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Electrochemical energy storage devices, such as supercapacitors, are essential contributors to the implementation of sustainable energy. Supercapacitors exhibit fast charging/discharging ability and have attracted considerable attention within the automotive, aerospace, and telecommunication industries. Although these devices show great potential to meet power density metrics, they lack in terms of their energy density. To overcome this challenge, we are investigating better materials, architectures, and additive manufacturing techniques to print electrodes that increase the energy density while maintaining their high-power densities. Topology optimization was used to design an electrode with optimum performance. These electrodes were printed by projection micro stereolithography (PµSL) using PR48, a commercially available polymer resin. The printed electrodes were converted to carbon electrodes through pyrolysis at 1050 ֯C and characterized by cyclic voltammetry (CV), galvanostatic charge/discharge (GCD), and electrical impedance spectroscopy. The performance of the PR48 optimized electrodes were compared against PR48 electrodes printed as a simple cubic lattice structure previously shown to improve capacitance and rate capability. The results show that our optimized electrodes have higher areal capacitances for all the current densities tested and they perform better in GCD and CV tests. Lastly, to increase the surface area of the electrodes and increase the capacitance further, we developed a resin formulation by combining graphene oxide (GO) into TMPTA polymer. Electrodes printed with 3%GO/TMPTA have improved electrochemical performance compared to PR48 as evidenced by their higher capacitances and their better GCD and CV curves. This work demonstrates the benefits of using topology optimization to design electrodes and materials development to improve the functional properties of 3D printable resins. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344. Lawrence Livermore National Security, LLC Figure 1

Electrochemical energy storage (EES) and conversion devices (e.g. batteries, supercapacitors, and reactors) are emerging as primary methods for global efforts to shift energy dependence from limited fossil fuels towards sustainable and renewable resources. These electric-based devices, while showing great potential for meeting some key metrics set by conventional technologies, still face significant limitations. For example, an EES device tends to exhibit large energy density (e.g. lithium-ion battery) or power density (e.g. supercapacitor), but not both. This inability of a single device to simultaneously achieve both metrics represents a major obstacle to widespread adoption of EES devices. Improvements in materials, such as the integration of 2D materials (e.g. graphene, dichalcogenides, MXene, etc.) into electrochemical devices has yielded some exciting results towards tackling this issue, but significant improvements are still needed. Our approach to simultaneously achieving high energy and power density is to focus on one of the fundamental processes that occur in these systems: mass (or charge) transport. The efficient transport of ions within EES devices is critical to realizing both large power and energy densities. The pore structure of the electrode is a key factor in determining this transport phenomena, but in many cases, engineering the pore structure in a highly deterministic fashion is not pursued or even possible for many electrode materials. In this work, we explore a number of additive manufacturing methods (e.g. direct ink write, projection microstereolithography, etc.) to engineer the pore structure of device electrodes. We also determine effective electrode geometries using both simple theory and topology optimization techniques. The topology optimization couples the solution of the forward electrochemical problem over the full electrode domain with gradient-based optimization. The output of our code is a three-dimensional CAD representation which optimizes over specific performance metrics and which can be used to print functional electrodes. This work provides a systematic path toward automatic design and fabrication of engineered electrodes with precise control over the fluid and species distribution.

Conventional porous electrodes normally consist of homogeneous, unorganized collections of small-scale particles that offer little opportunity in terms of designing higher performance electrochemical devices. Indeed, simply increasing the surface area to maximize activity is usually detrimental to electrochemical transport because of increased tortuosity. Luckily, modern advanced and additive manufacturing methods present an opportunity for porous electrode structures that span length scales. In this presentation, we consider topology optimization as a tool to inform the design of porous electrodes. We introduce an optimization framework for a generic porous electrode model and apply it to two applications: an electrode driving a steady Faradaic reaction, and a transiently operated electrode in a supercapacitor. In each case, computationally designed electrodes that maximize energy efficiency are shown to outperform monolithic, homogeneous electrodes. For low effective ionic conductivity materials, the optimized designs exhibit hierarchical features with macropores that facilitate ionic transport.

