| 1. |
- Goyenola, Cecilia, 1983-
(author)
-
Nanostructured carbon-based thin films : prediction and design
- 2015
-
Doctoral thesis (other academic/artistic)abstract
- Carbon-based thin films are a vast group of materials of great technological importance. Thanks to the different bonding options for carbon, a large variety of structures (from amorphous to nanostructured) can be achieved in the process of film synthesis. The structural diversity increases even more if carbon is combined with relatively small quantities of atoms of other elements. This results in a set of materials with many different interesting properties for a wide range of technological applications.This doctoral thesis is about nanostructured carbon-based thin films. In particular, the focus is set on theoretical modeling, prediction of structural features and design of sulfo carbide (CSx) and carbon fluoride (CFx) thin films.The theoretical approach follows the synthetic growth concept (SGC) which is based on the density functional theory. The SGC departure point is the fact that the nanostructured films of interest can be modeled as assemblies of low dimensional units (e.g., finite graphene-like model systems), similarly to modeling graphite as stacks of graphene sheets. Moreover, the SGC includes a description of the groups of atoms that act as building blocks (i.e., precursors) during film deposition, as well as their interaction with the growing film.This thesis consists of two main parts:Prediction: In this work, I show that nanostructured CSx thin films can be expected for sulfur contents up to 20 atomic % with structural characteristics that go from graphite-like to fullerene-like (FL). In the case of CFx thin films, a diversity of structures are predicted depending on the fluorine concentration. Short range ordered structures, such as FL structure, can be expected for low concentrations (up to 5 atomic %). For increasing fluorine concentration, diamond-like and polymeric structures should predominate. As a special case, I also studied the ternary system CSxFy. The calculations show that CSxFy thin films with nanostructured features should be possible to synthesize at low sulfur and fluorine concentrations and the structural characteristics can be described and explained in terms of the binaries CSx and CFx.Design: The carbon-based thin films predicted in this thesis were synthesized by magnetron sputtering. The results from my calculations regarding structure and composition, and analysis of precursors (availability and role during deposition process) were successfully combined with the experimental techniques in the quest of obtaining films with desired structural features and understanding their properties.
|
|
| 2. |
- Halim, Joseph, 1985-
(author)
-
Synthesis and Characterization of 2D Nanocrystals and Thin Films of Transition Metal Carbides (MXenes)
- 2014
-
Licentiate thesis (other academic/artistic)abstract
- Two dimensional (2D) materials have received growing interest because of their unique properties compared to their bulk counterparts. Graphene is the archetype 2D solid, but other materials beyond graphene, such as MoS2 and BN have become potential candidates for several applications. Recently, a new family of 2D materials of early transition metal carbides and carbonitrides (Ti2CTx, Ti3C2Tx, Ti3CNTx, Ta4C3Tx, and more), labelled MXenes, has been discovered, where T stands for the surface-terminating groups.Before the present work, MXenes had only been synthesized in the form of exfoliated and delaminated powders, which is not suitable for electronic applications. In this thesis, I demonstrate the synthesis of MXenes as epitaxial thin films, a more suitable form for electronic and photonic applications. Results show that 2D epitaxial Ti3C2Tx films - produced by HF and NH4HF2 etching of magnetron sputter-grown Ti3AlC2 - exhibit metallic conductive behaviour down to 100 K and are 90% transparent to light in the visible-infrared range. The results from this work may open the door for MXenes as potential candidates for transparent conductive electrodes as well as in electronic, photonic and sensing applications.MXenes have been shown to intercalate cations and molecules between their layers that in turn can alter the surface termination groups. There is therefore a need to study the surface chemistries of synthetized MXenes to be able to study the effect of intercalation as well as altering the