Dissertations / Theses on the topic 'Zinc Magnesium Oxide'

Dans ce travail de recherche, sont présentés les résultats de l'élaboration de couches minces d'oxydes à base d'éléments abondants par la technique de spray pyrolyse ultrasonique. Trois matériaux constituant les briques de base de la cellule solaire « tout oxyde » ont été développés : l'oxyde de zinc (ZnO) comme couche fenêtre ; l'oxyde de zinc et de magnésium (ZnMgO) comme couche tampon et l'oxyde de cuivre (Cu2O) comme couche absorbante. Un plan d'expériences précis a été mis en place pour chaque type d'élaboration afin de comprendre l'effet des paramètres d'élaboration sur les propriétés des films. Des caractérisations optiques, structurelles, morphologiques et électriques ont été utilisées pour étudier les propriétés du film et les résultats discutés et analysés en détail. Des films minces de ZnO avec une transparence élevée dans une large gamme d'épaisseurs ont été obtenus. Le ZnMgO a été élaboré avec une phase monocristalline et une transparence élevée. La limite de miscibilité du magnésium (près de 30 % dans notre cas) est supérieure à celle habituellement obtenue avec les méthodes d'élaboration sans vide. L'élaboration de l'absorbeur Cu2O a été optimisée avec un contrôle efficace de la température d'élaboration et de la concentration d'un nouvel agent réducteur (D-sorbitol). Pour élargir les perspectives de ce travail, deux autres matériaux, ZnAlO et ZnAlMgO, ont été élaborés. Nous avons ainsi mis en évidence le fait qu'avec de faibles concentrations d'aluminium (jusqu'à 2 %) et de magnésium (jusqu'à 7 %), les propriétés optiques, électriques et structurales des films de ZnAlO pouvaient être modulées pour une utilisation en tant que couche fenêtre ou TCO dans les cellules solaires « tout-oxyde ». De plus, les simulations réalisées à l'aide des logiciels Silvaco Atlas® et Solis démontrent également le potentiel de ces films pour les cellules solaires « tout-oxyde »
The results on elaboration of environmentally compatible, earth-abundant metal oxide thin films using the technique of ultrasonic spray pyrolysis are presented. Three essential materials are developed for the purpose of realization of an “all-oxide” solar cell device: Zinc oxide (ZnO) as window layer; zinc magnesium oxide (ZnMgO) as a buffer layer and cuprous oxide (Cu2O) used as an absorber layer. Comprehensive design of experiments was set up for the elaboration of each material. Highly transparent ZnO was elaborated in wide range of thickness with high crystalline qualities with specific elaboration temperature with a precise control on the concentration of the precursors. ZnMgO was elaborated by varying the molar compositions of the magnesium precursor in the precursor solution. Up to nearly 30 % of Mg, the ZnMgO films exhibited single crystalline phase with high transparencies. High-absorbing Cu 2 O elaboration was optimized with effective control on the elaboration temperature and the concentration of a new reducing agent (D-sorbitol). To expand the horizon of efficiency of our elaboration process, two more materials, ZnAlO and ZnAlMgO, were elaborated. It was found that the optical, electrical, and structural properties of the ZnAlO films could be modulated for use in “all-oxide” solar cells by varying magnesium (up to 7 mol%) and aluminum (up to 2 %). The bandgap energies and the electrical properties of the films were modulated with the co-doping so that they can be integrated as window/top-contact/buffer layers in “all-oxide” solar cells. Additionally, simulations performed using Silvaco Atlas® and Solis also demonstrates the applicability of these films for “all-oxide” solar cells

The work presented in this thesis focuses on the investigation and improvement of the window stack of layers for thin film CdTe solar cells fabricated in the Center for Renewable Energy Systems Technology (CREST) laboratories. In particular the aim was to change the standard structure including TCO, high resistive transparent (HRT)layer and CdS which is limited by the low transparency of the CdS layer, to a better performing one. The first result chapter of the thesis describes the study of ZnO HRT layers. ZnO thin films were deposited by radio frequency (RF) magnetron sputtering with different structural, optical and electrical properties which were characterized by X-ray diffraction, electron microscopy, spectrophotometry, Hall Effect method and 4-point probe. ZnO films were then incorporated in CdTe solar cells with the structure: FTO/ZnO/CdS/CdTe/Au back contact and the performance of these devices were compared with the film properties to single out trends and identify optimal film characteristics. By varying the deposition pressure of ZnO films, it was possible to increase their transparency and significantly increase their resistivity. While better transparency positively affected the solar cell current density output and efficiency, the resistivity of ZnO films did not show any clear impact on device efficiency. By increasing the deposition