Pore-Scale Investigation of Coupled Two-Phase and Reactive Transport in the Cathode Electrode of Proton Exchange Membrane Fuel Cells

A three-dimensional multicomponent multiphase lattice Boltzmann model (LBM) is established to model the coupled two-phase and reactive transport phenomena in the cathode electrode of proton exchange membrane fuel cells. The gas diffusion layer (GDL) and microporous layer (MPL) are stochastically reconstructed with the inside dynamic distribution of oxygen and liquid water resolved, and the catalyst layer is simplified as a superthin layer to address the electrochemical reaction, which provides a clear description of the flooding effect on mass transport and performance. Different kinds of electrodes are reconstructed to determine the optimum porosity and structure design of the GDL and MPL by comparing the transport resistance and performance under the flooding condition. The simulation results show that gradient porosity GDL helps to increase the reactive area and average concentration under flooding. The presence of the MPL ensures the oxygen transport space and reaction area because liquid water cannot transport through micropores. Moreover, the MPL helps in the uniform distribution of oxygen for an efficient in-plane transport capacity. Crack and perforation structures can accelerate the water transport in the assembly. The systematic perforation design yields the best performance under flooding by separating the transport of liquid water and oxygen.

Lithium capture in Seawater Reverse Osmosis (SWRO) Brine using membrane-based Capacitive Deionization (MCDI) System

Lithium-battery based industries including vehicles, electronics, fusion and thermonuclear, consume lithium rapidly, which raises the need for developing a lithium recovery system. Lithium global market consumption in 2016 was reported to be 35% in batteries manufacturing. The total content of lithium in seawater and oceans is estimated at 2.5 × 1014 kg, with an average concentration of 0.17 mg/L. Salt lakes contain 1,000–3,000 mg/L of lithium, while geothermal water up to 15 mg/L. In 2020, the US Geological Survey (USGS) reported that the total Li resource is about 80 million ton. In nature, lithium does not exist as pure metal owing to its high reactivity with water, air, and nitrogen. Commonly lithium is mined from metallic minerals from earth or brine salt marsh and used in various fields in the form of lithium carbonate (60%), lithium hydroxide (23%), lithium metal (5%), lithium chloride (3%), and butyl lithium (4%). The extraction of 1 kg of lithium needs around 5.3 kg of lithium carbonate. The amount required to produce lithium-ion batteries (LIB) for cell phones or electric cars is estimated to be 0.8 kg/s of lithium metal, which is equivalent to 25,000 tons per year. As we use this much of LIB, this will end up having significant amounts of lithium battery waste, thus recovering LIBS and using it as cathode electrode in MCDI is an excellent way with benefit. This work proposes to efficiently utilize seawater reverse osmosis (SWRO) brine as a medium to recover lithium from seawater followed by its selective capture of lithium element using SLIB as MCDI cathode electrode material. Thus, these attempts could be closer to an improved and more effective loop of lithium targeted capture-reuse system.

Fabrication of Eco-Friendly Graphene Nanoplatelet Electrode for Electropolishing and Its Properties

Electropolishing is one of the most widely applied metal polishing techniques for passivating and deburring metal parts. Copper is often used as cathode electrode for electropolishing due to its low electrical resistance and low flow values. However, during the electropolishing process, elution of the cathode electrode caused by the electrolyte and remaining oxygen gas also causes critical water pollution and inhibits electropolishing efficiency. Therefore, to achieve an efficient and eco-friendly electropolishing process, development of a highly corrosion resistive and conductive electrode is necessary. We developed a highly oriented graphene nanoplatelet (GNP) electrode that minimizes water pollution in the electropolishing process. We functionalized GNP by a one-step mass-productive ball-milling process and non-covalent melamine functionalization. Melamine is an effective amphiphilic molecule that enhances dispersibility and nematic liquid crystal phase transformation of GNP. The functionalization mechanism and the material interaction were confirmed by Raman spectroscopy after high-speed shear printing. After the electropolishing process by melamine-functionalized GNP electrodes, 304 stainless steel samples were noticeably polished as copper electrodes and elution of carbon was over 50 times less than was the case when using copper electrodes. This electropolishing performance of a highly oriented GNP electrode indicates that melamine-functionalized GNP has great potential for eco-friendly electropolishing applications.