently confirmed from the EDS analysis in the linearly selected area across the SEM image as shown in figure 2(d) that Si was deposited on the some portion of the surface of the MWCNTs. The line profile denoting Si K distinguishably appeared, demonstrating the presence of a-Si deposited layer. . 3. Electrochemical performances of the MWCNTs based anode systems 3. 3. 1. Charge/discharge capacities Electrochemical performance tests were conducted on these anode structures and the results were presented in Figure 3. First charge-discharge curves for all the anode systems were presented in Figure 3(a). The button cells were charged/discharged in a galvanostatic mode between 0. 01 and 3 V , at C-rate of 0. 1 C (specific current 38 mAg-1) determined by theoretical specific capacity of graphite (372 mAhg-1). In the case of MWCNTs on 3D Cu mesh electrodes, several samples with different solid loading of MWCNTs were measured under the same condition and showed average discharge capacity 474 mAhg-1, LiC4. 7. In Figure 3(a), all the discharge curves exhibited a plateau in the voltage range 0. 75 – 0. 9 V. Such plateau was found in most graphite or CNT based anodes and stemmed from the decomposition of electrolyte and the formation of solid electrolyte interphase (SEI) on the carbonaceous anode materials [3, 31]. Based on the very similar first discharge curves of the MWCNTs and the a-Si/MWCNTs electrodes, it was implied that the MWCNTs mainly controlled the electrochemical properties in both anode structures since the major weight (above 99% weight ratio) of the structure came from the MWCNTs. However, the effects of a-Si incorporation on the electrochemical performance were investigated by the first charge curves of the both anodes. The average specific charge capacities of the MWCNTs and the a-Si/MWCNTs electrodes were 299 mAhg-1 and 345 mAhg-1 (almost 16% improvement), respectively. In addition, the Coulombic efficiency of the a-Si/MWCNTs 67% was higher by around 4% than that of the MWCNTs 63%. The relatively higher irreversible capacity at the first charge-discharge cycle is considered a critical limitation of carbonaceous anode materials and the capacity loss may be mainly associated with solid electrolyte interphase (SEI) formation or a permanent alloy formation [31]. Another possible reason involved the insertion of lithium ions into defect sites (e. g. microcavities) residing in the MWCNTs and their entangled structures [32]. Li ions inserted into the defect regions at the first discharge process might be trapped and could not be completely extracted during the charge process. Lithium oxide formation at higher voltage could also be another reason for the initial capacity loss [33]. However, Figure 3(a) showed that most Li insertion process proceeded mostly below 1. 5V (versus Li/Li+) so that the possibility of charge consumption due to lithium oxide formation may be excluded, in the present case. It may be mentioned here that the higher values from the a-Si/MWCNTs indicated the a-Si thin layer could play a role in maintaining the stability f SEI formation [17]. On the contrary, the first discharge curves of all the specimens of the MWCNTs on 2D Cu foil represented the average specific discharge capacity 323 mAhg-1, LiC6. 9. The average capacity value was more than 3 times lower than that of our previous result [16]. It was speculated that the significant difference was due to different morphology of MWCNT s (average diameter 80 nm, which was thinner than that of the current MWCNTs). At higher growth temperature, the size of the catalytic Ni islands became larger on account of their more facile diffusion [34]. With respect to major electrochemically active sites being on and near the surface of MWCNTs [16], the thicker MWCNTs have less active surface area per mass available for participating in electrochemical reaction as compared to the thinner MWCNTs, thereby resulting in the lower specific capacity. During the initial cycle, the MWCNTs on 3D Cu mesh offered 47% higher average specific capacity compared to that of the MWCNTs on 2D Cu foil. It may be noted here that this specific capacity enhancement is close to surface area enhancement 60% also. Compared to the MWCNTs on 3D Cu anodes, the a-Si deposited MWCNT anodes offered the higher average specific discharge capacity 517 mAhg-1, LiC4. 