Nanoporous Metals Based on Metallic Glasses:Synthesis,Structure and Functional Applications

Nanoporous metals have emerged as a new class of functional materials with unique structures and properties.Compared to conventional metals and alloys,nanoporous metals possess a high surface area,unique pore size distribution and enhanced catalytic activity,making them highly desirable for a wide range of applications,such as photonics,sensing,supercapacitors and catalysis.In this review paper,we aim to summarize recent advances in the fabrication,structural regulation and functional applications of nanoporous metals and their composites via the dealloying of metallic glasses.Particularly,we will discuss the factors that affect the nanoporous structure,including precursor composition,dealloying conditions and post-treatment methods.We will also cover topics such as the preparation of immiscible nanoporous metals and the control of hierarchical nanoporous structures.Finally,we will provide a brief overview of the current situation and discuss the current challenges and potential research directions in the field.

An overview on metal-related catalysts: metal oxides, nanoporous metals and supported metal nanoparticles on metal organic frameworks and zeolites

Metal nanoparticles(NPs) supported on porous materials have shown great advantages in many catalytic application fields. Supported metal NPs are receiving extensive attention due to their significant contribution in a wide range of current and future applications, and this is arguably one of the fastest growing research fields. In this review, we highlight various types of metal catalysts that possess great potential in several catalytic reactions. The major focus has been on metal oxides, nanoporous metals and metal NPs supported on metal-organic frameworks(MOFs) and zeolites. Special attention has been given to the synthesis strategies and application of the NPs supported on MOFs and zeolites, which are considered highly interesting and rapidly expanding areas in heterogeneous catalysis. Finally, the prospects of these catalysts have been included in the concluding remarks.

Dealloying induced nanoporosity evolution of less noble metals in Mg ion batteries

Rechargeable Mg ion batteries(MIBs)have aroused great interests,and using alloy-type anodes and conventional electrolytes offers an effective way to develop high energy density Mg battery systems.However,the dealloying-induced nanoporosity evolution of alloy-type anodes during the charging process has received less attention.Herein,using a magnetron-sputtered Mg;Bi;film as an example,we investigate its electrochemical dealloying and associated structural evolution in an all-phenyl-complex electrolyte by in-situ and ex-situ characterizations.The microstructures and length scales of nanoporous Bi can be facilely regulated by changing electrochemical parameters,and there exists a good linear correlation between the surface diffusivity of Bi and the applied current density/potential scan rate on a logarithm scale.More importantly,the self-supporting nanoporous Bi electrodes deliver satisfactory Mg storage performance and alloy-type anodes show good compatibility with conventional electrolytes.Furthermore,the charging-induced dealloying in MIBs is a general strategy to fabricate nanoporous less noble metals like Sn,Pb,In,Cu,Zn and Al,which shows advantages over chemical dealloying in aqueous solutions.Our findings highlight the significance of nanoporosity evolution of alloy-type anodes during dealloying,and open opportunities for the fabrication of nanoporous reactive metals.

Self-Supported Nanoporous Gold with Gradient Tin Oxide for Sustainable and Efficient Hydrogen Evolution in Neutral Media

Hydrogen evolution reaction(HER)in neutral medium suffers from slow kinetics as compared to that in alkaline or acidic conditions,owing to larger Ohmic loss and low proton concentration.Here we report that a self-supported nanoporous Au-SnO_(x)(NP Au-SnO_(x))catalyst with gradient tin oxide surface could significantly enhance HER activity in neutral buffer solution(0.2 M PBS).The NP Au-SnO_(x)catalyst exhibits a low onset overpotential of 38 mV and a small Tafel slope of 79 mV dec^(−1).The current density of 10 mA cm^(−2)is manifested at an overpotential as low as 148 mV,representing the comparable performance of Pt/C catalyst.This high catalytic activity can retain at least 10 hours without any detectable decay.The superior HER activity is proposed to originate from the gradient SnO_(x)structure and metal/oxide interfaces in nanoporous ligaments.Furthermore,the X-ray photoelectron spectroscopy reveals that the gradient oxide in the ligament is remarkably stable during long-term reaction.

