Dealloying Ag–Al Alloy to Prepare Nanoporous Silver as a Substrate for Surface‐Enhanced Raman Scattering: Effects of Structural Evolution and Surface Modification

Sensitive detection of molecules by using the surface‐enhanced Raman scattering (SERS) technique depends on the nanostructured metallic substrate and many efforts have been devoted to the preparation of SERS substrates with high sensitivity, stability, and reproducibility. Herein, we report on the fabrication of stable monolithic nanoporous silver (NPS) by chemical dealloying of Ag–Al precursor alloys with an emphasis on the effect of structural evolution on SERS signals. It was found that the dealloying conditions had great influence on the morphology (the ligament/pore size) and the crystallization status, which determined the SERS signal of rhodamine 6G on the NPS. NPS with small pores, low residual Al, and perfect crystallization gave high SERS signals. A high enhancement factor of 7.5×10⁵ was observed on bare NPS obtained by dealloying Ag₃₀Al₇₀ in 2.5 wt % HCl at room temperature followed by 15 min aging at around 85 °C. After coating Ag nanoparticles on the NPS surface, the enhancement factor increased to 1.6×10⁸ owing to strong near‐field coupling between the ligaments and nanoparticles.     

Nanoporous platinum–cobalt alloy for electrochemical sensing for ethanol,hydrogen peroxide,and glucose

Nanoporous platinum–cobalt (NP–PtCo) alloy with hierarchical nanostructure is straightforwardly fabricated by dealloying PtCoAl alloy in a mild alkaline solution. Selectively etching Al resulted in a hierarchical three-dimensional network nanostructure with a narrow size distribution at 3 nm. The as-prepared NP–PtCo alloy shows superior performance toward ethanol and hydrogen peroxide (H₂O₂) with highly sensitive response due to its unique electrocatalytic activity. In addition, NP–PtCo also exhibits excellent amperometric durability and long-term stability for H₂O₂ as well as a good anti-interference toward ascorbic acid, uric acid, and dopamine. The hierarchical nanoporous architecture in PtCo alloy is also highly active for glucose sensing electrooxidation and sensing in a wide linear range. The NP–PtCo alloy holds great application potential for electrochemical sensing with simple preparation, unique catalytic activity, and high structure stability.     

Electrodeposition of Fe70Pd30 nanowires from a complexed ammonium–sulfosalicylic electrolyte with high stability

A highly stable plating bath for the electrodeposition of Fe–Pd nanowires into nanoporous alumina templates has been developed. Complexing of both metal ions and exchanging Fe²⁺ by Fe³⁺ avoid chemical reduction of Pd ions and, therefore, undesirable deposition. By using a pulse potential mode and appropriate adjustment of deposition potentials homogeneously filled templates without surface deposits and nanowires close to the desired composition of Fe₇₀Pd₃₀ have been achieved. These alloy nanowires represent a key step towards nanoactuators based on magnetic shape memory alloys.     

A Nanoporous PdCo Alloy as a Highly Active Electrocatalyst for the Oxygen‐Reduction Reaction and Formic Acid Electrooxidation

A nanoporous (NP) PdCo alloy with uniform structure size and controllable bimetallic ratio was fabricated simply by one‐step mild dealloying of a PdCoAl precursor alloy. The as‐made alloy consists of a nanoscaled bicontinuous network skeleton with interconnected hollow channels that extend in all three dimensions. With a narrow ligament size distribution around 5 nm, the NP PdCo alloy exhibits much higher electrocatalytic activity towards the oxygen‐reduction reaction (ORR) with enhanced specific and mass activities relative to NP Pd and commercial Pt/C catalysts. A long‐term stability test demonstrated that NP PdCo has comparable catalytic durability with less loss of ORR activity and electrochemical surface area than Pt/C. The NP PdCo alloy also shows dramatically enhanced catalytic activity towards formic acid electrooxidation relative to NP Pd and Pd/C catalysts. The as‐made NP PdCo holds great application potential as a promising cathode as well as an anode electrocatalyst in fuel cells with the advantages of superior catalytic performance and easy preparation.     

