Bicontinuous Nanoporous Structure Research Articles

Dealloyed Pt74Ni26 and Pt26Ni74 Electrodeposited Thin Film Electrocatalysts for Oxygen Reduction

Electrodeposition and microstructure of thin films close to Pt75Ni25 and Pt25Ni75 stoichiometry are described and their catalytic oxygen reduction reaction performance, dealloying, and strain evolution detailed. Multiple techniques are used to characterize the morphology, crystalline structure, and chemical homogeneity of the as-deposited and dealloyed films. A fine-scale percolating network of lower-density regions is evident in the as-deposited Pt74Ni26 films while the as-deposited Pt26Ni74 films are more homogenous and compact. Electrodeposition is accompanied by development of significant in-plane tensile stress that increases at more negative growth potentials to reach 1.28 GPa for as-deposited Pt26Ni74. Dealloying of the near-surface regions of Pt74Ni26 is accompanied by limited expansion or opening of the low-density regions while massive dealloying of the highly stressed Pt26Ni74 results in shrinkage, extensive cracking, and formation of a bi-continuous nanoporous structure with an average pore diameter close to 5 nm. Relative to electrodeposited Pt, the alloy films exhibit enhanced area-specific oxygen reduction reaction activity (at 0.95 V vs RHE, iR-corrected) that amounts to a factor of 3.4 for dealloyed Pt74Ni26 and 5.1 for dealloyed Pt26Ni74 while the Pt-based mass activity increased by a factor of 5.1 and 12.3, for the respective films.

Nanoporous Amorphous Carbon with Exceptional Ultra-High Strength.

Nanoporous materials show a promising combination of mechanical properties in terms of their relative density; while there are numerous studies based on metallic nanoporous materials, here we focus on amorphous carbon with a bicontinuous nanoporous structure as an alternative to control the mechanical properties for the function of filament composition.Using atomistic simulations, we study the mechanical response of nanoporous amorphous carbon with 50% porosity, with sp3 content ranging from 10% to 50%. Our results show an unusually high strength between 10 and 20 GPa as a function of the %sp3 content. We present an analytical analysis derived from the Gibson-Ashby model for porous solids, and from the He and Thorpe theory for covalent solids to describe Young's modulus and yield strength scaling laws extremely well, revealing also that the high strength is mainly due to the presence of sp3 bonding. Alternatively, we also find two distinct fracture modes: for low %sp3 samples, we observe a ductile-type behavior, while high %sp3 leads to brittle-type behavior due to high high shear strain clusters driving the carbon bond breaking that finally promotes the filament fracture. All in all, nanoporous amorphous carbon with bicontinuous structure is presented as a lightweight material with a tunable elasto-plastic response in terms of porosity and sp3 bonding, resulting in a material with a broad range of possible combinations of mechanical properties.

Potentiostatic dealloying of PdIn in molten LiCl–KCl eutectic

The high-temperature electrochemical dealloying of the PdIn intermetallic in the LiCl–KCl eutectic at the temperature of 450 °C in potentiostatic mode was carried out. The resulting formation of bi-continuous nano-porous structures with different residual indium content was analyzed at time intervals of 40, 120 and 300 min from the start of the dealloying process. Our results demonstrate that specific bi-continuous structures with a pore size of the order of 100 nm are formed while the temperature of electrolysis is maintained close to the temperature of palladium recrystallization. If the dealloying process is continued for 5 h it is possible to obtain a pure intermetallic Pd2In compound in nanoporous state.

Dealloying of Pt1Bi2 intermetallic toward optimization of electrocatalysis on a Bi-continuous nanoporous core-shell structure.

