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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 CA structures which have been demonstrated for 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 power densities. A major challenge to PEFC design is two-phase flow due to water production which causes pore flooding and leads to cell instability. 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. Methods employed include the addition of small holes to the gas-diffusion layer (GDL) for liquid drainage as well as porosity gradients to exploit capillary effects. 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 microporous 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 breakthrough pressures were measured to demonstrate the ability to tune the liquid pathways to achieve specific pressure thresholds. A discussion of the prospects for printed CA electrodes in PEFC will focus on material properties, synthesis techniques, and current challenges. *anthony.santamaria@wne.edu

Next-generation electro-bioreactors will require development of novel reactor-tailored components to improve reactor productivity while maintaining high energy efficiency and biocompatible reactor conditions.

Carbon aerogels (CAs) combine unique properties including ultra-high surface area, high electrical conductivity, corrosion resistance, and robust mechanical properties making them ideal materials for electrochemical applications. Traditional CA synthesis results in isotropic, random nanoporous networks that work well for applications relying on diffusional mass transport. However, many applications would benefit from integration of engineered macroporous network structures that enable directed pressure-gradient-driven mass transport. Here, we report on using 3D-printed sacrificial polymeric templates to generate templated CAs (t-CAs) with integrated engineered nonrandom macroporous network structures. Specifically, we used projection micro-stereo-lithography (PμSL) and two-photon polymerization direct laser writing (2PP-DLW) to fabricate millimeter-to-centimeter-sized 3D sacrificial polymeric templates with features ranging from tens of microns (PμSL) to 100s of nanometers (2PP-DLW). T-CAs were fabricated by infiltrating the templates with resorcinol-formaldehyde (RF) precursor solution, followed by carbonization at 1050 °C to simultaneously convert the RF gel to a CA and decompose the 3D-printed template, leaving an embedded templated macroporous network structure behind. X-ray computer tomography confirms integration of the macroporous architecture defined by the template. The templated macroporous architecture improves mass transport in t-CAs compared to traditional bulk CA as demonstrated by more uniform activation and their response in electrochemical cyclic voltammetry and galvanostatic charge-discharge tests.

Previous works from our laboratory have firmly established that aerogels are a suitable substrate to elicit accelerated neurite extension. On non-conducting aerogels, in the presence of an externally-applied DC bias, neurons extended neurites which were preferentially aligned towards the anode. In this investigation, we sought to determine whether electrically-conductive carbon aerogels elicited a more robust alignment of neurites toward the anode than non-conductive aerogels due to the capacity of conductive aerogels to sustain a current, thereby providing a direct interface between neurons and the external electrical stimulus. To determine if this was the case, we plated PC12 neuronal cells on electrically conductive carbon aerolges derived from acetic acid-catalized resorcinol formaldehyde aerogels (ARF-CA) and subjected them to an external electric field. The voltages applied at the electrodes of the custom-built electro-stimulation chamber were 0 V, 15 V, and 30 V. For each voltage, the directionality and length of the neurites extended by PC12 cells were determined and compared to those observed when PC12 cells were plated on non-conductive aerogels subjected to the same voltage. The results show that the directionality of neurite extension was similar between conductive and non-conductive aerogels. A higher neurite length difference was observed on conductive aerogels with increasing voltage, 43% and 106% for 0-15 V and 0-30 V respectively, compared to non-conductive aerogels, 12% and 20%. These findings indicate that conductive carbon aerogels have a greater potential as scaffolds for nerve regeneration than non-conductive ones.