Self‐Assembling Synthesis of Free‐standing Nanoporous Graphene–Transition‐Metal Oxide Flexible Electrodes for High‐Performance Lithium‐Ion Batteries and Supercapacitors

The synthesis of nanoporous graphene by a convenient carbon nanofiber assisted self‐assembly approach is reported. Porous structures with large pore volumes, high surface areas, and well‐controlled pore sizes were achieved by employing spherical silica as hard templates with different diameters. Through a general wet‐immersion method, transition‐metal oxide (Fe₃O₄, Co₃O₄, NiO) nanocrystals can be easily loaded into nanoporous graphene papers to form three‐dimensional flexible nanoarchitectures. When directly applied as electrodes in lithium‐ion batteries and supercapacitors, the materials exhibited superior electrochemical performances, including an ultra‐high specific capacity, an extended long cycle life, and a high rate capability. In particular, nanoporous Fe₃O₄–graphene composites can deliver a reversible specific capacity of 1427.5 mAh g^?1 at a high current density of 1000 mA g^?1 as anode materials in lithium‐ion batteries. Furthermore, nanoporous Co₃O₄–graphene composites achieved a high supercapacitance of 424.2 F g^?1. This work demonstrated that the as‐developed freestanding nanoporous graphene papers could have significant potential for energy storage and conversion applications.     

Fine tuning the surface acidity of titanate nanostructures

The effect of protonation on the surface acidic properties of titanate nanowires (TiONWs) was investigated. Nanowires were synthesized by the alkali hydrothermal method which resulted in one dimensional nanostructures of large external surface area and well-defined lamellar interlayer structure. The Na⁺/H⁺ ratio in the structure can be tuned by ion-exchange. Our aim was to characterize the morphology of the as-synthesized nanostructures by HRTEM and SEM measurements and assess their surface acidity using in situ infrared spectroscopic measurements and temperature programmed desorption. It was found that the numbers of Lewis and Brönsted acidic sites in the Na-form and the H-form of the TiONWs is different. The ratio and the nature of acidic sites can be tuned by the ion exchange process. The wire-like morphology and the tunable acidity are features of titanate nanowires that may render them a promising material in various heterogeneous catalytic applications.     

A novel synthesis of ultrathin CoPt3 nanowires by dealloying larger diameter Co99Pt1 nanowires and subsequent stress-induced crack propagation

A novel approach to the fabrication of ultrathin CoPt₃ nanowires with a diameter of a few nanometers has been developed, by taking advantage of the volume shrinkage and formation of nanoporous structures upon dealloying electrodeposited Co₉₉Pt₁ nanowires (28 nm in diameter), followed by an ultrasonication treatment. The as-produced ultrathin CoPt₃ nanowires have an average diameter of 5 nm and lengths of up to 10 μm, and are found to be ferromagnetic at room temperature.     

Nano‐Roughening a Pt Disk Microelectrode via Electrochemical Alloying‐Dealloying in Ionic Liquid Electrolyte

A green chemistry method to nano‐roughen a Pt disk microelectrode has been successfully developed via electrochemical alloying‐dealloying in an ionic liquid bath comprising of ZnCl₂ and 1‐ethyl‐3‐methylimidazolium chloride. The nano‐roughened Pt layer possesses bark‐like nanoporous structures characteristic of nano‐sized aggregates separated by nano‐cracks whose width ranging from around 50 to 200 nm. The nano‐roughened microelectrode possesses high surface area and diffusional properties typical of a microelectrode. Electrochemical oxidation and reduction of nitrite have been studied as an example for demonstrating that the nano‐roughened microelectrode is a promising technique for electroanalysis and electrocatalysis applications.     