Noble metal nanoporous materials hold great potential in the field of catalysis, owing to their high open structures and numerous low coordination surface sites. However, the formation of porous nanoparticles is restricted by particle size. Herein, we utilized a Pt1Bi2 intermetallic nanocatalyst to develop a dealloying approach for preparing nanoparticles with a bi-continuous porous and core-shell structure and proposed a mechanism for the formation of pores. The particle size used to form the porous structure can be <10 nm, which enhances the nanocatalyst's performance for the oxygen reduction reaction (ORR). This study provides a new understanding of the formation of porous materials via a dealloying approach.

Rapid Melt-Quenching Enables General Synthesis of High-Loading Single-Atom Catalysts with Bicontinuous Nanoporous Structure.

Single-atom catalysts have attracted extensive attention due to their unique atomic structures and extraordinary activities in catalyzing chemical reactions. However, the lack of general and efficient approaches for producing high-density single atoms on suitably tailored supporting matrixes hinders their industrial applications. Here, a rapid melt-quenching strategy with high throughput to synthesize single atoms with high metal-atom loadings of up to 9.7 wt% or 2.6 at% on nanoporous metal compounds is reported, representing several-fold improvements compared to benchmarks in the literature. Mechanism characterizations reveal that the high-temperature melting provides the essential liquid environment and activation energy to achieve the atomization of metals, while the following rapid-quenching pins the isolated metal atoms and stabilizes the coordination environment. In comparison with carbon-supported single-atom catalysts, various collaboration combinations of single atoms and nanoporous metal compounds can be synthesized using the strategy, thus achieving efficient hydrazine oxidation-assisted H2 production. This synthesis protocol is highly compatible with automatic operation, which provides a feasible and general route to design and manufacture specific single-atom catalysts with tunable atomic metal components and supporting matrixes, thus promoting the deployment of single-atom catalysts for various energy technology applications.

Controlled biomolecules separation by CO2-responsive block copolymer membranes

The intelligent responsive membranes have aroused much attention due to their distinctive capability to reversibly change separation performances under the stimulation of ambient environment. Especially, the responsive membranes derived from block copolymers, which have regular nanoporous structures, display great potential in high-precision controllable separation. Herein, we use CO2 gas as the non-toxic, mild stimulus, and develop the responsive membranes from a block copolymer of poly(2-diethylaminoethyl methacrylate)-block-polystyrene (PDEAEMA-b-PS) by the selective swelling method. The membranes exhibit a bi-continuous nanoporous structure and the surfaces and pore walls are rich with CO2-responsive PDEAEMA chains. Based on the reversible conformation transition of PDEAEMA chains between the collapsed state and extended state upon CO2/N2 stimulation, the membranes achieve the controllable regulation on the water permeances from ∼100 to ∼2100 L⋅h−1⋅m−2⋅bar−1, also realize the blocking/passing switch for varied proteins. More importantly, the extended PDEAEMA chains shrink the effective pore size down to less than 5 nm, moving the separation scope from ultrafiltration to tight-ultrafiltration. Thus, the membranes are capable to separate macromolecular proteins with small molecule polypeptide and vitamin with high separation efficiencies, demonstrating their application prospect in precise separation and fractionation of biomolecules.

Ultrathin Polyaniline-Coated Single-Crystalline Mn2O3 Nanoporous Ellipsoids with High Energy Density and Cyclability for Low-Cost Zinc-Ion Batteries

Secondary Zn-ion batteries (ZIBs) using aqueous electrolytes are very promising for safe and large-scale energy storage in the future. However, we still lack suitable cathode materials with high energy density and durability for Zn2+ storage. Herein, a three-dimensional nanoporous microellipsoid Mn2O3 covered with an ultrathin layer of polyaniline (PANI) composite (Mn2O3/PANI) is developed for advanced ZIBs. The synthesis of Mn2O3/PANI is quite easy: nanoporous Mn2O3 (which is obtained from the pyrolysis of MnCO3) is immersed into aniline, and the subsequent self-initiated polymerization of PANI will cover the Mn2O3 surface. The bicontinuous nanoporous structure with a pore size of ∼30 nm facilitates ion diffusion and provides an active interface for fast zinc-ion storage. Moreover, the uniformly coated ultrathin PANI cover not only inhibits Mn2O3 dissolution and protects the structural integrity but also provides a fast electron transport network during charge/discharge. Consequently, the designed Mn2O3/PANI achieves a high energy capacity, a high rate performance, and a much longer lifetime (86.6% capacity retention over 2000 cycles at 1 A g–1), outperforming those of most reported cathode materials. Detailed electrochemical studies and characterizations demonstrate that the H+ and Zn2+ coinsertion mechanism and the PANI cover can enlarge the Zn-ion diffusion coefficient. This work introduces a facile route to develop 3D bicontinuous nanoporous Mn2O3/PANI composites for highly reversible ZIBs.

