Much progress has recently been made in the development of active materials, electrode morphologies and electrolytes for lithium ion batteries. Well-defined studies on size effects of the ...three-dimensional (3D) electrode architecture, however, remain to be rare due to the lack of suitable material platforms where the critical length scales (such as pore size and thickness of the active material) can be freely and deterministically adjusted over a wide range without affecting the overall 3D morphology of the electrode. Here, we report on a systematic study on length scale effects on the electrochemical performance of model 3D np-Au/TiO2 core/shell electrodes. Bulk nanoporous gold provides deterministic control over the pore size and is used as a monolithic metallic scaffold and current collector. Extremely uniform and conformal TiO2 films of controlled thickness were deposited on the current collector by employing atomic layer deposition (ALD). Our experiments demonstrate profound performance improvements by matching the Li+ diffusivity in the electrolyte and the solid state through adjusting pore size and thickness of the active coating which, for 200 μm thick porous electrodes, requires the presence of 100 nm pores. Decreasing the thickness of the TiO2 coating generally improves the power performance of the electrode by reducing the Li+ diffusion pathway, enhancing the Li+ solid solubility, and minimizing the voltage drop across the electrode/electrolyte interface. With the use of the optimized electrode morphology, supercapacitor-like power performance with lithium-ion-battery energy densities was realized. Our results provide the much-needed fundamental insight for the rational design of the 3D architecture of lithium ion battery electrodes with improved power performance.
Gold is examined here as an alternative to copper for the selective dehydrogenation of ethanol to acetaldehyde and hydrogen. Despite its high selectivity, gold is only active at temperatures higher ...than 250 °C for this reaction. We demonstrate that addition of a small amount of Ni on either supported or unsupported Au surfaces induces resistance to sintering, along with a beneficial effect on the catalytic activity. NiAu alloys prepared here with Ni as the minority component to the limit of atomic dispersion in the gold surfaces, catalyze the reaction beginning below 150 °C. A significant decrease of the apparent activation energy from 96 ± 3 kJ/mol for the monometallic Au to 59 ± 5 kJ/mol for the alloy was found. The Ni dispersion and concentration as a function of gas environment was followed by in situ DRIFTS and by XPS. The stability of the catalyst morphology was investigated through post-reaction microscopy imaging and long-term stability tests under reaction conditions. As shown via dynamic reaction experiments, acetaldehyde and H
2
were selectively produced up to 280 °C. A small drop of selectivity at higher temperatures is attributed to the formation of Ni clusters, as proven by CO-DRIFTS on the used sample. Comparison with samples of higher Ni loading, where Ni clusters are formed, clearly shows that they catalyze the undesired full decomposition of ethanol to CO, CH
4
, and H
2
.
3D graphene foams exhibit immense degradation of mechanical properties. Micro-architecture can alleviate this problem, but no current technique meets the manufacturing requirements. Herein we ...developed a light-based 3D printing process to create hierarchical graphene structures with arbitrary complexity and order-of-magnitude finer features, showing enhanced mechanical properties at decreasing density.
Porous materials with engineered stretching-dominated lattice designs, which offer attractive mechanical properties with ultra-light weight and large surface area for wide-ranging applications, have ...recently achieved near-ideal linear scaling between stiffness and density. Here, rather than optimizing the microlattice topology, we explore a different approach to strengthen low-density structural materials by designing tube-in-tube beam structures. We develop a process to transform fully dense, three-dimensional printed polymeric beams into graphitic carbon hollow tube-in-tube sandwich morphologies, where, similar to grass stems, the inner and outer tubes are connected through a network of struts. Compression tests and computational modelling show that this change in beam morphology dramatically slows down the decrease in stiffness with decreasing density. In situ pillar compression experiments further demonstrate large deformation recovery after 30-50% compression and high specific damping merit index. Our strutted tube-in-tube design opens up the space and realizes highly desirable high modulus-low density and high modulus-high damping material structures.
Monolithic nanoporous metals, derived from dealloying, have a unique bicontinuous solid/void structure that provides both large surface area and high electrical conductivity, making them ideal ...candidates for various energy applications. However, many of these applications would greatly benefit from the integration of an engineered hierarchical macroporous network structure that increases and directs mass transport. We report on 3D (three-dimensional)-printed hierarchical nanoporous gold (3DP-hnp-Au) with engineered nonrandom macroarchitectures by combining 3D printing and dealloying. The material exhibits three distinct structural length scales ranging from the digitally controlled macroporous network structure (10 to 1000 μm) to the nanoscale pore/ligament morphology (30 to 500 nm) controlled by dealloying. Supercapacitance, pressure drop, and catalysis measurements reveal that the 3D hierarchical nature of our printed nanoporous metals markedly improves mass transport and reaction rates for both liquids and gases. Our approach can be applied to a variety of alloy systems and has the potential to revolutionize the design of (electro-)chemical plants by changing the scaling relations between volume and catalyst surface area.
a-ordm Individual phases in a cast Al0.8CoCrCuFeNi high entropy alloy (HEAs) were characterized with high resolution scanning electron microscopy and micro-compression. a-ordm Neutron diffraction ...enabled the detection of a new phase which was otherwise unobservable by conventional X-ray diffraction. a-ordm The delicate micro-scale characterization of individual phase provides new insights for the design of novel HEAs with desirable mechanical properties. The microstructural features and micromechanical behavior of individual phases in a cast Al0.8CoCrCuFeNi high-entropy alloy (HEA) were characterized by high-resolution scanning electron microscopy and micro-compression tests. Use of neutron diffraction enabled the detection of a new phase which was otherwise unobservable by conventional X-ray diffraction. The identified phase constitution agreed well with the compositional analysis and the micro-compression results. The delicate microscale characterization of individual phase provides new insights for the design of novel HEAs with desirable mechanical properties.
