Engineering topics
Chandrasekaran, Swetha
Publications and source records attributed to Chandrasekaran, Swetha.
UHTC-TPMS Heat Exchangers for Concentrating Solar Power Applications with Thermal Energy Storage in Molten Chlorides
Concentrating solar power (CSP) plants convert energy from sunlight into electricity. Generally, a heliostat field is used to reflect sunlight and concentrate it onto a receiver, which heats the receiver and/or the media flowing through it. A flow loop transports the media through the system to a heat exchanger before returning the media back to the receiver to be reheated. The heat extracted by the heat exchanger is then converted into electricity using a conventional heat engine.
3D printed optimized electrodes for electrochemical flow reactors
Recent advances in 3D printing have enabled the manufacture of porous electrodes which cannot be machined using traditional methods. With micron-scale precision, the pore structure of an electrode can now be designed for optimal energy efficiency, and a 3D printed electrode is not limited to a single uniform porosity. As these electrodes scale in size, however, the total number of possible pore designs can be intractable; choosing an appropriate pore distribution manually can be a complex task. To address this challenge, we adopt an inverse design approach. Using physics-based models, the electrode structure is optimized to minimize power losses in a flow reactor. The computer-generated structure is then printed and benchmarked against homogeneous porosity electrodes. We show how an optimized electrode decreases the power requirements by 16% compared to the best-case homogeneous porosity. Future work could apply this approach to flow batteries, electrolyzers, and fuel cells to accelerate their design and implementation.
Formulation of Conductive Inks for DIW Printed Battery Electrodes
Ink formulations for DIW printing of Li ion battery electrodes were optimized for high conductivity, surface area and printability. Our focus is particularly on optimizing Li-ion battery electrodes for low temperature applications by 3-D printing the cathodes into high surface area shapes. The sluggish kinetics of ion transport at the solid-electrolyte phase boundary can be a major problem in batteries at low temperatures, so optimizing for ion transport can help combat these issues. Two families of DIW ink were investigated; aqueous conductive polymer suspension with graphene nano platelets (GNP) ink, and “oil in water” graphene oxide (GO) micro emulsion ink which carbonizes to an open cell graphene aerogel. By iterative formulation changes, the conductivity of PEDOT:PSS based ink was increased over tenfold, and stiffness of GO emulsion ink was increased to provide better printability without sacrificing porosity.
Transforming nanoscale VO 2 (B) into a scalable sodium-ion electrode
The intermittent nature of renewable energies requires highly reliable grid-level energy storage approaches. A critical consideration in developing this technology is the areal capacity which determines battery performance and influences the cost of battery technology. Of related importance is finding new ways of developing scalable electrodes. In recent years, three-dimensional (3D) printing of conductive scaffolds has emerged as an alternative to overcome the scalability limitations of commercial tape cast electrodes. The research carried out in the current study demonstrates a successful scalability pathway for nanoscale VO 2 (B), a desirable cathode for sodium-ion batteries which has a nano-flower morphology with a crystallite size < 20 nm. By electrodepositing VO 2 (B) onto a graphene aerogel scaffold, we were able to achieve mass loading of over 100 mg·cm −2 and still possess an areal capacity of 10 mAh·cm −2 at a current density of 5 mA·cm −2 . Moreover, after 1000 cycles, these electrodes retained 75% to 80% of their initial capacity. Even at high loading levels, the electrodeposited VO 2 (B) exhibits pseudocapacitive material signatures such as a box-like voltammetry response, linear galvanostatic response, and no phase change upon lithiation. The scalability of the VO 2 (B) electrode is demonstrated in a series of experiments which show the areal capacity to scale upon increase in both mass loading and electrode thickness, with only small changes in specific capacity. Furthermore, this study establishes that nanoscale materials can be scaled up to achieve thick electrodes without compromising their electrochemical properties.
Products having sheets of 2D materials and related inks for direct ink writing
In one inventive concept, an ink includes a precursor of a graphene analogue, a thickener, and a solvent. In another inventive concept, an ink includes a graphene analogue, a thickener, and a solvent. In yet another inventive concept, an aerogel includes a three-dimensional printed structure having printed features comprised of two dimensional sheets of a graphene analogue.