Electrochemical energy storage (EES) and conversion devices (e.g. batteries, supercapacitors, and reactors) are emerging as primary methods for global efforts to shift energy dependence from limited fossil fuels towards sustainable and renewable resources. These electric-based devices, while showing great potential for meeting some key metrics set by conventional technologies, still face significant limitations. For example, an EES device tends to exhibit large energy density (e.g. lithium-ion battery) or power density (e.g. supercapacitor), but not both. This inability of a single device to simultaneously achieve both metrics represents a major obstacle to widespread adoption of EES devices. Improvements in materials, such as the integration of 2D materials (e.g. graphene, dichalcogenides, MXene, etc.) into electrochemical devices has yielded some exciting results towards tackling this issue, but significant improvements are still needed. Our approach to simultaneously achieving high energy and power density is to focus on one of the fundamental processes that occur in these systems: mass (or charge) transport. The efficient transport of ions within EES devices is critical to realizing both large power and energy densities. The pore structure of the electrode is a key factor in determining this transport phenomena, but in many cases, engineering the pore structure in a highly deterministic fashion is not pursued or even possible for many electrode materials. In this work, we explore a number of additive manufacturing methods (e.g. direct ink write, projection microstereolithography, etc.) to engineer the pore structure of device electrodes. We also determine effective electrode geometries using both simple theory and topology optimization techniques. The topology optimization couples the solution of the forward electrochemical problem over the full electrode domain with gradient-based optimization. The output of our code is a three-dimensional CAD representation which optimizes over specific performance metrics and which can be used to print functional electrodes. This work provides a systematic path toward automatic design and fabrication of engineered electrodes with precise control over the fluid and species distribution. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Flow through electrodes are the core, active component in a number of electrochemical systems including fuel cells and flow batteries. Controlling fluid flow and mass transport is a core engineering challenge in these systems and has a dramatic impact on cell power, utilization, and efficiency. Most advanced electrode materials are composed of microscale, disordered porous media. The length scales of these materials allow for very large surface area but at the cost of low flow speeds, low surface mass transfer rates, high pressure drops, and added complexity and cost from the need to use external flow distribution systems like flowfields. The multiscale control over electrode architecture enabled by using additively manufactured electrodes could provide a potential resolution to these trade-offs. To elucidate the mass transport of these electrodes, we use resolved, continuum computation to analyze the fluid flow and species transport in direct ink-write printed, carbon aerogel electrodes. We determine the mass transfer correlations (Sh ~ Pea) across two different lattice aerogel geometries and validate these results against the experimentally manufactured and tested flow-through electrodes operated at limiting current. In contrast to conventional electrodes, the mesoscopic length scales in our electrodes lead to finite Reynolds numbers and we find an increase in the mass correlation exponent (a) as inertial effects become important. We analyze the local mass transfer coefficients in the electrode and correlate regions of enhanced mass transfer with secondary flows in the electrode. Our work provides a promising new pathway to increased mass transfer rates in flow-through electrodes. LLNL-ABS- 810719 This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Electrochemical systems such as fuel cells, flow batteries, and electrochemical reactors are prevalent in industry, but few tools for their numerical design and optimization exist. Controlling fluid flow, active species distribution, and mass transport in the electrode has a dramatic impact on power and efficiency. However, this control is often limited to changing a quasi-two-dimensional flowfield and selecting bulk properties of a monolithic porous material electrode like carbon felt or paper. This can lead to non-uniform reaction rates, underutilized regions of the flow cell, and can limit the ultimate performance of the devices. To address these limitations, we propose using electrodes composed of a micro-architected variable porosity medium. As a specific example, we enable variable porosity by leveraging advances in the additive manufacture of microscale iso-truss lattices. We employ physics-based homogenization of the governing microscopic, continuum transport equations to develop a descriptive model and enable the design of this variable porosity electrode. Our tool is used to generate optimized architectures which are predicted to outperform monolithic electrodes when used in a standard flow-through configuration. We conclude by demonstrating how the optimal porosity distribution changes to retain the performance benefits as the electrode is scaled beyond benchtop-experiments LLNL-ABS- 810799 This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Electrochemical energy storage (EES) and conversion devices (e.g. batteries, supercapacitors, and reactors) are emerging as primary methods for global efforts to shift energy dependence from limited fossil fuels towards sustainable and renewable resources. These electric-based devices, while showing great potential for meeting some key metrics set by conventional technologies still face significant limitations. For example, an EES device tends to exhibit large energy density (e.g. lithium-ion battery) or power density (e.g. supercapacitor), but not both. This inability of a single device to simultaneously achieve both metrics represents a major obstacle to widespread adoption of EES devices. Improvements in materials, such as the integration of 2D materials (e.g. graphene, dichalcogenides, MXene, etc.) into electrochemical devices has yielded some exciting results towards tackling this issue, but significant improvements are still needed. Our approach to simultaneously achieving high energy and power density is to focus on one of the fundamental processes that occur in these systems: mass (or charge) transport. The efficient transport of ions within EES devices is critical to realizing both large power and energy densities. The pore structure of the electrode is a key factor in determining this transport phenomena, but in many cases, engineering the pore structure in a highly deterministic fashion is not pursued or even possible for many electrode materials. In this work, we explore a number of additive manufacturing methods (e.g. direct ink write, projection microstereolithography, etc.) to engineer the pore structure of device electrodes. We also determine effective electrode geometries using both simple theory and topology optimization techniques. The topology optimization couples the solution of the forward electrochemical problem over the full electrode domain with gradient-based optimization. The output of our code is a three-dimensional CAD representation which optimizes over specific performance metrics and which can be used to print functional electrodes. This work provides a systematic path toward automatic design and fabrication of engineered electrodes with precise control over the fluid and species distribution. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