temperature the ZnO film grain size was increased. Increased FF was observed in devices incorporating ZnO layers with bigger grains, although this gain was partially counterbalanced by the Voc degradation, leading to a limited efficiency improvement. Finally the addition of oxygen had the main effect of increasing the resistivity of ZnO films, similarly to what happened with the increase of the sputtering pressure. In this case however, an improvement of FF, Jsc and efficiency was observed, especially at an O2/Ar ratio of 1%. By simulating the solar cells behavior with SCAPS-1D, it was found that these performance change can be explained by the variation of interface properties, precisely the amount of interface defects, rather than by bulk properties. The study presented in the second result chapter focuses on magnesium-doped zinc oxide (MZO) and the variation of its energy band structure. MZO was initially used as the HRT layer within a solar cell structure: FTO/MZO/CdS/CdTe/Au back contact. Sputtering MZO films with a target containing MgO 11 weight% and ZnO 89 weight% allowed for and increased band gap from 3.3 eV of intrinsic ZnO to 3.65 eV for MZO deposited at room temperature. Increasing the superstrate deposition temperature allowed for a further band gap increase up to 3.95 eV at 400 °C due mainly to an conduction band minimum upward shift. It was highlighted the importance to create a positive conduction band offset with the MZO layer conduction band slightly above the CdS conduction band, with an optimum found in this case to be 0.3 eV (efficiency 10.6 %). By creating a positive conduction band offset all the performance parameters (Voc, FF, Jsc, efficiency) significantly increased. One of the reasons for this improvement was found to be a diminished interface recombination due to a more ideal MZO/CdS band alignment. In the second part of this investigation the MZO was used as a replacement for the CdS in a simplified structure: FTO/MZO/CdTe/Au back contact. The concepts used to optimise the performance of these devices also involved tuning the conduction band alignment between MZO/CdTe and efficiencies of 12.5 % were achieved with a at conduction band offset. The efficiency increase was achieved mainly thanks to a better transparency of the MZO layer and a higher Jsc output, compared to devices using a CdS buffer layer. The MZO buffers have been tested in combination with different TCOs. Results are presented in the third result chapter and showed that AZO is a good alternative to FTO working effectively in combination with MZO. AZO/MZO efficiency thin film CdTe solar cells (12.6%, compared to 12.5% with FTO). It was found that increasing the IR transparency of the TCOs leads to a potentially higher Jsc. Achieving a better transparency was obtained by using TCOs with high mobility and lower carrier concentration (AZO and ITiO) and also by using a boro-aluminosilicate glass with low iron content. ITiO yielded the best opto-electrical properties among all the TCO materials. Devices incorporating ITiO however, showed lower performance then those using FTO and AZO. ITO/MZO windows also yielded poor performance. In addition, the ITO films deposited had a high carrier concentration leading to a high NIR absorption by plasma resonance and resulted not ideal for application in thin film CdTe PV.

The synthesis of complexes [M(OCHMeCH2NMeCH2)2] (5, M = Mg; 7, M = Zn) is described. Treatment of MeHNCH2CH2NMeH (1) with 2-methyloxirane (2) gave diol (HOCHMeCH2NMeCH2)2 (3), which upon reaction with equimolar amounts of MR2 (4, M = Mg, R = Bu; 6, M = Zn, R = Et) gave 5 and 7. The thermal behavior and vapor pressure of 5 and 7 were investigated to show whether they are suited as CVD (= chemical vapor deposition) and/or spin-coating precursors for MgO or ZnO layer formation. Thermogravimetric (TG) studies revealed that 5 and 7 decompose between 80–530 °C forming MgO and ZnO as evidenced by PXRD studies. In addition, TG-MS-coupled experiments were carried out with 7 proving that decomposition occurs by M–O, C–O, C–N and C–C bond cleavages, as evidenced from the detection of fragments such as CH4N+, C2H4N+, C2H5N+, CH2O+, C2H2O+ and C2H3O+. The vapor pressure of 7 was measured at 10.4 mbar at 160 °C, while 5 is non-volatile. The layers obtained by CVD are dense and conformal with a somewhat granulated surface morphology as evidenced by SEM studies. In addition, spin–coating experiments using 5 and 7 as precursors were applied. The corresponding MO layer thicknesses are between 7–140 nm (CVD) or 80 nm and 65 nm (5, 7; spin-coating). EDX and XPS measurements confirm the formation of MgO and ZnO films, however, containing 12–24 mol% (CVD) or 5–9 mol% (spin-coating) carbon. GIXRD studies verify the crystalline character of the deposited layers obtained by CVD and the spin-coating processes.

Yau Man Yan Eric = 鎂和氧化鋅反應製備氧化鎂納米棒 / 游文仁.
Thesis (M.Phil.)--Chinese University of Hong Kong, 2004.
Includes bibliographical references.
Text in English; abstracts in English and Chinese.