3. This enhancement could be related to the presence of a-Si thin layer with its high specific capacity on the MWCNTs. It was observed that the weight of the deposited a-Si was lower than 1% of that of the MWCNTs; therefore, the a-Si thin layer did not have any major contribution except slight increase in the overall specific capacity of the anode, unlike the previous results from Si nanotubes [6] and Si nanowires [7]. . 3. 2. Cycling stability Cycling stability tests are essential to prove electrochemical performance of the anodes at long cycling operation in the real application. Figure 3(b) illustrates a comparison of the cycling stabilities obtained from the three different kinds of anode systems up to 50 cycles at 1 C-rate (current density 372 mAg-1). In the case of the MWCNTs on 3D Cu mesh electrode, the reversible capacity slightly in creased from 226 mAhg-1 at first cycle to 258 mAhg-1 at 39th cycle and then gradually faded to 254 mAhg-1 until 50th cycles. Such a trend of increase in capacity over the whole cycles is inconsistent with previous results from the constant capacity of MWCNT [16-17]. It was speculated that the continuous charge-discharge process led to create more surface area on the densely entangled MWCNT network structure. We also investigated whether such an activation process was due to more defects in the structures of MWCNTs induced by the charge-discharge process. According to the SEM images presented in Figure 4(a) and (b), it was not evident that severe defects or structural damages appeared in the both 150 cycled and just one discharged anode systems. HRTEM images revealed that for both the anode systems, the structural integrity of graphene layers still remained with the shallow amorphous second phase region on the edge of the MWCNTs as shown in Figure 4(c) and (d). In addition, it was pointed out that there was no appreciable volume variation during lithiation and delithiation. No clear evidence of diameter change was observed between the as-grown MWCNTs and the MWCNTs subjected to 150 charge-discharge cycles (Figure 2(b) and 4(a)). This observation is in agreement with small volume change of graphitic carbon upon lithium insertion and extraction (typically LiC6, around 12%) [35]. In the same manner, it was confirmed that the specific capacity of the a-Si/MWCNTs on 3D Cu was gradually increased. Along with the electrochemical activation process of MWCNTs, the result could reveal the effect of capacity improvement with additionally incorporated a-Si to take more Li+ ion intakes (almost 10% enhancement of the reversible capacity). Furthermore, the Si-C bonding at the interface between a-Si and MWCNTs was strong enough to avoid peeling off of the a-Si layer during the cycling test. It was highlighted that MWCNTs and a-Si/MWCNTs grown on 3D Cu mesh showed good cycling stability without severe capacity degradation. However, for the MWCNTs on 2D Cu foil, the average reversible capacity 163 mAhg-1 was kept constant until the number of 50 cycles. It should be noted that the larger reversible capacity of the 3D MWCNTs was presumably due to their large surface area to accommodate more Li+ ion intercalation. In terms of the reversibility of charge-discharge process, the Coulombic efficiency of the MWCNTs on 3D Cu mesh was more than 98% after the initial 4 cycles at 1. 0 C-rate and then increased to 99% after 22 cycles according to the result shown in Figure 3(c). Such reversibility was ascribed to the sufficient supply of Li+ ions from Li metal foil used as the reference electrode and counter electrode in the button cell. 3. 3. 3. Rate capability Rate capability tests are also crucial to prove electrochemical performance of the anodes at higher charge-discharge rate operation. Figure 3(d) showed the rate capability of the proposed anodes. The discharge capacity of the MWCNTs on 3D Cu mesh was almost constant around 300 mAhg-1 until reaching 1 C-rate (372 mAg-1) and then decreased to 283 mAhg-1 at 3 C-rate (1,116 mAg-1) and further to 250 mAhg-1 at 5 C-rate (1,860 mAg-1). It may be highlighted that discharge capacity slightly increased with C-rate from 0. 1 C to 1 C and the phenomenon could be attributed to the electrochemical activation process of MWCNTs during cycling as mentioned above. At higher C-rates (e. g. 3 C and 5 C), Li+ ions were inserted and extracted into and from the only surface regions of the forest-like MWCNTs structure due to the limitation of diffusion length of Li+ ions. Another interesting observation was slight increase in specific capacity from 283 mAhg-1 at 1st cycle to 320 mAhg-1 at 22nd cycle at the same 0. 