Electrochemical Synthesis of Mesoporous Pt–Au Binary Alloys with Tunable Compositions for Enhancement of Electrochemical Performance

Facile one-step synthesis of mesoporous Pt-based alloy nanospheres for ethanol electrooxidation

Mesoporous Pt-based alloy nanospheres were prepared via a one-step soft-template strategy. The regulation of electronic structure, lattice contraction and abundant active sites endowed the mesoporous Pt-based catalysts with remarkable electrochemical activity towards ethanol oxidation reaction.

Precision Synthesis of Bimetallic Nanoparticles via Nanofluidics in Nanopipets

Bimetallic nanoparticles often show properties superior to their single-component counterparts. However, the large parameter space, including size, structure, composition, and spatial arrangement, impedes the discovery of the best nanoparticles for a given application. High-throughput methods that can control the composition and spatial arrangement of the nanoparticles are desirable for accelerated materials discovery. Herein, we report a methodology for synthesizing bimetallic alloy nanoparticle arrays with precise control over their composition and spatial arrangement. A dual-channel nanopipet is used, and nanofluidic control in the nanopipet further enables precise tuning of the electrodeposition rate of each element, which determines the final composition of the nanoparticle. The composition control is validated by finite element simulation as well as electrochemical and elemental analyses. The scope of the particles demonstrated includes Cu-Ag, Cu-Pt, Au-Pt, Cu-Pb, and Co-Ni. We further demonstrate surface patterning using Cu-Ag alloys with precise control of the location and composition of each pixel. Additionally, combining the nanoparticle alloy synthesis method with scanning electrochemical cell microscopy (SECCM) allows for fast screening of electrocatalysts. The method is generally applicable for synthesizing metal nanoparticles that can be electrodeposited, which is important toward developing automated synthesis and screening systems for accelerated material discovery in electrocatalysis.

Monitoring of Pore Orientation by in Operando Grazing Incidence Small-Angle X-ray Scattering during Templated Electrodeposition of Mesoporous Pt Films

We have used in operando grazing incidence small-angle X-ray scattering (GISAXS) to monitor structural changes during templated electrodeposition of mesoporous platinum films on gold electrodes from a ternary lyotropic liquid crystalline mixture of aqueous hexachloroplatinic acid and the diblock copolymer surfactant Brij56. While the cylindrical micelles of the lyotropic liquid crystal (LLC) in the hexagonal phase have a center-to-center distance of 7.5 nm with a preferential alignment parallel to the electrode surface, the electrodeposited platinum films contain highly ordered mesopores arranged in a 2D hexagonal structure, with a center-to-center distance of about 8.5 nm and a preferential orientation perpendicular to the electrode surface. The progression of structural changes of the LLC template and the deposited mesoporous Pt could be monitored for the first time in operando by GISAXS: within the first 14 s of deposition, a nucleation burst of Pt coincides with a loss of preferential alignment of the LLC. Initially, the morphology of the 2-dimensionally nucleated Pt replicates the Au substrate. During the following 5 to 7 min, the growth morphology of the Pt film changes, and vertically aligned mesopores form. Our results indicate mutual interaction between the species involved in the electrodeposition and the LLC template, leading to a partial loss of horizontal orientation of the LLC during Pt nucleation before vertical rearrangement of the micelles to the electrode surface. The vertically aligned mesopores in the Pt and the possibility to produce freestanding films make these materials interesting in fields such as electrocatalysis, energy harvesting, and nanofluidics.

Bimetallic Nanoalloy Catalysts for Green Energy Production: Advances in Synthesis Routes and Characterization Techniques

Bimetallic Nanoalloy catalysts have diverse uses in clean energy, sensing, catalysis, biomedicine, and energy storage, with some supported and unsupported catalysts. Conventional synthetic methods for producing bimetallic alloy nanoparticles often produce unalloyed and bulky particles that do not exhibit desired characteristics. Alloys, when prepared with advanced nanoscale methods, give higher surface area, activity, and selectivity than individual metals due to changes in their electronic properties and reduced size. This review demonstrates the synthesis methods and principles to produce and characterize highly dispersed, well-alloyed bimetallic nanoalloy particles in relatively simple, effective, and generalized approaches and the overall existence of conventional synthetic methods with modifications to prepare bimetallic alloy catalysts. The basic concepts and mechanistic understanding are represented with purposely selected examples. Herein, the enthralling properties with widespread applications of nanoalloy catalysts in heterogeneous catalysis are also presented, especially for Hydrogen Evolution Reaction (HER), Oxidation Reduction Reaction (ORR), Oxygen Evolution Reaction (OER), and alcohol oxidation with a particular focus on Pt and Pd-based bimetallic nanoalloys and their numerous fields of applications. The high entropy alloy is described as a complicated subject with an emphasis on laser-based green synthesis of nanoparticles and, in conclusion, the forecasts and contemporary challenges for the controlled synthesis of nanoalloys are addressed.