Yau Man Yan Eric = Mei he yang hua xin fan ying zhi bei yang hua mei na mi bang / You Wenren.
Acknowledgement --- p.i
Abstract --- p.ii
摘要 --- p.iii
Table of contents --- p.iv
List of tables --- p.viii
List of figures --- p.ix
Chapter Chapter 1 --- Introduction
Chapter 1.1 --- Nanostructured materials --- p.1-1
Chapter 1.2 --- Application of nano-materials --- p.1-1
Chapter 1.3 --- Current development of nano-materials --- p.1-2
Chapter 1.4 --- Synthesis of nano-materials --- p.1-2
Chapter 1.4.1 --- Physical methods --- p.1-3
Chapter 1.4.1.1 --- Physical vapor deposition --- p.1-3
Chapter 1.4.1.2 --- Arc-discharge process --- p.1-3
Chapter 1.4.1.3 --- Laser ablation --- p.1-4
Chapter 1.4.2 --- Chemical methods --- p.1-4
Chapter 1.4.2.1 --- Chemical vapor deposition --- p.1-4
Chapter 1.4.2.2 --- Metal-organic chemical vapor deposition (MOCVD) --- p.1-4
Chapter 1.4.2.3 --- Solgel method --- p.1-5
Chapter 1.5 --- Study on growth mechanism of nano-materials --- p.1-5
Chapter 1.5.1 --- Vapor-liquid-solid (VLS) mechanism --- p.1-5
Chapter 1.5.2 --- Vapor-solid (VS) mechanism --- p.1-6
Chapter 1.6 --- Applications of Magnesium Oxide (MgO) materials --- p.1-7
Chapter 1.7 --- Previous works on MgO nanostructures --- p.1-8
Chapter 1.7.1 --- Network like MgO nanobelts --- p.1-8
Chapter 1.7.2 --- Decorated MgO crystalline fibers --- p.1-9
Chapter 1.7.3 --- Mg2Zn11 - MgO belt-like nanocables --- p.1-9
Chapter 1.7.4 --- MgO nanowires with uniform diameter distribution --- p.1-10
Chapter 1.7.5 --- Aligned MgO nanorods on MgO (100) substrates --- p.1-11
Chapter 1.8 --- Objectives and approaches of this project --- p.1-12
Chapter 1.8.1 --- Addition of sodium chloride (NaCl) --- p.1-13
Chapter 1.9 --- Thesis Layout --- p.1-13
Chapter 1.10 --- References --- p.1-15
Chapter Chapter 2 --- Methodology and Instrumentation
Chapter 2.1 --- Introduction --- p.2-1
Chapter 2.2 --- Powder Metallurgy --- p.2-1
Chapter 2.3 --- Sample fabrication --- p.2-1
Chapter 2.3.1 --- Starting materials --- p.2-1
Chapter 2.3.2 --- Cold pressing --- p.2-2
Chapter 2.3.2.1 --- Single pellet method --- p.2-2
Chapter 2.3.2.2 --- Double pellet method --- p.2-3
Chapter 2.3.3 --- Argon tube furnace sintering --- p.2-3
Chapter 2.4 --- Study of fabrication parameters --- p.2-4
Chapter 2.4.1 --- Heat treatment temperature --- p.2-4
Chapter 2.4.2 --- NaCl content in sample --- p.2-4
Chapter 2.4.3 --- Duration of heat treatment --- p.2-5
Chapter 2.5 --- Control Experiments --- p.2-5
Chapter 2.5.1 --- Effect of addition of NaCl --- p.2-5
Chapter 2.5.2 --- Effect of residual oxygen --- p.2-5
Chapter 2.5.3 --- Geometrical effect of experimental setup --- p.2-6
Chapter 2.5.3.1 --- Compressed double pellet method --- p.2-6
Chapter 2.5.3.2 --- Powder on Magnesium pellet method --- p.2-6
Chapter 2.5.3.3 --- Single pellet method --- p.2-7
Chapter 2.6 --- Characterization Methods --- p.2-7
Chapter 2.6.1 --- Thermal analysis - Differential thermal analyzer (DTA) --- p.2-7
Chapter 2.6.2 --- Structural analysis --- p.2-7
Chapter 2.6.2.1 --- Scanning electron microscopy (SEM) --- p.2-7
Chapter 2.6.2.2 --- Transmission electron microscopy (TEM) --- p.2-8
Chapter 2.6.3 --- Phases determination - X-ray powder diffractometry (XRD) --- p.2-8
Chapter 2.7 --- References --- p.2-9
Chapter Chapter 3 --- Results of Mg-ZnO-NaCl System
Chapter 3.1 --- Introduction --- p.3-1
Chapter 3.2 --- Results of thermal analysis --- p.3-1
Chapter 3.2.1 --- Chemical reactions --- p.3-1
Chapter 3.2.2 --- DTA results --- p.3-2
Chapter 3.3 --- Variation of heat treatment temperature --- p.3-3
Chapter 3.3.1 --- XRD pattern --- p.3-3
Chapter 3.3.2 --- SEM images --- p.3-4
Chapter 3.4 --- Variation of NaCl content --- p.3-5
Chapter 3.4.1 --- TEM analysis --- p.3-5
Chapter 3.5 --- Variation of duration of heat treatment --- p.3-6
Chapter 3.6 --- Additional findings --- p.3-7
Chapter 3.7 --- Discussions --- p.3-7
Chapter 3.8 --- References --- p.3-10
Chapter Chapter 4 --- Results of Control Experiments
Chapter 4.1 --- Introduction --- p.4-1
Chapter 4.2 --- The study of Mg-ZnO system --- p.4-1