1 C (38 mAg-1) rate. It was again confirmed that higher number of cycles during C-rate tests could be a reason to effectively carry out electrochemical activation process in the MWCNT structures. On the contrary, the MWCNTs on 2D Cu foil electrode showed a typical staircase type decreasing capacity behavior till the tested limit of 5 C-rate. The direct comparison revealed the higher C-rate capability of the MWCNTs on 3D Cu mesh electrode, as compared to the MWCNTs on 2D Cu foil. In particular, at 5 C, the average specific discharge capacity of the MWCNTs on 3D Cu mesh was 249 mAhg-1 (14% increase), whereas that of the MWCNTs on 2D Cu foil was 218 mAhg-1. The result could be strongly associated with the higher surface area for Li+ ion intercalation due to approximately 4 times higher solid loading of MWCNTs on 3D Cu mesh. Furthermore, the higher C-rate capability is significantly attributed to the strong bonding and the lower electric resistance between Cu and MWCNTs, through TiC interface layer [36-37]. Moreover, at 5 C, the average capacity of the a-Si/MWCNTs on 3D Cu mesh electrode was 334 mAhg-1 (34% enhancement), while that of the MWCNTs on 3D Cu mesh was 249 mAhg-1. In addition, the average capacity ratios at 5 C/0. C of the MWCNTs on 3D Cu mesh and the MWCNTs on 2D Cu foil were 0. 86 and 0. 8, respectively, whereas the ratio of the a-Si/MWCNTs on 3D Cu mesh was around 0. 93. According to the better performances, it was proved that a-Si thin layer coating on MWCNTs could play an important role in the enhancement of C-rate capability. 4. Conclusion A novel 3D MWCNTs on Cu current collectors as an anode of LIB was developed. The 3 D anodes showed higher specific capacity, cycling stability and C-rate efficiency as compared to those of the MWCNTs on 2D Cu foil anodes. The better performances of the 3D anodes were attributed to the higher average solid loading of MWCNTs, which was 4 times higher than that of the 2D anodes. Addition of the a-Si onto the 3D MWCNTs/Cu showed the further enhancement of electrochemical properties. Acknowledgment Authors thank N. Ricks and Y. Liu for Nano fabrication facility and FESEM characterization, S. Saxena for allowing to use the Raman facility and J. Hwang and R. Banerjee for HRTEM characterization. It is grateful that J. Kim and D. Kim who provided us with the schematic diagrams. This research was, in part, supported by WCU (World Class University) program through the Korea Science and Engineering Foundation funded by the Ministry of Education, Science and Technology (R31-2008-000-10092) and AFOSR Grant (FA9550-09-1-0544). Appendix A. Supplementary data List of figure captions Figure 1. (a) A schematic model of an anode stack assembled using 4 numbers of converted uniform stacking cuboid arrays from the geometry of a real 3D Cu mesh (The bottom right inset shows a unit cell of the cuboid arrays. , (b) SEM images exhibiting a cross-section perpendicular to the anode system stacked by 9 individual MWCNTs on 3D Cu mesh and highly entangled structures of MWCNTs, (c) The surface area and its increment of the 3D Cu mesh and the 2D Cu foil and the average real weight of MWCNTs as a function of different thickness and hole sizes (The inset illustrates a unit cell of the 3D Cu mesh with its dimension. ). Figure 2. Morphology and structure of the proposed anode systems . a) A plane view of SEM image showing the MWCNTs covered on the 3D Cu mesh, (b) The threadlike grass structures of MWCNTs on the 3D Cu mesh with their diameter in the range of 200 – 300 nm, (c) Schematic diagram (not to scale) of the geometry of the MWCNTs grown on the 3D Cu mesh and the a-Si deposited MWCNTs structure on the 3D Cu mesh, (d) EDS elemental analysis of the a-Si/MWCNTs hybrid structure in the linearly selected area across the SEM image, (e) Raman spectroscopic response indicating high defect density of MWCNTs according to ID/IG ratio around 1 and the amorphous Si peak at around 480 cm-1 in the a-Si/MWCNTs. Figure 3. Electrochemical performance of the anode structures of as-grown MWCNTs on 3D Cu mesh, MWCNTs on 2D Cu foil and a-Si/MWCNTs core-shell composite on 3D Cu mesh. 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Debut Albums and Blue Face free essay sample