Nanofabrication techniques that can generate large and complex 3D structures with nanoscale features are becoming increasingly important in the fields of biomedicine, micro-optics, and microfluidics. Direct laser writing via two-photon polymerization (DLW-TPP) is one such technique that relies on nonlinear absorption of light to form nanoscale 3D features. Although DLW-TPP provides the required nanoscale resolution, its built height is often limited to less than a millimetre. This height limitation is driven by the need to tightly focus the laser beam at arbitrary depths within the photopolymer. This requirement necessitates matching the photopolymer's refractive index to specific values but the required techniques have not been disseminated widely in the open scientific literature. To address this knowledge gap, we test two universal, different approaches to generate refractive index-matched polymeric and preceramic resins and demonstrate their performance by printing of fine submicron features in 3D structures as tall as 2.5 mm. Specifically, we achieve index-matching by mixing commercially-available resins or covalent modification of functional monomers. This work investigates the relationship of voxel shape to RI mismatch, and presents tuning of RI through mixing and covalent modification to a nonconventional material system of preceramic resin which has never been demonstrated before. We demonstrate the material flexibility by generating 3D silicon oxycarbide structures from preceramic resists while simultaneously eliminating the part-height limitation of conventional DLW-TPP.

Electrochemical reactors utilizing flow-through electrodes (FTEs) provide an attractive path toward the efficient utilization of electrical energy, but their commercial viability and ultimate adoption hinge on attaining high currents to drive productivity and cost competitiveness. Conventional FTEs composed of random, porous media provide limited opportunity for architectural control and engineering of microscale transport. Alternatively, the design freedom engendered by additively manufacturing FTEs yields additional opportunities to further drive performance via flow engineering. Through experiment and validated continuum computation we analyze the mass transfer in three-dimensional (3D)-printed porous FTEs with periodic lattice structures and show that, in contrast to conventional electrodes, the mesoscopic length scales in 3D-printed electrodes lead to an increase in the mass correlation exponent as inertial flow effects dominate. The inertially enhanced mass transport yields mass transfer coefficients that exceed previously reported 3D-printed FTEs by 10 to 100 times, bringing 3D-printed FTE performance on par with conventional materials.

Water absorption-desorption-resorption and swelling were studied for a DGEBA-based amine-cured epoxy resin filled with four types of carbon nanoparticles: multiwall carbon nanotubes (MWCNT), graphite nano-platelets (GnP), expanded graphite platelets, and carbon black. Nanocomposites are characterised by lower diffusivity (down to 20% for epoxy/GnP) and increased water sorption capacity compared to the neat epoxy. Anomalous water absorption and swelling of nanocomposites is finely described by the diffusion-relaxation model. The relaxation times, considered as quantitative indicators of changes in segmental mobility of the polymer, increased with addition of nanoparticles and decreased with temperature. Epoxy/MWCNT composites are characterised by the longest relaxation times (twofold increase) and highest Deborah numbers compared to the neat epoxy and other nanocomposites. Hydrothermal ageing effects and efficiency of nanoparticles on thermal and thermomechanical properties of the epoxy were estimated. Water uptake in nanocomposites is accompanied by several competing processes: plasticization, after-cure, and physical ageing of the polymer matrix.

Summary 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. Here, we demonstrate a 3D printed 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. 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 revolutionize pseudocapacitor fabrication.

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.

Fabrication of boron carbide (B4C) parts through direct ink writing at room temperature has been demonstrated. The 3D printed B4C parts were made from aqueous, thixotropic ink consisting of B4C particles with a solid loading ranging from 50.0 to 59.3 vol%. The porous B4C parts were infiltrated with molten aluminum (Al) to form a dense B4C-Al cermet. Simple cubic samples with varied spacing between B4C filaments were printed to tailor the density profile within the part. The Rockwell hardness of such parts ranges from 20 to 90 Ra (60 kg) depending on the overall density of the B4C structure. Parts were printed with variable spacings between filaments to systematically determine the upper limit for Al infiltration (800 μm). Elemental analysis revealed a homogenous infiltration both between and within the filaments of 3D printed B4C. Keywords: Additive manufacturing, Boron carbide, Cermet, Direct ink writing

Medical implants are routinely tracked and monitored using different techniques, such as MRI, X-ray, and ultrasound. Due to the need for ionizing radiation, the two former methods pose a significant risk to tissue. Ultrasound imaging, however, is non-invasive and presents no known risk to human tissue. Aerogels are an emerging material with great potential in biomedical implants. While qualitative observation of ultrasound images by experts can already provide a lot of information about the implants and the surrounding structures, this paper describes the development and study of two simple B-Mode image analysis techniques based on attenuation measurements and echogenicity comparisons, which can further enhance the study of the biological tissues and implants, especially of different types of biocompatible aerogels.