Scalable-doped Nanoporous 1T″ ReSe2 via a General Surface Co-Alloy Strategy.

Reliable and controllable doping of 2D transition metal dichalcogenides is an efficient approach to tailor their physicochemical properties and expand their functional applications. However, precise control over dopant distribution and scalability of the process remains a challenge. Here, we report a general method to achieve scalable in situ doping of centimeter-sized bicontinuous nanoporous ReSe2 films with transition metal atoms via surface coalloy growth. The distinct strains induced by the bending curvature of nanoporous structures and uniform dopants result in a local 1T' to 1T″ structure phase transition over nanoporous ReSe2 films. The as-prepared nanoporous Ru-ReSe2 with high 1T″ phase exhibits preferable electrochemical activity in hydrogen evolution reaction. The work demonstrates a unique and general approach to synthesize uniformly-doped transition metal dichalcogenides with 3D bicontinuous nanoporous structure, which can be scaled up to batch production for various applications.

Facile fabrication of free-standing nanoporous CuAg structures for high-performance non-enzymatic glucose sensing by dealloying glassy precursors

We report free-standing bimetallic nanoporous CuAg (NPCuAg) structures prepared via a facile one-step electrochemical dealloying proccess. The Ag/Cu ratio and the thickness of the NPCuAg structures could be tuned by the composition of the corresponding metallic glass (MG) precursors and dealloying time. All dealloyed samples exhibited a uniform three-dimensional bi-continuous nanoporous structure and homogeneous chemical composition. The effects of the Ag/Cu ratio and dealloying time on the electrocatalytic performance toward glucose oxidation were systematically investigated. It was found that the NPCu4.5Ag-1 H electrode showed the highest enhanced electrocatalytic activity due to the high surface area of the nanoporous structure and the optimal synergistic effect. Furthermore, this electrode exhibited an outstanding sensitivity of 5.91 mA cm−2 mM−1, a wide linear range up to 6 mM, a low detection limit of 0.5 μM, fast response time within 1.3 s, excellent selectivity and good stability. Considering these advantages, the designed electrode can be a promising electrochemical sensing platform for highly efficient glucose detection.

Designing independent water transport channels to improve water flooding in ultra-thin nanoporous film cathodes for PEMFCs

Utilization of 3D nanostructured Pt cathodes could obviously improve performances of proton exchange membrane fuel cells (PEMFCs) owing to the reduced tortuosity and the bi-continuous nanoporous structure. However, these cathodes usually suffer from the flooding problem ascribed to the ionomer-free and nanoscale pores which are more susceptible to water condensation. In this paper, ultra-thin nanoporous metal films (100 nm) were utilized to construct PEMFC cathodes and independent transport channels were designed separately for water and gas aiming at the flooding problem. Nanoporous gold (NPG) film was used as the model support for loading Pt nanoparticles owing to its controllable and stable structure. After optimizing the polytetrafluoroethylene (PTFE) content and carbon loading in the gas diffusion layer (GDL), plasma treatment under O2 atmosphere was used to pattern the GDL with independent water transport channels. The obtained liquid permeation coefficients and oxygen gains demonstrated the obviously improved water and O2 transport. By using a home-made optimized GDL and a nanoporous film cathode with pore size ∼60 nm, the flooding problem could be facilely solved. With a Pt loading of ∼16 μg cm−2, this 3D nanostructured cathode exhibits a PEMFC performance of ∼957 mW cm−2 at 80 °C. The Pt power efficiency is about 4 times higher than that of the commercial Pt/C cathode (50 μg cm−2, 756 mW cm−2). Obviously, this study provides a simple but effective methodology to solve the water flooding problem in the ultra-thin nanoporous film cathodes which is applicable for other types of 3D nanostructured PEMFC cathodes.