Engineering composition-varied Au/PtTe hetero-junction-abundant nanotrough arrays as robust electrocatalysts for ethanol electrooxidation

Pt-based multi-metallic electrocatalysts containing hetero-junctions are found to have superior catalytic performance to composition-equivalent counterparts. However, in bulk solution, controllable preparation of Pt-based hetero-junction electrocatalyst is an extremely random work owing to the complexity of solution reactions. Herein, we develop an interface-confined transformation strategy, subtly achieving Au/PtTe hetero-junction-abundant nanostructures by employing interfacial Te nanowires as sacrificing templates. By controlling the reaction conditions, composition-varied Au/PtTe can be easily obtained, such as Au₇₅/Pt₂₀Te₅, Au₅₅/Pt₃₄Te₁₁, and Au₅/Pt₆₉Te₂₆. Moreover, each Au/PtTe hetero-junction nanostructure appears to be an array consisting of side-by-side Au/PtTe nanotrough units and can be directly used as a catalyst layer without further post-treatment. All Au/PtTe hetero-junction nanostructures show better catalytic activity towards ethanol electrooxidation than commercial Pt/C because of the combining contributions of Au/Pt hetero-junctions and the collective effects of multi-metallic elements, where Au₇₅/Pt₂₀Te₅ exhibits the best electrocatalytic performance among three Au/PtTe nanostructures owing to its optimal composition. This study may provide technically feasible guidance for further maximizing the catalytic activity of Pt-based hybrid catalysts.

The role of the gold-platinum interface in AuPt/TiO2-catalyzed plasmon-induced reduction of CO2 with water

Bimetallic gold-platinum nanoparticles have been widely studied in the fields of nanoalloys, catalysis and plasmonics. Many preparation methods can lead to the formation of these bimetallic nanoparticles (NPs), and the structure and related properties of the nanoalloy often depend on the preparation method used. Here we investigate the ability of thermal dimethylformamide (DMF) reduction to prepare bimetallic gold-platinum sub-nm clusters supported on titania. We find that deposition of Pt preferentially occurs on gold. Formation of sub-nm clusters (vs. NPs) appears to be dependent on the metal concentration used: clusters can be obtained for metal loadings up to 4 wt% but 7-8 nm NPs are formed for metal loadings above 8 wt%, as shown using high resolution transmission electron microscopy (HRTEM). X-ray photoelectron spectroscopy (XPS) shows electron-rich Au and Pt components in a pure metallic form and significant platinum enrichment of the surface, which increases with increasing Pt/Au ratio and suggests the presence of Au@Pt core-shell type structures. By contrast, titania-supported bimetallic particles (typically >7 nm) obtained by sodium borohydride (NaBH₄) reduction in DMF, contain Au/Pt Janus-type objects in addition to oxidized forms of Pt as evidenced by HRTEM, which is in agreement with the lower Pt surface enrichment found by XPS. Both types of supported nanostructures contain a gold-platinum interface, as shown by the chemical interface damping, i.e. gold plasmon damping by Pt, found using UV-visible spectroscopy. Evaluation of the materials for plasmon-induced continuous flow CO₂ reduction with water, shows that: (1) subnanometer metallic clusters are not suitable for CO₂ reduction with water, producing hydrogen from the competing water reduction instead, thereby highlighting the plasmonic nature of the reaction; (2) the highest methane production rates are obtained for the highest Pt enrichments of the surface, i.e. the core-shell-like structures achieved by the thermal DMF reduction method; (3) selectivity towards CO₂ reduction vs. the competing water reduction is enhanced by loading of the plasmonic NPs, i.e. coverage of the titania semi-conductor by plasmonic NPs. Full selectivity is achieved for loadings above 6 wt%, regardless of the NPs composition and alloy structure.

Nanotechnology‐based electrochemical biosensors for monitoring breast cancer biomarkers

Breast cancer is categorized as the most widespread cancer type among women globally. On-time diagnosis can decrease the mortality rate by making the right decision in the therapy procedure. These features lead to a reduction in medication time and socioeconomic burden. The current review article provides a comprehensive assessment for breast cancer diagnosis using nanomaterials and related technologies. Growing use of the nano/biotechnology domain in terms of electrochemical nanobiosensor designing was discussed in detail. In this regard, recent advances in nanomaterial applied for amplified biosensing methodologies were assessed for breast cancer diagnosis by focusing on the advantages and disadvantages of these approaches. We also monitored designing methods, advantages, and the necessity of suitable (nano) materials from a statistical standpoint. The main objective of this review is to classify the applicable biosensors based on breast cancer biomarkers. With numerous nano-sized platforms published for breast cancer diagnosis, this review tried to collect the most suitable methodologies for detecting biomarkers and certain breast cancer cell types.

Mesoporous Gold Nanostructures: Synthesis and Beyond

Mesoporous metal nanostructures have offered multiple advantages that cannot be realized elsewhere. These materials have been attracting more research attention in catalysis and electrocatalysis owing to their functional structures and compositions. Of the various mesoporous metals available, mesoporous gold (mesoAu) nanostructures are of special interest in surface-enhanced Raman scattering (SERS) and related applications because of their strong electromagnetic field (localized surface plasmon resonance). In the last few decades, various synthesis strategies have been developed to prepare mesoAu nanostructures with controllable morphologies that exhibit fascinating physicochemical properties and increase applications in SERS, catalysis, and electrocatalysis. In this Perspective, we systematically summarize recent advances in synthesis and applications of mesoAu nanostructures. Four synthesis strategies, including dealloying, nanocasting, electrochemical deposition, and intermediate template, are discussed in detail. Moreover, physicochemical properties and promising applications of mesoAu nanostructures are presented. Finally, we describe current challenges and give a general outlook to explore further directions in synthesis and applications of mesoAu nanostructures.