Chapter 4.3 --- The study of residual oxygen effect --- p.4-2
Chapter 4.4 --- The study of geometrical effect of experiment setup --- p.4-2
Chapter 4.5 --- Discussions --- p.4-3
Chapter 4.5.1 --- Effect of addition of NaCl --- p.4-3
Chapter 4.5.2 --- Effect of residual oxygen --- p.4-3
Chapter 4.5.3 --- Role of ZnO --- p.4-4
Chapter 4.5.4 --- Growth model --- p.4-4
Chapter 4.6 --- References --- p.4-7
Chapter Chapter 5 --- Conclusions and Further Studies
Chapter 5.1 --- Conclusion --- p.5-1
Chapter 5.2 --- Further studies --- p.5-2
Chapter 5.3 --- References --- p.5-3

碩士
國立雲林科技大學
電子工程系
106
In this work, RF magnetron sputtering method has been used to deposit MGZO thin films on silicon substrates (100) and glass substrates at room temperature, respectively. The properties of the MGZO films have been optimized by changing the parameters of deposition and post-annealing processes. The effects of working pressure, sputtering gas flow rate, film thickness, target composition ratio, annealing temperature, annealing time, heating rate, and annealing ambience to the MGZO film properties have been investigated. The morphology, microstructure, composition, electrical properties and optical properties of the MGZO films have been characterized for optoelectronic applications. According to our experimental results, the optimal p-type MGZO film has a resistivity as low as 5.167"×" 10-2 Ω-cm, hall mobility as high as 8.33 cm2/V-s, and carrier concentration as high as 2.834"×" 1018 cm-3; while the optimal n-type MGZO film has a resistivity as low as 2.629"×" 10-2 Ω-cm, hall mobility as high as 7.124 cm2/V-s, and carrier concentration as high as 2.138"×" 1019 cm-3. All of the MGZO films made in this work have achieved more than 90% transmittance in visible region (380 nm - 780 nm). A heterojunction diode has been fabricated on the n-type silicon substrate (111) with the optimal p-type MGZO film.

碩士
長庚大學
化工與材料工程學系
99
The objectives of this research are to preare the ceramic targets of aluminum-doped magnesium zinc oxid (AMZO) by solid-state reactions and the thin films of AMZO by RF magnetron sputtering. In addition, the effects of the amount of alumina and magnesium dopant in the AMZO targets as well as other sputtering parameters on the electrical, optical, and structural properties of AMZO thin films was also investigated. Finally, AMZO thin film would be applied for CIGS solar cell. In the result, the Zn0.94Mg0.06O with 1 wt% Al2O3 at different sintering temperature exhibit the same hexagonal wurtzite ZnO structure. The lowest resistivity of 6.2×10-3 Ω-cm was abtained for the sintering of AMZO target at temperature of 1400℃ and less than 5% weight loss. It was also found that the AMZO ceramic targets with different Al2O3 or Mg contents at sintering temperature of 1400℃ excludes the possibility of ant extra phases. In conclusion, the resistivity and the relative density of the target by AMZO target were 2.6 x 10-3 Ω-cm and 98.46%, respectively. The best performance of the electricity could achieve under the hybrid amount of Al2O3 and the sintered temperature were 3 wt% and 1400 ℃, respectively. Following the application by the AMZO target, the thin films were prepared by RF sputtering system and subtract temperature, power and working pressure were be discussed of the thin film were studied. Compared to the performance of AMZO thin film, the resistivity, mobility concentration, mobility, average transmittance (400 -1200 nm ) and band gap were 1.7 x 10-3 Ω-cm, 3.25 x 1020 cm-3, 11.3 cm2/Vs, 93.1% and 3.68 eV, respectively, under the subtract temperature, power, working pressure and deposited minutes were 320℃, 80 W, 9 mtorr and 15 min, respectively. By implying the AMZO target with different amounts of Al2O3 wt%, compared to the electricity and the optic properties of the AMZO thin film, the best resistivity, mobility concentration, mobility, average transmittance ( 400 -1200 nm ) and band gap were 7.61 x 10-4 Ω-cm, 5.01 x 1020 cm-3, 16.4 cm2/Vs, 91.5% and 3.7 eV, respectively, by the AMZO target with 2 wt% Al2O3：Zn0.98Mg0.02O.