The generation of hydrogen from renewable sources is of great interest in sustainable fuel production and storage. Emerging technologies such as photocatalytic water splitting are being considered as cost effective solutions for the production of hydrogen. In these applications Pt is commonly employed as it is highly effective for the hydrogen evolution reaction (HER), however loss of efficiency can be a problem due to back-reactions (for example the oxygen reduction reaction (ORR)) and to a lesser extent poisoning from contaminants (e.g. CO). CrOx-based protective layers have been shown to improve selectivity towards hydrogen for Pt catalysts, for which lower concentrations of the chromate precursor are preferred due to toxicity issues. Still, there is a lack of fundamental understanding of coating procedures and the levels required. In this study cyclic voltammetry and eQCM have been used to systematically investigate the dependence of concentration and deposition time on the extent of film growth and activity in the relevant reactions for photocatalytic water splitting. Specifically we highlight trends in the HER and ORR activity on the buried Pt surface and evaluate stability as a function of CrOx coverage. It has been shown by the experimental results that an optimum can be found between minimising the overpotential required for HER whilst fully protecting against the oxygen reduction back-reaction. Thus, these results reveal the lowest Cr precursor concentrations that can be effectively applied in photocatalysis.

Retaining sound electrochemical performance of electrodes at high mass loading holds significant importance to energy storage. Pseudocapacitive materials such as manganese oxide (MnO2) deposited on current collectors have achieved outstanding gravimetric capacitances, sometimes even close to their theoretical values. Yet, this is only achievable with very small mass loading of active material typically less than 1 mg cm-2. Increasing mass loading often leads to drastic decay of capacitive performance due to sluggish ion diffusion in bulk material. In this talk, I will demonstrate a 3D printed macroporous graphene aerogel electrode with MnO2 loading of 182.2 mg cm-2, which achieves a record-high areal capacitance of 44.13 F cm-2. The engineered porous structure allows efficient ion diffusion and therefore enables the ultrahigh mass loading of pseudocapacitive materials without sacrificing their gravimetric and volumetric capacitive performance. Most importantly, this 3D printed graphene aerogel/MnO2 electrode can simultaneously achieve excellent capacitance normalized to area, gravimetry, and volume, which is the trade-off for most electrodes. This work successfully validates the feasibility of printing practical pseudocapacitive electrodes, which might innovate the conventional layer-by-layer stacking fabrication process of commercial supercapacitors. Figure 1