Electrically conducting substrates have shown much promise as neuronal scaffolds and in other biologic and biomedical applications where a smart and electrically interactive material is needed. Most materials that are inherently conducting are not suitable for biomedical applications and lack biocompatibility or biostability. On the other hand, biologically stable and compatible materials must first be manipulated, modified, and treated in order to impart the necessary electrical conductivity to the material. Here, the authors have investigated the response of PC-12 cells to two types of conducting carbon-based aerogels with different surface roughness. Results show that carbon-based aerogels support cell adhesion, proliferation, and neurite extension. The effects of surface roughness have also been investigated.

Complex shaped boron carbide with carbon (B4C/C) at near-full densities were achieved for the first time using negative additive manufacturing techniques via gelcasting. Negative additive manufacturing involves 3D printing of sacrificial molds used for casting negative copies. B4C powder distributions and rheology of suspensions were optimized to successfully cast complex shapes. In addition to demonstrating scalability of these complex geometries, hierarchically meso-porous structures were also shown to be possible from this technique. Resorcinol-Formaldehyde (RF) polymer was selected as the gelling agent and can also pyrolyze into a carbon aerogel network to act as the sintering aid for B4C. Due to the highly effective distribution of in situ carbon for the B4C matrix, near-full sintered density of 97–98% of theoretical maximum density was achieved. Keywords: Boron carbide, Gelcasting, Negative additive manufacturing, Resorcinol formaldehyde, Sintering

We report 3D printing of a ‘pure’ thermal cure cyanate ester for the fabrication of robust 3D printed structures through the formulation, tailoring and post processing of a custom ‘ink’ for Direct Ink Writing. Printed structures exhibit impressive thermo-oxidative stability, mechanical response.

The use of additive manufacturing to 3D print aerogels has the potential to impact several important technologies such as energy storage, catalysis, and desalination. While there has been a great deal of focus on graphene aerogels, reports of 3D printed conventional carbon aerogels (CAs) are sparse. Activated CAs are particularly compelling because in addition to having a lower cost than a comparable graphene aerogel, they can achieve much higher surface areas (>3000 m2 g−1). Herein we report a 3D printable ink based on traditional resorcinol–formaldehyde sol–gel chemistry that can produce a final activated carbon aerogel with surface areas approaching 2000 m2 g−1 and good electrical conductivities (∼200 S m−1). Direct ink writing (DIW) is used to then fabricate electrodes, which demonstrate excellent electrochemical properties with a high specific capacitance of 215 F g−1 at 1 A g−1 and 83% capacitive retention at higher current densities (10 A g−1). The DIW electrode significantly outperformed its bulk counterpart and provides an example of how one can use 3D printed aerogel electrodes to overcome mass transport limitations and boost energy storage performance.

Carbon aerogels (CAs) are a unique class of high surface area materials derived by sol–gel chemistry. Their high mass-specific surface area and electrical conductivity, environmental compatibility, and chemical inertness make them very promising materials for many applications, such as energy storage, catalysis, sorbents, and desalination. Since the first CAs were made via pyrolysis of resorcinol–formaldehyde (RF)-based organic aerogels in the late 1980s, the field has really grown. Recently, in addition to RF-derived amorphous CAs, several other carbon allotropes have been realized in aerogel form: carbon nanotubes (CNTs), graphene, graphite, and diamond. Furthermore, the popularity of graphene aerogels has inspired research into aerogels made of a host of graphene analog materials (e.g., boron nitride, transition metal dichalcogenides, etc.), with potential for an even wider array of applications. Finally, the development of three-dimensional-printed aerogels provides the potential for CAs to have an even broader impact on energy-related technologies. Here, we will present recent work covering the novel synthesis of RF-derived, CNT, graphene, graphite, diamond, and graphene analog aerogels.