We report on the grain size dependent morphological, physical and chemical properties of thick microwave-plasma assisted chemical vapor deposited (MPCVD) diamond films that are used as target ...materials for high energy density physics experiments at the Lawrence Livermore National Laboratory. Control over the grain size, ranging from several μm to a few nm, was achieved by adjusting the CH4 content of the CH4/H2 feed gas. The effect of grain size on surface roughness, morphology, texture, density, hydrogen and graphitic carbon content was systematically studied by a variety of techniques. For depositions performed at 35 to 45mbar and 3000W microwave power (power density ~10Wcm−3), an abrupt transition from micro-crystalline diamond to nanocrystalline diamond was observed at 3% CH4. This transition is accompanied by a dramatic decrease in surface roughness, a six percent drop in density and an increasing content in hydrogen and graphitic carbon impurities. Guided by these results, layered nano-microhybrid diamond samples were prepared by periodically changing the growth conditions from nano- to microcrystalline.
•Thick diamond films were grown by microwave-plasma assisted CVD.•Grain size control was achieved by adjusting the CH4 content of the CH4/H2 feed gas.•The density of the CVD diamond films decreases with decreasing grain size.•Hydrogen and graphitic carbon impurities increase with decreasing grain size.•Nanocrystalline films have a pronounced 110 oriented fiber texture.
Materials with three-dimensional micro- and nanoarchitectures exhibit many beneficial mechanical, energy conversion and optical properties. However, these three-dimensional microarchitectures are ...significantly limited by their scalability. Efforts have only been successful only in demonstrating overall structure sizes of hundreds of micrometres, or contain size-scale gaps of several orders of magnitude. This results in degraded mechanical properties at the macroscale. Here we demonstrate hierarchical metamaterials with disparate three-dimensional features spanning seven orders of magnitude, from nanometres to centimetres. At the macroscale they achieve high tensile elasticity (>20%) not found in their brittle-like metallic constituents, and a near-constant specific strength. Creation of these materials is enabled by a high-resolution, large-area additive manufacturing technique with scalability not achievable by two-photon polymerization or traditional stereolithography. With overall part sizes approaching tens of centimetres, these unique nanostructured metamaterials might find use in a broad array of applications.
The tensile properties of additively manufactured (AM) metals and alloys are among the most important variables that impact the potential applications of these materials. Here we examine and report ...on the tensile properties of AM 316L stainless steels fabricated by the laser powder-bed-fusion (L-PBF) technique, via twelve sets of optimized laser processing parameters that produce materials with density >98.8 ± 0.10%. A heterogeneous microstructure is observed in all L-PBF samples, including microscopic features such as dislocations, cellular walls, elemental segregations, local misorientations, impurities, precipitates, and a large fraction of low-angle grain boundaries (2-10°, ∼40–60%). The derived average grain size defined by high-angle grain boundaries (>10°) is ∼30–50 μm. Tensile testing reveals a yield strength ranging from 552 to 635 MPa and a tensile-elongation-to-failure (TEF) of 0.09–0.42 for directly-printed samples, whereas these values are 592–690 MPa and 0.29–0.50 for samples machined from the as-built rectangular thin plates. In all samples, we observe a variation of tensile yield strength within ∼15% but not the TEF, suggesting marginal microstructural changes despite a wide range of laser processing parameters. The large scatter of TEF in directly-printed samples originates from the sensitivity of thin gauge geometry (∼2 mm2 cross-section area) to the built-in flaws. We measured a substantially higher strain rate sensitivity (m∼0.02–0.03) of L-PBF 316L compared to the coarse-grained counterparts (∼0.006), together with a small activation volume of ∼20–30b3 (where b is the Burgers vector of 316L). These deformation kinetics parameters suggest that the tensile plasticity of L-PBF 316L is controlled by a much finer microstructural length scale than the measured grain size, consistent with the high strength and juxtaposed nano- to macro-structures seen in these materials. Strategies to optimize the tensile properties of AM materials are discussed.
•The yield strength of L-PBF 316L from a single build machine exhibits a variation within ∼15% but not the tensile elongation-to-failure (TEF).•The large variation of TEF in L-PBF 316L is due to its sensitivity to sample geometry and built-in flaws.•An m∼0.02–0.03 is measured in L-PBF 316L compared to coarse-grained counterpart (∼0.0061), together with a small V∼20–30b3.•Nanoinclusions in L-PBF 316L SS were found located in the dimple center and may impact its fracture strength.
Two photon polymerization (TPP) is a precise, reliable, and increasingly popular technique for rapid prototyping of micro-scale parts with sub-micron resolution. The materials of choice underlying ...this process are predominately acrylic resins cross-linked via free-radical polymerization. Due to the nature of the printing process, the derived parts are only partially cured and the corresponding mechanical properties, i.e. modulus and ultimate strength, are lower than if the material were cross-linked to the maximum extent. Herein, post-print curing via UV-driven radical generation, is demonstrated to increase the overall degree of cross-linking of low density, TPP-derived structures.
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