Pursuing sustainable and efficient energy storage technologies has led to advancements in iron-air batteries. Understanding the intricate relationship between the microstructural features of iron electrodes and their oxidation and reduction behaviour is crucial for optimizing battery performance and lifespan. This thesis aims to investigate the impact of microstructural characteristics, such as phases, grain size, and defect density, on the formation of stable iron oxide/hydroxide compounds and the evolution of hydrogen gas (HER), using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) experiments in 6M KOH. The influence of an electrolyte additive, sodium stannate trihydrate, and an iron foam functioning as alternative electrode material are also examined. Hot-rolled, pure iron samples were subjected to annealing heat treatments, resulting in different grain-sized specimens. A dual-phase steel, DP1000 steel composed of ferrite and martensite phases as well as hot-rolled and cold-rolled iron electrodes, completed the materials that formed this study’s basis. Initial surface identification via optical microscopy (OM), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), atomic force microscopy (AFM) and X-ray diffraction (XRD) have been performed. Results indicate a relatively lower formation of FeOOH for a DP1000 steel anode compared to cold-rolled alpha iron over 12 cycles. A marginally larger decline in HER kinetics is observed for a hot-rolled small grained anode compared to a coarse grained anode, while a clear effect of grain size on the development of Fe3O4 and FeOOH could not be established. An iron foam electrode showcases greatly enhanced anodic and cathodic current densities in comparison to solid sheet iron electrodes, due to its cellular structure. The effect of 0.01M sodium stannate added to the electrolyte illustrates a significant reduction in HER intensity for both foam and solid iron samples.

This study aims to assess the suitability of iron oxyfluoride (FeOF) as cathode material for fluoride-ion batteries based on the electrochemical performance and fluorination capability of ferrous oxide (FeO), as well as the defluorination of FeOF. Due to the pressing demand for electrochemical storage, alternatives to the widespread lithium-ion battery must be sought. One alternative can be the fluoride-ion battery (FIB). By trying to combine the stability of intercalation-based electrode materials and the high energy density of conversion-based materials, oxyfluorides might be the answer, especially if based on an abundant transition metal such as iron. In this report, the suitability of iron oxyfluoride as cathode material was evaluated. This was done by synthesising the electrode composites, evaluating their performance in a custom-made electrochemical cell and investigating the phase transitions of the researched materials. It was found that the ferrous oxide could not be fluorinated in an electrochemical environment and only reached a capacity of 0.75 mAh/g, which is equal to 0.2% of the theoretical capacity. It was also found that the iron oxyfluoride could not be electrochemically defluorinated. Therefore it is concluded that iron oxyfluoride is not suitable as cathode material for fluoride ion batteries.

Microchips are made from circular silicon discs called wafers and are manufactured with photolithography. A critical step of a photolithography process is when a wafer with a photoresist is placed on a wafer table (WT) and exposed to light to form patterns that build up components of an integrated circuit (IC). The dimensions of the IC are in nanometer scale and are becoming increasingly smaller. Any changes to the wafer table can contribute to alignment issues or increase overlay between successive exposures and is dependent on interaction with the wafer backside. Common wafer backside materials are silicon, silicon oxide and silicon nitride, which are hydrophilic, so they readily interact with water and adsorb it from the atmosphere. Furthermore, their surface conductivity is highly dependent on the relative humidity (RH) of the air. Additionally, silicon oxide and silicon nitride generate surface charge from single-wafer wet spin tools that are a part of the critical toolset for advanced IC fabrication. In the presence of water, a charged wafer backside can conduct unwanted current through the surface. The occurrence of this phenomena can affect both the performance and yield of the components that the wafer backside comes in contact with during photolithography. This thesis studies reducing the charge generation and surface conductivity of a hydrophilic silicon and silicon nitride wafer backside by depositing hydrophobic self-assembled monolayers (SAM) with silane coupling agents. They are less likely to form surface charge and have lower surface conductivity. The hydrophobic monolayers that are studied are deposited from hexamethyldisilazane (HMDS) and a non-disclosed fluorinated molecule, called F-SAM. HMDS is already used in photolithography on the wafer frontside to promote adhesion to the photoresist and fluorinated molecules are known to be hydrophobic, inert and with high electrical resistance. This surface modification tackles both the water content on the surface and the charging via single wafer wet-spin tools. The monolayers are characterized in terms of surface chemistry, surface free energy, wear resistance, zeta potential, surface charge and conductivity. Lastly, the charge diffusion is measured when a wafer is put in contact with a wafer table in an experimental setup, where the discharge current is registered. The outcome of this study shows that modified surfaces are found to be homogenous to a sub nanometer level and uniform. Compared to typical silicon nitride wafers, the surface conductivity is lowered by a factor of 1000 and is not affected by the RH. This results in the total measured charge diffused to a wafer table to be reduced by at least a factor of 17. As a conclusion, modified surface can be considered a promising option in reducing any unwanted current leakage from a wafer backside to surrounding components.