Annie finally went home but no one was home. She waited at the front of the house for her parents or her brother to come home. While kip was with Andrew trying to find grace. Kip has lost his sense of purpose, he doesnt know what he wants to be anymore. He doesnt feel like the compassion to swim like before he is confused and lost. Nannies mother and her brother finally came home. They saw her but not grace entering where she is. Annie told her mum that she doesnt know where she is, making her mother worried and scared what might of happen to her. Kip and Andrew went to find shelter while the police come to find grace and a boy. When the police came they started to ask questions about the where about grace was while looking for her. Kip saw a boogie bored and taught someone was on it so he knew the one thing he could do, was to swim. We will write a custom essay sample on Debut Albums and Blue Face or any similar topic specifically for you Do Not WasteYour Time HIRE WRITER Only 13.90 / page When he swam to the bored he felt a strong current coming and that he couldnt control himself. As kip was getting bushed by the waves Annie went with her family to look for grace and where was the last place Annie saw grace making the police think that she must have dropped into the water. When kip was floating into the water a boat came and saved him and took care of him. When he was awake he saw a figure with a blue face and mouth It was a boy.

Napoleon free essay sample

In 1800, the French people vote in favour of a new Constitution Napolean made a series of reforms to improve the government, economy, and lives for French citizens To fix the French economy, he introduced a fair tax system and a Bank of France to regulate the money supply He created a merit based system for government bureaucrats He created public schools for students of all backgrounds He issued s comprehensive set of laws called the Napoleonic Code that provided order, freedom of religion, and eliminated privileges by estates. In 1804, Napolean ordered an election and the French people voted Napolean emperor for life. Napolean wanted control of a global empire in North America and Europe But, the revolution in Haiti convinced Napolean to abandon North America In 1803, Napolean sold territory in Louisiana to the United States for 15 million; The Louisiana Purchase doubled the size of the USA. During the Napoleonic Wars, Napoleon sowed his military genius by debating Austria and Prussia and conquering Spain, Italy, and central. We will write a custom essay sample on Napoleon or any similar topic specifically for you Do Not WasteYour Time HIRE WRITER Only 13.90 / page During his rule over Europe, Napoleon made a number of devastating decisions. The one nation Napoleon could not defeat was England. He ordered a blockade, called the Continental System, to cut off all trade with England. The Continental System was a failure and hurt the French economy more than Englands economy. Napoleans insistence that nations obey French laws led to a rise in nationalism and uprisings against France. In 1812, Napoleon made his greatest mistake and invaded Russia The harsh winter and Russias scorned-earth policy devastated the French army and forced Napoleon to retreat In 1814, the weakened French army was defeated; Napoleon surrendered, was forced to give up his throne and was exiled to the island of Elba. The French monarchy was restored, but King Louis XVII was unpopular in 1815, Napoleon escaped and triumphantly gained the throne Only 100 days after napoleons return, he built a new army but was defeated by a European coalition at the Battle of Waterloo in 1815. After his defeat, Napoleon was exiled to the remote island of St. Helena in the South Atlantic where he died after six years What was napoleons impact? He created reforms that ended the financial crisis and unequal class system and made public schools and the Napoleonic law code. His massive empire brought glory to the French people. His rise as emperor ended the Enlightened ideas of democracy that led to the French Revolution The fall of empire led to a conflict between rule by strong monarchs and democratic governments Other Accomplishments of Napoleon The Concordant (1801) Gave Catholic Church status as official state Church; French state would choose and pay clergy; Pope would consecrate The era after the fall of Napoleon was a conflict among conservative, liberal and radical