Flow batteries are a promising technology for large scale energy storage and load balancing from intermittent power sources, but their viability hinges on our ability to attain high-power outputs while minimizing costs and meeting performance constraints. Controlling fluid flow, active species distribution, and mass transport in the electrode has a dramatic impact on cell power and efficiency. However, this control is often limited to changing a quasi-two-dimensional flow field and selecting bulk properties of a monolithic electrode. This can lead to non-uniform reaction rates, underutilized regions of the flow cell, and can limit the ultimate performance of the devices. We propose an alternative approach which seeks to control the fluid distribution in the cell by controlling the electrode geometry. Our approach is enabled by additive manufacturing techniques which allow us to directly build three-dimensional morphologies. Further, to determine effective electrode geometries, we employ topology optimization techniques that couple solution of the forward electrochemical problem over the full electrode domain with gradient-based optimization. The output of our code is a three-dimensional CAD representation which optimizes over specific performance metrics and which can be used to print functional electrodes. We will demonstrate the process for generating the electrodes using our optimization framework and present experiments comparing the performance of the optimized geometries across designs and against conventional electrodes. This work provides a systematic path toward automatic design of engineered electrodes with precise control over the fluid and species distribution. LLNL-ABS-764035 This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Nanoporous metals which have a continuous solid/void structure attracted great attention due to their low density, outstanding mechanical properties, large surface area and excellent electrical conductivity. However, it is difficult to shape these nanoporous metals, especially with hierarchical pores using conventional synthesis techniques. Besides, purely stochastic porous networks may limit their performance for specific applications compared with the potential use of an engineered architecture via proper design. Here we report the fabrication of hierarchical nanoporous gold with deterministic architecture using a combination of 3D printing and dealloying. The 3D printed hierarchical nanoporous gold shows designable three levels of pores and structures with the first level size from 10-1000 microns by controlling the printing nozzle size and spacing, the second level size around several microns adjusted via changing the portion of polymer, and the third level size from 30 nm to microns depending on post-annealing and dealloying conditions. This work widens the choice of materials for 3D printing and enables the creation of a shape-controllable hierarchical nanoporous gold, which has many potential applications in both industry and fundamental science.

Aerogels are nanoporous solids used in electrochemical processes relevant to a number of applications including, catalysis, batteries, supercapacitors, and sensing due to their high internal surface, composition, and small pore/particle size. Two-dimensional (2D) nanomaterials, such as graphene, boron nitride, transition metal dichalcogenides, also exhibit a range of distinct electronic and chemical properties, but are typically limited to thin films and coatings. Assembling 2D nanomaterials into monolithic aerogels expands their application space to include technologies and manufacturing processes that require a macroscopic 3D form factor. Furthermore, realizing the unique inherent qualities of 2D materials in a low-density, high surface area architecture creates new materials with novel properties and features only displayed within an aerogel framework. Here, we demonstrate recent work on assembling and tailoring various properties of aerogels made from several different 2D materials, (e.g. boron nitride, graphene, dichalcogenides, etc.). In particular, methods of controlling the composition via doping or hybrid aerogels (e.g. combining two or more layered materials), crystallinity, and macroscale architecture will be presented. The impact of those changes on aerogel properties and performance in energy storage and sensing devices will be discussed. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Aerogels are porous solids used in a wide range of applications including sorbents, filtration, insulation, hydrogen storage, catalysis, batteries, and supercapacitors. Their unique properties are related to their high internal surface, low-density, and small pore/particle size. Two-dimensional (2D) nanomaterials, such as boron nitride and graphene, also exhibit a range of distinct optical, electronic, and mechanical properties, but are typically limited to thin films and coatings. Assembling 2D nanomaterials into monolithic aerogels expands their application space to include technologies and manufacturing processes that require a macroscopic 3D form factor. Furthermore, placing the novel intrinsic properties of 2D materials in a low-density, high surface area architecture has the potential to unlock exciting new properties and features only displayed in the aerogel system. Here, we present synthesis schemes for aerogels made from several different 2D materials, (e.g. boron nitride, graphene, dichalcogenides, etc.), including hybrid aerogels, combining two or more layered materials. Applications of these novel aerogels in applications including sorbents, sensing, energy storage, and catalysis will be covered. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