surface termination groups on the electronic structure and chemical states of the elements present in MXene layers. X-ray Photoelectron Spectroscopy (XPS) in-depth characterization was used to investigate surface chemistries of Ti3C2Tx and Ti2CTx. This thesis includes the discussion of the effect of Ar+ sputtering and the number of layers on the surface chemistry of MXenes. This study serves as a baseline for chemical modification and tailoring of the surface chemistry groups to potential uses and applications.New MXene phases, Nb2CTx and V2CTx, are shown in this thesis to be produced from HF chemical etching of Nb2AlC and V2AlC powders. Characterization of the produced MXenes was carried out using Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD), Transmission Electron Microscope (TEM) and XPS. Nb2CTx and V2CTx showed promising performance as electrodes for Li-ion batteries.In this thesis, electrochemical etching was used in an attempt to produce 2D metal carbides (MXene) from their ternary metal carbides, Ti3SiC2, Ti3AlC2 and Ti2AlC MAX phases. MAX phases in the form of highly dense bulk produced by Hot Isostatic Press. Several etching solutions were used such as HF, NaCl and HCl. Unlike the HF chemical etching of MAX phases, which results in MXenes, the electrochemical etching resulted in Carbide Derived Carbon (CDC). Here, I show the characterization of the produced CDC using several techniques such as XRD, TEM, Raman spectroscopy, and XPS. Electrochemical characterization was performed in the form of cyclic voltammetry, which sheds light on the etching mechanism.
|
|
| 3. |
- Volkov, Anton, 1989-
(author)
-
Ionic and electronic transport in electrochemical and polymer based systems
- 2017
-
Doctoral thesis (other academic/artistic)abstract
- Electrochemical systems, which rely on coupled phenomena of the chemical change and electricity, have been utilized for development an interface between biological systems and conventional electronics. The development and detailed understanding of the operation mechanism of such interfaces have a great importance to many fields within life science and conventional electronics. Conducting polymer materials are extensively used as a building block in various applications due to their ability to transduce chemical signal to electrical one and vice versa. The mechanism of the coupling between the mass and charge transfer in electrochemical systems, and particularly in conductive polymer based system, is highly complex and depends on various physical and chemical properties of the materials composing the system of interest.The aims of this thesis have been to study electrochemical systems including conductive polymer based systems and provide knowledge for future development of the devices, which can operate with both chemical and electrical signals. Within the thesis, we studied the operation mechanism of ion bipolar junction transistor (IBJT), which have been previously utilized to modulate delivery of charged molecules. We analysed the different operation modes of IBJT and transition between them on the basis of detailed concentration and potential profiles provided by the model.We also performed investigation of capacitive charging in conductive PEDOT:PSS polymer electrode. We demonstrated that capacitive charging of PEDOT:PSS electrode at the cyclic voltammetry, can be understood within a modified Nernst-Planck-Poisson formalism for two phase system in terms of the coupled ion-electron diffusion and migration without invoking the assumption of any redox reactions.Further, we studied electronic structure and optical properties of a self-doped p-type conducting polymer, which can polymerize itself along the stem of the plants. We performed ab initio calculations for this system in undoped, polaron and bipolaron electronic states. Comparison with experimental data confirmed the formation of undoped or bipolaron states in polymer film depending on applied biases.Finally, we performed simulation of the reduction-oxidation reaction at microband array electrodes. We showed that faradaic current density at microband array electrodes increases due to non-linear mass transport on the microscale compared to the corresponding macroscale systems. The studied microband array electrode was used for developing a laccase-based microband biosensor. The biosensor revealed improved analytical performance, and was utilized for in situ phenol detection.