Three-Phases Interface Induced Local Alkalinity Generation Enables Electrocatalytic Glucose Oxidation in Neutral Electrolyte

Electrocatalytic glucose oxidation is crucial to the development of non-enzymatic sensors, an attractive alternative for enzymatic biosensors. However, due to OH^- consumption during the catalytic process, non-enzymatic detection generally requires electrolytes having an alkaline pH value, limiting its practical application since biofluids are neutral. Herein, via interfacial microenvironment design, we addressed this limitation by developing a non-enzymatic sensor with an air-solid-liquid triphase interface electrodes that synergistically integrates the functions of local alkalinity generation and electrocatalytic glucose oxidation. A sufficiently high local pH value was achieved via oxygen reduction reaction at the triphase interface, which consequently enabled the electrochemical oxidation (detection) of glucose in neutral solution. Moreover, we found that the linear detection range and sensitivity of triphase non-enzymatic sensor can be tuned by changing the electrocatalysts of the detection electrode. The triphase electrode architecture provides a new platform for further exploration and promotes practical application of non-enzymatic sensors.

AuPt Bimetallic Nanozymes for Enhanced Glucose Catalytic Oxidase

Au metal nanoparticles as artificial nanozymes have attracted wide interest in biotechnology due to high stability and easy synthesis. Unfortunately, its catalytic activity is limited by the uniform surface electron distribution, fundamentally affecting the oxidation efficiency of glucose. Here, we synthesized AuPt bimetallic nanoparticles with unique surface electron structure due to the coupling effect of the two metal components, achieving improved glucose catalytic oxidase. Because of the effective work function difference between the two metals in AuPt, the electrons will transfer from Au to accumulate on Pt, simultaneously contributing to the substantial enhancement of Au-induced glucose oxidase and Pt-induced catalase performance. We systematically studied the enzyme-catalytic efficiency of AuPt with varied two metal proportions, in which Au:Pt at 3:1 showed the highest catalytic efficiency of glucose oxidase in solution. The AuPt nanoparticles were further co-cultured with cells and also showed excellent biological activity for glucose oxidase. This work demonstrates that the physicochemical properties between different metals can be exploited for engineering high-performance metal nanoparticle-based nanozymes, which opens up a new way to rationally design and optimize artificial nanozymes to mimic natural enzymes.

Coupling Natural Halloysite Nanotubes and Bimetallic Pt-Au Alloy Nanoparticles for Highly Efficient and Selective Oxidation of 5-Hydroxymethylfurfural to 2,5-Furandicarboxylic Acid

The aerobic oxidation of 5-hydroxymethylfurfural (HMF), a key platform compound derived from biomass, to 2,5-furandicarboxylic acid (FDCA) is a highly important reaction in the production of green and sustainable chemicals. Here, we developed a highly efficient and stable halloysite-supported Pt-Au alloy catalyst for the selective oxidation of HMF to FDCA. The catalyst was synthesized through the organosilane functionalization of halloysite nanotubes, followed by the in situ formation and dispersion of Pt-Au alloy nanoparticles on the internal and external surfaces of nanotubes. The composition, morphology, and structure of the prepared catalyst were characterized. The catalyst with the optimal composition of Pt/Au molar ratio of 1/4 and metal loading of 1.5 wt % exhibited outstanding catalytic activity for the oxidation of HMF to FDCA using O₂ as an oxidant with 100% conversion of HMF and 99% selectivity of FDCA. This excellent catalytic performance is mainly attributed to the high dispersion and alloying effects of bimetallic nanoparticles, which promoted the activation of reactants or intermediates and further improved FDCA selectivity. Furthermore, the halloysite-supported Pt/Au bimetallic catalyst showed high stability and reusability. This study provides a promising strategy by combining clay mineral halloysite and bimetallic alloys for developing efficient catalysts with high FDCA selectivity and stability for the oxidation of HMF to FDCA.

The alloying-induced electrical conductivity of metal-chalcogenolate nanowires

Alloying is one of the most effective strategies to change the properties of inorganic-organic hybrid materials, but there are few reports of the alloying of one-dimensional nanowires with precise atomic structure due to the difficulties in obtaining the single crystals of nanowires themselves. Herein, we describe the synthesis and characterization of an alloyed one-dimensional Ag-Cu nanowire [Ag_2.5Cu_1.5(S-Adm)₄]_n. Compared with the unalloyed [Ag₄(S-Adm)₄]_n, our novel alloyed nanowire exhibits good conductivity, and its resistivity (as a powder) was determined to be 107 Ω m by impedance analysis-consistent with that of a semiconductor. Accordingly, based on these properties combined with its excellent thermal stability and high-yielding, gram-scale synthesis, [Ag_2.5Cu_1.5(S-Adm)₄]_n is proposed for electronic-device applications.

Ruthenium nanodendrites on reduced graphene oxide: an efficient water and 4-nitrophenol reduction catalyst

A green and efficient protocol is reported for the elegant design of reduced graphene oxide (rGO)-supported Ru nanodendrites for promotion of electrochemical water reduction in a wide pH range as well as for environmental remediation.