Facile fabrication of nanoporous PdFe alloy for nonenzymatic electrochemical sensing of hydrogen peroxide and glucose

Nanoporous (NP) PdFe alloy is easily fabricated through one step mild dealloying of PdFeAl ternary source alloy in NaOH solution. Electron microscopy characterization demonstrates that selectively dissolving Al from PdFeAl alloy generates three-dimensional bicontinuous nanospongy architecture with the typical ligament size around 5 nm. Electrochemical measurements show that the NP-PdFe alloy exhibits the superior electrocatalytic activity and durability towards hydrogen peroxide (H₂O₂) detection compared with NP-Pd and commercial Pd/C catalysts. In addition, NP-PdFe performs high sensing performance towards H₂O₂ in a wide linear range from 0.5 to 6 mM with a low detection limit of 2.1 μM. This nanoporous structure also can sensitively detect glucose over a wide concentration range (1–32 mM) with a low detection limit of 1.6 μM and high resistance against chloride ions. Along with these attractive features, the as-made NP-PdFe alloy also has a good anti-interference towards ascorbic acid, uric acid, and dopamine.     

Simultaneous Al2O3 Doping and Sulfation in Hierarchically Porous ZrO2 Solid Acids by an One‐pot Synthesis for Enhanced Recycling Catalytic Performances

Alumina doping and sulfation in hierarchically porous zirconia solid acids have been achieved simultaneously via one‐pot and bi‐surfactant‐assisted self‐assembly process, using aluminum sulfate as both Al and SO₄^2? sources. The prepared composite solid acids showed much enhanced acidity and recycling catalytic activity for an esterification reaction compared with sulfated zirconia without alumina doping and Al‐doped sulfated zirconia without hierarchically porous structure.     

纳米多孔Ni和NiO的制备及电催化析氧性能

采用快速凝固与脱合金相结合的方法制备了纳米多孔Ni, 经热处理氧化获得纳米多孔NiO, 利用X射线衍射仪(XRD)、 扫描电子显微镜(SEM)、 透射电子显微镜(TEM)和氮气吸附-脱附仪(BET)对纳米多孔Ni和NiO的物相、 形貌结构和孔径分布进行了表征, 并通过循环伏安、 稳态极化和电化学阻抗分析研究了电极的电催化析氧性能. 结果表明, 由Ni₃₀Al₇₀所得纳米多孔Ni具有多层次纳米多孔结构, 在10 mA/cm ²电流密度下析氧过电位仅为224 mV, 交换电流密度为0.63297 mA/cm ², 表观活化自由能为40.297 kJ/mol, 经1000次循环后, 过电位降低了5 mV(j=10 mA/cm ²), 表现出良好的催化稳定性和耐久性; 热处理氧化降低了NiO的比表面积与电化学活性面积, 平衡电位下扩散传质速率明显减小, 析氧活性较Ni电极有所下降.     

A Dewetted‐Dealloyed Nanoporous Pt Co‐Catalyst Formed on TiO2 Nanotube Arrays Leads to Strongly Enhanced Photocatalytic H2 Production

Pt nanoparticles are typically decorated as co‐catalyst on semiconductors to enhance the photocatalytic performance. Due to the low abundance and high cost of Pt, reaching a high activity with minimized co‐catalyst loadings is a key challenge in the field. We explore a dewetting‐dealloying strategy to fabricate on TiO₂ nanotubes nanoporous Pt nanoparticles, aiming at improving the co‐catalyst mass activity for H₂ generation. For this, we sputter first Pt‐Ni bi‐layers of controllable thickness (nm range) on highly ordered TiO₂ nanotube arrays, and then induce dewetting‐alloying of the Pt‐Ni bi‐layers by a suitable annealing step in a reducing atmosphere: the thermal treatment causes the Pt and Ni films to agglomerate and at the same time mix with each other, forming on the TiO₂ nanotube surface metal islands of a mixed PtNi composition. In a subsequent step we perform chemical dealloying of Ni that is selectively etched out from the bimetallic dewetted islands, leaving behind nanoporous Pt decorations. Under optimized conditions, the nanoporous Pt‐decorated TiO₂ structures show a>6 times higher photocatalytic H₂ generation activity compared to structures modified with a comparable loading of dewetted, non‐porous Pt. We ascribe this beneficial effect to the nanoporous nature of the dealloyed Pt co‐catalyst, which provides an increased surface‐to‐volume ratio and thus a more efficient electron transfer and a higher density of active sites at the co‐catalyst surface for H₂ evolution.     