Surface‑Alloyed Nanoporous Zinc as Reversible and Stable Anodes for High‑Performance Aqueous Zinc‑Ion Battery

Metallic zinc(Zn)is one of the most attractive multivalent-metal anode materials in post-lithium batteries because of its high abundance,low cost and high theoretical capacity.However,it usually suffers from large voltage polarization,low Coulombic efficiency and high propensity for dendritic failure during Zn stripping/plating,hindering the practical application in aqueous rechargeable zinc-metal batteries(AR-ZMBs).Here we demonstrate that anionic surfactant-assisted in situ surface alloying of Cu and Zn remarkably improves Zn reversibility of 3D nanoporous Zn electrodes for potential use as high-performance AR-ZMB anode materials.As a result of the zincophilic ZnxCuy alloy shell guiding uniform Zn deposition with a zero nucleation overpotential and facilitating Zn stripping via the ZnxCuy/Zn galvanic couples,the self-supported nanoporous ZnxCuy/Zn electrodes exhibit superior dendrite-free Zn stripping/plating behaviors in ambient aqueous electrolyte,with ultralow polarizations under current densities up to 50 mA cm^(‒2),exceptional stability for 1900 h and high Zn utilization.This enables AR-ZMB full cells constructed with nanoporous ZnxCuy/Zn anode and K_(z)MnO_(2)cathode to achieve specific energy of as high as~430 Wh kg^(‒1)with~99.8%Coulombic efficiency,and retain~86%after long-term cycles for>700 h.

Self-standing 3D nanoporous Ag_(2)Al with abundant surface oxygen species facilitating oxygen electroreduction for efficient hybrid Zn battery

The hybrid battery integrating a typical Zn redox battery and a Zn-air battery is a promising green technology for energy storage,and the cathode integrating the redox reaction and electrocatalytic oxygen reduction is a key point for efficient electrochemical energy conversion.Herein,we report a scalable strategy to fabricate nanoporous Ag2 Al internetallic compound as a self-standing cathode for the hybrid Zn battery.The abundant surface oxygen species,the Ag-Al intermetallic interaction and the npAg_(2)Al@AgAlOx interface cooperatively contributed to the catalytic ORR activity.The electrode endows efficient catalytic oxygen reduction(a Tafel slope of 38.0 mV/dec and an onset potential of 0.998 V)and regulated redox activity as compared with Ag.The nanoporous channels allow efficient ion transport,interface charge exchange and gas molecular diffusion.Significantly,the assembled hybrid Zn-Ag_(2) Al/air battery delivers a high capacity of 3.23 mAh/cm^(2) as compared with recent reports.As far as we know,this is the first exploration for the electrochemical property of Ag2 Al,and it would inspire more exploration in developing multifunctional materials and robust hybrid batteries for practical applications.

Fracture toughness and destructive mechanism of ductile nanoporous metallic glass and its crystal-impregnated nanocomposite

Nanoporous metallic glasses(NPMGs)and crystalline/amorphous nanocomposites exhibit superior ductility over bulk macroscopic metallic glasses(MGs).Their fracture behaviors remain a mystery due to experimental technical limitations.In this work,the fracture behaviors of pre-cracked NPMGs and crystal-impregnated nanoporous metallic glasses(CINPMGs)are investigated through large-scale molecular dynamics simulations,and the MG and crystal phases are amorphous Cu_(50)Zr_(50)and crystalline B2CuZr,respectively.Fracture toughness is determined by simultaneously considering the surface energy and plastic dissipated energy.Our results confirm the excellent plasticity of both the pre-cracked NPMGs and CINPMGs.The progressive necking and ductile rupture of ligaments are responsible for generating NPMGs with prominent ductility and fracture toughness.Meanwhile,secondary cracking is also triggered,which can consume energy without extending the major crack,thus further improving fracture resistance.It is also found that the fracture toughness of NPMGs can be improved by increasing the solid fraction of MG,and linear relation between fracture toughness and solid fraction can be expected.Crystal impregnation effectively inhibits global failure as the crystal phase shields the individual amorphous ligaments.Homogeneous plastic flow characterized by shear bands is observed in CINPMGs,and this homogeneous global deformation is facilitated by the crystalline/amorphous interface.Besides,the fracture toughness of CINPMGs is higher than that of the constituent single phases,regardless of the volume fraction of each phase.Ashby material charts manifest that these two types of materials demonstrate promising potential in the material selection library for advanced structural design.