Electrochemical Synthesis of Mesoporous Architectured Ru Films Using Supramolecular Templates

The electrochemical synthesis of mesoporous ruthenium (Ru) films using sacrificial self-assembled block polymer micelles templates, and its electrochemical surface oxidation to RuO_x is described. Unlike standard methods such as thermal oxidation, the electrochemical oxidation method described here retains the mesoporous structure. Ru oxide materials serve as high-performance supercapacitor electrodes due to their excellent pseudocapacitive behavior. The mesoporous architectured film shows superior specific capacitance (467 F g^-1_Ru ) versus a nonporous Ru/RuO_x electrode (28 F g^-1_Ru ) that is prepared via the same method but omitting the pore-directing polymer. Ultrahigh surface area materials will play an essential role in increasing the capacitance of this class of energy storage devices because the pseudocapacitive redox reaction occurs on the surface of electrodes.

Recent Advances in Noble Metal Catalysts for Hydrogen Production from Ammonia Borane

Interest in chemical hydrogen storage has increased, because the supply of fossil fuels are limited and the harmful effects of burning fossil fuels on the environment have become a focus of public concern. Hydrogen, as one of the energy carriers, is useful for the sustainable development. However, it is widely known that controlled storage and release of hydrogen are the biggest barriers in large-scale application of hydrogen energy. Ammonia borane (NH3BH3, AB) is deemed as one of the most promising hydrogen storage candidates on account of its high hydrogen to mass ratio and environmental benignity. Development of efficient catalysts to further improve the properties of chemical kinetics in the dehydrogenation of AB under appropriate conditions is of importance for the practical application of this system. In previous studies, a variety of noble metal catalysts and their supported metal catalysts (Pt, Pd, Au, Rh, etc.) have presented great properties in decomposing the chemical hydride to generate hydrogen, thus, promoting their application in dehydrogenation of AB is urgent. We analyzed the hydrolysis of AB from the mechanism of hydrogen release reaction to understand more deeply. Based on these characteristics, we aimed to summarize recent advances in the development of noble metal catalysts, which had excellent activity and stability for AB dehydrogenation, with prospect towards realization of efficient noble metal catalysts.

Recent advances in amphiphilic block copolymer templated mesoporous metal-based materials: assembly engineering and applications

Mesoporous metal-based materials (MMBMs) have received unprecedented attention in catalysis, sensing, and energy storage and conversion owing to their unique electronic structures, uniform mesopore size and high specific surface area. In the last decade, great progress has been made in the design and application of MMBMs; in particular, many novel assembly engineering methods and strategies based on amphiphilic block copolymers as structure-directing agents have also been developed for the "bottom-up" construction of a variety of MMBMs. Development of MMBMs is therefore of significant importance from both academic and practical points of view. In this review, we provide a systematic elaboration of the molecular assembly methods and strategies for MMBMs, such as tuning the driving force between amphiphilic block copolymers and various precursors (i.e., metal salts, nanoparticles/clusters and polyoxometalates) for pore characteristics and physicochemical properties. The structure-performance relationship of MMBMs (e.g., pore size, surface area, crystallinity and crystal structure) based on various spectroscopy analysis techniques and density functional theory (DFT) calculation is discussed and the influence of the surface/interfacial properties of MMBMs (e.g., active surfaces, heterojunctions, binding sites and acid-base properties) in various applications is also included. The prospect of accurately designing functional mesoporous materials and future research directions in the field of MMBMs is pointed out in this review, and it will open a new avenue for the inorganic-organic assembly in various fields.

Self-assembly of block copolymers towards mesoporous materials for energy storage and conversion systems

This paper reviews the progress in the field of block copolymer-templated mesoporous materials, including synthetic methods, morphological and pore size control and their potential applications in energy storage and conversion devices.

Microstructure evolution of sandwich graphite oxide/interlayer-embedded Au nanoparticles induced from γ-rays for carcinoembryonic antigen biosensor

With the capability of inducing small particle sizes of supported metal in graphite oxide (GO), the γ-ray irradiation method applied for preparing graphite oxide-gold (GO-Au) nanocomposites as electrochemical immunosensors has attracted specific attention recently. To study the accurate factors influencing the precise morphology and final performance of the prepared composites in the γ-irradiation system, we proposed a facile method to investigate the evolution of the GO structure, size and dispersion of Au nanoparticles (AuNPs) produced with the addition of isopropyl alcohol to the system. The GO-Au nanocomposites were characterized by Fourier transform infrared spectroscopy, x-ray diffraction spectra, Raman spectra, x-ray photoelectron spectroscopy and high resolution transmission electron microscopy. These nanocomposites with sandwich morphology exhibited an excellent immunosensor performance with a low detection limit of 15.8 pg ml^-1 (S/N = 3) and a wide linear range from 1 to 40 ng ml^-1 for detecting carcinoembryonic antigens. The enhanced biosensing performance is attributed to the synergistic effect of γ-irradiation and the precise structure of GO, which endows the smaller size and more uniform distribution of AuNPs on the GO as well as the good signal amplification capability. Furthermore, adopting the γ-irradiation method and use of GO as a precursor is propitious for application in large-scale production because of its high-efficiency and high-yielding characteristics.