We present the reversible assembly of colloidal nanoparticles in organic solvents using low voltage and low frequency pulsed DC electric fields. Commercially available and custom nanoparticles (diameter ~ 50-200 nm) were suspended in organic solvents at concentrations of 0.25-50 wt% and sandwiched between indium tin oxide (ITO) electrodes of spacing 25 μm-2mm. Using square waves of frequency 0.25-5 Hz, voltages 0.5-5V, and DC offset 0.25-2.5V, colloidal suspensions were actuated for switchable contrast. Upon switching off the electric field, the assembled nanoparticles are able to resuspend within seconds. Using patterned electrodes, lateral electromigration of the particles was demonstrated. Depletion of the particles to the electrode regions resulted in transparency in the non-patterned regions. The distinct contrast generated can be exploited for tunable display applications. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. LLNL-ABS-679931.

Gradient and laminate materials are an emerging area with the potential to impact a wide range of technologies including structural materials, energy storage, and defense applications. However, fine control of gradients is a challenge for many material types. This work aims to demonstrate the capability to tune the properties of ceramic-metal composites (cermets) by using electrophoretic deposition (EPD) to create compositional/microstructural gradients within the cermet part. Controlling the outcome of microstructural features and phase composition enables the tailoring of the final product for desired applications. B4C green body compacts comprised of tailored microstructures through EPD are then infused with Al during pressureless sintering.

Aerogels are porous solids used in a wide range of applications including sorbents, filtration, insulation, hydrogen storage, catalysis, batteries, and supercapacitors. Their unique properties are related to their high internal surface, low-density, and small pore/particle size. Two-dimensional (2D) nanomaterials, such as boron nitride and graphene, also exhibit a range of distinct optical, electronic, and mechanical properties, but are typically limited to thin films and coatings. Assembling 2D nanomaterials into monolithic aerogels expands their application space to include technologies and manufacturing processes that require a macroscopic 3D form factor. Furthermore, placing the novel intrinsic properties of 2D materials in a low-density, high surface area architecture has the potential to unlock exciting new properties and features only displayed in the aerogel system. Here, we present synthesis schemes for aerogels made from several different 2D materials, (e.g. boron nitride, graphene, dichalcogenides, etc.). Hybrid aerogel synthesis, combining two or more layered materials, will also be presented. Characterization of aerogels will include textural, transport, mechanical properties, and more. Results will be discussed in light of theory and existing literature. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Printed micro-batteries could be used in a variety of small electric circuits such as RFID and sensors. Printing techniques can facilitate high volume manufacture in economical processes that have much to offer in energy storage applications. Utility scale electrochemical energy storage will also become an important topic as countries across the globe set targets for highly distributed electricity generation from renewable sources. Time shifting via appropriate energy storage installations as well as peak shaving to stabilise national grids will become an important part of future electricity infrastructures where electrification of transport and heating become commonplace. To meet the demands of such a market stationary, utility scale energy storage technologies must be safe, offer long lifetimes and have inherently low cost. This can be achieved by the use of earth abundant materials and by employing rapid, roll-to-roll, solution coating or printing processes. Micro-batteries and utility scale energy storage solutions all have different demands in terms of capacity and rate capabilities. Design of electrodes to optimise energy storage can hinder the ability to deliver power and achieve high current densities. This study describes how print parameters and sinter conditions can be varied to find compromises between kWh capacity stored and kW power that can be delivered on demand. Typical strategies to reduce activation polarisation and increase conductivity of electrode pastes usually result in less available active material to support charge transfer, thus lowering the useful capacity of the cell. This work describes how optimising printing processes to deliver a balance of active material availability and high rate capability can produce versatile electrodes. Sinter conditions are also investigated to strike a balance between the adhesion of the sintered electrode material to the substrate and controlled highly porous sintered structures required to promote adequate mass transport through the porous network of the electrode. Physical characteristics of the printed electrodes are confirmed by SEM micrographs, profilometery and BET surface area and porosity measurements with the rate capabilities and capacities assessed galvanostatically. EIS and novel scanning electrochemical techniques shed further light on the impact of print and sinter parameters in electrochemical performance.

