Acetic acid-assisted mild dealloying of fine CuPd nanoalloys achieving compressive strain toward high-efficiency oxygen reduction and ethanol oxidation electrocatalysis

Dealloying by which the transition metal is partially or completely leached from an alloy precursor is an effective way to optimize the fundamental effects for further enhancing the electrocatalysis of a catalyst.Herein,to address the deficiencies associated with the commonly used dealloying methods,for example,electrochemical and sulfuric acid/nitric acid treatment,we report an acetic acid-assisted mild strategy to dealloy Cu atoms from the outer surface layers of CuPd alloy nanoparticles to achieve high-efficiency electrocatalysis for oxygen reduction and ethanol oxidation in an alkaline electrolyte.The leaching of Cu atoms by acetic acid exerts an additional compressive strain effect on the surface layers and exposes more active Pd atoms,which is beneficial for boosting the catalytic performance of a dealloyed catalyst for the oxygen reduction reaction(ORR)and the ethanol oxidation reaction(EOR).In particular,for ORR,the CuPd nanoparticles with a Pd/Cu molar ratio of 2:1 after acetic dealloying show a half-wave potential of 0.912 V(vs.RHE)and a mass activity of 0.213 AmgPd^(-1) at 0.9 V,respectively,while for EOR,the same dealloyed sample has a mass activity and a specific activity of 8.4 Amg^(-1) and 8.23 mA cm^(-2),respectively,much better than their dealloyed counterparts at other temperatures and commercial Pd/C as well as a Pt/C catalyst.

Dealloying of an amorphous TiCuRu alloy results in a nanostructured electrocatalyst for hydrogen evolution reaction

Development of an electrocatalyst that is cheap and has good properties to replace conventional noble metals is important for H_(2) applications.In this study,dealloying of an amorphous Ti_(37)Cu_(60)Ru_(3) alloy was performed to prepare a freestanding nanostructured hydrogen evolution reaction(HER)catalyst.The effect of dealloying and addition of Ru to TiCu alloys on the microstructure and HER properties under alkaline conditions was investigated.3 at.%Ru addition in Ti_(40)Cu_(60) decreases the overpotential to reach a current density of 10mA cm^(-2) and Tafel slope of the dealloyed samples to 35 and 34mV dec−1.The improvement of electrocatalytic properties was attributed to the formation of a nanostructure and the modification of the electronic structure of the catalyst.First-principles calculations based on density function theory indicate that Ru decreases the Gibbs free energy of water dissociation.This work presents a method to prepare an efficient electrocatalyst via dealloying of amorphous alloys.

Development of 3D bicontinuous metal-intermetallic composites through subsequent alloying process after liquid metal dealloying

This study presents a novel process for the fabrication of metal-intermetallic composites with a 3D bicontinuous structure, achieved through a combination of liquid metal dealloying(LMD) and subsequent alloying. Initially, porous Ti structures are produced using the LMD process, followed by immersion in a molten Mg-3Al(wt%) metal. Due to the higher thermodynamic miscibility of Al with Ti compared to Mg, the concentration of Al in the Ti matrix increases as the immersion time increases. This results in a sequential phase transition within the Ti matrix: α-Ti → Ti_(3)Al → Ti Al. The phase transition considerably affects the hardness and strength of the composite material,with the Mg-Ti_(3)Al-Ti Al composite exhibiting a maximum hardness nearly twice as high as that of the conventional Mg-Ti composite. This innovative process holds potential for the development of various bicontinuous metal-intermetallic composites.

Evolution of porous structure with dealloying corrosion on Gasar Cu-Mn alloy

The evolution of nanoporous structure with dealloying condition was investigated, thus, the mechanism of porous structure evolution was uncovered. The Gasar Cu-Mn alloy was dealloyed by room and elevated temperature chemical corrosion, low and high current level electrochemical corrosion, four types of porous structures, including uneven corrosion pits, hybrid porous, haystack type and bicontinuous model were prepared by chemically and electrochemically dealloying the porous Cu-34.6%Mn alloy made by the Gasar process. Then, the surface diffusion coefficient(DS) and the diffusion frequency(kD) of Cu atom, as well as the dissolution frequency(kE) of Mn atom were calculated with dealloying condition. The dealloyed morphologies for room temperature chemical corrosion and low current level electrochemical corrosion were similar due to the same DS. While the dealloyed structures changed from bulk hybrid porous structure to bicontinuous porous film with decreasing kD/kE.