forces Conservatives were usually wealthy land owners and. Nobles; They typically supported traditional monarchies Liberals were usually from the middle class; They supported Enlightenment ideas like limited monarchies and voting rights for educated landowners Radicals were usually from the lower classes; They supported extending democracy to all citizens When Napoleon was defeated in 1815, European leaders met at the Congress of Vienna to retire peace and bring stability back to Europe Congress of Vienna was attended by conservatives from Austria, Prussia, Russia, Britain, France and was led by Austrian minister Klemons von Metternich Metternich and other delegates disliked democracy, feared the ideas of the French Revolution, and wanted to restore Europe to the way it was before Napoleon. One goal was go prevent future French aggression This was accomplished taking from France all lands it gained under Napoleon and making the nations around France stronger The kingdom of Netherlands was created Switzerland became a nation 39 states joined to form the German Confederation Sardinia merged with Genoa Buffer zone was created between France and the major European powers One goal was to restore monarchs to power in Europe This was done by restoring kings in France, Portugal, Spain, and many Italian and German states One goal was to maintain a balance of power in Europe This was done by forming the Concert of Europe, an alliance among Russia, Austria, Prussia and Britain to maintain peace and stop future revolutions The decisions made at the Congress of Vienna helped maintain peace in Europe for almost 40 years But the decisions of the Congress of Vienna did not make liberals or radicals happy The restoration of kings led to an increase in demand for democracy in Europe In 1848, a surge of nationalism swept through Europe which sparked revolutions for democracy and the formation of new nations The Battle of Trafalgar Napoleons plan to invade Britain shattered by a huge British victory at the naval battle of Trafalgar (1805)

Hitler Essays (380 words) - Hitler Family, Adolf Hitler, Hitler

Hitler Essays (380 words) - Hitler Family, Adolf Hitler, Hitler Hitler He stands motionless with crossed arms and resting eyes focused straight ahead. He is completely immobile, expressionless, and says absolutely nothing. Surrounded by some fifteen thousand audience members filing into the great auditorium to hear this man speak, the presence he commands brings order to the environment almost immediately. There is little doubt that Adolf Hitler projected a commanding presence. The aforementioned was merely a description of events which took place prior to one of his famous speeches during the pre-war Nazi years, when his party was only coming into power and Adolf Hitler, as a personality, was making his presence known on the scene. This historical backdrop of Germany in the 1930's reveals a country knee-deep in economic depression, and as would well be expected, the climate was ripe for a new leader. Adolf Hitler made his presence known in the form of a Messiah rather than a political leader, offering his countrymen not only economic but political salv ation as well as the kind of cultural magnificence which he truly believed in, i.e. the Aryan race. Adolf Hitler was born on April 20, 1889 in the Austrian town of Braunau am Inn, the son of Alois, a customs official, and Klara Hitler. He was not a successful student, and his earlier years are said to have been characterized by melancholy, aimlessness and racial hatred. It was in Vienna where he developed what is considered to be a life-long obsession with the danger that the world Jewery posed to the Aryan race. It was after Hitler relocated to Munich in 1913 and served in the Bavarian 16th Regiment that he distinguished himself for bravery and was awarded the Iron Cross First Class. It was during this time that Hitler had found a home and glorified the raw majesty of life under fire, the beauty of comradeship and the nobility of the warrior. His soldierly dreams of victory and fulfillment were shattered, however, by Germany's defeat. He became convinced that Germany had been stabb ed in the back by Jews and Marxists.1 Oratory and the printed word were much a part of Adolf Hitler's rise to save the fatherland. It is my personal view that Hitler acquired his oratory skills and acuity through his earlier experiences.