Three‐component solventless Strecker synthesis of α‐aminonitriles catalysed by a renewable sulfonated nanoporous carbon catalyst (CMK‐5‐SO3H)

The one‐pot three‐component synthesis of a variety of α‐aminonitriles has been studied using a catalytic amount of a sulfonic acid‐functionalized ordered nanoporous carbon catalyst, CMK‐5‐SO₃H, at room temperature under solvent‐free reaction conditions. The heterogeneous catalyst could be readily isolated from the reaction mixture and reused at least ten times without significant loss in activity. A clean, rapid and simple method for the preparation of α‐aminonitriles using the recoverable CMK‐5‐SO3H catalyst is described.     

Nanoporous ultra-high-entropy alloys containing fourteen elements for water splitting electrocatalysis

High-entropy alloys (HEAs) are near-equimolar alloys comprising five or more elements. In recent years, catalysis using HEAs has attracted considerable attention across various fields. Herein, we demonstrate the facile synthesis of nanoporous ultra-high-entropy alloys (np-UHEAs) with hierarchical porosity via dealloying. These np-UHEAs contain up to 14 elements, namely, Al, Ag, Au, Co, Cu, Fe, Ir, Mo, Ni, Pd, Pt, Rh, Ru, and Ti. Furthermore, they exhibit high catalytic activities and electrochemical stabilities in the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in acidic media, superior to that of commercial Pt/graphene and IrO₂ catalysts. Our results offer valuable insights for the selection of elements as catalysts for various applications.

Nanoporous ultra-high-entropy alloys containing 14 elements (Al, Ag, Au, Co, Cu, Fe, Ir, Mo, Ni, Pd, Pt, Rh, Ru, and Ti) were obtained by dealloying. The products showed excellent electrocatalytic performance for water splitting in acidic media.     

Utilization of Active Ni to Fabricate Pt–Ni Nanoframe/NiAl Layered Double Hydroxide Multifunctional Catalyst through In Situ Precipitation

Integration of different active sites into metallic catalysts, which may impart new properties and functionalities, is desirable yet challenging. Herein, a novel dealloying strategy is demonstrated to decorate nickel–aluminum layered double hydroxide (NiAl–LDH) onto a Pt–Ni alloy surface. The incorporation of chemical etching of Pt–Ni alloy and in situ precipitation of LDH are studied by joint experimental and theoretical efforts. The initial Ni‐rich Pt–Ni octahedra transform by interior erosion into Pt₃Ni nanoframes with enlarged surface areas. Furthermore, owing to the basic active sites of the decorated LDH together with the metallic sites of Pt₃Ni, the resulting Pt–Ni nanoframe/NiAl–LDH composites exhibit excellent catalytic activity and selectivity in the dehydrogenation of benzylamine and hydrogenation of furfural.     

A three-dimensional hierarchical nanoporous PdCu alloy for enhanced electrocatalysis and biosensing

Nanoporous copper (NPC) obtained by dealloying CuAl alloy is used as both three-dimensional template and reducing agent for the fabrication of nanoporous PdCu alloy with hollow ligaments by a simple galvanic replacement reaction with H₂PdCl₄ aqueous solution. Electron microscopy and X-ray diffraction characterizations demonstrate that after the replacement reaction, the ligaments become hollow tubular structure and the ligament shell is also comprised of small pores and nanoparticles with a typical size of ∼4 nm (third order porosity). The as-prepared nanotubular mesoporous PdCu alloy (NM-PdCu) structure exhibits remarkably improved electrocatalytic activity towards the oxidation of formic acid and H₂O₂ compared with nanoporous Pd (NP-Pd), and can be used for sensitive electrochemical sensing applications. After coupled with glucose oxidase (GOx), the enzyme modified NM-PdCu electrode can sensitively detect glucose over a wide linear range (0.5–20 mM).     