Nanowire Genome: A Magic Toolbox for 1D Nanostructures

1D nanomaterials with high aspect ratio, i.e., nanowires and nanotubes, have inspired considerable research interest thanks to the fact that exotic physical and chemical properties emerge as their diameters approach or fall into certain length scales, such as the wavelength of light, the mean free path of phonons, the exciton Bohr radius, the critical size of magnetic domains, and the exciton diffusion length. On the basis of their components, aspect ratio, and properties, there may be imperceptible connections among hundreds of nanowires prepared by different strategies. Inspired by the heredity system in life, a new concept termed the "nanowire genome" is introduced here to clarify the relationships between hundreds of nanowires reported previously. As such, this approach will not only improve the tools incorporating the prior nanowires but also help to precisely synthesize new nanowires and even assist in the prediction on the properties of nanowires. Although the road from start-ups to maturity is long and fraught with challenges, the genetical syntheses of more than 200 kinds of nanostructures stemming from three mother nanowires (Te, Ag, and Cu) are summarized here to demonstrate the nanowire genome as a versatile toolbox. A summary and outlook on future challenges in this field are also presented.

Self-standing hollow porous AuPt nanospheres and their enhanced electrocatalytic performance

In this paper, we present a template method to fabricate AuPt hollow nanospheres by depositing Au inner layer and dendritic Pt outer layer onto PS template. The as-prepared AuPt hollow nanospheres can form self-standing hollow nanostructures under thermal treatment which is confirmed by small-angle X-ray scattering results. We believe that the self-standing structural features of them result from different thermal stability of Au and Pt elements. The small-angle X-ray diffraction measurements and X-ray photoelectron spectroscopy of binding energies certify the existing interaction between Au and Pt. It is suggested that Pt mole contents of AuPt hollow nanospheres can be varied by changing H₂PtCl₄ concentration during chemical deposition process. The methanol electrochemical oxidation reaction indicates these as-prepared AuPt hollow nanospheres possessing excellent potential applications on catalysts. Moreover, synthesis of multilayer hollow porous nanospheres such as Pt@Au@Pt proves that our method greatly enriches the species of the self-standing, hollow and porous functional nanomaterials.

Atomic Carbon Layers Supported Pt Nanoparticles for Minimized CO Poisoning and Maximized Methanol Oxidation

Maximizing activity of Pt catalysts toward methanol oxidation reaction (MOR) together with minimized poisoning of adsorbed CO during MOR still remains a big challenge. In the present work, uniform and well-distributed Pt nanoparticles (NPs) grown on an atomic carbon layer, that is in situ formed by means of dry-etching of silicon carbide nanoparticles (SiC NPs) with CCl₄ gas, are explored as potential catalysts for MOR. Significantly, as-synthesized catalysts exhibit remarkably higher MOR catalytic activity (e.g., 647.63 mA mg^-1 at a peak potential of 0.85 V vs RHE) and much improved anti-CO poisoning ability than the commercial Pt/C catalysts, Pt/carbon nanotubes, and Pt/graphene catalysts. Moreover, the amount of expensive Pt is a few times lower than that of the commercial and reported catalyst systems. As confirmed from density functional theory (DFT) calculations and X-ray absorption fine structure (XAFS) measurements, such high performance is due to reduced adsorption energy of CO on the Pt NPs and an increased amount of adsorbed energy OH species that remove adsorbed CO fast and efficiently. Therefore, these catalysts can be utilized for the development of large-scale and industry-orientated direct methanol fuel cells.

Salt-Templated Platinum-Copper Porous Macrobeams for Ethanol Oxidation

Platinum nanomaterials provide an excellent catalytic activity for diverse applications and given its high cost, platinum alloys and bi-metallic nanomaterials with transition metals are appealing for low cost and catalytic specificity. Here the synthesis of hierarchically porous Pt–Cu macrobeams and macrotubes templated from Magnus’s salt derivative needles is demonstrated. The metal composition was controlled through the combination of [PtCl4]2− with [Pt(NH3)4]2+ and [Cu(NH3)4]2+ ions in different ratios to form salt needle templates. Polycrystalline Pt–Cu porous macrotubes and macrobeams 10’ s–100’ s μm long with square cross-sections were formed through chemical reduction with dimethylamine borane (DMAB) and NaBH4, respectively. Specific capacitance as high as 20.7 F/g was demonstrated with cyclic voltammetry. For macrotubes and macrobeams synthesized from Pt2−:Pt2+:Cu2+ salt ratios of 1:1:0, 2:1:1, 3:1:2, and 1:0:1, DMAB reduced 3:1:2 macrotubes demonstrated the highest ethanol oxidation peak currents of 12.0 A/g at 0.5 mV/s and is attributed to the combination of a highly porous structure and platinum enriched surface. Salt templates with electrochemical reduction are suggested as a rapid, scalable, and tunable platform to achieve a wide range of 3-dimensional porous metal, alloy, and multi-metallic nanomaterials for catalysis, sensor, and energy storage applications.

Cyanogel auto-reduction induced synthesis of PdCo nanocubes on carbon nanobowls: a highly active electrocatalyst for ethanol electrooxidation

Direct ethanol fuel cells (DEFCs) with a high conversion efficiency are quite promising candidates for energy conversion devices. Herein, we have successfully synthesized PdCo alloy nanocubes supported on carbon nanobowl (denoted as Pd₂Co₁/CNB) nanohybrids by using the cyanogel auto-reduction method at high temperature. The morphology, composition and structure of Pd₂Co₁/CNB nanohybrids are characterized in detail, revealing that PdCo nanocubes have a high alloying degree and special {110} facets. In cyclic voltammetry measurements, Pd₂Co₁/CNB nanohybrids show a mass activity of 1089.0 A g _Pd^-1 and a specific activity of 40.03 mA cm^-2 for ethanol electrooxidation at peak potential, which are much higher than that of the commercial Pd/C electrocatalyst (278.2 A g_Pd^-1 and 8.22 mA cm^-2). Additionally, chronoamperometry measurements show that Pd₂Co₁/CNB nanohybrids have excellent durability for ethanol electrooxidation. A high alloying degree, special {110} facets and the CNB supporting material contribute to the high activity and durability of Pd₂Co₁/CNB nanohybrids, making them a highly promising Pt-alternative electrocatalyst for ethanol electrooxidation in DEFCs.