American Political Parties Essay Example | Topics and Well Written Essays - 1500 words

American Political Parties - Essay Example 791, divisions began to grow as Madison urged Jefferson to join him in organizing against Hamilton leading to formation of the Democratic - Republican Party mainly by anti-federalists. The founders of this party included: Madison, Jefferson, Robert Livingstone and George Clinton of New York and Senator Aaron Burr of Virginia. In midterm Congressional elections, the party garnered majority seats in Congress with 65 members. Madison was supported by Virginia, North Carolina, Georgia, New York and Pennsylvania while New England opposed him (Reichley 32). The Democratic - Republican Party appealed to rural population and farmers; it was an agrarian party. It also advocated economic and social equality and liberal ideals. The French revolution also was an issue at the time and its supporters formed democratic societies (Democratic or Republican) and campaigned in 1794 elections for Republicans (Democratic - Republican Party). They were joined by some federalists’ to become majority party in 1795. Washington did not seek reelection for third term thus the 1996 elections pitted Adams a federalist against Jefferson a Republican. The Republican Party was defeated narrowly by Adams with 71 votes against 68. Thomas Pinckney a federalist got 59 votes and Burr (Republican) 30 votes. Jefferson became the vice president (Reichley 39). The party build up organizations to support Republican candidates and in mid elections Republicans garnered majority seats in Congress. In New York, Burr managed to get a uniform vote for the party ticket. The party got support from evangelicals who were Presbyterian New lights. Support also came from converts of rural families in South and Western frontier (Baptists and M ethodists) and Catholics because of it equalitarian ideals (Maisel, 31-75). In 1800 elections Republicans won with narrow margin with Jefferson 73 votes and Aaron Burr 73 votes, Adams 65, Pinckney 64. Due to tie, the winner was decided by House of Representatives whereby

Final Exam questions Assignment Example | Topics and Well Written Essays - 500 words

Final Exam questions - Assignment Example Qualitative risk assessment however applies rationale to develop fixed values of factors to risk. Qualitative risk assessment method is the most suitable for homeland security. This is because of its diversified advantages, over the quantitative method, that meets the scope of Homeland security’s need for fast and accurate reactions. The advantages include simple analysis and results that facilitates prompt detection and response to risks (Landon, 2011). Risk management refers to a strategic process of managing probability of loss that is associated with a peril. Risk management strategies involve identification of involved risk, followed by its analysis that culminates to mitigation. The strategies are â€Å"avoidance, reduction,† and transfer (Akitonye, and Beck, 2009, p. 245). The three major threats facing the United States today are terrorism, natural disasters, and cyber crime. Terrorism is however the greatest of these threats because of its source and its political aspects. Being caused by human beings means that it can happen any time and its risk is enhanced by the United States international positions as a world power. The nation’s participation in international wars, especially in the Middle East also identifies significance of the threat. The relationship between risk, critical assets, threats, vulnerability, and consequences is that risk is a factor of critical assets, threats, and vulnerability, and its occurrence leads to adverse consequences. Risk defines exposure to a peril or potential peril. Critical assets define those assets that are instrumental to attainment of an objective while threats define phenomena that induce unpleasant effects. Vulnerability refers to the susceptibility to a threat and consequences define the results of manifestation of a threat. The presence of critical assets, threats, and vulnerability integrates to

Role of Ecotourism in Sustainable Development

Role of Ecotourism in Sustainable Development Nowadays in developing countries, ecotourism is used as an excellent tool for promoting sustainable development. It is very beneficial for local communities creating environmental, economic and social benefits. Ecotourism is carried out by many tourism planners and marketers nowadays. The important aspect involved in ecotourism is its proper planning and implementation. In the case of improper planning it converts all the economic gains into social and environmental disasters. Ecotourism has gained popularity developed into a worldwide phenomenon showing no signs of slowing down. Even though it is not a universal remedy for attaining sustainable development, its potential towards promoting sustainable development deserves considerable attention. The purpose of this paper is to analyze the impact of ecotourism in attaining sustainable development in Costa Rica. Ecotourism The concept of ecotourism was well identified in 1960s by Hetzer who contributed to this by identifying four