Preparation and electro-catalytic activity of nanoporous palladium by dealloying rapidly-quenched Al_(70)Pd_(17)Fe_(13) quasicrystalline alloy

The formation of nanoporous Pd was studied by electro-chemical dealloying a rapidly-quenched Al70Pd17Fe13 quasicrystal alloy in dilute NaCl aqueous solution,and the electro-catalytic activity of the nanoporous Pd towards methanol electro-oxidation was evaluated by cyclic voltammetry in 1 mol/L KOH solution.XRD and TEM analyses revealed that nano-decomposition of quasicrystal grains occurred in the initial stage of dealloying,and the fully dealloyed sample was composed of FCC-Pd phase.Scanning electron microscopy observation indicated that a maze-like nanoporous pattern was formed in the dealloyed sample,consisting of percolated pores of 5.20 nm in diameter in a skeleton of randomly-orientated Pd nano-ligaments with a uniform thickness of^5 nm.A retention of^12 at.%Al in the Pd nano-ligments was determined by energy dispersive X-ray spectroscopy(EDS).The nanoporous Pd demonstrated obvious electro-catalytic activity towards methanol electro-oxidation in alkaline environment.

Effect of heat treatment of Mn-Cu precursors on morphology of dealloyed nanoporous copper

Nanoporous copper with nano-scale pore size was synthesized by dealloying Mn-Cu precursor alloy using a free corrosion method. The effects of heat treatment of Mn-Cu precursors on alloy phase, morphology and composition of the resultant nanoporous copper were investigated. It is revealed that the compositions distribute homogeneously in the bulk Mn-Cu precursors, which consequently results in a more fully dealloying for forming nanoporous copper. The alloy phase changes from Cuo.a9Mno.51 and Cuo.21Mno.79 of non-thermally treated precursor to Cuo.33Mn0.67 of heat treated alloy. The residual Mn content in nanoporous copper is decreased from 12.97% to 2.04% （molar fraction） made from the precursor without and with 95 h heat treatment. The typical pore shape of nanoporous copper prepared by dealloying the precursor without the heat treatment is divided into two different zones： the uniform bi-continuous structure zone and the blurry or no pore structure zone. Nanoporous copper is of a uniform sponge-like morphology made from the heat-treated precursor, and the average ligament diameter is 40 nm, far smaller than that from the non-thermally treated precursor, in which the average ligament diameter is estimated to be about 70 nm.

Fabrication of nanoporous Ni and NiO via a dealloying strategy for water oxidation catalysis

Nickel oxides and(oxy)hydroxides are promising replacements for noble-metal-based catalysts owing to their high activity and good long-term stability for the oxygen evolution reaction(OER). Herein, we developed nanoporous Ni by a method of combined rapid solidification and chemical dealloying. Subsequently,nanoporous Ni O was obtained via heating treatment, the macropore and skeleton sizes of the NiO originated from Ni10Al90 alloy are 100–300 nm and 80–200 nm, respectively. Benefiting from the multi-stage nanoporous structure and high specific surface area, the nanoporous NiO demonstrates an outstanding OER, reaching 20 mA cm-2 at an overpotential of 356 mV in 1 M KOH. The corresponding Tafel slope and apparent activation energy are measured to be 76.73 mV dec-1 and 29.0 kJ mol-1, respectively. Moreover,kinetic analysis indicates that the Ni O catalyst shows pseudocapacitive characteristics, and the improved current is attributed to the high-rate pseudocapacitive behavior that efficiently maintains increased nickel redox cycling to accelerate the reaction rates. After 1000 cycles of voltammetry, the overpotential of the NiO decreases by 22 mV(j = 10 mA cm-2), exhibiting excellent stability and durability.

Degradation efficiency of Mg_(65)Cu_(25-x)Ag_(x)Y_(10) nanoporous dealloyed ribbons on pesticide wastewater

Dealloyed ribbons with a layer of networked nanoporous structure of different pore sizes were fabricated by dealloying the as-spun Mg_(65)Cu_(25-x)Ag_(x)Y_(10)(x=0,5,10,at.%)ribbons in dilute H_(2)SO_(4) solution in order to enhance the degradation efficiency of pesticide wastewater.Compared to the as-spun ribbons,it is found that the dealloyed ribbons with the networked nanoporous structure exhibit higher degradation efficiency due to their large specific surface areas and enough active sites for the degradation process.Both the average pore sizes of the nanoporous structure and the degradation efficiency of the pesticide wastewater increase with the increase of Ag addition in the dealloyed ribbons.The maximum degradation efficiency up to 95.8%is obtained for the Mg_(65)Cu_(15)Ag_(10)Y_(10)dealloyed ribbon under the optimal conditions of pH being 3,the initial cis-cypermethrin concentration being 500 mg/L,and the dosage of dealloyed ribbon being 1.33 g/L.