In situ redox growth of mesoporous Pd-Cu2O nanoheterostructures for improved glucose oxidation electrocatalysis

Interfaces of metal-oxide heterostructured electrocatalyst are critical to their catalytic activities due to the significant interfacial effects. However, there are still obscurities in the essence of interfacial effects caused by crystalline defects and mismatch of electronic structure at metal-oxide nanojunctions. To deeply understand the interfacial effects, we engineered crystalline-defect Pd-Cu₂O interfaces through non-epitaxial growth by a facile redox route. The Pd-Cu₂O nanoheterostructures exhibit much higher electrocatalytic activity toward glucose oxidation than their single counterparts and their physical mixture, which makes it have a promising potential for practical application of glucose biosensors. Experimental study and density functional theory (DFT) calculations demonstrated that the interfacial electron accumulation and the shifting up of d bands center of Cu-Pd toward the Fermi level were responsible for excellent electrocatalytic activity. Further study found that Pd(3 1 0) facets exert a strong metal-oxide interface interaction with Cu₂O(1 1 1) facets due to their lattice mismatch. This leads to the sinking of O atoms and protruding of Cu atoms of Cu₂O, and the Pd crystalline defects, further resulting in electron accumulation at the interface and the shifting up of d bands center of Cu-Pd, which is different from previously reported charge transfer between the interfaces. Our findings could contribute to design and development of advanced metal-oxide heterostructured electrocatalysts.

Solid-solution alloy nanoparticles of a combination of immiscible Au and Ru with a large gap of reduction potential and their enhanced oxygen evolution reaction performance

Au and Ru are elements that are immiscible in the bulk state and have the largest gap in reduction potential among noble metals. Here, for the first time, Au x Ru1-x solid-solution alloy nanoparticles (NPs) were successfully synthesized over the whole composition range through a chemical reduction method. Powder X-ray diffraction and scanning transmission electron microscopy coupled with energy-dispersive X-ray spectroscopy showed that Au and Ru atoms are homogeneously mixed at the atomic level. We investigated the catalytic performance of Au x Ru1-x NPs for the oxygen evolution reaction, for which Ru is well known to be one of the best monometallic catalysts, and we found that even alloying with a small amount of Au could significantly enhance the catalytic performance.

Biomolecule-Assisted Synthesis of Hierarchical Multilayered Boehmite and Alumina Nanosheets for Enhanced Molybdenum Adsorption

The effective utilization of various biomolecules for creating a series of mesoporous boehmite (γ-AlOOH) and gamma-alumina (γ-Al₂ O₃ ) nanosheets with unique hierarchical multilayered structures is demonstrated. The nature and concentration of the biomolecules strongly influence the degree of the crystallinity, the morphology, and the textural properties of the resulting γ-AlOOH and γ-Al₂ O₃ nanosheets, allowing for easy tuning. The hierarchical γ-AlOOH and γ-Al₂ O₃ multilayered nanosheets synthesized by using biomolecules exhibit enhanced crystallinity, improved particle separation, and well-defined multilayered structures compared to those obtained without biomolecules. More impressively, these γ-AlOOH and γ-Al₂ O₃ nanosheets possess high surface areas up to 425 and 371 m²  g^-1 , respectively, due to their mesoporous nature and hierarchical multilayered structure. When employed for molybdenum adsorption toward medical radioisotope production, the hierarchical γ-Al₂ O₃ multilayered nanosheets exhibit Mo adsorption capacities of 33.1-40.8 mg g^-1 . The Mo adsorption performance of these materials is influenced by the synergistic combination of the crystallinity, the surface area, and the pore volume. It is expected that the proposed biomolecule-assisted strategy may be expanded for the creation of other 3D mesoporous oxides in the future.

Highly Excavated Octahedral Nanostructures Integrated from Ultrathin Mesoporous PtCu3 Nanosheets: Construction of Three-Dimensional Open Surfaces for Enhanced Electrocatalysis

Developing electrocatalysts with ultrathin nanostructures and high mesoporosity is a relevant high-priority research direction toward enhancing the performance of noble metals. Herein, mesoporous, highly excavated octahedral PtCu₃ nanostructures are prepared by a facile one-pot synthesis. The mesoporous, highly excavated octahedral PtCu₃ nanostructures are built with mutually perpendicular interlaced mesoporous nanosheets with a thickness of ≈4.5 nm. Benefiting from its mesoporous features, three-dimensional (3D) open surfaces, ultrathin nanosheets, and a Cu-rich surface, PtCu₃ exhibits excellent electrocatalytic performance and high antipoisoning activity toward the methanol oxidation reaction.