Achieving an efficient hydrogen evolution reaction with a bicontinuous nanoporous PtNiMg alloy of ultralow Noble-metal content at an ultrawide range of current densities

Electrochemical water splitting powered by green electricity generated from intermittent geothermal, wind and solar power is a promising approach to realize large-scale hydrogen production owing to its sustainable and clean characteristics. Developing electrocatalysts with high electrocatalytic activity and long-term stability for the hydrogen evolution reaction (HER) at an ultrahigh current density (>1000 mA cm−2) still needs a breakthrough. Here, a bicontinuous nanoporous PtNiMg alloy with an ultralow noble metal content for the HER is fabricated by a facile high-temperature sintering method based on the nanoscale Kirkendall effect. A bicontinuous nanoporous alloy electrode with an ultralow content of approximately 1 at % Pt for the HER in an alkaline medium achieves an extremely low overpotential of 22 mV at a current density of 10 mA cm−2 and a Tafel slope (30.9 mV dec-1) of the Volmer-Tafel mechanism. The alloy electrode for the HER at a wide current density of 1–2000 mA cm−2 displays superior stability in alkaline media. The 3D bicontinuous nanoporous structure, perfect synergistic effect of Ni and Pt species, high structural stability and excellent conductivity of the 1-PtNiMg-900 alloy achieve outstanding electrocatalytic activity and long-term stability at an ultrawide range of HER current densities. This study greatly improves the electrochemical performance of Pt-based electrocatalysts for the HER via a novel fabrication approach and provides the possibility of large-scale industrial application for H2 production.

A novel dealloying strategy for fabricating nanoporous Ag via ζ′-AgGa alloy

A mild strategy for fabricating nanoporous silver (np-Ag) pieces was reported via preparation of Ag–Ga alloys in relatively low temperature and subsequent electrochemical dealloying in nitric acid (HNO3) aqueous solution. After selectively etching Ga out of the Ag–Ga alloy, a typical three-dimensional (3D) bicontinuous nanoporous structure with a pore size of ∼67.21–159.33 nm was observed. A series of studies have shown that the addition of sodium dodecyl sulfate (SDS) results in minimum pore size. The coarsen exponent (n) is 1.61, and the activation energy was calculated to be 27.04 kJ mol−1. The ζ′-AgGa alloy prepared at low temperature can be used as the precursor for the preparation of fine np-Ags, and this method provides a new strategy for the industrial production of dealloyed np-Ag.

Pore Size Dependence of Permeability in Bicontinuous Nanoporous Media.

In this work, we employ many-body dissipative particle dynamics (mDPD) simulations to investigate the fluid flow process through bicontinuous nanoporous media, which are representative models for a broad class of nanoporous materials. The mDPD formulation includes attractive and repulsive interactions describing accurately fluid-fluid and fluid-solid interactions. As a mesoscale simulation method, mDPD can bridge the length and time scale gap between continuum and atomistic simulations. The bicontinuous nanoporous models are constructed considering a defined morphology, the porosity level, and varying pore sizes in the range from 3.41 to 13.63 nm. All models have a 0.65 porosity level and the same topology. The models provide a stochastic description of the morphology and pore size distribution and allow for a direct investigation of the dependence of permeability on the average pore size. The stationary nanoporous models are filled with fluid particles, and flow is induced by the action of confining pistons. Simulation results, obtained by imposing different pressure differences on the surfaces of the nanoporous media, indicate a linear pressure drop within the nanoporous model. Regardless of the complexities and different scales of the porous media considered, the steady-state fluid flow through the nanoporous models is proportional to the pressure gradient applied, in agreement with Darcy's law. The calculated pore size dependence of permeability is well described by the Hagen-Poiseuille law, considering a single shape correction factor that accounts for the flow resistance due to the complex nanoporous morphology. This work highlights the effect of the average pore size of a complex stochastic bicontinuous nanoporous medium on fluid properties. The results indicate rather a relatively simple dependence of permeability on the average pore size. The novel method we employ to generate the stochastic bicontinuous nanoporous structure allows the control of different geometric features that can be explored in future studies.