Effects of dealloying and heat treatment parameters on microstructures of nanoporous Pd

Microstructures of nanoporous Pd are essentially important for its physical and chemical properties.In this work,we show that the microstructures of nanoporous Pd can be tuned by adjusting compositions of the precursor alloys,and dealloying and heat treatment parameters.Both the ligament and pore sizes decrease with increasing the electrochemical potential upon dealloying and the concentration of noble component in the precursor alloys.Heat treatment causes coarsening of the nanoporous structure.Above a critical temperature,the nanoporous structures are subjected to significant coarsening.Below the critical temperature,surface diffusion is believed to dominate the coarsening process.Above the critical temperature,the nanoporous structure coarsens remarkably at a rather high rate,which is ascribed to a multiple-mechanism controlled process.

Understanding the macroscopical flexibility/fragility of nanoporous Ag:Depending on network connectivity and micro-defects

The effective engineering applications of nanoporous metals(NPMs)in flexible energy storage and wearable healthcare biosensor monitoring require its uniform ligaments network,specifically crack-free and flexible monolithic bodies.However,the macroscopic fragility of NPMs restricts their applications in wearable electronics fields.Here we focus on the synthetization of highly flexible NPMs.The effects of structural factors,e.g.ligament-network connectivity and micro-cracks on the mechanical properties of nanoporous Ag(np Ag)are investigated.The well-interconnected np Ag metal exhibits higher tensile strength,nanohardness and Vickers hardness than those for the ill-interconnected np Ag metal.The quality of the network connectivity dominates the strength and hardness of the np Ag.The flexibility/fragility is determined by the micro-crack in np Ag.The crack-free np Ag exhibits good flexible behavior.When micro-cracks are introduced,the np Ag becomes fragile.The control of soft volume shrinkage rate(Vsr)and slow surface diffusivity(Ds)effectively suppresses the crack initiation and propagation of as-formed np Ag.These results provide useful insights to synthesize more flexible and crack-free NPM materials for effective use in public wearable electronics and diverse flexible engineering applications in the future.

Liquid metal assisted regulation of macro-/micro-structures and mechanical properties of nanoporous copper

Nanoporous metals have received significant attention as a new class of structural and functional materials.However,the macroscopic brittle fracture under the tensile test is an impediment to their practical applications.Thus,it is of central importance to develop nanoporous materials with low cost and high tensile ductility.Herein,a nanoporous Cu film supported on a pure Cu substrate(NPC@Cu)was fabricated by utilizing a liquid Ga assisted alloying-dealloying strategy,and the thickness of NPC film can be precisely regulated by changing the mass loading of liquid Ga.In-situ X-ray diffraction was performed to further explore the alloying/dealloying mechanisms.The NPC@Cu films show good tensile mechanical properties with a minimum elongation of 13.5%,which can be attributed to the good interface bonding and certain modulus matching between the nanoporous Cu layer and the Cu substrate.Our findings demonstrate that the design of film-substrate structure provides a feasible strategy for enhancing the mechanical properties of nanoporous metals.

Facile fabrication of ultrathin freestanding nanoporous Cu and Cu-Ag films with high SERS sensitivity by dealloying Mg-Cu(Ag)-Gd metallic glasses

Nanoporous metals prepared by dealloying have attracted increasing attention due to their interesting size-dependent physical,chemical,and biological properties.However,facile fabrication of metallic ultrathin freestanding nanoporous films(UF-NPFs)by dealloying is still challenging.Herein,we report a novel strategy of facile preparation of flexible Cu,Cu_(3)Ag,and CuAg UF-NPFs by dealloying thick Mg-Cu(Ag)-Gd metallic glass ribbons.During dealloying,the local reaction latent heat-induced glass transition of the precursor ribbons leads to the formation of a solid/liquid interface between the initially dealloyed nanoporous layer and the underlying supercooled liquid layer.Due to the bulging effect of in situ generated H2 on the solid/liquid interface,Cu,Cu_(3)Ag,and CuAg UF-NPFs with thicknesses of~200 nm can self-peel off from the outer surface of the dealloying ribbons.Moreover,it was found that the surfaceenhanced Raman scattering(SERS)detection limit of Rhodamine 6G(R6G)on the Cu and CuAg UF-NPF substrates are 10^(-6)M and 10^(-11)M,respectively,which are lower than most of the Cu and Cu-Ag substrates prepared by other methods.This work presents a reliable simple strategy to synthesize a variety of cost effective and flexible metallic UF-NPFs for functional applications.