碩士
長庚大學
化工與材料工程學系
100
The preparation of transparent conductive gallium-doped magnesium zinc oxide (GMZO) thin films with good near infrared transmission by radio frequency (RF) magnetron sputtering using a single GMZO ceramic target was explored In addition, the different of GMZO target conditions on the structural, electrical and optical properties on the RF-sputtered GMZO thin films was also investigated and sputtering processes prepared optimization GMZO transparent conductive film application in the CIGS solar cells. Then, the window on the component layer (buffer layer / intrinsic layer / transparent conductive layer) was optimized to increase the optical transmittance by the optical simulation software, increasing the efficiency of photoelectric conversion in the CIGS solar cells. This study results show that the ceramic target in GMZO, that in the amount of 3 wt% Ga2O3 and amount of 2 at% Mg doped with hexagonal wurtzite ZnO structure, the lowest resistivity of 1.2×10-3 Ω cm and the weight loss is less than 5% conditions was held at sintering conditions of a positive argon pressure of 50 kPa and the sintering temperature of 1400 ° C The preparation of the GMZO transparent thin film by RF magnetron sputtering method use to the above-mentioned preparation GMZO ceramic target, that was investigated the structure, electrical and optical properties. The sputtering process conditions on GMZO transparent conductive film structure has not changed much, their preferred orientations are (002) direction, and all belong to the ZnO wurtzite structure. Transparent conductive GMZO thin films with resistivity as low as 2.89 x10-4 Ω cm with a higher carrier concentration of 11.8 x1021 cm-3 and electron mobility of 18.2 cm2/ Vs, good near infrared transmittance (>89%) and bandgap value of about 3.73 eV were successfully prepared on glass substrates by single cathode RF magnetron sputtering using a GMZO ceramic target with the composition of 95 % Zn0.98Mg0.02O and 5 wt% Ga2O3 without post deposition annealing. The preparation of the window layer antireflection coating design and application to CIGS solar cell by using optical simulation software (Film Star) was explored. Finally, Anti-reflective coating was optimized and applied in window layer of CIGS solar cell. Experimental results show that the window layer penetration to enhance short-circuit current and the photoelectric conversion efficiency of CIGS solar photoelectric conversion element of the phenomenon of both increased. The maximum conversion efficiency was 8.22%,and short-circuit current increased 38 percent.

碩士
崑山科技大學
電機工程研究所
104
In this study,IMZO was co-sputted on a glass substrate by changing process parameters such as MgO doped with different power, different process time, different substrate temperature, in order to develop the opto -electronic characteristics of IMZO films Moreover, a different process pressure of IMZO films were deposited on silicon substrates, and then platinum (Pt) films were coated on the films as an interdigitated electrode sensing electrode to study sensing properties of H2. 　　Experimental results show that, IMZO thin film in XRD diffraction analysis are no obvious diffraction peak in three different parameters specimen, so the film exists amorphous structure. By the Ultraviolet -Visible analyzer measurements, films reached more than 80% in visible wavelength range. During MgO doped test, the results show that the resistivity can be reduced in a few MgO doped. We can get the best resistivity value of 5.8x10-3Ω-cm at 80W doped power. At different process time experiment, when time increases, the particles formed on film surface with different types of accumulation from loose to dense. The phenomenon makes the carrier concentration and mobility increased, as well the resistivity value tend to a downward trend. When the process time of 20 minutes, we obtain the best resistivity value of 5.81x10-3Ω-cm. At different substrate temperature test, due to the thermal energy in a ion sputtering process getting more energy, the process can improve the movement of deposited atoms. The results can let the film more uniform, thus the resistivity value decreased. We obtain optimal resistance of 5.21x10-3Ω-cm at 200oC substrate temperature. 　　Hydrogen sensing experiments of IMZO film are mainly carried out at room temperature (28oC), The dry air and the drying air mixing with hydrogen (H2) atmosphere are inputed for looping sensing. Two kind of process pressures, 3 mtorr and 35 mtorr were investigated for IMZO film on silicon substrate and then Pt was plated on the films as interdigitated electrode for sensing. The results show that the sample prepared at 3 mtorr and 35 mtorr obtains the sensitivity of 6.7% and 27.5% respectively in 1000ppm hydrogen concentration. Therefore high process pressure have more fast-growing and let the surface more roughness, the surface area increase can enhance the sensing property. For different hydrogen concentrations tests at 35 mtorr sensing sensitivity, the sensitivity increase with H2 concentration increase and then decrease at high H2 concentration. The reason may be the surface of a thin film containing a saturated hydrogen atoms at high H2 concentration, therefore hydrogen can not be completely desorbed at next run.