principles of ecotourism. They are minimizing environmental impacts, respecting host cultures, maximizing benefits to local communities maximizing tourist satisfaction. Ecotourism is an integration of social, environmental and economical benefits meeting both human and environmental needs. One of the major causes for the evolution of ecotourism is the dissatisfaction with mass tourism creating over development, pollution and foreign investment. According to International Ecotourism Society (2004) Ecotourism is a Responsible travel to natural areas that conserves the environment and sustains the well-being of local people. Sustainable Development The term sustainable development received international recognition in 1980s. In 1987, Bruntland commission defined sustainable development as Development that meets the needs of the present without compromising the ability of the future generations to meet their own needs. It is a combination of social, economical and environmental development. Ecotourism Sustainable Development It is nothing but sustainable tourism. In 1995 World Trade Organization stated in Agenda 21 that Sustainable tourism development meets the needs of present tourists and host regions while protecting and enhancing opportunity for the future. Sustainable tourism involves a number of principles in it. Sustainable development is not the only goal of ecotourism, but sustainable development is very important for achieving the goal of ecotourism. About Costa Rica Costa Rica which means Rich Cost is a country in South America bordered by Nicaragua in north, Panamma in south, Caribbean Sea in east and Pacific Ocean in west. The government is constitutionally democratic. It constitutionally abolished its army permanently in 1949 becoming military neutral. It was ranked first among the Americas for Environmental Performance Index in 2010. Total area 19,653 sq.m Water percentage 0.7 Population 4,253,897 GDP (nominal) $29.318 billion It contains 5% of the worlds biodiversity. Around 25% of the countrys land area is covered by protected national parks and protected areas. About 24 national parks are found in Costa Rica. The Monteverde cloud forest reserve is a home for about 2000 plant species, over 400 birds, over 100 species of mammals and numerous orchids. Growth of ecotourism in Costa Rica Costa Rica earned reputation as a premier ecotourism destination in the world also considered as ecotourisms post child. Some of the factors that influenced ecotourism in Costa Rica are pleasant climate, excellent national park, best public health care system, best public education, highest literacy rate in Latin America etc. It is also blessed with abundant natural resources such as beaches, mangroves, mountains, caves, waterfalls, volcanoes and tropical rainforests which is one of the most biologically diverse areas of the world containing 5% of entire planets biodiversity. In a short period Costa Rica has reached high level of maturity in ecotourism creating both beneficial effects and detrimental consequences on sustainable development. It is considered as a model in implementing ecotourism in many other areas. Economic impacts Globalization plays an important role in global economic decision making. As globalization and unbridled economic competition continue to dominate the global agenda, the travel agents who came up with the idea of ecotourism were now looking for new markets and not the ways to save the world. Because of this issue, many protected regions of Costa Rica are increasingly integrated into the global economy. Park entry fees and other form of revenues increase the value of protected land rather than the revenue obtained from deforestation. Ecotourism also earns foreign exchange to developing countries by bringing tourists from north ( from developed countries). A survey states that in early 1990s Costa Rica was the leading overseas ecotourism destination for U.S travellers, but only 20% of its revenue went to the local community and the remaining was paid to the tour operators, tickets on foreign owned airlines, to import products that appeal foreign tourists. A certain percentage of profits can be recycled to the local community development through legislation so that revenue leakage is reduced. In general, the employment opportunities of the people living near to ecotourism destinations is based on the tourists. In Costa Rica, people living near to Monteverde cloud forest reserve is an excellent example who have gained great economic values with this. Contrast to the previous point, Osa peninsula a ecotourism spot in Costa Rica has made its inhabitants even more poorer than before over attraction by ecotourists which created profit to outsiders. Marketing in general is used to elaborate a buisness scale. In Costa Rica in regions where outsiders dominate, marketing is used es an efficient tool by the local community to elaborate their buisness. Fake marketing is also done in some regions which is of no environmental responsibility. Since ecotourism is a seasonal activity, it can fluctuate over time to time and the local community cannot entirely depend on this for their earnings which leads to economic discomfort. Outsiders