Browsing by Author "Prasad, Ajay K."
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Item 3D Computational Model for an Electrochemical Gas Separation and Inerting System(Journal of The Electrochemical Society, 2022-04-25) Aryal, Utsav Raj; Aziz, Majid; Prasad, Ajay K.Aircraft fuel tank inerting is employed to reduce the flammability of the fuel vapor in the ullage (air volume above the fuel) by restricting its oxygen concentration to a safe value—12% for commercial aircraft and 9% for military aircraft. Inerting is typically accomplished by displacing oxygen in the ullage with an inert gas like nitrogen. Electrochemical gas separation and inerting system (EGSIS) is an on-board method to generate and supply nitrogen-enriched air (NEA) to the fuel tank. EGSIS combines a polymer electrolyte membrane (PEM) electrolyzer anode which dissociates water to evolve oxygen, and a PEM fuel cell cathode which reduces oxygen from atmospheric air to produce NEA at its outlet. This paper represents the first attempt to model and simulate EGSIS using a three-dimensional, steady state, isothermal model. Various EGSIS performance indicators such as current density, reactant concentration distribution, and polarization curves are studied as a function of operating conditions and design parameters. The results from the computational model are validated against our previous experimental results for various operating conditions. The simulation results reveal the effects of temperature, reactant flowrates, and material property optimization on EGSIS performance. Different operating strategies are explored with the goal of improving system performance.Item Adaptive Thermal Control of Cell Groups to Extend Cycle Life of Lithium-Ion Battery Packs(Applied Sciences, 2023-04-07) Connor, Wesley D.; Advani, Suresh G.; Prasad, Ajay K.We present a novel approach for a battery management system in which adaptive thermal control is employed to balance the capacities of individual groups of cells within a lithium-ion battery pack. Maintaining capacity balance within the battery pack in this manner can significantly extend its cycle life. We explore the physical implementation of this concept and demonstrate that it is a viable way to extend the life of battery packs. The experimental setup consists of three pairs of cells connected electrically in series and supplied with coolant flow from a chiller. All cells are initially in capacity balance and are cooled uniformly for the first 50 fast charge/discharge cycles. Subsequently, cooling is halted to specific cell pairs to deliberately unbalance their capacities. Finally, cooling is selectively restored to correct the capacity imbalance between the cell groups by the end of 100 charge/discharge cycles. These results suggest that adaptive thermal control can be used effectively to maintain capacity balance within the battery pack.Item Biosourced Antioxidants for Chemical Durability Enhancement of Perfluorosulfonic Acid Membrane(Advanced Functional Materials, 2024-01-02) Agarwal, Tanya; Adhikari, Santosh; Babu, Siddharth Komini; Prasad, Ajay K.; Advani, Suresh G.; Borup, Rodney L.The chemical durability of perfluorosulfonic acid (PFSA) membranes is a topic of growing interest to meet Department of Energy (DOE) durability targets for heavy-duty vehicle (HDV) applications. State-of-the-art membranes like Nafion, rely on the use of cerium, heteropolyacids, and other inorganic additives to increase PFSA chemical durability. A less explored avenue for the oxidative stabilization of PFSA and hydrocarbon membranes is the use of organic antioxidants. No reversible organic antioxidant has been demonstrated to date which can enhance membrane lifetime by factors comparable to cerium. Here, ellagic acid (EA) is demonstrated as a promising radical scavenger for PFSA's. It is found that the incorporation of EA enhances the chemical durability of Nafion by 160%. EA, when incorporated with cerium as an electron donorenhances Nafion durability by at least 80% compared to a membrane incorporated with just cerium in DOE-defined durability tests. EA is found to be reversible in acidic conditions like those of fuel cells and its reversibility could be further enhanced by the use of suitable co-antioxidants.Item Composite Membrane Based on Graphene Oxide Sheets and Nafion for Polymer Electrolyte Membrane Fuel Cells(Electrochemical Society, 2014-10-29) Wang, Liang; Kang, Junmo; Nam, Jae-Do; Suhr, Jonghwan; Prasad, Ajay K.; Advani, Suresh G.; Liang Wang, Junmo Kang, Jae-Do Nam, Jonghwan Suhr, Ajay K. Prasad and Suresh G. Advani; Wang, Liang; Prasad, Ajay K.; Advani, Suresh G.A composite membrane for fuel cell