Electrochemical energy storage (EES) devices, such as lithium-ion batteries and supercapacitors, are emerging as primary power sources for global efforts to shift energy dependence from limited fossil fuels towards sustainable and renewable resources. These EES devices, while renowned for their high energy or power densities, portability, and long cycle life, are still facing significant performance hindrance due to manufacturing limitations. One major obstacle is the ability to engineer macroscopic components with designed and highly resolved nanostructures with optimal performance, via controllable and scalable manufacturing techniques. 3D printing covers several additive manufacturing methods that enable well-controlled creation of functional nanomaterials with three-dimensional architectures, representing a promising approach for fabrication of next-generation EES devices with high performance. In this review, we summarize recent progress in fabricating 3D functional electrodes utilizing 3D printing-based methodologies for EES devices. Specifically, laser-, lithography-, electrodeposition-, and extrusion-based 3D printing techniques are described and exemplified with examples from the literatures. Current challenges and future opportunities for functional materials fabrication via 3D printing techniques are also discussed.

The performance of pseudocapacitive electrodes at fast charging rates are typically limited by the slow kinetics of Faradaic reactions and sluggish ion diffusion in the bulk structure. This is particularly problematic for thick electrodes and electrodes highly loaded with active materials. Here, a surface-functionalized 3D-printed graphene aerogel (SF-3D GA) is presented that achieves not only a benchmark areal capacitance of 2195 mF cm-2 at a high current density of 100 mA cm-2 but also an ultrahigh intrinsic capacitance of 309.1 µF cm-2 even at a high mass loading of 12.8 mg cm-2 . Importantly, the kinetic analysis reveals that the capacitance of SF-3D GA electrode is primarily (93.3%) contributed from fast kinetic processes. This is because the 3D-printed electrode has an open structure that ensures excellent coverage of functional groups on carbon surface and facilitates the ion accessibility of these surface functional groups even at high current densities and large mass loading/electrode thickness. An asymmetric device assembled with SF-3D GA as anode and 3D-printed GA decorated with MnO2 as cathode achieves a remarkable energy density of 0.65 mWh cm-2 at an ultrahigh power density of 164.5 mW cm-2 , outperforming carbon-based supercapacitors operated at the same power density.

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.

A successful exploitation of nanocomposite materials founds on the development of models capable of predicting the macroscopic mechanical behaviour as a function of the nanostructure. To this end the most critical issue to overcome is the identification of the inherent mechanisms at the very nanoscale which might depend on the type, the morphology and the functionalisation of the nanofilleras well as on the loading conditions. Within this scenario, this work aims to review the main damage mechanisms reported in the literature for nano-reinforced thermosetting polymers, to include new insights and to discuss predictive models incorporating these mechanisms.

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.

Boron carbide (B(4)C) is one of the hardest materials in existence. However, this attractive property also limits its machineability into complex shapes for high wear, high hardness, and lightweight material applications such as armors. To overcome this challenge, negative additive manufacturing (AM) is employed to produce complex geometries of boron carbides at various length scales. Negative AM first involves gelcasting a suspension into a 3D-printed plastic mold. The mold is then dissolved away, leaving behind a green body as a negative copy. Resorcinol-formaldehyde (RF) is used as a novel gelling agent because unlike traditional hydrogels, there is little to no shrinkage, which allows for extremely complex molds to be used. Furthermore, this gelling agent can be pyrolyzed to leave behind ~50 wt% carbon, which is a highly effective sintering aid for B(4)C. Due to this highly homogenous distribution of in situ carbon within the B(4)C matrix, less than 2% porosity can be achieved after sintering. This protocol highlights in detail the methodology for creating near fully dense boron carbide parts with highly complex geometries.