took over many regions in Costa Rica which have become distorted and the prices have increased drastically so that many Costa Ricans have been priced out of land and home ownership. Social impacts Even though the local communities are not traditionally involved in ecotourism planning and implementation, it becomes essential for them to get involved in different phases of it for their own benefits. Also the local communities are very familiar with the local resources, it makes them essential to involve in decision making. Stakeholder participation and community involvement are very important in decision making process since they have the greatest stake in the outcome of any ecotourism project. The culture of the local community plays an important role in ecotourism. For a sustainable ecotourism, cultural structures of the local community must be well understood so that the disintegration of the local communities can also be avoided. In Costa Rica, people in many rural areas did not support ecotourism instead they felt it as a threat to their cultural dynamics. Ecotourism brings many advantages to the local community if they integrate themselves with it otherwise it can lead to commofication resulting in erosion of culture and community cohesion. Ecotourism provides some employment opportunities to the local community such as hotel servicing, crafting, government agency staff, tour operators etc. In Costa Rica local community people are trained in the areas of park maintanance, habitat restoration, management etc in order to incorporate them in protected area management. Govrnment should provide some subsidies and intensives to local poor people to own a buisness. Many innovative and resposible locally owned ecotourism projects fail due to insufficient investments and their competition with large foreign companies. The goal of ecotourism is that the profits from ecotourism must be reinvested into the local community to meet their basic needs. Additional revenues are channeled into programmes which directly benefit the local people in their health and education. When people get focused to ecotourism getting support from their community, they will devote their time and energy to it, understanting that the success of ecotourism is directly linked to their individual capacity to achieve greater standards of life. Environmental impacts National parks in Costa Rica are the backbone of its ecotourism industry contributing much to the countrys tourism industry as a whole. In 1960s Costa Ricas first strictly protected area was established, after that four national parks were offically created in 1970s to preserve its biodiversity. There are 30 and above national parks and more than 230 protected areas in costa Rica. Cost Rica forms a variety of ecosystem with 850 bird species, 1260 tree species, 1200 orchid species, 270 mammal species, 361 species of reptiles and amphibians and more than 35,000 species of insects. The creation of parks and protected areas protect natural species, but it resulted in deforestation. National parks form the crucial part of ecotourism in Costa Rica which was increasing since 1980s and attained maturity at the end of 1990s. Even ecotourism earnings have contuined to increase, the Costa Rican government is not properly funding to the parks and protected areas leading to dependancy on foreign donations much. Other than national parks and protected areas, private reserves have emerged as another important way to protect Costa Ricas natural resources and biodiversity. About 68 reserves were found in Costa Rica in which more than 40 involves in ecotourism in which La Selva, Rara Avis, Monteverde cloud forest reserve are some of those in it. Monteverde forest reserve recieves nearly 50,000 visitors per year which contains most important population of quetzal, an endangered bird species. Private reserves serve as an intimation to the government that ecotourism has good earning potential and it can be economically viable when sufficient resources are invested. Ecotourism projects results in natural degradations when the natural areas are overcroweded with visitors. Solid waste generation, pollution, habitat destructions, forest degradations and trail erosion results in increase of local carrying capacities. The negative effects of ecoourism can be minimized by emphasising low- impact construction, controlling the number of visitors, taking care in interacting with local flora and fauna. A balance between development and conservation should be created in order to avoid the degradation of natural environment. Education is often cited as on of the most crucial element for every individual as well as for a society. Environmental education contributes much for ecotourism. Knowledgable tour guides can provide a quality environmental education. Local guides have more advantage over foreign guides since they have more knowledge about local ecologic, natural history and local culture. Lack of experienced and knowledgable trail guides is one of the major problems with ecotourism in Costa Rica. Creating educated public understanding the importance of ecotourism in Costa Rica will help the countries benefit for long run.