Silver UPD ultra-thin film modified nanoporous gold electrode with applications in the electrochemical detection of chloride

Nanoporous noble metals are usually expected to exhibit much higher surface areas than smooth ones, making them of particular importance in many electrochemical applications. This paper describes a simple electrochemical method to modify a nanoporous Au (NPG) surface by using an under potentially deposited (UPD) Ag adlayer. The NPG electrode was obtained by the dealloying of Zn from Au_xZn_1−x in a 40-60 mol% zinc chloride-1-ethyl-3-methylimidazolium chloride (ZnCl₂-EMIC) ionic liquid. The Ag UPD modified nanoporous gold (NPG/Ag(UPD)) electrode possessed dual properties, including an intrinsic high surface area from the nanoporous structure and the characteristics of the Ag UPD adlayer. The potential utility of using NPG/Ag(UPD) for sensors was demonstrated by its excellent sensitivity and selectivity in the electrochemical determination of chloride ions. An atomic scale metal monolayer obtained in the UPD process was selected as a sensing agent. The long-term storability and operational stability of the electrode were strongly demonstrated. Specifically, two couples of redox waves at ∼552 mV and ∼272 mV, respectively, were observed in the cyclic voltammograms (CVs) of the NPG/Ag(UPD) after the adsorption of chloride ions. The first couple of redox waves was related to the UPD and silver stripping and the second couple of redox waves was induced by the adsorption of Cl⁻. The Cl⁻ adsorption process on the NPG/Ag(UPD) electrode followed the transient Langmuir adsorption kinetic model. The ratio of the integrated charges for these two anodic stripping peaks was selectively used to determine dilute chloride ion levels. The calibration curve was linear in the Cl⁻ concentration range of 0.5-30.0 μM.     

Fabrication of porous bismuth by electrochemical dealloying of Sn–Bi alloys: From microporous structures to nanowire matrix composites

The fabrication of three-dimensional (3D) porous bismuth by electrochemical dealloying of two-phase Sn–Bi alloys was investigated. The results show that the resulting porous bismuth changes from a microporous structure composed of bismuth microparticles to an aligned nanowire matrix composite as the Bi content in the Sn–Bi master alloy decreases. Single-crystal bismuth nanowires growing in the [110] direction were fabricated by the selective dissolution of the Sn phase from an alloy with ultralow Bi content. The influence of the two states of elemental Bi existing in smelted Sn–Bi alloys during dealloying was systematically analyzed and discussed. This report presents a novel strategy for direct fabrication of bismuth nanowires by electrochemical dealloying.     

Nanoporous PtRu Alloys with Unique Catalytic Activity toward Hydrolytic Dehydrogenation of Ammonia Borane

Nanoporous (NP) PtRu alloys with three different bimetallic components were straightforwardly fabricated by dealloying PtRuAl ternary alloys in hydrochloric acid. Selective etching of aluminum from source alloys generates bicontinuous network nanostructures with uniform size and structure. The as‐made NP‐PtRu alloys exhibit superior catalytic activity toward the hydrolytic dehydrogenation of ammonia borane (AB) than pure NP‐Pt and NP‐Ru owing to alloying platinum with ruthenium. The NP‐Pt₇₀Ru₃₀ alloy exhibits much higher specific activity toward hydrolytic dehydrogenation of AB than NP‐Pt₃₀Ru₇₀ and NP‐Pt₅₀Ru₅₀. The hydrolysis activation energy of NP‐Pt₇₀Ru₃₀ was estimated to be about 38.9 kJ mol^?1, which was lower than most of the reported activation energy values in the literature. In addition, recycling tests show that the NP‐Pt₇₀Ru₃₀ is still highly active in the hydrolysis of AB even after five runs, which indicates that NP‐PtRu alloy accompanied by the network nanoarchitecture is beneficial to improve structural stability toward the dehydrogenation of AB.     

多孔铜基催化剂的制备及对苯甲醇的选择性催化氧化

采用去合金化法制备了多孔铜(PC), 并以此为还原剂和模板与含有贵金属离子的溶液进行置换反应, 简单有效地制备了多孔M/PC(M=Ag, Au, Pt, Pd)双金属催化剂, 并对样品的形貌\, 结构和化学组成进行了表征, 利用苯甲醇气相选择性催化氧化实验评价了其催化性能. 实验结果表明, 所制备的多孔铜基催化剂具有良好的双金属协同催化效应, 对苯甲醇气相选择性氧化具有很好的催化活性和选择性, 其中Ag/PC具有最优的催化性能.