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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Utilizing ink composition to tune bulk-electrode gas transport, performance, and operational robustness for a Fe-N-C catalyst in polymer electrolyte fuel cell

With lower site density and turnover frequency, platinum group metal (PGM)-free catalysts based electrodes are often greater than 50 mu m thick in order to increase performance across the fuel cell operating range. Consequently, PGM-free electrodes have an additional bulk electrode transport resistance beyond the local or aggregate level transport in thin platinum-based electrodes. In parallel to the development of more active and durable PGM-free catalysts, advancements in understanding the interplay between PGM-free electrode fabrication, bulk-electrode transport, proton conductivity and performance are needed. Here, the relationship between ionic and gas phase transport through the electrode thickness is modified by adjusting electrocatalyst and ionomer flocculation/interaction at the ink level. The influence of the ink composition (water/n-propanol content) is examined via various in-situ electrochemical and ex-situ characterization techniques and the resulting electrode structure/performance relationship contrasted with electrode performance robustness across a range of relative humidity (RH). For the electrocatalyst examined here, a water-rich (82 wt% H2O) ink formulation was favorable for operation at high RH due to improved molecular diffusion through larger electrode pores. In contrast, the improved interactions between ionomer and electrocatalyst enabled a more robust electrode and higher performance during low RH operation for the 50 wt% H2O content ink.

08 HYDROGEN↗
DOE OSTI2024

Nanosurfactant formulations and use therefor

Provided are an ink composition, comprising greater than 0.2% by weight a graphene quantum dot nanosurfactant, a printable material, and a solvent, wherein the printable material is dispersed in the solvent by the graphene quantum dot nanosurfactant, and a method of preparing an ink composition. Advantageously, the present ink composition may be printed onto 2D and 3D substrates to form printed films with improved mechanical stability and photoconductance.

Zhang, Yanliang↗
DOE OSTI2022

3D-printed electrode, gas diffusion electrode (GDE) and gas diffusion layer (GDL) for fuel cell applications

An electrocatalytically active ink composition is used with an additive manufacturing process, such as 3D printing, to produce electrodes having consistent, adaptable, and high surface area structures. The electrocatalytically active ink composition includes a mixed powdered precursor and a polymer matrix. The mixed powdered precursor includes a carbon source, a dopant source, and/or a metal-containing catalyst. The material and electrochemical properties of the ink composition may facilitate 3D printing of electrochemically active electrodes for energy conversion and storage devices, and may allow fine-tuning of macro- and microstructures to develop electrodes having improved activity and efficiency.

Lee, Kwan-Soo↗
DOE OSTI2022

Structural stability of thin overhanging walls during material extrusion additive manufacturing of thermoset-based ink

Recent developments have enabled material extrusion additive manufacturing of thermoset-based composite inks on the large scale. In addition, printing out-of-plane components is of broad interest to the polymer material extrusion community. Here, we address some of the challenges associated with both large-scale and out-of-plane thermoset material extrusion additive manufacturing by studying the height at which thin overhanging walls collapse. Walls at a range of overhang angles were printed until they collapsed. An optical camera captured the profile of each wall throughout the print, allowing the collapse height to be identified and the geometric fidelity to the programmed angle to be evaluated. Using previously measured rheological properties, predictive models were generated to approximate the collapse height and profile of the deflected walls. First, an analytical model was created to predict the height at which the walls would yield. The analytical model assumes the walls exhibit a perfectly linear profile; however, experiments proved this assumption to be false. Therefore, a finite element simulation was developed to account for the elastic deflection that occurs during printing. The finite element simulation predicts both the yield height and the deflected profile after the deposition of each layer. For the properties of the thermoset ink used here, the yield height predicted by the analytical model and finite element simulation are virtually identical. These predictions match experimental data reasonably well, but minor errors are observed. Accounting for the fully plastic moment appears to explain the small mismatch between experimental data and predictions. Additionally, the finite element simulation provides an excellent prediction of the deflected profile before the wall begins to collapse. Finally, by demonstrating that the collapse height and deflected profile of thin overhanging walls can be predicted, this work illustrates how the soft viscoelastic properties of thermoset-based composite inks limit the scale of a key feature required to print some nonplanar components. It also provides a basis to tailor in-process curing systems to suppress deflection and collapse of thin overhanging walls.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Llama 20, 40, 50 and 60 Siloxanes for Direct Ink Write – Compositional Information

The following information provides a quick lookup table for compositions that relate to the constituents within a series of variable hardness [Durometer, Shore A] siloxanes useful for 3D printing using Direct Ink Write [DIW]. These siloxanes are formulated to have a thixotropic character with long pot life and are thermally cured for 16 hours at 150 °C prior to use.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Degradation of Platinum-Cobalt Alloy PEMFC Cathode Catalysts in Catalyst-Ionomer Inks

In this paper we report on studies of the effects of catalyst-ionomer ink composition: ionomer equivalent weight (EW), ink solvent, and ink mixing on a commercial PtCo alloy PEMFC cathode catalyst. X-ray absorption spectroscopy (XAS) and wide-angle X-ray scattering (WAXS) are utilized to determine catalyst atomic structure, catalyst crystallite composition, and extent of loss of Co into the ionomer-solvent phase. Three different n-propanol to water weight ratios (7:3, 5:5, and 3:7) and two different ionomers (3 M 800 EW and Nafion 1000 EW) were studied. Cobalt loss from the PtCo particles was found to increase with increasing water content in the inks and to be more extensive for the 800 EW ionomer inks, causing loss of contraction of the PtCo lattice and formation of a Pt shell-PtCo alloy core intraparticle structure.

