The research objective of this award is to gain a fundamental understanding of the manufacturing process of thin-film coatings and address a range of issues that impact their performance. The challenge of flexibly fabricating uniform defect-free functional materials for applications such as bioengineering, apparels, electronics, energy and so forth is not trivial, due to the interfacial phenomena between the material and coated solution. This project will address the relationship between processing and performance for complex polymer solutions directly coated onto woven structures through a synergistic mix of experimentation, modeling and performance testing. The flexibility and repeatability of the manufacturing process will be analyzed based on changing the processing conditions (i.e., temperature, velocity, casting thickness, etc.), using design of experiments (DOEs), and evaluated using destructive and non-destructive evaluation techniques. A theoretical model that predicts the required operating conditions to fabricate uniform defect-free carbon woven structures CWSs will be developed based on fundamental principles and validated against data collected from the DOE. Finally, performance analysis will be conducted to evaluate the film properties of the resulting functional material.
Successful completion of this research will fundamentally broaden the knowledge base on how functional coated woven structures are fabricated in a uniform, defect-free manner. Although this work is applicable to many areas, due to the advancements needed in the renewable energy area, this project will focus on understanding the mechanisms that prohibit direct coating of polymer solutions onto functional materials, such as gas diffusion layers for fuel cell applications. Success of this investigation will present an approach to fabricate such functional materials more flexibly, with increased production rates, decreased waste, and using a more robust process, which will have an exponential economical impact, due to their use in transportation, stationary, and portable devices. To broaden the participation of underrepresented groups at minority and primary institutions not traditionally exposed to research, Dr. Harris has co-developed a program called ELECTRoDE: Educators Leading Energy Conservation and Training Researchers of Diverse Ethnicities.
The objective of this proposal was to understand the relationship between directly coating porous media to their performance, in order to scale production of materials used in the renewable energy sector. Specifically, this work relates to materials used in polymer electrolyte membrane fuel cells (PEMFCs). The tasks associated with this research included: (1) conducting experiments to investigate direct coating of a fluid onto a woven structure; (2) developing a theoretical model that predicts the operating conditions required to uniformly coat the fluid directly onto a porous substrate; and (3) to characterize the electrochemical behavior of the formed composite material. The research group developed a new fabrication technique to directly coat polymer fluids onto carbon based porous materials, based on a scalable manufacturing process known as slot die extrusion. An experimental study revealed that a polymer electrolyte membrane fluid (Nafion) can be directly coated onto carbon paper, which serves as a gas diffusion layer in PEMFCs. Electrochemical tests validate that adequate performance can be achieved with the directly coated porous media, if the penetration depth of the coated fluid is not excessive. To this end, the group investigated the penetration of a fluid into a porous medium, using sophisticated theoretical and computational modeling approaches, including a modified periodic surface model coupled with commercially available computational fluid dynamics models. These models helped demonstrate that fundamentally the penetration depth of a fluid as it is coated onto a porous media can be predicted, and thus minimized. This was validated with experiments. However, the models are only appropriate for fluids coated on surface that exhibit little or no capillary effects. This work suggest that the traditionally labor intensive fabrication approach which is done by hand, can be automated using scalable roll-to-roll processes, thereby reducing processing time and cost. The results from this work are expected to have a significant impact on how porous media is coated and/or developed at the macro-scale for functional material, such as separation membranes used in fuel cells and water filtration applications. The depth of fluid penetration into the pores limits the ability to directly coat porous media during the coating process. To date, there exist limited understanding in this regard. This work provides a framework for understanding the relationship between directly coating porous media and penetration and offer modeling tools to conduct deeper studies into the subject matter. From an educational standpoint, the PIs developed graduate students and undergraduate students in research that is applicable to the advancement of renewable energy technology, directly through the research as well as through new course development. To the broadening participation of under-represented group, the PIs actively participated in an existing program called ELECTRoDESM, which stands for Educators Leading Energy Conservation and Training Researchers of Diverse Ethnicities. This program was co-developed by Drs. Comas Haynes and Tequila Harris at Georgia Tech, with an inherent objective of broadening the participation of underrepresented minorities and students at primary institutions, while simultaneously engaging students at majority universities (specifically Georgia Tech), in year round research experiences. In this regard, a very diverse group of individuals were involved in the research program. Through the ELECTRoDE program several undergraduate students participated in undergraduate research most of them for multiple semesters. As a consequence, three student participants are co-authors on papers, which are under review or being written. As outreach to the K-12 community, the group participated in the Georgia Tech GoSTEM program for 8th graders. During this time sixteen students (primarily of Hispanic descent) conducted experiments in the Harris Research Lab, where they coated various substrates, porous and non-porous, and learned about the connectivity between processing conditions, materials, and substrates to gain a basic understanding of hydrophobicity. The results from this work have been broadly disseminated through invited lectures, conference talks and journal publications. Three invited talks (at Texas Tech University, Purdue University, and Rensselaer Polytechnic Institute) and a Keynote at the ASME 11th Fuel Cell Science and Technology Conference, were given. The work has also resulted in six accepted journal papers (Int. J. of Hydrogen Energy, Chemical Engineering Science, J. of Coatings Technology and Research, and the J. of Electrochemical Society). Three additional journal papers have been submitted and are currently under review. Furthermore, nine presentations were given by the PI, co-PI, and graduate and undergraduate student participants at major conferences including ASME Fuel Cell Science and Technology Conference, the Electrochemical Society Meeting and the International Symposium on Coating Science and Technology.