Nanoporous Au-Sn with solute strain for simultaneously enhanced selectivity and durability during electrochemical CO2 reduction

Electrochemical carbon dioxide reduction meditated by metallic catalysts suffers from restricted selectivity and competition from hydrogen evolution, which sensitively depends on ambiguous contributions of alloying and strain state in bimetallic catalysts. Herein, nanoporous Au-Sn(NPAS) containing trace tin solute in Au lattices is delicately designed to convince real strain effect, while eliminating other undesirable factors, such as alloying, crystal facets and surface composition. Compared with nanoporous gold(NPG), the NPAS with a solute strain of ~2.2% enables more efficient CO2-to-CO conversion, with an efficiency as high as 92% at-0.85 V versus reversible hydrogen electrode(vs. RHE), and the high activity can retain for more than 8 h. The combination of HRTEM and surface valence band photoemission spectra reveals that the tensile strain on the surface of 3 D nanoporous structure promotes the catalytic activity by shifting up the d-band center and strengthening the adsorption of key intermediate *COOH. A small amount of Sn solute in the nanoporous alloy can prevent ligament coarsening effectively and improve the electrochemical stability.

Ultrathin nanoporous metal electrodes facilitate high proton conduction for low-Pt PEMFCs

Design of catalyst layers(CLs)with high proton conductivity in membrane electrode assemblies(MEAs)is an important issue for proton exchange membrane fuel cells(PEMFCs).Herein,an ultrathin catalyst layer was constructed based on Pt-decorated nanoporous gold(NPG-Pt)with sub-Debye-length thickness for proton transfer.In the absence of ionomer incorporation in the CLs,these integrated carbon-free electrodes can deliver maximum mass-specific power density of 198.21 and 25.91 kW·gPt^(-1) when serving individually as the anode and cathode,at a Pt loading of 5.6 and 22.0 pg·cm^(-2),respectively,comparable to the best reported nano-catalysts for PEMFCs.In-depth quantitative experimental measurements and finite-element analyses indicate that improved proton conduction plays a critical role in activation,ohmic and mass transfer polarizations.

Ultrahigh-energy and-power aqueous rechargeable zinc-ion microbatteries based on highly cation-compatible vanadium oxides

Aqueous multivalent-metal-ion intercalation chemistries hold genuine promise to develop safe and powerful microbatteries for potential use in many miniaturized electronics.However,their development is beset by state-of-the-art electrode materials having practical capacities far below their theoretical values.Here we demonstrate that high compatibility between layered transition-metal oxide hosts and hydrated cation guests substantially boost their multi-electron-redox reactions to offer higher capacities and rate capability,based on typical bipolar vanadium oxides preintercalated with hydrated cations(M_(x)V_(2)O_(5)).When seamlessly integrated on Au current microcollectors with a three-dimensional bicontinuous nanoporous architecture that offers high pathways of electron transfer and ion transport,the constituent Zn_(x)V_(2)O_(5) exhibits specific capacity of as high as∼527 mAh g^(−1) at 5 mV s^(−1) and retains∼300 mAh g^(−1) at 200 mV s^(−1) in 1 M ZnSO_(4) aqueous electrolyte,outperforming the M_(x)V_(2)O_(5)(M=Li,Na,K,Mg).This allows aqueous rechargeable zinc-ion microbatteries constructed with symmetric nanoporous Zn_(x)V_(2)O_(5)/Au interdigital microelectrodes as anode and cathode to show high-density energy of∼358 mWh cm^(−3)(a value that is forty-fold higher than that of 4 V/500μAh Li thin film battery)at high levels of power delivery.

