Metal Nanofoams Research Articles

Multiscale modeling of copper and copper/nickel nanofoams under compression

Pure metal nanofoams in the form of interconnected ligament networks have shown strong potential over the last few years in areas such as catalysts, batteries, and optics. However, they are often fragile and therefore difficult to integrate into engineering applications. For these reasons, a new class of materials, composite metallic nanofoams made of ligaments coated with thin metallic layers, have been proposed to solve these issue. The mechanical properties of these nanofoams depend on their relative density and their internal geometrical structure. In this work, we combine molecular dynamics (MD) and finite element method (FEM) to investigate the compressive behavior of nanofoams made of copper ligaments coated with nickel. We also investigate how this behavior relates to their microstructures. For that purpose, we built different types of representative cell structures, and atomistic simulations of multiaxial compression tests were performed to produce yield surfaces. Then the generated yield surfaces were curve fitted into a normalized model to obtain the shape parameters. Last, a plasticity model was introduced to study and compare their mechanical behavior under compression. The results suggest that the coating of the ligaments can improve the mechanical behavior of the nanofoams. They also reveal the importance and the limitations of the microstructural geometry on the strengthening of these structures. These findings can be used for the design of metallic nanofoams with tailored mechanical properties.

Highly adjustable 3D nano-architectures and chemistries via assembled 1D biological templates.

Porous metal nanofoams have made significant contributions to a diverse set of technologies from separation and filtration to aerospace. Nonetheless, finer control over nano and microscale features must be gained to reach the full potential of these materials in energy storage, catalytic, and sensing applications. As biologics naturally occur and assemble into nano and micro architectures, templating on assembled biological materials enables nanoscale architectural control without the limited chemical scope or specialized equipment inherent to alternative synthetic techniques. Here, we rationally assemble 1D biological templates into scalable, 3D structures to fabricate metal nanofoams with a variety of genetically programmable architectures and material chemistries. We demonstrate that nanofoam architecture can be modulated by manipulating viral assembly, specifically by editing the viral surface coat protein, as well as altering templating density. These architectures were retained over a broad range of compositions including monometallic and bi-metallic combinations of noble and transition metals of copper, nickel, cobalt, and gold. Phosphorous and boron incorporation was also explored. In addition to increasing the surface area over a factor of 50, as compared to the nanofoam's geometric footprint, this process also resulted in a decreased average crystal size and altered phase composition as compared to non-templated controls. Finally, templated hydrogels were deposited on the centimeter scale into an array of substrates as well as free standing foams, demonstrating the scalability and flexibility of this synthetic method towards device integration. As such, we anticipate that this method will provide a platform to better study the synergistic and de-coupled effects between nano-structure and composition for a variety of applications including energy storage, catalysis, and sensing.

Molecular Dynamics Simulations of Aluminum Foams under Tension: Influence of Oxidation

For materials with high surface-to-volume ratio and high oxygen affinity, oxide layers will significantly change the material properties. However, oxidation effects have not been studied for metal nanofoams, which have many applications because of their light weight and high stiffness. We use molecular dynamics simulations to show that oxidized aluminum nanofoams possess significantly improved ductility without reduction in tensile strength. The Al–O interface leads to an increased defect nucleation rate at the oxide interface, preventing localized deformation. At the same time, the enthalpy of mixing between aluminium and oxygen decreases for increasing O concentrations, reaching a minimum at the stoichiometric ratio of Al2O3, resulting in stabilized bonds and increased strength.

Metal nanofoams via a facile microwave-assisted solvothermal process.

A novel, facile, non-hazardous, low temperature/pressure microwave solvothermal method of producing pure copper, silver, and nickel metal nanofoams is presented. The nanofoams have been produced using inexpensive metal acetates and polyglycol solvent. The nanofoam formation proceeds in two steps within a single-pot synthesis: formation of metal nanoparticles, followed by the sintering of nanoparticles into nanofoams. The nanofoams have many potential uses in clean energy applications, particularly lithium-ion batteries.