Electrochemical Fabrication of Porous Au Film on Ni Foam for Nitrogen Reduction to Ammonia

Electrochemical reduction of N₂ to NH₃ provides an alternative strategy to replace the industrial Haber-Bosch process for facile and sustainable production of NH₃ . The development of efficient electrocatalysts for the nitrogen reduction reaction (NRR) is highly desired. Herein, a micelle-assisted electrodeposition method is presented for the direct fabrication of porous Au film on Ni foam (pAu/NF). Benefiting from its interconnected porous architectonics, the pAu/NF exhibits superior NRR performance with a high NH₃ yield rate of 9.42 µg h^-1 cm^-2 and a superior Faradaic efficiency of 13.36% at -0.2 V versus reversible hydrogen electrode under the neutral electrolyte (0.1 m Na₂ SO₄ ). The proposed micelle-assisted electrodeposition strategy is highly valuable for future design of active NRR catalysts with desired compositions toward various electrocatalysis fields.

Large Magnetoelectric Effects in Electrodeposited Nanoporous Microdisks Driven by Effective Surface Charging and Magneto-Ionics

A synergetic approach to enhance magnetoelectric effects (i.e., control of magnetism with voltage) and improve energy efficiency in magnetically actuated devices is presented. The investigated material consists of an ordered array of Co-Pt microdisks, in which nanoporosity and partial oxidation are introduced during the synthetic procedure to synergetically boost the effects of electric field. The microdisks are grown by electrodeposition from an electrolyte containing an amphiphilic polymeric surfactant. The bath formulation is designed to favor the incorporation of oxygen in the form of cobalt oxide. A pronounced reduction of coercivity (88%) and a remarkable increase of Kerr signal amplitude (60%) are observed at room temperature upon subjecting the microdisks to negative voltages through an electrical double layer. These large voltage-induced changes in the magnetic properties of the microdisks are due to (i) the high surface-area-to-volume ratio with ultranarrow pore walls (sub-10 nm) that promote enhanced electric charge accumulation and (ii) magneto-ionic effects, where voltage-driven O^2- migration promotes a partial reduction of CoO to Co at room temperature. This simple and versatile procedure to fabricate patterned "nano-in-micro" magnetic motifs with adjustable voltage-driven magnetic properties is very appealing for energy-efficient magnetic recording systems and other magnetoelectronic devices.

New insights into the structure-performance relationships of mesoporous materials in analytical science

Mesoporous materials are ideal carriers for guest molecules and they have been widely used in analytical science. The unique mesoporous structure provides special properties including large specific surface area, tunable pore size, and excellent pore connectivity. The structural properties of mesoporous materials have been largely made use of to improve the performance of analytical methods. For instance, the large specific surface area of mesoporous materials can provide abundant active sites and increase the probability of contact between analytes and active sites to produce stronger signals, thus leading to the improvement of detection sensitivity. The connections between analytical performances and the structural properties of mesoporous materials have not been discussed previously. Understanding the "structure-performance relationship" is highly important for the development of analytical methods with excellent performance based on mesoporous materials. In this review, we discuss the structural properties of mesoporous materials that can be optimized to improve the analytical performance. The discussion is divided into five sections according to the analytical performances: (i) selectivity-related structural properties, (ii) sensitivity-related structural properties, (iii) response time-related structural properties, (iv) stability-related structural properties, and (v) recovery time-related structural properties.

Preparation of platinum-based 'cauliflower microarrays' for enhanced ammonia gas sensing

In amperometric gas sensors, the flux of gas to electrode surfaces determines the analytical response and detection limit. For trace concentration detection, the resulting low current prevents the miniaturisation of such sensors. Therefore, in this study, we have developed repeating arrays of nanostructures which maximise flux towards their surface. Unique platinum 3D cauliflower-shaped deposits with individual floret-shaped segments have been produced in a single step electrodeposition process. The confined walls of recessed microelectrode arrays (10 μm in diameter, 90 electrodes) are utilized to produce these structures with a high surface area. Distinct segments are observed, with the gaps corresponding to electrodes adjacent in the microarray; thus the majority of the deposits face the primary diffusion zones. The sizes and shapes of the deposits are characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM) and the largest structures are found to be 22 ± 1 μm in width and 7.9 ± 0.2 μm in height over the microhole. These modified electrodes are employed to detect ammonia using the room temperature ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [C₂mim][NTf₂], as an electrolyte. Current responses on the cauliflower arrays were seven times higher for linear sweep voltammetry and ca. 12 times higher for chronoamperometry, relative to the bare microrrays, and limits of detection were less than 1 part per million of ammonia (gas phase concentration). This work highlights the use of modified microarrays with highly accessible 3D structures for enhanced electroanalytical detection of analyte species at ultra low concentrations.

Electrochemical deposition of large-sized mesoporous nickel films using polymeric micelles

Stable mesoporous nickel (Ni) films can be prepared using polystyrene-b-poly-(oxyethylene) (PS-b-PEO) micelles as sacrificial templates. In this method, positively charged Ni precursors form hydrogen bonds with the PEO segments of the micelles, which are then co-electrodeposited on the surface of a working electrode. Changing the applied voltage during electrodeposition modifies the deposition rate and ultimately controls the architecture of the mesoporous Ni film.