Fast attenuation of high-frequency acoustic waves in bicontinuous nanoporous gold

We studied the formation and attenuation of GHz elastic waves in free-standing nanoporous gold films by MeV ultrafast electron diffraction and finite element simulations. By tracing the evolution of the high frequency acoustic waves in time domain, we found that the bicontinuous nanoporous structure in nanoporous gold films results in three-dimensionally acoustic response with low coherence, leading to fast attenuation of the elastic waves in comparison with solid gold films. The morphologically dominated dynamics indicates the nanoporosity plays an important role in the high-frequency acoustic energy relaxation, which shines a light on the applications of dealloyed nanoporous materials in nanodevices and sensors as GHz and THz acoustic filters and dampers.

Nanoporous Intermetallic Pd3Bi for Efficient Electrochemical Nitrogen Reduction

AbstractElectrocatalytic nitrogen reduction at ambient temperature is a green technology for artificial nitrogen fixation but greatly challenging with low yield and poor selectivity. Here, a nanoporous ordered intermetallic Pd3Bi prepared by converting chemically etched nanoporous PdBi2 exhibits efficient electrocatalytic nitrogen reduction under ambient conditions. The resulting nanoporous intermetallic Pd3Bi can achieve high activity and selectivity with an NH3 yield rate of 59.05 ± 2.27 µg h−1 mgcat−1 and a Faradaic efficiency of 21.52 ± 0.71% at −0.2 V versus the reversible hydrogen electrode in 0.05 m H2SO4 electrolyte, outperforming most of the reported catalysts in electrochemical nitrogen reduction reaction (NRR). Operando X‐ray absorption spectroscopy studies combined with density functional theory calculations reveal that strong coupling between the Pd–Bi sites bridges the electron‐transfer channel of intermetallic Pd3Bi, in which the Bi sites can absorb N2 molecules and lower the energy barrier of *N2 for N2 adsorption and activation. Meanwhile, the intermetallic Pd3Bi with bicontinuous nanoporous structure can accelerate the electron transport during the NRR process, thus improving the NRR performance.

Synthesis of a Pd2In-Pd3In bi-continuous nanoporous structure by electrochemical dealloying in molten salts.

A study of the high-temperature electrochemical selective dissolution of PdIn intermetallics in molten mixtures of alkali chlorides with the formation of nanoporous structures has been carried out to obtain a coherent structure consisting of Pd2In and Pd3In intermetallics. The smallest pore size (approximately 100 nanometers) with a bi-continuous structure of Pd2In-Pd3In is obtained from the PdIn intermetallic phase at a temperature of 450 °C and a current density of 50 mA cm-2 in a molten LiCl-KCl eutectic. It has been shown that the temperature of the anodic dissolution process is the most important factor in controlling the pore size and structural morphology. The morphology of pores and ligaments in the sample at 600 °C is a 3D hierarchy with pore sizes from several hundred nanometers to a micron-scale but with the same Pd2In-Pd3In (2 : 1) composition.