|
|
| 4. |
- Kumar, Divyaratan, 1995-
(author)
-
Water-in-polymer Salt Electrolyte (WIPSE) for Sustainable Lignin Batteries
- 2023
-
Doctoral thesis (other academic/artistic)abstract
- Organic electrolytes are widely used in energy storage technologies, but they are known to have safety, cost, and eco friendliness concerns. Water based electrolytes do not have those issues but are limited by their narrow range potential range of operation to 1.2V. Above that voltage, significant side reactions lead to gas evolution, side reaction and high selfdischarge rate in organic batteries. Because of their superior ionic conductivities, which are critical for reducing device resistance and improving power; as well as their cost-effective ness and non-flammability, researchers have had a second look at water-based electrolyte and found out that super concentrated aqueous solutions behave differently, and their electrochemical stability window can be widened.In this thesis, polyacrylate (PAAK) based "water in polymer salt" electrolyte (WIPSE) has been identified as a promising solution for large-scale energy storage devices. This new family of "water in salt" electrolytes offers a broad electrochemical stability window of up to 3V, a high ionic conductivity (100 mS/cm) and is non-flammable, making it ideal for high power electrochemical storage devices. However, little is known about the matter transport in PAAK based WIPSE and in "water in salt" electrolytes in general. Therefore, this thesis also aims to investigate the properties of PAAK using spectroscopic techniques such as Raman spectroscopy and diffusion NMR to understand the behavior of water and the mechanism of ionic transport in relation to water and polymer chain dynamics. Since the electrolyte only transports cations, it is suitable for use in "cation rocking chair" batteries that utilize two types of polymeric quinones, lignin, and polyimide redox polymers, as positive and negative electrodes, respectively. The electrochemically active redox polymers with K+ ions at neutral pH are ions at neutral pH are advantageous for avoiding corrosion in metal collectors. Further for understanding the fundamental of self-discharge mechanism, the impact of some critical chemical and physical parameters on performance of lignin-based batteries have been investigated.The final chapter of the thesis introduces a novel approach to address the challenges associated with Zn-ion batteries by utilizing the "water-inpolymer salt" electrolyte concept modified by salt additives. The goal is to enable the use of lignin-carbon (L-C) electrodes in a Zinc battery. Lignin, carbon and zinc are among the most affordable, environmentally friendly and sustainable options for energy storage for energy storage. By incorporating WIPSE electrolytes these batteries can offer additional benefits, such as improved safety and the prevention of dendrite formation. Our findings demonstrate that acrylate groups in the electrolyte stabilize the flux on the zinc electrode surface, promoting parallel deposition and significantly reducing dendritic formation through vertical growth. The assembled Zn-lignin battery delivers a maximum energy of 23 Wh/kg and a maximum power of 610 W/kg, with an exceptional 82% retention after 8000 cycles. With the reduced expected environmental impact of green and the cost- effectiveness of these polymer electrolytes, the resulting battery shows great promise in the battery market. Its emergence has opened a new avenue in the pursuit of safe and efficient batteries, which has been a major area of focus within the energy storage industry.
|
|
| 5. |
- Downes, Marley, et al.
(author)
-
M5X4: A Family of MXenes
- 2023
-
In: ACS Nano. - : AMER CHEMICAL SOC. - 1936-0851 .- 1936-086X. ; 17:17, s. 17158-17168
-
Journal article (peer-reviewed)abstract
- MXenes are two-dimensional (2D) transition metal carbides, nitrides, and carbonitrides typically synthesized from layered MAX-phase precursors. With over 50 experimentally reported MXenes and a near-infinite number of possible chemistries, MXenes make up the fastest-growing family of 2D materials. They offer a wide range of properties, which can be altered by their chemistry (M, X) and the number of metal layers in the structure, ranging from two in M2XTx to five in M5X4T x . Only one M5X4 MXene, Mo4VC4, has been reported. Herein, we report the synthesis and characterization of two M(5)AX(4) mixed transition metal MAX phases, Ti2.5Ta2.5AlC4 and Ti2.675Nb2.325AlC4, and their successful topochemical transformation into Ti2.5Ta2.5C4T x and Ti2.675Nb2.325C4Tx MXenes. The resulting MXenes were delaminated into single-layer flakes, analyzed structurally, and characterized for their thermal and optical properties. This establishes a family of M(5)AX(4) MAX phases and their corresponding MXenes. These materials were experimentally produced based on guidance from theoretical predictions, leading to more exciting applications for MXenes.
|
|