Nickel Network Derived from a Block Copolymer Template for MnO2 Electrodes as Dimensionally Stabilized Lithium‐Ion Battery Anodes

AbstractTo improve lithium‐ion batteries further, novel concepts for the reproducible preparation of highly structured bicontinuous battery electrodes are required. With this in mind, the main focus of this work is based on the block copolymer template‐directed synthesis of metal nanofoams suitable for the rational study and design of the final conductive matrix through molecular engineering of the starting polymer. As a proof of concept, diverse MnO2 electrodes with nickel foam as substrates are prepared and morphologically and structurally characterized by means of SEM, Raman spectroscopy, and XRD. To investigate the electrochemical properties of the prepared MnO2–nickel foam electrodes, cyclic voltammetry and galvanostatic cycling experiments, including C‐rate tests, are performed and the obtained results are discussed with respect to the deposition time. Compared with the reference, namely, bulk MnO2–nickel foil electrodes, superior electrochemical characteristics, particularly regarding C‐rate capability and long‐term cycling stability, are achieved, which is attributed to better dimensional stability of the composite electrode.

Virus-Based Metal Nanofoams As Scalable Three-Dimensional Current Collectors

In this work, we demonstrate the use of M13 virus to produce metal nanofoams that can be used as current collectors in lithium ion battery electrodes. Metal foam current collectors have been demonstrated to promote rapid electronic conduction in battery electrodes while maintaining a high active material mass fraction. An ideal three dimensional metal current collector comprises a nanofoam, with pore size on the order of one lithium diffusion distance through the active material on the timescale of one (dis)charge. In such a structure, the high specific surface area of a metal nanofoam allows deposition of large quantities of active material, while a continuous metal network embedded within the electrode provides an electronically conductive pathway. However, unlike macroscopic metal foams, metal nanofoams are not widely available because robust and scalable synthetic routes for their production are difficult to achieve. Our lab has taken steps toward this by producing metal nanofoams using M13 virus as a biological template, and showing that these materials can be used as 3D current collectors. M13 is a filamentous virus that has been used as a template for nanomaterials for both electronic and non-electronic applications. Its utility arises from its nanoscale dimensions, as well as the fact that its surface chemistry and morphological properties can be controlled genetically. To fabricate metal nanofoams, we treat the M13 virus capsid as a high aspect ratio nanoparticle and use it to assemble a template. The process uses amino acid residues at three positions on the pVIII major capsid protein: the lysine residue located at position 14 (L14), a glutamic acid fusion to the protein’s N terminus (EEAE), and a tyrosine to methionine point mutation at site 21 (Y21M). The first step in nanofoam fabrication uses glutaraldehyde to crosslink a concentrated virus solution, making use of the lysine residues exposed on the virus capsid. This facile crosslinking process results in a hydrogel. These hydrogels can be formed on a wide range of substrates, and freestanding hydrogels can be produced. The virus used for this process is genetically modified with an EEAE amino acid fusion that increases its negative surface charge. That surface charge is used to bind a palladium-based catalyst, which is then used for electroless deposition of nickel onto the hydrogel. The resulting open-cell nanofoam comprises struts that are templated onto the filamentous virus. As such, modifying the morphology of the virus particles was expected to affect the foam morphology. Because virus genes encode the amino acid sequence of the proteins forming the virus capsid, this can be done genetically. We demonstrate this control using the Y21M mutation, a point mutation shown to increase the persistence length of the virus. Using a Y21M variant as a genetically programmable control, we are able to lower the relative density of our foams. We also demonstrate control over foam morphology using virus concentration, and by controlling immersion time in the electroless bath. Lithium ion battery active materials were deposited on the nanofoam surface using electrodeposition. This technique is employed to deposit a controllable thickness of manganese oxide onto the surface of our biologically derived metal nanofoams. The resulting foams are then assembled into half cells. Using pulsed electrodeposition, the active material thickness was controlled by varying the number of pulses. By depositing thin active materials, we demonstrate that it is possible to produce ‘capacitor-like’ biotemplated electrodes with excellent rate capability. Thicker active material layers are used to produce more energy-dense electrodes with lower rate capability. Beyond the use of virus to synthesize three-dimensional current collectors for coin cells, we demonstrate that the biological templating method allows scale-up of the nanofoams to produce larger batteries. As the foams are based on self-assembling virus nanoparticles, it is possible to obtain large quantities of the template through biological amplification. Unlike a process employing extensive top-down fabrication techniques, genetically programmable templates provide a facile route toward large-format electrodes with control over nanoscale morphology. Through amplification of the virus and scale-up of the nanofoam production process, we demonstrate 4”x3” pouch cells. These electrodes are shown to be flexible, allowing compatibility with a wide range of systems. This demonstrates our biological templating method as an advance toward practical metal nanofoam engineering materials. Figure: an M13-templated nickel nanofoam before active material deposition. Figure 1