Electromethanogenesis reactor
Generation of energy and storage of energy for subsequent use is provided by electromethanogenesis of carbon dioxide into a fuel gas and the storage of the fuel gas for subsequent use. An electromethanogenic reactor includes an anode conductor and a cathode conductor wherein the cathode conductor includes submicron to micron scale pores. Electromethanogenesis microbes and/or enzymes are located in the micron scale pores of the cathode electrode conductor. Carbon dioxide is introduced into the electromethanogenic reactor and the electromethanogenesis microbes/enzymes and the carbon dioxide interact and produce a fuel gas. The fuel gas is stored for subsequent use, for example use in power generation.
Base-catalyzed sol-gel inks for direct ink writing of high resolution hierarchically porous carbon aerogels
According to one aspect of an inventive concept, an ink includes a base catalyst, a sol gel precursor composition, and a block copolymer. According to another aspect of an inventive concept, an aerogel includes a three-dimensional printed structure having printed ligaments geometrically arranged, where an average diameter of the printed ligaments is in a range of greater than 0 microns and less than 50 microns. In addition, an average distance between a center of a first of the printed ligaments and a center of a second of the printed ligaments is at least equal to the average diameter of the printed ligaments, where the first and the second of the printed ligaments are adjacent. Each printed ligament includes of a plurality of random pores, where an average diameter of the random pores is less than 50 nanometers.
Three-dimensional printing of ceramic materials
An ink, and products formed from the ink, formulated at least in part from ceramic particles. The ink is formulated so that it can be used in additive manufacturing processes to form three-dimensional printed bodies. The three-dimensional printed bodies can have graded density and can be infiltrated by an infiltration material.
Mechanical responses of architected boron carbide-aluminum lattice composites fabricated via reactive metallic infiltration of hierarchical pore structures
The incorporation of micro and nanoscale constituents in a hierarchical order improves mechanical properties of bulk structures while inducing controlled deformation. However, these features have seldomly been applied to the fabrication of cermet materials due to manufacturing constraints. Here, overcoming previous limitations, boron carbide cermets with embedded aluminum lattices were produced using a combination of additive manufacturing and gelcasting techniques. Kelvin cell and octet truss scaffolds were printed, cast and burned out so the negative volume could be infiltrated with metal to form an architected cermet. Computed microtomography scans reveal full aluminum infiltration of the volume with high fidelity to the target architecture. Equibiaxial flexural tests showed localized crack propagation in lattice-reinforced cermets and that samples with imbedded architecture required nearly double the energy for complete failure. Overall, the addition of an internal aluminum lattice limits abrupt fracture of the composite and provides a method for tuning its mechanical response with architected ratios of metal to ceramic.
TCF Project - Printable low-cost catalyst for Industrial decarbonization (LLNL/MilliporeSigma)
This proposal centers in catalysts for the generation of hydrogen as a renewable energy source and other value- added carbon utilization. The goal of this project is to commercialize an LLNL-developed, low-cost 3D printable graphene oxide/MoS 2 ink tailored for DIW fabrication of a 3D catalyst electrode for hydrogen evolution. LLNL and MS will scale up and field test the catalyst inks for hydrogen evolution, benchmark them against non-3D printed electrodes, and adjust the compositions based on feedback to improve the technology's market potential and customer/user demands.