Coins as a means of exchange or barter have existed for over 2000 years. Early examples from the Bronze Age were stamped from crudely shaped discs of metal and this principle of manufacture has continued through to the present day. With the face value of modern coins usually being significantly higher than the material value and production cost, they can be prone to forgery, with a reported 3% of certain denominations in the UK being counterfeit1. In an effort to combat this and to add distinguishing features to the different denominations, an increasing number of coins around the world consist of two or more alloys. These are usually arranged as an inner and outer piece, to form two concentric rings. With two different alloys in electrical contact there exists the possibility for bimetallic corrosion to occur; hence it is important that the two alloys are potentiometrically matched. In this study, a selection of bimetallic coins has been examined via 3D-SKP and 3D-SVET. The SKP technique is used to examine the surface potential differences between the two alloys. The SKP scans have been performed using height scanning mode in order to compensate for the topographical features present and enable a sufficiently close scan distance to elucidate good potential measurements. Subsequently the coins have then been subjected to 3D SVET scans while immersed in an electrolyte, in order to assess if the potential differences identified during the SKP assessment result in measureable galvanic corrosion. The SKP was able to determine a Volta potential difference of between 50 – 100mV for the paired alloys. When investigated via the SVET, this relatively small potential difference was sufficient to generate measureable galvanic corrosion currents when immersed in weak electrolyte and scanned using the 3D-SVET. The anodic and cathodic sites detected via the SVET corresponded to the relative Volta potentials as detected with the SKP. Osbourne, G. (2014), Chancellor George Osborne's Budget 2014 speech , Available: https://www.gov.uk/government/speeches/chancellor-george-osbornes-budget-2014-speech [20 March 2014].

The 3D-SVET is a valuable technique for the examination of corrosion phenomena on non-planar samples. A bi-functional probe is first used to record topographical data to obtain a surface height map; subsequently this height map is used to retrace the surface, obtaining current density data at a known fixed height. In this work the apparatus was utilized to investigate the effects of forming and irradiation on model plasticized PVC coatings and specifically the influence on the barrier properties of the coating. Samples were prepared via bar casting onto galvanneal steel substrate and then either examined in a planar state or after a bending process that created a 30° deflection from flat. Samples were examined via 3D-SVET either as cast or after irradiation with UV in order to investigate the effects of weathering. In addition, an industrially produced coating that had undergone natural weathering for a period of 17 years in a coastal industry environment was also analyzed as a comparison. The model study demonstrated that both the planar non-irradiated and the planar irradiated samples retained their coating integrity, with the 3D SVET detecting no corrosion activity during a 24hr immersion study. In contrast, the samples that underwent a forming process showed evidence of a cathodic band of activity that coincided with the peak of the bend. This band increased in activity during the period of immersion, most likely due to the improved oxygen availability at the thinnest part of the coating. Findings from the industrial coating (See Fig 1A-C) showed the presence of numerous penetrative defects and it was found that the majority of the longer lived defects existed within the emboss pattern, coinciding with thinnest part of the coating. Subsequent removal of the industrial coating evidenced the extent of the zinc dissolution that occurred during the samples lifetime. Figure 1: A) The surface profile of the industrial coating, illustrating the leathergrain emboss pattern within the paint. B) A Surface image of the coating overlaid with the most active anodic areas as measured over 24hrs immersion in 5% NaCl. C) The resulting galvanneal surface post removal of the plastisol coating, illustrating the metal dissolution during the samples life. .

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