The reliability of battery performance is crucial for the implementation of long-term large-scale energy storage. The promising Iron-Air battery is known for its suitable properties relying on its advantageous iron-based anode, characterized by its high volumetric energy density, robustness, material abundance, low cost and scalability. The anode does however present drawbacks, such as self-discharge, hydrogen evolution reaction (HER) and initial- and gradual surface passivation. In previous studies the effect of porosity and specific additives have been presented as important factors in tackling these drawbacks. This multidisciplinary research aimed to study porosity and additive effects on the electrochemical behaviour and performance of iron-based mechanically-stable anodes, manufactured at elevated temperature and pressure. Specifically, the effect of 10wt% pore former K2CO3 on the initial capacity and on the passivation behaviour was studied by galvanostatic charge-discharge, with prior investigation on pore formation. In addition, the effect of high-performance additives (Bi2S3, Bi2O3, ZnS and FeS) was investigated on HER kinetics and the passivation behaviour, by cyclic voltammetry (CV) and galvanostatic cycling, respectively. Surface characterization was performed by optical microscopy, scanning electron microscopy (SEM), and profilometry. Post-test analysis was carried out by optical microscopy and X-ray Photoelectron Spectroscopy (XPS). An intensification of surface cracks was observed for the K2CO3-rich sample before testing and its initial discharge capacity is 27 mAh/g less than a sample without pore former, but passivated later than the pristine sample in the full cell. Amongst the additives, the highest cycle of 100% capacity retention was marked at cycle 41 for FeS and for Bi2S3 at cycle 29 in the full cell, both showing 100% retention in the half cell up to 36 cycles. FeS might benefit from its readily available soluble reservoir of S2− ions. Bi2O3 showed the lowest capacity retention which might be explained by low conductivity, low solubility and/or lack of beneficial role of S2− ions. However, the additive Bi2O3 showed great reversibility of discharge products in the CV, confirmed by the lower O1s peaks and the lower respective Fe2O3 and FeOOH peak in XPS spectra. The pristine sample showed in the CV over the cycles increased current density and slope near the HER potential, with low reversibility. Apart from Bi2O3 and ZnS, the pristine sample showed lower capacity retention than FeS and Bi2S3, confirming the effective working of these additives. This systematic study portrays a good starting point for further studying porosity and additive effects on the electrochemical behaviour in hot-pressed anodes for the upcoming Iron-Air battery. Improvements can be assigned to cell design, electrolyte control and further detailed porosity characterization. Another type of current collector might withstand higher current densities and anode thickness reduction can lead to higher discharge capacities over its lifespan.

Al-Li alloys were introduced for the use in aerospace applications due to its many advantages over steel such as its low density, good thermal and electrical conductivity and corrosion resistance of these alloys. The current generation of Al-Li alloys were developed to replace the currently used AA2024 alloy in commercial airframes, military and space applications. Traditional joining methods cannot be used to join dissimilar aluminium alloys. Thus, friction stir welding (FSW) was used to join the 2 dissimilar Al-Li alloys - AA2099 T83 and AA2060 T8E30 alloys. FSW causes several changes in the microstructure due to the rotational movement of the tool which results in localised plastic deformation and a thermal cycle in the alloys. This leads to 4 distinct zones in the alloys - the stir zone, thermo-mechanically affected zone, heat affected zone, and the base metal. The differences in microstructure is suggested to cause a change in the mechanical properties and localised corrosion behaviour of the alloys. In this work, the localised corrosion behaviour of the friction stir welded Al-Li alloys were investigated. The effect of FSW on the microstructure and corrosion behaviour was also studied. Microstructural characterisation was done for both the alloys and their respective weld zones. Coarse constituent particles were found in all weld zones with a decreasing trend in average size towards the weld centre. Strengthening precipitates such as the T_1 phase particles were observed on the grain boundaries of the alloys. This had a decreasing trend of distribution density towards the weld centre with virtually no precipitates in the SZ. In order to assess the corrosion performance potentiodynamic polarisation, open circuit potential, linear polarisation resistance, and immersion tests were deployed. Furthermore, scanning electron microscopy with energy dispersive X-ray spectroscopy was used to evaluate the morphology and chemical composition of the of the corroded surface. It was found that for the BM and HAZ regions of both alloys, the attack occurred mainly on the grain boundaries which were sites for the T_1 particles. These particles were suggested to be the controlling factor of localised corrosion behaviour in these regions due to their high electrochemical behaviour, which also resulted in almost no passivity in these regions. A large attack site was also observed on the surface of the matrix which was the site of hydrogen evolution during initial immersion time periods. Pits were also formed on the sites of coarse intermetallic particles. For the SZ regions the dominating attack was due to the coarse particles in the matrix. The effect of anodising the surface and sol-gel coating of the surface on the corrosion behaviour was determined in this project. It was found that the anodised layer did enhance the corrosion performance of the alloys. The SZ of the anodised sample was found to be most prone to corrosion compared to the anodised base metals. The sol-gel coating on the surface was also found to increase the corrosion resistance of the surface due to its self healing properties thus protecting the surface of the alloys.