碩士
長庚大學
化工與材料工程學系
101
Magnesium zinc oxide (MgxZn1-xO ) thin films were prepared by RF- magnetron sputtering and attempted to used as buffer layer and intrinsic layer in Cu(In,Ga)Se2 solar cells. The effects of substrate temperature, sputtering power, working pressure, and oxygen flow rate on the structural, electrical and optical properties of Mg0.02Zn0.98O thin films were also investigated. Mg0.02Zn0.98O thin films with resistivity as low as 2.96 ×103 Ω-cm were obtained at the deposition condition of substrate temperature 150 ℃, sputtering power 40 W, working pressure 3 mtorr, pure Ar atmosphere with Ar flow arte being 10 sccm. By increasing the oxygen flow rate in the working gas, the resistivity of Mg0.02Zn0.98O thin films was found to increase. By using Mg0.02Zn0.98O thin films deposited without substrate being heated to replace CdS as buffer layer (CIGS/Mg0.02Zn0.98O/i-ZnO/GMZO) or ZnO as intrinsic layer (CIGS/CdS/Mg0.02Zn0.98O/GMZO), the photovoltaic conversion efficiencies of the CIGS solar cells were, respectively, 1.618% and 1.693%, which were better than that of the CIGS solar cells (1.363%) with the structure of CIGS/Mg0.02Zn0.98O/GMZO. However, by replacing Mg0.02Zn0.98O with Mg0.05Zn0.95O, the photovoltaic conversion efficiency of the CIGS solar cells with the structure of CIGS/Mg0.05Zn0.95O/GMZO improved to 3.513%.

Global warming and depletion in fossil fuels have forced the society to search for alternate, clean sustainable energy sources. An obvious solution to the aforesaid problem lies in electrochemical energy storage systems like fuel cells and batteries. The desirable properties attributed to these devices like quick response, long life cycle, high round trip efficiency, clean source, low maintenance etc. have made them very attractive as energy storage devices. Compared to many advanced battery chemistries like nickel-metal hydride and lithium - ion batteries, metal-air batteries show several advantages like high energy density, ease of operation etc. The notable characteristics of metal - air batteries are the open structure with oxygen gas accessed from ambient air in the cathode compartment. These batteries rely on oxygen reduction and oxygen evolution reactions during discharging and charging processes. The efficiency of these systems is determined by the kinetics of oxygen reduction reaction. Platinum is the most preferred catalyst for many electrochemical reactions. However, high cost and stability issues restrict the use of Pt and hence there is quest for the development of stable, durable and active electrocatalysts for various redox reactions. The present thesis is directed towards exploring the electrocatalytic aspects of titanium carbonitride. TiCN, a fascinating material, possesses many favorable properties such as extreme hardness, high melting point, good thermal and electrical conductivity. Its metal-like conductivity and extreme corrosion resistance prompted us to use this material for various electrochemical studies. The work function as well as the bonding in the material can be tuned by varying the composition of carbon and nitrogen in the crystal lattice. The current study explores the versatility of TiCN as electrocatalyst in aqueous and non-aqueous media. One dimensional TiC0.7N0.3 nanowires are prepared by simple one step solvothermal method without use of any template and are characterized using various physicochemical techniques. The 1D nanostructures are of several µm size length and 40 ± 15 nm diameter (figure 1). Orientation followed by attachment of the primary particles results in the growth along a particular plane (figure 2). (a) (b) (c) Figure 1. (a) SEM images of TiC0.7N0.3 nanowires (b) TEM image and (c) High resolution TEM image showing the lattice fringes. (a) (b) (d) Figure 2. Bright field TEM images obtained at different time scales of reaction. (a) 0 h; (b) 12 h; (c) 72 h and (d) 144 h. The next aspect of the thesis discusses the electrochemical performance of TiC0.7N0.3 especially for oxygen reduction. Electrochemical oxygen reduction reaction (ORR) reveals that the nanowires possess high activity for ORR and involves four electron process leading to water as the product. The catalyst effectively converts oxygen to water with an efficiency of 85%. A comparison of the activity of different (C/N) compositions of TiCN is shown in figure 3. The composition TiC0.7N0.3 shows the maximum activity for the reaction. The catalyst is also very selective for ORR in presence of methanol and thus cross-over issue in fuel cells can be effectively addressed. Density functional theory (DFT) calculations also lead to the same composition as the best for electrocatalysis, supporting the experimental observations. Figure 3. Linear sweep voltammetric curves observed for different compositions of titanium carbonitride towards ORR. The next chapter deals with the use of TiC0.7N0.3 as air cathode for aqueous metal - air batteries. The