In order to capitalize on the cost-effectiveness of additive manufacturing (AM), it is critical to understand how to build components with consistency and high quality. Directed energy deposition (DED) is an AM method for creating parts layer by layer through the use of a moving heat source and powder material inserted into the melt pool generated on the substrate. DED, like most AM processes, is highly complex due to the rapid thermal gradients experienced during processing. These thermal gradients are determined by a variety of processing parameters, which include laser power, powder feed rate, travel speed, layer height hatch spacing, etc. A lot of effort has been carried out in the additive manufacturing community to understand what these critical parameters are and how they influence the thermal gradients. Despite all these efforts, AM industries rely on a trial-and-error-based approach to find the right set of parameters to produce a quality part. This is time-consuming and not a cost-effective use of AM technology. The aim of our research is to reduce the amount of experimental data in combination with numerical analysis to optimize this relationship. Physics-based two-dimensional melt-pool modeling and experimental results from an OPTOMEC 850M LENS will be utilized to investigate the effects of processing parameters on melt-pool geometry, and the results from this study will provide key processing guidelines to achieve desirable clad geometry and powder efficiency for the DED method.

The aluminum–air (or oxygen) battery has received intense attention in the past because of its excellent benefits such as low cost and high energy density, but due to the challenging issues such as hydrogen evolution and inactive oxide film formation on the Al surface, it could not be fully applied. In this study, 1-Ethyl 3-Methyl Imidazolium Chloride ([EmIm]Cl) and aluminum chloride (AlCl₃) are applied to resolve the aforementioned issues. Ex situ component-level and in situ cell-level open circuit voltage (OCV) tests combined with the physics-based model analyses were conducted to investigate the electrochemical reaction behaviors of the Al–air cell. Especially, the effect of aluminum oxide formation on the anode- and cathode-side reactions were analyzed in detail. The oxide film formed at the Al surface strongly was found to significantly impede the electrochemical reaction at the surface, and the film growth was controlled by decreasing the surface tension by aggressive anions. In the cathode side, the aluminum oxide precipitated in the porous cathode electrode was found to decrease the porous reaction area and block reactant access into the reaction sites. The effects of O₂ solubility in the electrolyte, initial porosity and thickness of the porous electrode are compared in detailed, and optimal thickness is suggested.

A promising redox-mediated bromate-ion (BrO₃⁻) based system was investigated through research combined with mathematical modeling, analytical study, and full-cell test to understand the characteristic effect of electrochemical reaction coupled with chemical reaction, called catalytic regenerative reaction (EC’), on the cell behaviors. From the full-cell based discharge test, a unique unsteady behavior induced by the catalytic regenerative reaction was found for the first time, and to understand the underlying physics and nature of the system, theoretical study was conducted through mathematical modeling and analytical method. Three reaction mechanisms (E, EC, and EC’) were compared in their characteristic reaction behaviors to understand the nature of each reaction mechanism, and the results were analyzed with respect to reaction time and species concentration at the electrode surface. Furthermore, the effect of actual condition of bromate system (i.e. non-unity stoichiometry and limited amount of bromate) was analyzed at unsteady condition for the first time to understand its characteristic behavior in the actual battery condition. It was found that cell voltage and operation time were increased substantially by the catalytic regenerative reaction, and inclusion of non-unity stoichiometric coefficients induced a significant change in the concentration profiles for reactant and product species, leading to operation time about 4.2 times longer than the unity stoichiometric EC’ reaction. As a final step, the effect of catalytic reaction was analyzed in analytical method to define the parameters to control the catalytic reaction, and especially, the relative effect of electrochemical reaction and coupled chemical reaction rates on the autocatalytic reaction was compared through a zone diagram where conditions for pure diffusion controlled and pure kinetic controlled cases were defined.

In this study, a new type of redox flow battery (RFB) named “membrane-less hydrogen-iron RFB” was investigated for the first time. The membrane is a cell component dominating the cost of RFB, and iron is an abundant, inexpensive, and benign material, and thus, this iron RFB without the membrane is expected to provide a solution to the challenging issues of current battery systems such as high cost and safety concerns. The research focus in this study was placed on defining key design parameters to make this new system promising as an RFB. Crossing rate of reactants over carbon porous electrode (CPE) was controlled by modifying its pore structure with Teflon impregnation, and the effects of the Teflon on crossover, kinetic, Ohmic, and mass transfer was investigated by cell-based test and one-dimensional computational model. It was found that the cell performance (i.e., charge and discharge polarization) of the new membrane-less system was equivalent to that of the conventional membrane-system (i.e., RFB having a membrane). Especially, the Ohmic properties of the new system were constant and stable, while in the conventional membrane system, they were significantly varied and deteriorated as cell tests were continued, indicating that degradation or contamination of membrane affecting Ohmic properties could be mitigated effectively in the membrane-less system, which was found first in this research. The modeling analysis provided insight into the system, showing that the effect of reactant crossover on performance decay was not significant, and Teflon impregnation in the CPE caused significant kinetic and Ohmic losses by impeding ion transport and reactant access to reaction sites. From this study, it was found that the membrane-less H₂-iron system is feasible and promising in resolving the challenge issues of the conventional systems. And the results of this study are expected to provide guidelines for research and development of flow battery systems without having a membrane.