Gyroid Nickel Nanostructures from Diblock Copolymer Supramolecules

Nanoporous metal foams possess a unique combination of properties - they are catalytically active, thermally and electrically conductive, and furthermore, have high porosity, high surface-to-volume and strength-to-weight ratio. Unfortunately, common approaches for preparation of metallic nanostructures render materials with highly disordered architecture, which might have an adverse effect on their mechanical properties. Block copolymers have the ability to self-assemble into ordered nanostructures and can be applied as templates for the preparation of well-ordered metal nanofoams. Here we describe the application of a block copolymer-based supramolecular complex - polystyrene-block-poly(4-vinylpyridine)(pentadecylphenol) PS-b-P4VP(PDP) - as a precursor for well-ordered nickel nanofoam. The supramolecular complexes exhibit a phase behavior similar to conventional block copolymers and can self-assemble into the bicontinuous gyroid morphology with two PS networks placed in a P4VP(PDP) matrix. PDP can be dissolved in ethanol leading to the formation of a porous structure that can be backfilled with metal. Using electroless plating technique, nickel can be inserted into the template's channels. Finally, the remaining polymer can be removed via pyrolysis from the polymer/inorganic nanohybrid resulting in nanoporous nickel foam with inverse gyroid morphology.

Gyroid nickel nanostructures from diblock copolymer supramolecules.

Nanoporous metal foams possess a unique combination of properties - they are catalytically active, thermally and electrically conductive, and furthermore, have high porosity, high surface-to-volume and strength-to-weight ratio. Unfortunately, common approaches for preparation of metallic nanostructures render materials with highly disordered architecture, which might have an adverse effect on their mechanical properties. Block copolymers have the ability to self-assemble into ordered nanostructures and can be applied as templates for the preparation of well-ordered metal nanofoams. Here we describe the application of a block copolymer-based supramolecular complex - polystyrene-block-poly(4-vinylpyridine)(pentadecylphenol) PS-b-P4VP(PDP) - as a precursor for well-ordered nickel nanofoam. The supramolecular complexes exhibit a phase behavior similar to conventional block copolymers and can self-assemble into the bicontinuous gyroid morphology with two PS networks placed in a P4VP(PDP) matrix. PDP can be dissolved in ethanol leading to the formation of a porous structure that can be backfilled with metal. Using electroless plating technique, nickel can be inserted into the template's channels. Finally, the remaining polymer can be removed via pyrolysis from the polymer/inorganic nanohybrid resulting in nanoporous nickel foam with inverse gyroid morphology.

Shear‐Induced Orientation of Gyroid PS‐b‐P4VP(PDP) Supramolecules

The phase behavior of block copolymer based supramolecular complexes polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) and amphiphilic pentadecylphenol (PDP) molecules resembles the phase behavior of conventional block copolymers. Several PS-b-P4VP(PDP) complexes are found to self-assemble into gyroid nanostructures. Typically, the grains are randomly oriented with a maximal size of several micrometers. Here, the orientation of a gyroid PS-b-P4VP(PDP) complex upon shearing is reported. It is found that the (111) gyroid lattice direction orients parallel to the shear direction after only several seconds of large amplitude oscillatory shearing. Oriented gyroid complexes can be used as templates for the preparation of metal nanofoams with improved ordering with potentially superior properties.

Supramolecular Route to Well-Ordered Metal Nanofoams

Metal nanofoams with a porosity above 50% v/v have recently attracted great interest in materials science due to their interesting properties. We demonstrate a new straightforward route to prepare such nanofoams using diblock copolymer-based PS-block-P4VP(PDP) supramolecules that self-assemble into a bicontinuous gyroid morphology, consisting of PS network channels in a P4VP(PDP) matrix. After dissolving the PDP, the P4VP collapses onto the PS struts and a free-standing bicontinuous gyroid template of 50-100 μm thickness and interconnected, uniformly sized pores is formed. The hydrophilic P4VP corona facilitates the penetration of water-based plating reagents into the porous template and enables a successful metal deposition. After plating, the polymer is simply degraded by heating, resulting in a well-ordered inverse gyroid nickel foam. Essential to this approach is the removal of only one part of the matrix (i.e., PDP). Therefore, the template accounts for 50% v/v or more. The porosity characteristics (amount, size of pores) can be tuned by selecting the appropriate copolymer and by adjusting the amount of PDP.