batteries show remarkable performance in the gel- and in liquid- based electrolytes for zinc - air and magnesium - air batteries. A partial potassium salt of polyacrylic acid (PAAK) is used as the polymer to form a gel electrolyte. The cell is found to perform very well even at very high current densities in the gel electrolyte (figures 4 and 5). Figure 4 Photographs of different components of the gel - based zinc - air battery. (a) (b) Figure 5. a) Discharge curves at different current densities of 5, 20, 50 and 100 mA/cm2 for zinc-air system with TiC0.7N0.3 cathode b) Charge – discharge cycles at 50 mA/cm2 for the three electrode configuration with TiC0.7N0.3 nanowire for ORR and IrO2 for OER and Zn electrode (2h. cycle period). Similarly, the catalytic activity of TiC0.7N0.3 has also been explored in non-aqueous electrolyte. The material acts as a bifunctional catalyst for oxygen in non- aqueous medium as well. It shows a stable performance for more than 100 cycles with high reversibility for ORR and OER (figure 6). Li-O2 battery fabricated with a non-aqueous gel- based electrolyte yields very good output. (a) (b) (c) Figure 6. Galvanostatic charge –discharge cycles. (a) at 1 mA/cm2 (b) specific capacity as a function of no. of cycles (c) photographs of PAN-based gel polymer electrolyte. Another reaction of interest in non –aqueous medium is I-/I3-. redox couple. TiC0.7N0.3 nanowires show small peak to peak separation, low charge transfer resistance and hence high activity. The catalyst is used as a counter electrode in dye sensitized a solar cell that shows efficiencies similar to that of Pt, state of the art catalyst (figure 7). (a) (b) (c) Figure 7 (a) Cyclic voltammograms for I-/I3 - redox species on TiC0.7N0.3 nanowires (red), TiC0.7N0.3 particle (black) and Pt (blue). (b) Photocurrent density - voltage characteristics for DSSCs with different counter electrodes. TiC0.7N0.3 nanowire (black), TiC0.7N0.3 particle (blue), Pt (red). (c) Photograph of a sample cell. (a) (b) (c) (d) Figure 8 a) Comparison ORR activity for (i) NiTiO3(black), (ii) N-rGO (red), (iii) NiTiO3 – N-rGO (green) and (iv) Pt/C (blue) (b) Linear sweep voltammograms for OER observed on NiTiO3 – N-rGO composite (black), NiTiO3 (brown), N-rGO (blue), glassy carbon (red) in 0.5 M KOH. (c) Galvanostatic discharge curves of NiTiO3 – N-rGO as air electrode (d) Charge – discharge cycle at 5 mA/cm2 for the rechargeable battery with 10 min. cycle period. The last part of the thesis discusses about a ceramic oxide, nickel titanate. The electrocatalytic studies of the material towards ORR and OER reveal that the catalyst shows remarkable performance as a bifunctional electrode. A gel - based zinc - air battery fabricated with nickel titanate – reduced graphene oxide composite shows exceptional performance of 1000 charge-discharge cycles in the rechargeable mode (figure 8). Of course, the primary battery configuration works very well too The thesis contains seven chapters on the aspects mentioned above with summary and future perspectives given as the last chapter. An appendix based on TiN nanotubes and supercapacitor studies is given at the end.

Global warming and depletion in fossil fuels have forced the society to search for alternate, clean sustainable energy sources. An obvious solution to the aforesaid problem lies in electrochemical energy storage systems like fuel cells and batteries. The desirable properties attributed to these devices like quick response, long life cycle, high round trip efficiency, clean source, low maintenance etc. have made them very attractive as energy storage devices. Compared to many advanced battery chemistries like nickel-metal hydride and lithium - ion batteries, metal-air batteries show several advantages like high energy density, ease of operation etc. The notable characteristics of metal - air batteries are the open structure with oxygen gas accessed from ambient air in the cathode compartment. These batteries rely on oxygen reduction and oxygen evolution reactions during discharging and charging processes. The efficiency of these systems is determined by the kinetics of oxygen reduction reaction. Platinum is the most preferred catalyst for many electrochemical reactions. However, high cost and stability issues restrict the use of Pt and hence there is quest for the development of stable, durable and active electrocatalysts for various redox reactions. The present thesis is directed towards exploring the electrocatalytic aspects of titanium carbonitride. TiCN, a fascinating material, possesses many favorable properties such as extreme hardness, high melting point, good thermal and electrical conductivity. Its metal-like conductivity and extreme corrosion resistance prompted us to use this material for various electrochemical studies. The work function as well as the bonding in the material can be tuned by varying the composition of carbon and nitrogen in the crystal lattice. The