applications was prepared by incorporating custom-made graphene oxide (GO) in Nafion resin. The GO was used to provide mechanical reinforcement to Nafion. Transmission electron microscopy confirmed the formation of highly crystalline and individually-dispersed graphene oxide sheets. Tensile strength, water uptake, swelling, proton conductivity and electrical conductivity of the composite membranes were measured and compared with pure Nafion. The polarization curves indicated that the fuel cell performance of the 3wt% GO/Nafion composite membrane was similar to that of the pure Nafion membrane, but the composite membrane was superior to Nafion in terms of mechanical properties.Item Design, Operation, Control, and Economics of a Photovoltaic/Fuel Cell/Battery Hybrid Renewable Energy System for Automotive Applications(MDPI AG, 2015-06-09) Whiteman, Zachary S.; Bubna, Piyush; Prasad, Ajay K.; Ogunnaike, Babatunde A.; Zachary S. Whiteman, Piyush Bubna, Ajay K. Prasad and Babatunde A. Ogunnaike; Whiteman, Zachary S.; Bubna, Piyush; Prasad, Ajay K.; Ogunnaike, Babatunde A.Meeting rapidly growing global energy demand—without producing greenhouse gases or further diminishing the availability of non-renewable resources—requires the development of affordable low-emission renewable energy systems. Here, we develop a hybrid renewable energy system (HRES) for automotive applications—specifically, a roof-installed photovoltaic (PV) array combined with a PEM fuel cell/NiCd battery bus currently operating shuttle routes on the University of Delaware campus. The system’s overall operating objectives—meeting the total power demand of the bus and maintaining the desired state of charge (SOC) of the NiCd battery—are achieved with appropriately designed controllers: a logic-based “algebraic controller” and a standard PI controller. The design, implementation, and performance of the hybrid system are demonstrated via simulation of real shuttle runs under various operating conditions. The results show that both control strategies perform equally well in enabling the HRES to meet its objectives under typical operating conditions, and under sudden cloud cover conditions; however, at consistently high bus speeds, battery SOC maintenance is better, and the system consumes less hydrogen, with PI control. An economic analysis of the PV investment necessary to realize the HRES design objectives indicates a return on investment of approximately 30% (a slight, but nonetheless positive, ~$550 profit over the bus lifetime) in Newark, DE, establishing the economic viability of the proposed addition of a PV array to the existing University of Delaware fuel cell/battery bus.Item Electrochemical gas separation and inerting system(Journal of Power Sources, 2021-05-15) Aryal, Utsav Raj; Chouhan, Ashish; Darling, Robert; Yang, Zhiwei; Perry, Mike L.; Prasad, Ajay K.Following the TWA 800 flight disaster in 1996 which was attributed to an explosion in the fuel tank, inerting of the ullage (air volume above the fuel in the tank) has gained prominence. Fuel tank inerting is the process of reducing the flammability of the ullage by supplying it with an inert gas like nitrogen. Current inerting techniques are expensive, consume large amounts of energy, and fail prematurely. Here, we propose a novel in-flight electrochemical gas separation and inerting system (EGSIS) to produce and supply nitrogen-enriched air (NEA). EGSIS combines a polymer electrolyte membrane (PEM) fuel cell cathode with a PEM electrolyzer anode to generate humidified NEA as the cathode output which can be dehumidified and supplied directly to the fuel tank. The required rate of NEA varies during a typical flight and a major advantage of EGSIS is that the rate of NEA generation can be conveniently controlled by varying the voltage applied to the system. Here, we report on the performance of a single-cell EGSIS apparatus and evaluate its suitability for aircraft fuel tank inerting.Item Electrophoretic Deposition as a Versatile Low-Cost Tool to Construct a Synthetic Polymeric Solid-Electrolyte Interphase on Silicon Anodes: A Model System Investigation(ACS Applied Materials and Interfaces, 2024-02-14) Mou, Rownak J.; Barua, Sattajit; Prasad, Ajay K.; Epps, Thomas H. III; Yao, Koffi P. C.The cycling of next-generation, high-capacity silicon (Si) anodes capable of 3579 mAh·g–1 is greatly hindered by the instability of the solid-electrolyte interphase (SEI). The large volume changes of Si during (de)lithiation cause continuous cracking of the SEI and its reconstruction, leading to loss of lithium inventory and extensive consumption of electrolyte. The SEI formed in situ during cell cycling is