Fabrication of high-strength duplex nanoporous Cu by dealloying a dual-phase Mg-Cu precursor alloy

Duplex nanoporous Cu was successfully fabricated by dealloying a dual-phase Mg-Cu precursor alloy consisting of intermetallic Mg2Cu and MgCu2.The duplex nanoporous Cu with embedded nanoporous struts exhibited highly enhanced strength compared to the typical monolithic nanoporous Cu under both compressive and flexural test conditions at room temperature;the duplex np-Cu sample exhibited a 12 times higher compressive strength and a 40 times greater flexural strength than the monolithic np-Cu sample.Factors responsible for the strength enhancement in the duplex nanoporous Cu are discussed.

Dealloying-induced dual-scale nanoporous indium-antimony anode for sodium/potassium ion batteries

InSb alloy is a promising candidate for sodium/potassium ion batteries(SIBs/PIBs)but challenged with achieving high performance by dramatic volumetric changes.Herein,nanoporous(np)-InSb with dualscale phases(cubic/hexagonal(C/H)-InSb)was fabricated by chemical dealloying of ternary Mg-In-Sb precursor.Operando X-ray diffraction(XRD)and ex-situ characterizations well rationalize the dealloying/alloying mechanisms and the formation of dual-scale microstructures/phases.As an anode for SIB/PIBs,the np-InSb electrode exhibits superior reversible capacities and lifespan compared with the monometallic porous(p)-In electrode,stemming from the dealloying-induced dual-scale nanoporous architecture and alloying strategy with proper composition.The operando XRD results demonstrate that the(de)sodiated mechanism of the np-InSb electrode involves a two-step(de)alloying process,while the(de)potassiated mechanism is associated with a full electrochemically-driven amorphization upon cycling.Additionally,the gas evolution during the(dis)charge process was monitored by on-line mass spectrometry.

Facile synthesis and enhanced catalytic activity of electrochemically dealloyed platinum–nickel nanoparticles towards formic acid electro-oxidation

To obtain the electrocatalyst with an improved electrocatalytic performance towards formic acid electrooxidation(FAEO), a simple impregnation method is used to prepare Pt3Ni nanoparticles loaded on carbon black, assisted with electrochemically dealloying process. The X-ray powder diffraction(XRD) results as well as transmission electron microscopy(TEM) analysis of as-synthesized electrocatalyst demonstrates that the reduction temperature has a great influence on the FAEO activity of the dealloyed Pt3Ni nanoparticles. X-ray photoelectron spectroscopy(XPS) analyses confirm the variation in the electronic structure of platinum by incorporation of nickel atoms which reduces chemisorption of toxic carbon monoxide and promotes the dehydrogenation pathway of FAEO. The size of the dealloyed Pt3Ni nanoparticles remains within the range of about 2.7 nm. All electrochemical results illustrate that the performance of the asobtained electrocatalyst towards the FAEO is significantly enhanced. Moreover, the carbon black content,incorporation of Ni atoms, and reduction temperature conditions have been proven to be the key factors for modification of the crystal structure and morphology which leads to enhanced catalytic performance.

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.

Molecular Dynamics Simulation of Dealloyed Layer-induced Tensile Stress in Cu_3Au

During stress corrosion cracking of Cu3Au alloy, there is a dealloyed layer on its surface because of preferential dissolution of Cu, and there is a linear distribution of Cu vacancy concentration in the dealloyed layer. Molecular dynamics simulation has been done on the three-dimensional crystal (about 148 000 atoms) by employing the embedded-atom method (EAM) potential. Simulation shows that Cu3Au crystal in which there is a dealloyed layer on one surface and one end is fixed will be deflected after relaxing for a long time because of a tensile stress generated at or near the dealloyed layer interface. The deflection and then the tensile stress increase with increasing the depth of dealloyed layer and the vacancy concentration in the dealloyed layer.