双相纳米结构化可实现纳米多孔金属的优异柔性与综合力学性能

纳米多孔金属的力学性能对其在柔性电子领域的应用具有重要意义.本文报道了一种高强度、高硬度、柔韧性好的纳米多孔Cu@Zr-Cu-Al金属玻璃(NP Cu@Zr-Cu-Al MG)复合材料,该材料采用两步脱合金法合成.首先,从Cu_(46)Zr_(23.5)Y_(23.5)Al_(7)合金的伪二元MG体系(Zr_(47)Cu_(46)Al_(7)MG+Y_(47)Cu_(46)Al_(7)MG)中选择性蚀刻活性富Y的MG相,制备了柔性纳米多孔Zr-Cu-Al金属玻璃(NP Zr-Cu-Al MG).进一步蚀刻得到NP Cu@Zr-Cu-Al MG,其中Cu层均匀地覆盖在MG韧带基体上.由于NP Cu@Zr-Cu-Al MG的无裂纹结构和柔性Zr-Cu-Al MG的存在,使其具有良好的柔性.NP Cu@Zr-Cu-Al MG的抗拉强度高达143.9 MPa,纳米硬度高达0.79 GPa.Zr-Cu-Al MG强化相抑制了Cu@Zr-Cu-Al韧带的断裂,有效抑制了裂纹在NP Cu@Zr-Cu-Al MG中的萌生和扩展,提高了复合材料的综合力学性能.NP Cu@Zr-Cu-Al MG可直接用作超级电容器和葡萄糖生物传感器的电极,比纯NP Zr-Cu-Al MG电极展现出更好的电导率和超电容容量.

通过气相合金化-脱合金化实现对纳米多孔金属宏观/微观结构的耦合调控

具有双连续韧带-孔隙结构的纳米多孔金属在催化、电催化、驱动、能源储存和转化领域起着越来越重要的作用.然而,纳米多孔金属的本征脆性一直是制约其实际应用的“阿喀琉斯之踵”.针对这个问题,本文利用不同金属的蒸气压差,提出了一种具有普适性的气相合金化(VPA)-脱合金策略来制备同种金属基底支撑的纳米多孔层.通过调节VPA的时间和温度,结合不同的脱合金方式,可以实现对纳米多孔层宏观厚度和微观结构的调控.此外,具有不同宏观尺寸和形状的金属,如Ag,Au,Cu,Co和Ni,均可以通过此策略制备成纳米多孔结构.更重要的是,由于基底对纳米多孔层的支撑作用,其拉伸塑性得到了大幅度的提高;获得的纳米多孔金属应用于析氢反应时也表现出良好的催化性能.本文研究结果表明气相合金化-脱合金策略在实际应用中具有极大的潜力.

Recent progress on three-dimensional nanoarchitecture anode materials for lithium/sodium storage

High-performance batteries with high density and low cost are needed for the development of largescale energy storage fields such as electric vehicles and renewable energy systems.The anode with threedimensional(3D)nanoarchitecture is one of the most attractive candidates for high-performance lithiumion batteries(LIBs)and sodium-ion batteries(SIBs)due to its efficient electron/ion transport and high active material mass loading.Although some important breakthroughs have been made in 3D nanoarchitecture anode materials,more improvements are still needed for high cycling stability and high energy density.Herein,the latest research progress of 3D nanoarchitecture anode materials for LIBs and SIBs is reviewed,including nanoporous metal,nanoporous graphene,and their derived foams.Specifically,the storage properties of Li/Na ions,the kinetics of ion/electron transport,and specific chemical interactions are discussed based on the structure design.In addition,the research strategies and structural characteristics of 3D nanoarchitecture anode materials are summarized,providing a reference for the further development of LIBs and SIBs.Meanwhile,the future research directions of LIBs and SIBs have also prospected.

Nickel nanopore arrays as promising current collectors for constructing solid-state supercapacitors with ultrahigh rate performance

In this work, nickel nanopore arrays with a highly-oriented nanoporous structure inherited from por- ous alumina membranes were used as nanostructured current collectors for constructing ultrahigh rate solid-state supercapacitors. A thin layer of poly（3,4-ethylenediox- ythiophene） （PEDOT） as electroactive materials was conformally coated onto nickel nanopores to form heterostructured electrodes. The as-prepared electrodes have a large specific surface area to ensure a high capacity, and the highly-oriented nanoporous structure of nickel nanopores reduces the ion transport resistance, allowing the ions in the solid-state electrolytes to quickly access the PEDOT surface during the fast charge-discharge process. As a result, the assembled solid-state supercapacitor in a symmetric configuration exhibits an ideal capacitive behavior and a superior rate capability even at an ultrahigh scan rate of 50 V· s^-1.