mostly composed of molecular fragments and oligomers, the structure of which is difficult to tailor. In contrast, ex situ formation of a synthetic SEI provides greater flexibility to deposit long-chain, polymeric, and elastomeric components potentially capable of maintaining integrity against the large ∼350% volume expansion of Si while also enabling electronic passivation of the surface for longer cycling and calendar life. Furthermore, polymers are amenable to structural modifications, and the desired elasticity can be targeted by selection of the SEI polymer feedstock. Herein, electrophoretic deposition (EPD) is used to apply chitosan as a synthetic SEI on model Si thin film electrodes. Comparison of synthetic SEIs obtained without (Si/Chit) and with CH3COOLi (Si/Chit+CH3COOLi) added during EPD is performed to demonstrate a facile route to tuning of the polymer SEI chemistry. Atomic force and scanning electron microscopy reveal that addition of CH3COOLi at EPD assists in conformal deposition of the synthetic SEI. During electrochemical cycling, the Chit+CH3COOLi coating nearly doubles the capacity retention versus the reference bare Si thin film. X-ray photoelectron and Fourier transform infrared spectroscopy reveal that CH3COOLi caps the −NH2 groups of chitosan through amidation during EPD, which suppresses the catalytic reduction of the electrolyte. The presented approach demonstrates and validates EPD as a low-capital route to achieving and chemistry-tuning synthetic SEIs on Si electrodes. More broadly, the method is a promising avenue toward controlled and tailored polymeric SEIs on various conversion-type electrodes with high particle volumetric expansion.Item Fluoroalkyl phosphonic acid radical scavengers for proton exchange membrane fuel cells(Journal of Materials Chemistry A, 2023-04-06) Agarwal, Tanya; Adhikari, Santosh; Kim, Yu Seung; Babu, Siddharth Komini; Tian, Ding; Bae, Chulsung; Pham, Nguyet N. T.; Lee, Seung Geol; Prasad, Ajay K.; Advani, Suresh G.; Sievert, Allen; Rasika, Wipula Priya Liyanage; Hopkins, Timothy E.; Park, Andrew; Borup, RodRadical-induced degradation of proton exchange membranes limits the durability of proton-exchange membrane fuel cells. Cerium is widely used as a radical scavenger, but the migration of cerium ions to the catalyst layer has been an unresolved issue, reducing its effectiveness over time. Here, we report phosphonic acids as a promising class of radical scavengers, showing competent radical scavenging activity compared to cerium without the migration issue. The ex situ Fenton test shows that the fluoride emission rate for Nafion membrane incorporated with fluoroalkyl phosphonic acid ranged from 0.22 to 0.37 μg F cm−2 h−1, lower than that of the cerium-incorporated Nafion™ membrane (0.39 μg F cm−2 h−1). The in situ open circuit voltage hold test confirmed that a phosphonic acid-incorporated Nafion™ membrane has a 58% lower fluoride emission rate compared to the baseline. Density functional theory calculations indicate that the activation energy of the hydroxyl radical scavenging reaction of an alkyl phosphonic acid is only 0.68 eV, suggesting an effective radical scavenging pathway.Item Optimization of an Electrochemical Gas Separation and Inerting System(Journal of The Electrochemical Society, 2022-06-17) Prasad, Ajay K.; Aryal, Utsav RajAircraft fuel tank inerting is typically accomplished by supplying nitrogen enriched air (NEA) into the ullage (volume of air above the fuel level in the tank). We have developed a novel on-board electrochemical gas separation and inerting system (EGSIS) to generate NEA for fuel tank inerting. EGSIS is an electrically powered system that functionally combines a proton exchange membrane (PEM) fuel cell cathode with an electrolyzer anode. Water management is important in such a PEM-based system because proton transfer requires proper hydration of the membrane. Extremes of both dryout and flooding conditions should be avoided for optimal EGSIS performance. Previous single-cell EGSIS experiments revealed that supplying liquid water at the anode will maintain sufficient membrane hydration even when the system is operated under dry cathode conditions. However, it was difficult to avoid flooding at low cathode air stoichiometries when parallel flow field channels were employed. Here, we implement various strategies to optimize EGSIS performance such as using serpentine and interdigitated flow field channels, as well as a double-layer gas diffusion layer with graded hydrophobicity to mitigate flooding and improve water management. We also present a theoretical analysis of various stack configurations for a practical EGSIS module.