Inhomogeneous dealloying kinetics along grain boundaries during liquid metal dealloying

In this study, the inhomogeneous dealloying phenomenon during the liquid metal dealloying(LMD) was investigated using FeNi+Mg and(FeCo)Ni+Mg systems. For the FeNi+Mg system, the inhomogeneous dealloying and wetting of Mg melt occurred along triple junction(TJ) and grain boundary(GB).Temperature increase enhances the inhomogeneous dealloying kinetics and leads to the formation of the plate-shaped abnormal ligaments at the GB region. The energy banlance between a GB energy(γGB)and solid-liquid interface energies(γsl) is the key factor governing the inhomogeneous dealloying and wetting. Particularly, the low-energy twin boundaries were unaffected by the inhomogeneous dealloying.Therefore, precursor microstructure is an important factor determining the final morphology of dealloyed material as well as its physical properties. In the case of the(FeCo)Niprecursor, all TJ and GB were stable against the preferred penetration of Mg melt from 600 ℃ to 800 ℃. It was concluded that a minor addition of alloying elements(VorCr) changes GB characteristics as well as γslof the precursor alloy.Consequently, this significantly influences dealloying mechanisms and final morphology of the dealloyed material. The current findings demonstrate the importance of GB engineering in the precursor materials for the technological application of liquid metal dealloying for the synthesis of advanced structural and functional materials.

In-situ building of multiscale porous NiFeZn/NiZn-Ni heterojunction for superior overall water splitting

The development of efficient nonprecious bifunctional electrocatalysts for water electrolysis is crucial to enhance the sluggish kinetics of the oxygen evolution reaction(OER)and hydrogen evolution reaction(HER).A self-supporting,multiscale porous NiFeZn/NiZn-Ni catalyst with a triple interface heterojunction on nickel foam(NF)(NiFeZn/NiZn-Ni/NF)was in-situ fabricated using an electroplating-annealing-etching strategy.The unique multiinterface engineering and three-dimensional porous scaffold significantly modify the mass transport and electron interaction,resulting in superior bifunctional electrocatalytic performance for water splitting.The NiFeZn/NiZn-Ni/NF catalyst demonstrates low overpotentials of 187 m V for HER and 320 mV for OER at a current density of 600 mA/cm^(2),along with high durability over 150 h in alkaline solution.Furthermore,an electrolytic cell assembled with NiFeZn/NiZn-Ni/NF as both the cathode and anode achieves the current densities of 600 and 1000 m A/cm^(2) at cell voltages of 1.796 and 1.901 V,respectively,maintaining the high stability at 50 mA/cm^(2) for over 100 h.These findings highlight the potential of NiFeZn/NiZn-Ni/NF as a cost-effective and highly efficient bifunctional electrocatalyst for overall water splitting.

Facile electrochemical surface-alloying and etching of Au wires to enable high-performance substrates for surface enhanced Raman scattering

Surface-enhanced Raman Spectroscopy(SERS)is a nondestructive technique for rapid detection of analytes even at the single-molecule level.However,highly sensitive and reliable SERS substrates are mostly fabricated with complex nanofabrication techniques,greatly restricting their practical applications.A convenient electrochemical method for transforming the surface of commercial gold wires/foils into silver-alloyed nanostructures is demonstrated in this report.Au substrates are treated with repetitive anodic and cathodic bias in an electrolyte of thiourea,in a one-pot one-step manner.X-rays absorption fine structure(XAFS)spectroscopy confirms that the AuAg alloy is induced at the surface.The unique AuAg alloyed surface nanostructures are particularly advantageous when served as SERS substrates,enabling a remarkably sensitive detection of Rhodamine B(a detection limit of 10^(-14)M,and uniform strong response throughout the substrates at 10^(-12)M).

Progress and prospects of Mg-based amorphous alloys in azo dye wastewater treatment

Mg-based amorphous alloys exhibit efficient catalytic performance and excellent biocompatibility with a promising application probability,specifically in the field of azo dye wastewater degradation.However,the problems like difficulty in preparation and poor cycling stability need to be solved.At present,Mg-based amorphous alloys applied in wastewater degradation are available in powder and ribbon.The amorphous alloy powder fabricated by ball milling has a high specific surface area,and its reactivity is thousands of times better than that of gas atomized alloy powder.But the development is limited due to the high energy consumption,difficult and costly process of powder recycling.The single roller melt-spinning method is a new manufacturing process of amorphous alloy ribbon.Compared to amorphous powder,the specific surface area of amorphous ribbon is relatively lower,therefore,it is necessary to carry out surface modification to enhance it.Dealloying is a way that can form a pore structure on the surface of the amorphous alloys,increasing the specific surface area and providing more reactive sites,which all contribute to the catalytic performance.Exploring the optimal conditions for Mg-based amorphous alloys in wastewater degradation by adjusting amorphous alloy composition,choosing suitable method to preparation and surface modification,reducing cost,expanding the pH range will advance the steps to put Mg-based amorphous alloys in industrial environments into practice.