25 ENERGY STORAGE↗
DOE OSTI2021

Processing and mechanical characterization of short carbon fiber-reinforced epoxy composites for material extrusion additive manufacturing

Fiber-reinforced polymer composites have been extensively utilized in recent years as feedstock materials for material extrusion additive manufacturing (AM) processes to improve strength, stiffness, and functionality of printed parts over unfilled printed polymers. However, the widespread adoption of AM of fiber-reinforced polymer composites requires a deeper understanding of the process-structure-property relationships in printed components, and such relationships are not well understood yet. Fiber length is critically important to the mechanical performance of short fiber composites, but very few studies to-date have focused on how the fiber length distribution (FLD) evolves during processing of composite feedstocks and how this evolution affects printing behavior and mechanical properties in 3D-printed composites. Here, FLD is measured for carbon fiber reinforced epoxy composites over a wide range of ink compositions and shear mixing times, and the distributions are fit with a Weibull-type distribution function. The effects of FLD on the tradeoff between ink processability, ink rheology, printing behavior and mechanical properties are investigated. Furthermore, the effects of printing parameters (nozzle size and print speed) on mechanical anisotropy and fiber orientation distribution (FOD) in printed composites are explored. Mechanical properties of printed composites are characterized via 3 pt-flexural testing, and microstructure is investigated using optical and scanning electron microscopy (SEM), and x-ray computed tomography. Finally, the fitted Weibull parameters are fed into a composite model that incorporates FLD and FOD, and model predictions are found to be in excellent agreement with experimental observations.

3D printing↗
DOE OSTI2025

Embedded 3D printing of isotropically enhanced lattice structure with programmable elasticity via three-dimensional fiber alignment

Engineered composites with fiber orientation in a complete three-dimensional (3D) context are highly desired for maximizing structural performance as they mimic the well-organized fiber arrangement in natural composites. However, most fabrication techniques lack the capability for through-plane (z-axis) alignment, limiting the possibility for structural design and performance optimization. In this study, we present an embedded 3D printing approach that enables complete 3D fiber alignment, including region-specific alignment control along the through-plane direction. Our method utilizes the extrusion and suspension of composite inks within a supporting matrix. By regionally adjusting the ink extrusion rate and nozzle translation rate, we locally manipulated the fiber arrangement within the composite 3D architecture. Here, we demonstrate that the 3D alignment of carbon fibers in a structural composite significantly enhances both mechanical properties and thermal conductivity in the in-plane and through-plane directions. Furthermore, by strategically arranging regional fiber orientations within micro-architected materials, we fabricated metamaterial engineered composites with programmable anisotropy ratio and directional moduli.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Improving and Understanding the Hydrogen Evolving Activity of a Cobalt Dithiolene Metal–Organic Framework

Despite the promising previous reports on the development of electrocatalytic dithiolene-based metal–organic frameworks (MOFs) for the hydrogen evolution reaction (HER), these materials often display poor reproducibility of the HER performance because of their poor bulk properties upon integration with electrode materials. In this work, we demonstrate an in-depth investigation of the electrocatalytic HER activity of a cobalt 2,3,6,7,10,11-triphenylenehexathiolate (CoTHT) MOF. To enhance the durability and charge transport properties of the constructed CoTHT/electrode architecture, CoTHT is deposited as an ink composite (1) composed of Nafion and carbon black. We leverage here the well-established use of catalyst inks in the literature to increase adhesion of the catalyst to the electrode surface and to improve the overall electrical conductivity of the integrated catalyst/electrode. The utilization of the composite 1 leads to a significant improvement in the overpotential (η) to reach a current density of 10 mA/cm 2 (η = 143 mV) compared to prior reports, resulting in the most active MOF-based electrocatalyst for the HER that contains only earth-abundant elements. Extensive density functional theory (DFT) calculations were applied to understand the structure of CoTHT and the mechanistic pathways of the HER. The computational results suggest that an AB stacking geometry is energetically favorable, where one layer is slipped by 1.6 Å relative to the neighboring one along the a and b vectors. Additionally, the DFT calculations indicate that the catalytic cycle likely involves a Volmer discharge step to generate a cobalt hydride, followed by a Heyrovsky step to form a cobalt–H 2 intermediate, and finally the dissociation of H 2 .