current study explores the versatility of TiCN as electrocatalyst in aqueous and non-aqueous media. One dimensional TiC0.7N0.3 nanowires are prepared by simple one step solvothermal method without use of any template and are characterized using various physicochemical techniques. The 1D nanostructures are of several µm size length and 40 ± 15 nm diameter (figure 1). Orientation followed by attachment of the primary particles results in the growth along a particular plane (figure 2). (a) (b) (c) Figure 1. (a) SEM images of TiC0.7N0.3 nanowires (b) TEM image and (c) High resolution TEM image showing the lattice fringes. (a) (b) (d) Figure 2. Bright field TEM images obtained at different time scales of reaction. (a) 0 h; (b) 12 h; (c) 72 h and (d) 144 h. The next aspect of the thesis discusses the electrochemical performance of TiC0.7N0.3 especially for oxygen reduction. Electrochemical oxygen reduction reaction (ORR) reveals that the nanowires possess high activity for ORR and involves four electron process leading to water as the product. The catalyst effectively converts oxygen to water with an efficiency of 85%. A comparison of the activity of different (C/N) compositions of TiCN is shown in figure 3. The composition TiC0.7N0.3 shows the maximum activity for the reaction. The catalyst is also very selective for ORR in presence of methanol and thus cross-over issue in fuel cells can be effectively addressed. Density functional theory (DFT) calculations also lead to the same composition as the best for electrocatalysis, supporting the experimental observations. Figure 3. Linear sweep voltammetric curves observed for different compositions of titanium carbonitride towards ORR. The next chapter deals with the use of TiC0.7N0.3 as air cathode for aqueous metal - air batteries. The batteries show remarkable performance in the gel- and in liquid- based electrolytes for zinc - air and magnesium - air batteries. A partial potassium salt of polyacrylic acid (PAAK) is used as the polymer to form a gel electrolyte. The cell is found to perform very well even at very high current densities in the gel electrolyte (figures 4 and 5). Figure 4 Photographs of different components of the gel - based zinc - air battery. (a) (b) Figure 5. a) Discharge curves at different current densities of 5, 20, 50 and 100 mA/cm2 for zinc-air system with TiC0.7N0.3 cathode b) Charge – discharge cycles at 50 mA/cm2 for the three electrode configuration with TiC0.7N0.3 nanowire for ORR and IrO2 for OER and Zn electrode (2h. cycle period). Similarly, the catalytic activity of TiC0.7N0.3 has also been explored in non-aqueous electrolyte. The material acts as a bifunctional catalyst for oxygen in non- aqueous medium as well. It shows a stable performance for more than 100 cycles with high reversibility for ORR and OER (figure 6). Li-O2 battery fabricated with a non-aqueous gel- based electrolyte yields very good output. (a) (b) (c) Figure 6. Galvanostatic charge –discharge cycles. (a) at 1 mA/cm2 (b) specific capacity as a function of no. of cycles (c) photographs of PAN-based gel polymer electrolyte. Another reaction of interest in non –aqueous medium is I-/I3-. redox couple. TiC0.7N0.3 nanowires show small peak to peak separation, low charge transfer resistance and hence high activity. The catalyst is used as a counter electrode in dye sensitized a solar cell that shows efficiencies similar to that of Pt, state of the art catalyst (figure 7). (a) (b) (c) Figure 7 (a) Cyclic voltammograms for I-/I3 - redox species on TiC0.7N0.3 nanowires (red), TiC0.7N0.3 particle (black) and Pt (blue). (b) Photocurrent density - voltage characteristics for DSSCs with different counter electrodes. TiC0.7N0.3 nanowire (black), TiC0.7N0.3 particle (blue), Pt (red). (c) Photograph of a sample cell. (a) (b) (c) (d) Figure 8 a) Comparison ORR activity for (i) NiTiO3(black), (ii) N-rGO (red), (iii) NiTiO3 – N-rGO (green) and (iv) Pt/C (blue) (b) Linear sweep voltammograms for OER observed on NiTiO3 – N-rGO composite (black), NiTiO3 (brown), N-rGO (blue), glassy carbon (red) in 0.5 M KOH. (c) Galvanostatic discharge curves of NiTiO3 – N-rGO as air electrode (d) Charge – discharge cycle at 5 mA/cm2 for the rechargeable battery with 10 min. cycle period. The last part of the thesis discusses about a ceramic oxide, nickel titanate. The electrocatalytic studies of the material towards ORR and OER reveal that the catalyst shows remarkable performance as a bifunctional electrode. A gel - based zinc - air battery fabricated with nickel titanate – reduced graphene oxide composite shows exceptional performance of 1000 charge-discharge cycles in the rechargeable mode (figure 8). Of course, the primary battery configuration works very well too The thesis contains seven chapters on the aspects mentioned above with summary and future perspectives given as the last chapter. An appendix based on TiN nanotubes and supercapacitor studies is given at the end.