Aerographite (AG) is a mechanically robust, lightweight synthetic cellular material, which consists of a 3D interconnected network of tubular carbon [1]. The presence of open channels in AG aids to infiltrate them with polymer matrices, thereby yielding an electrical conducting and lightweight composite. Aerographite produced with densities in the range of 7-15 mg/cm(3) was infiltrated with a low viscous epoxy resin by means of vacuum infiltration technique. Detailed morphological and structural investigations on synthesized AG and AG/epoxy composite were performed by scanning electron microscopic techniques. The present study investigates the fracture and failure of AG/epoxy composites and its energy absorption capacity under compression. The composites displayed an extended plateau region when uni-axially compressed, which led to an increase in energy absorption of similar to 133% per unit volume for 1.5 wt% of AG, when compared to pure epoxy. Preliminary results on fracture toughness showed an enhancement of similar to 19% in K-IC for AG/epoxy composites with 0.45 wt% of AG. Observations of fractured surfaces under scanning electron microscope gives evidence of pull-out of arms of AG tetrapod, interface and inter-graphite failure as the dominating mechanism for the toughness improvement in these composites. These observations were consistent with the results obtained from photoelasticity experiments on a thin film AG/epoxy model composite. Published by Elsevier Ltd.

The present study investigates the effect of addition of three different types on carbon nano-fillers on fracture toughness ( K IC ) and failure mechanism of epoxy based polymer nano-composites. The carbon nano-fillers were dispersed in the epoxy matrix using a three-roll mill and the three nano-fillers used for this experiment were (i) thermally reduced graphene oxide (TRGO); (ii) graphite nano-platelets (GNP); and (iii) multi-wall carbon nano-tubes (MWCNT). The fracture toughness was measured as a function of weight percentage of the filler using single edge notch three-point-bending tests. The toughening effect of TRGO was most significant resulting in 40% increase in K IC for 0.5 wt% of filler. On the other hand, the enhancements in toughness were 25% for GNP/epoxy and 8% for MWCNT/epoxy. Investigations on fracture surface revealed that crack pinning or bi-furcation by TRGO and crack face separation initiated from TRGO contributed to enhance the fracture toughness. Based on the observations, a schematic explaining the crack propagation in graphene/epoxy composite and the interaction of crack front with graphene particles was proposed.

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.

Epoxy based polymer nano-composite was prepared by dispersing graphite nano-platelets (GNPs) using two different techniques: three-roll mill (3RM) and sonication combined with high speed shear mixing (Soni_hsm). The influence of addition of GNPs on the electrical and thermal conductivity, fracture toughness and storage modulus of the nano-composite was investigated. The GNP/epoxy prepared by 3RM technique showed a maximum electrical conductivity of 1.8 × 10 −03 S/m for 1.0 wt% which is 3 orders of magnitude higher than those prepared by Soni_hsm. The percentage of increase in thermal conductivity was only 11% for 1.0 wt% and 14% for 2.0 wt% filler loading. Dynamic mechanical analysis results showed 16% increase in storage modulus for 0.5 wt%, although the Tg did not show any significant increase. Single edge notch bending (SENB) fracture toughens ( K IC ) measurements were carried out for different weight percentage of the filler content. The toughening effect of GNP was most significant at 1.0 wt% loading, where a 43% increase in K IC was observed. Among the two different dispersion techniques, 3RM process gives the optimum dispersion where both electrical and mechanical properties are better.

In this study fibre reinforced laminates with a graphene oxide modified epoxy matrix were manufactured using a filament winding technology for prepreg production. Dispersion of the nano-particles was achieved with a three roll mill. Cross-ply laminates with carbon and glass fibres and different nano-particle loadings were produced. Impact damage was introduced with an instrumented drop weight tower. Prior to mechanical testing damage size was determined using ultrasonic c-scans and pulse phase thermography. The defect size was reduced significantly with increasing graphene oxide loading in the matrix. Residual compressive properties of the laminates improved significantly for the modified specimen, with the glass fibre laminates showing the highest improvement of 55% when compared to unmodified specimens. In addition to the improved mechanical properties the matrix modification also improved the phase contrast of the thermography data thus enabling better detection of defects and improved detection limits.