A Chemical Dealloying Approach for Pt Surface-enriched Pt_(3)Co Alloy Nanoparticles as Oxygen Reduction Reaction Electrocatalysts

Pt-based alloys are the optimal electrocatalysts for oxygen reduction reaction(ORR)currently.Dealloying of Pt-based alloys has shown to be an effective approach to improving ORR activity.Electrochemical dealloying is controllable for morphology by changing electrochemical parameters but is difficult to scale up due to complex operation and energy consumption.Chemical dealloying is suitable for a large scale but it is not easy to control the morphology because highly corrosive acids(HNO_(3) or H2SO4)are commonly used.In this work,a facile chemical dealloying method for Pt_(3)Co/C has been employed to synthesize electrocatalysts for ORR using weak acids and buffer solutions of different pH,which could slow down the dissolution rate for Co atoms and increase the diffusion time for Pt atoms to improve ORR activity.It can be observed that the mass activities(MA)of the Pt_(3)Co/C alloy after dealloying with H3PO4 and NaH2PO4/Na2HPO4 buffer solution of pH=6 are close to that after electrochemical dealloying process,and are more than two times that of commercial Pt/C.In addition,Pt_(3)Co/C after dealloying with a buffer solution of pH=6 only showed a slight degradation in the half-wave potential and electrochemical surface area(ECSA)after stability test for 5000 cycles,which is more stable than commercial Pt/C.It shows that by controlling pH of the solvent,the ORR activity can be further increased.This facile approach provides a new strategy to control morphology of Pt-based electrocatalysts by chemical dealloying,which can contribute to promising application for cathodic electrocatalysts design of proton exchange membrane fuel cells(PEMFCs).

Macro-/micro-coupling regulation of nanoporous metals via vapor phase alloying-dealloying

Nanoporous metals with bicontinuous ligament-channel structure are of great importance in catalysis,electro-catalysis,actuation and energy storage and conversion.However,the intrinsic brittleness of nanoporous metals has always been the“Achilles heel”that impedes their practical applications.Utilizing the vapor pressure difference of metals,herein we propose a flexible and general vapor phase alloying(VPA)-dealloying strategy to fabricate nanoporous layers supported on the substrates with the same element.By adjusting the VPA time and temperature,the thickness and microstructure control over nanoporous layers can be realized by combining with diverse dealloying methods.Besides,various metals including Ag,Au,Cu,Co and Ni with different macro sizes and shapes can be fabricated into nanoporous structures through this method.More importantly,the greatly improved tensile ductility owing to the nanoporous layersubstrate structure and well enhanced catalytic performance for hydrogen evolution reaction of the as-fabricated nanoporous metals signify great potentials of the VPA-dealloying strategy for practical applications.

Dealloying corrosion of anodic and nanometric Mg41Nd5 in solid solution-treated Mg-3Nd-1Li-0.2Zn alloy

The microstructure and chemical compositions of the solid solution-treated Mg-3 Nd-1 Li-0.2 Zn alloy were characterized using optical microscope,scanning electron microscope(SEM),transmission electron microscope(TEM),electron probe micro-analyzer(EPMA)and X-ray photoelectron spectroscopy(XPS).The corrosion behaviour of the alloy was investigated via electrochemical polarization,electrochemical impedance spectroscopy(EIS),hydrogen evolution test and scanning Kelvin probe(SKP).The results showed that the microstructure of the as-extruded Mg-3 Nd-1 Li-0.2 Zn alloy containedα-Mg matrix and nanometric second phase Mg_(41)Nd_(5).The grain size of the alloy increased significantly with the increase in the heat-treatment duration,whereas the volume fraction of the second phase decreased after the solid solution treatment.The surface film was composed of oxides(Nd_(2)O_(3),Mg O,Li_(2)O and Zn O)and carbonates(Mg CO3 and Li_(2)CO3),in addition to Nd.The as-extruded alloy exhibited the best corrosion resistance after an initial soaking of 10 min,whereas the alloy with 4 h-solution-treatment possessed the lowest corrosion rate after a longer immersion(1 h).This can be attributed to the formation of Nd-containing oxide film on the alloys and a dense corrosion product layer.The dealloying corrosion of the second phase was related to the anodic Mg_(41)Nd_(5)with a more negative Volta potential relative toα-Mg phase.The preferential corrosion of Mg_(41)Nd_(5)is proven by in-situ observation and SEM.The solid solution treatment of Mg-3 Nd-1 Li-0.2 Zn alloy led to a shift in corrosion type from pitting corrosion to uniform corrosion under long-term exposure.