DFT calculations↗
DOE OSTI2025

Spatially programmed alignment and actuation in printed liquid crystal elastomers

Liquid crystal elastomers (LCEs) exhibit reversible shape morphing behavior when cycled above their nematic-to-isotropic transition temperature. During extrusion-based 3D printing, LCE inks are subjected to coupled shear and extensional flows that can be harnessed to spatially control the alignment of their nematic director along prescribed print paths. Here, we combine experiment and modeling to elucidate the effects of ink composition, nozzle geometry, and printing parameters on director alignment. From rheological measurements, we quantify the dimensionless Weissenberg number ( Wi ) for the flow field each ink experiences as a function of printing conditions and demonstrate that Wi is a strong predictor of LCE alignment. We find that director alignment in LCE filaments printed through a tapered nozzle varies radially when Wi < 1, while it is uniform when Wi ≫ 1. Based on COMSOL simulations and in operando X-ray measurements, we show that LCE inks printed through nozzles with an internal hyperbolic geometry exhibit a more uniform director alignment for a given Wi compared to those through tapered nozzles. Concomitantly, the stiffness along the print direction and actuation strain of printed LCEs increases substantially under such conditions. By varying Wi during printing through adjusting the flow rate “on the fly”, LCE architectures with uniform composition, yet locally encoded shape morphing transitions can be realized.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Integrating helicoid channels for passive control of fiber alignment in direct-write 3D printing

3D printing of fiber-reinforced composites has been receiving increasing attention as an efficient additive approach enabling lightweight, functional, and high-performance components required for industrial applications. The properties of fiber composites significantly depend on internal microstructures, including fiber orientation, distribution, and degree of alignment. Although multiple strategies have been introduced for controlling the fiber composites microstructures, these strategies are mostly active approaches relying on additional control of mechatronics parts, external forces, or intentionally introduced unstable flows inside narrow nozzles. These methods suffer from higher risk of nozzle clogging and requiring extra parts in 3D printing. Here, we introduce helicoid channels into extrusion system as a passive approach to control the fiber alignment without any additional moving parts in direct-write 3D printing. The helicoid channels automatically guide the composite inks and align fibers before flowing into narrow nozzle space, avoiding clogging and improving printability. The analyses indicate that both helicoid surface to volume ratio and helix angle affect the pre-alignment of fibers, leading to tunable mechanical properties of printed fiber-reinforced composites with increased stiffness and strength up to 77.6% and 47.8%, respectively.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Oxygen Reduction at PtNi Alloys in Direct Methanol Fuel Cells—Electrode Development and Characterization

Catalyst layers made from novel catalysts must be fabricated in a way that the catalyst can function to its full potential. To characterize a PtNi alloy catalyst for use in the cathode of Direct Methanol Fuel Cells (DMFCs), the effects of the manufacturing technique, ink composition, layer composition, and catalyst loading were here studied in order to reach the maximum performance potential of the catalyst. For a more detailed understanding, beyond the DMFCs performance measurements, we look at the electrochemically active surface area of the catalyst and charge-transfer resistance, as well as the layer quality and ink properties, and relate them to the aspects stated above. As a result, we make catalyst layers with optimized parameters by ultrasonic spray coating that shows the high performance of the catalyst even when containing less Pt than commercial products. Using this approach, we can adjust the catalyst layers to the requirements of DMFCs, hydrogen fuel cells, or polymer electrolyte membrane electrolysis cells.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2020

In-Operando Study of Shape Retention and Microstructure Development in a Hydrolyzing Sol–Gel Ink during 3D-Printing

3D printing of amorphous and crystalline ceramics is of paramount importance for the fabrication of a wide range of devices with applications across different technology fields. Printed ceramics are remarkably enabled by the sol-gel synthesis method in conjunction with continuous filament direct ink writing. During printing, multiple processes contribute to the evolution of inks including shape retention, chemical conversion, solidification, and microstructure formation. Traditionally, depending on the ink composition and printing environment, several mechanisms have been associated with the shape retention and solidification of 3D printed structures: gelation, rapid solvent evaporation, energy-driven phase transformation, and chemical-driven phase transformation. Understanding the fundamental differences between these mechanisms becomes key since they strongly influence the spatiotemporal evolution of the materials, as the out-of-equilibrium processes inherent to the extrusion, relaxation, and solidification of printed materials have significant effects on the materials properties. Herein, we investigate the shape retention mechanism and the hydrolysis-induced material conversion and microstructure formation during the 3D printing of a water reactive sol-gel ink that transforms into titanium dioxide-based ceramic. This study aims at identifying characteristic mechanisms associated with the material transformation, establishing connections between the microstructure development and the timescales associated with solidification under operando 3D-printing conditions. The investigation of this material's out-of-equilibrium pathways under processing conditions is enabled by time-resolved coherent X-ray scattering, providing simultaneous access to temporospatially resolved microstructural and dynamics information. Furthermore, we explore X-ray speckle tracking as a tool to resolve deformations of the microstructure in a printed filament associated with the deposition of consecutive filaments. Through this work, we aim at providing a fundamental understanding of the relationships behind these transformative processes in 3D printing and their timescales as the basis for achieving unprecedented control over printed materials microstructure.

36 MATERIALS SCIENCE↗