The effect of thermally reduced graphene oxide (TRGO) on the electrical percolation threshold of multi wall carbon nanotube (MWCNT)/epoxy cured composites is studied along with their combined rheological/electrical behavior in their suspension state. In contrast to MWCNT and carbon black (CB) based epoxy composites, there is no prominent percolation threshold for the bi-filler (TRGO–MWCNT/epoxy) composite. Furthermore, the electrical conductivity of the bi-filler composite is two orders of magnitude lower (∼1 × 10 −5 S/m) than the pristine MWCNT/epoxy composites (∼1 × 10 −3 S/m). This result is primarily due to the strong interaction between TRGO and MWCNTs. Optical micrographs of the suspension and scanning electron micrographs of the cured composites indicate trapping of MWCNTs onto TRGO sheets. A morphological model describing this interaction is presented.

This study is focused on the investigation of thermo-mechanical properties of an epoxy resin filled with thermally reduced graphene oxide (TRGO) and multi-wall carbon nanotubes (MWCNT) after exposure of samples to hot distilled water. Addition of low contents of TRGO and MWCNTs greatly reduces the water sorption capacity of the epoxy polymer and improves its resistance to hydrothermal ageing. The glassy and rubbery moduli of the neat epoxy decreased for about 20% and 80%, respectively, while TRGO-based epoxy filled with 0.3 wt.% of TRGO showed only 6% reduction of both moduli. Hydrothermal ageing resulted in an enormous drop in the glass transition temperature (Tg) of the neat epoxy, by about 90 °C, while the shift in Tg of the nanocomposites did not exceed 8 °C. After re-drying of samples, the position and shape of the peak was completely recovered for the nanocomposites. Irreversibility of water influence on the neat polymer appeared in the broadened and shifted glass transition region. The improvement of the thermo-mechanical properties of the neat epoxy from the addition of TRGO is higher than that achieved by incorporating MWCNTs. This trend is valid in both unexposed state and after hydrothermal ageing of the nanocomposites.

In the present work, the functionalisation of oxidised SWCNTs and MWCNTs is studied. The functionalised fillers are characterised by Raman spectroscopy and TGA. The functionalised fillers are dispersed in a PBT-PTMO thermoplastic elastomer matrix via in situ polymerisation. The functionalisation causes a fine filler dispersion right at beginning of nanocomposite manufacturing. The fillers act as nucleating agents for crystallisation and evidences for a grafting from PBT at the surface of the functionalised nanotubes are found. An outstanding reinforcement effect by the functionalised CNTs is confirmed by tensile tests.

Fiber-reinforced composites have superior properties compared to conventional structural materials. They already gain a very high standard, resulting in application in the aerospace and other important industries, however, there is still room for further improvement. These aim toward manufacturing, cost reduction during material processing, application, and last but not least superior material properties. Nanocomposites (polymers filled with nanoparticles as carbon nanotubes, graphene, etc.) have been under investigation in the last decade and they resulted in tremendous improvements in mechanical properties, as fracture toughness or electrical conductivity. Nanocomposites used as matrix for fiber-reinforced polymers (FRPs) have the potential to improve overall mechanical properties as interlaminar shear stress, first-ply failure, impact and compression after impact, etc. At the same time, the polymer matrix being an isolator by nature can be turned into an electrically conductive material. This additional function can not only be used for electric charge ablation but also be used for sensing deformation and/or damage. Especially, their potential for strain sensing applications with electrical conductivity methods can be used to investigate the electromechanical response of nanocomposites or FRP deformation when subjected to mechanical load. An integration of carbon nanoparticles into the matrix of FRPs not only improves the overall properties, they turn into a multifunctional material. Superior mechanical properties combine with sensing capabilities. Composite materials can even better compete with conventional structural materials, respectively, are an even more attractive alternative.