Bicontinuous nanoporous design induced homogenization of strain localization in metallic glasses

Bicontinuous nanoporous metallic glasses (MG) synergize the outstanding properties of MGs and open-cell nanoporous materials. The low-density and high-specific-surface-area of bicontinuous nanoporous structures have the potential to enhance the applicability of MGs in catalysis, sensors, and lightweight structural designs. Here, we report molecular dynamics simulations of tensile loading deformation and failure of bicontinuous nanoporous Cu64Zr36 MG with 55% porosity and 4.4 nm ligament size. Results indicate an anomalous mechanical behavior featuring delocalized plastic deformation preceding ductile failure. The deformation follows two mechanisms: i) Necking of ligaments aligned with the loading direction and ii) progressive alignment of randomly oriented ligaments. Failure occurs at 0.16 strain, following massive rupture of ligaments. This work indicates that a bicontinuous nanoporous design is able to effectively delocalize strain localization in a MG due to a combination of size effect on the ductility of MGs resulting in nano ligaments necking and progressive asynchronous alignment of ligaments.

Dealloying Kinetics of AgAu Nanoparticles by In Situ Liquid-Cell Scanning Transmission Electron Microscopy.

Understanding the formation and evolution of bicontinuous nanoporous structure during dealloying has been one of the most challenging subjects of dealloying research. However, previous in situ investigations either suffer from insufficient spatial resolution (e.g., X-ray tomography) or lack morphology visualization and mass information (e.g., scanning tunneling microscopy). In this work, we report the kinetics of the whole course of dealloying by utilizing liquid-cell aberration-corrected scanning transmission electron microscopy. With Z-contrast imaging analysis, the in situ sub-nanoscale characterization reveals two new phenomena, an initial period of dealloying indicative of an initial length scale for bulk dealloying and a large volume shrinkage in a nanoscale alloy precursor. We explain the particle-size-dependent volume shrinkage with the formation of a dense shell and quantify the dependence with a simple geometric model. These insights into the mechanisms of dealloying will enable deliberate designs of nanoporous structures.

Bicontinuous Nanoporous Design Induced Homogenization of Strain Localization in Metallic Glasses

Bi-continuous nano-porous metallic glasses (MG) synergize the outstanding properties of MGs and open-cell nano-porous materials. The low-density and high-specific-surface-area of bi-continuous nano-porous structures have the potential to enhance the applicability of MGs in catalysis, sensors, and lightweight structural designs. Here, we report molecular dynamics simulations of tensile loading deformation and failure of bi-continuous nano-porous Cu64Zr36 MG with 55% porosity and 4.4 nm ligament size. Results indicate an anomalous mechanical behavior featuring delocalized plastic deformation preceding ductile failure. The deformation follows two mechanisms: i) Necking of ligaments aligned with the loading direction and ii) progressive alignment of randomly oriented ligaments. Failure occurs at 0.16 strain, following successive necking and rupture events. This work indicates that a bi-continuous nano-porous design is able to effectively delocalize strain localization in a MG due to a combination of size effect on the ductility of MGs resulting in nano-ligaments necking and progressive asynchronous alignment of ligaments.

Nano-assembly and mechanical performance of cold-welded nanoporous Au

The increased diversity of microstructure of nanoporous materials can be expected to greatly expand their functional application in more industries. By incorporating nanoporous metals into cold-welding technology, we report an approach to directly forming the nanoporous materials with various microstructure inside. Nanoporous gold (Au) with ideal bi-continuous nanoporous structures was modeled using spinodal decomposition. Understanding the mechanical properties is the primary step to improve the reliability on the operational performance of nanoporous structures. After the process of cold-welding manufacture, the well-interconnected nanoporous Au was successfully fabricated and the mechanical properties of cold-welded structures were studied. Molecular dynamic simulations on samples with ligament diameter ranging from 3.264 to 6.528 nm and relative density ranging from 0.30 to 0.45 were also carried out to study how these factors affect the assembly process. These results are believed to facilitate the bottom-up nanofabrication and nanoassembly of composite structures for better mechanical performance.