3D-Printed Graded Electrode with Ultrahigh MnO 2 Loading for Non-Aqueous Electrochemical Energy Storage
Electrolytic manganese dioxide is one of the promising cathode candidates for electrochemical energy storage devices due to its high redox capacity and ease of synthesis. Yet, high-loading MnO 2 often suffers from sluggish reaction kinetics, especially in non-aqueous electrolytes. The non-uniform deposition of MnO 2 on a porous current collectors also makes it difficult to fully utilize the active materials at high mass loading. Here, a 3D printed graded graphene aerogel (3D GA) that contains sparsely separated exterior ligaments is developed to create large open channels for mass transport as well as densely arranged interior ligaments providing large ion-accessible active surface. The unique structural design homogenizes the thickness of electro deposited MnO 2 even at an ultrahigh mass loading of ≈70 mg cm -2 . The electrode achieves a remarkable volumetric capacity of 29.1 mA h cm -3 in the non-aqueous electrolyte. A Li-ion hybrid capacitor device assembled with a graded 3D GA/MnO2 cathode and graded 3D GA/VO x anode exhibits a wide voltage window of 0–4 V and a superior volumetric energy density of 20.2 W h L -1 . The findings offer guidance on 3D printed electrode design for supporting ultrahigh loading of active materials and developments of high energy density energy storage devices.
Tailoring of pores in aerogels using 3D printed structures
In one embodiment, a method includes acquiring a three-dimensional printed template created using an additive manufacturing technique, infilling the template with an aerogel precursor solution, allowing formation of a sol-gel, and converting the sol-gel to an aerogel. In another embodiment, a product includes an aerogel having inner channels corresponding to outer walls of a three-dimensional printed template around which the aerogel was formed.
Design and additive manufacturing of optimized electrodes for energy storage applications
Supercapacitors exhibit fast charging/discharging ability and have attracted considerable attention within the automotive, aerospace, and telecommunication industries. Porous carbons, prized for their high electrical conductivity and high surface area, have been attractive candidates for supercapacitor electrodes. Moving to thick electrodes is one strategy to further increase energy density due to a higher volume fraction of active material. However, thick electrodes suffer from sluggish charged species transport, which is why thin electrodes are currently favored. In this work, we investigate the use of computational optimization and additive manufacturing to design and fabricate thick porous electrodes with improved performance. Electrode performance was maximized by designing their morphologies via topology optimization and printing by projection micro stereolithography (PμSL) using commercial resin (PR48). The PR48 resin was then pyrolyzed (PR48-P) to create the final conductive electrode. The optimized PR48-P electrodes exhibited 99% improvement in capacitance compared to control electrodes printed with cubic lattice morphologies. To further improve performance, we formulated a resin combining graphene oxide (GO) and trimethylolpropane triacrylate (TMPTA). Electrodes printed with 3 wt% GO in TMPTA exhibited improved capacitance retention after pyrolysis compared to the PR48-P electrodes. Finally, this work demonstrates the benefits of using topology optimization to design electrodes and material development to improve functional properties of 3D printable electrodes.
3D Printed Carbon Aerogels for Polymer-Electrolyte Fuel Cells
Carbon aerogels (CA) are known for ultra-low density, very high surface area, fine porous structure, and excellent electrical conductivity. Recent advances in high resolution 3D printing at LLNL enable the manufacturing of complex structured CA electrodes which have been demonstrated in electrolysis, flow battery, and supercapacitor applications. Polymer-electrolyte fuel cells (PEFC) may be an excellent candidate for these materials/methods as designers seek to optimize membrane-electrode assemblies to achieve higher efficiencies. A major challenge to PEFC design is two-phase flow due to water production which causes pore flooding and leads to cell instability and degradation. To mitigate these effects, groups have investigated the creation of liquid specific pathways in the porous layers to alleviate liquid buildup and enhance gas diffusion. While some progress has been made, traditionally manufactured GDLs, which consist of randomly distributed carbon fibers, are limiting. 3D printed CAs are a promising solution as complex macroporous electrode structures can be manufactured out of micro and nano porous filaments with a high level of control. Additionally, the process may allow for the consolidation of multiple layers (MPL, GDL, & flow channels) into a single printed architecture. In this work various CA lattice structures were printed using a direct ink write (DIW) method and liquid breakthrough pressures were measured to demonstrate the ability to tune the water pathways to achieve specific pressure thresholds. Furthermore, a discussion of the prospects for printed CA electrodes in PEFC will focus on material properties, synthesis techniques, and current challenges.
Three-Dimensional Printed MoS 2 /Graphene Aerogel Electrodes for Hydrogen Evolution Reactions
Not Available