Microstructure-corrosion property correlation is an open question in the field of materials science. The microstructure of metals and alloys consists of several features with different individual corrosion response. The corrosion behavior of the macroscopic system is an outcome of the complex interaction of the components of microstructure. Hence, a definitive understanding of the corrosion response of the microstructural features is needed for improving the material durability and design.In the present work, the effect of grain size  on the active corrosion behavior of pure iron is investigated. Samples with different grain sizes are obtained by annealing heat-treatment. The microstructure of samples is characterized by optical microscopy, electron backscatter diffraction and X-ray diffraction. Electrochemical characterization using potentiodynamic polarization and electrochemical impedance spectroscopy are performed on the samples in deaerated 0.1 M and 0.01 M H2SO4 solutions. The surface topography of the corroded sample surface is characterized by atomic force microscopy. Following the experiments, a numerical corrosion model is attempted to replicate the observations. The results reveal an aggregate effect of grain size and crystallographic orientation of grains on the corrosion behavior of the samples.

Studies on the impact of Hydrogen on the electrochemical and mechanical behaviour of Iron-based materials have been increasingly conducted in the past few years. This is mainly due to the ever-growing demand for sustainable energy sources, which involve Hydrogen and to meet the high structural and economic demands from the automobile sector and other industrial demands for which high strength steels like dual-phase steels have been developed. Steels may absorb hydrogen both throughout the production process and during different phases of use. High-strength steels (particularly dual phase steels) and martensitic stainless steels are highly susceptible to hydrogen embrittlement. Moreover, hydrogen embrittlement is already possible at quantities as low as 0.1 ppm[1]. Therefore, understanding Metal-hydrogen interactions is essential. This thesis aims to study the effect of Hydrogen charging on three different iron-based materials and the possible effect on the electrochemical/corrosion performance. The Iron-based materials used in the study are Pure Iron, DP1000 and AISI 420. The methodology involves using an electrochemical procedure based on potentiostatic Hydrogen charging and Cyclic Voltammetry (CV), applied on these Iron-based materials having different phases to monitor H-uptake in the materials. The materials are charged with Hydrogen both on the active and passive surfaces. The electrochemical method is capable of measuring the diffusible H concentration (including mobile Hydrogen) for the steel alloys under H-charging conditions. Using X-Ray Diffraction (XRD) Technique, microstructural analysis is carried out on Pure Iron, DP1000 and AISI 420 stainless steel to identify the different phases interacting with Hydrogen. To gain additional insights relating to the electrochemical/corrosion performance of the investigated materials and into the H-related findings, potentiostatic polarization techniques, Electrochemical Impedance Spectroscopy (EIS) and Scanning Kelvin Probe (SKP) are carried out. As a result, it was discovered that Pure Iron had the maximum amount of diffusible Hydrogen under the charging conditions tested, followed by DP1000 and then AISI 420 Steel with the lowest amount. EIS technique was useful in identifying a trend between the barrier properties of the passive layer and the H desorption values for the three materials. The results also revealed that materials charged with Hydrogen on active and passive surfaces behaved differently with respect to the amount of Hydrogen desorption. The microstructural features of the active surface and the passive oxide film that formed on the materials are further discussed in relation to this.