Shape-dependent thermo-plasmonic effect of nanoporous gold at the nanoscale for ultrasensitive heat-mediated remote actuation

Nanoporous gold (NPG) promises efficient light-to-heat transformation, yet suffers limited photothermal conversion efficiency owing to the difficulty in controlling its morphology for the direct modulation of thermo-plasmonic properties. Herein, we showcase a series of shape-controlled NPG nanoparticles with distinct bowl- (NPG-B), tube- (NPG-T) and plate-like (NPG-P) structures for quantitative temperature regulation up to 140 °C in <1 s using laser irradiation. Notably, NPG-B exhibits the highest photothermal efficiency of 68%, which is >12 and 39 percentage points better than those of other NPG shapes (NPG-T, 56%; NPG-P, 49%) and Au nanoparticles (29%), respectively. We attribute NPG-B's superior photothermal performance to its >13% enhanced light absorption cross-section compared to other Au nanostructures. We further realize an ultrasensitive heat-mediated light-to-mechanical "kill switch" by integrating NPG-B with a heat-responsive shape-memory polymer (SMP/NPG-B). This SMP/NPG-B hybrid is analogous to a photo-triggered mechanical arm, and can be activated swiftly in <4 s simply by remote laser irradiation. Achieving remotely-activated "kill switch" is critical in case of emergencies such as gas leaks, where physical access is usually prohibited or dangerous. Our work offers valuable insights into the structural design of NPG for optimal light-to-heat conversion, and creates opportunities to formulate next-generation smart materials for on-demand and multi-directional responsiveness.

Electrochemical Deposition: An Advanced Approach for Templated Synthesis of Nanoporous Metal Architectures

Well-constructed porous materials take an essential role in a wide range of applications, including energy conversion and storage systems, electrocatalysis, photocatalysis, and sensing. Although the tailored design of various nanoarchitectures has made substantial progress, simpler preparation methods are compelled to meet large-scale production requirements. Recently, advanced electrochemical deposition techniques have had a significant impact in terms of precise control upon the nanoporous architecture (i.e., pore size, surface area, pore structure, etc.), enabling access to a wide range of compositions. In this Account, we showcase the uniqueness of electrochemical deposition techniques, detail their implementation toward the synthesis of novel nanoporous metals, and finally outline the future research directions. Nanoporous metallic structures are attractive in that they can provide high surface area and large pore volume, easing mass transport of reactants and providing high accessibility to catalytically active metal surface. The great merit of the electrochemical deposition approach does not only lie in its versatility, being applicable to a wide range of compositions, but also in the nanoscale precision it affords when it comes to crystal growth control, which cannot be easily achieved by other bottom-up or top-down approaches. In this Account, we describe the significant progress made in the field of nanoporous metal designed through electrochemical deposition approaches using hard templates (i.e., porous silica, 3D templates of polymer and silica colloids) and soft templates (i.e., lyotropic liquid crystals, polymeric micelles). In addition, we will point out how it accounts for precise control over the crystal growth and describe the unique physical and chemical properties emerging from these novel materials. Up to date, our group has reported the synthesis of several nanoporous metals and alloys (e.g., Cu, Ru, Rh, Pd, Pt, Au, and their corresponding alloys) under various conditions through electrochemical deposition, while investigating their various potential applications. The orientation of the channel structure, the composition, and the nanoporosity can be easily controlled by selecting the appropriate surfactants or block copolymers. The inherent properties of the final product, such as framework crystallinity, catalytic activity, and resistance to oxidation, are depending on both the composition and pore structure, which in turn require suitable electrochemical conditions. This Account is divided into three main sections: (i) a history of electrochemical deposition using hard and soft templates, (ii) a description of the important mechanisms involved in the preparation of nanoporous materials, and (iii) a conclusion and future perspectives. We believe that this Account will promote a deeper understanding of the synthesis of nanoporous metals using electrochemical deposition methods, thus enabling new pathways to control nanoporous architectures and optimize their performance toward promising applications such as catalysis, energy storage, sensors, and so forth.

Salt-Mediated Au-Cu Nanofoam and Au-Cu-Pd Porous Macrobeam Synthesis

Multi-metallic and alloy nanomaterials enable a broad range of catalytic applications with high surface area and tuning reaction specificity through the variation of metal composition. The ability to synthesize these materials as three-dimensional nanostructures enables control of surface area, pore size and mass transfer properties, electronic conductivity, and ultimately device integration. Au-Cu nanomaterials offer tunable optical and catalytic properties at reduced material cost. The synthesis methods for Au-Cu nanostructures, especially three-dimensional materials, has been limited. Here, we present Au-Cu nanofoams and Au-Cu-Pd macrobeams synthesized from salt precursors. Salt precursors formed from the precipitation of square planar ions resulted in short- and long-range ordered crystals that, when reduced in solution, form nanofoams or macrobeams that can be dried or pressed into freestanding monoliths or films. Metal composition was determined with X-ray diffraction and energy dispersive X-ray spectroscopy. Nitrogen gas adsorption indicated an Au-Cu nanofoam specific surface area of 19.4 m²/g. Specific capacitance determined with electrochemical impedance spectroscopy was 46.0 F/g and 52.5 F/g for Au-Cu nanofoams and Au-Cu-Pd macrobeams, respectively. The use of salt precursors is envisioned as a synthesis route to numerous metal and multi-metallic nanostructures for catalytic, energy storage, and sensing applications.

Generalized Access to Mesoporous Inorganic Particles and Hollow Spheres from Multicomponent Polymer Blends

Mesoporous inorganic particles and hollow spheres are of increasing interest for a broad range of applications, but synthesis approaches are typically material specific, complex, or lack control over desired structures. Here it is reported how combining mesoscale block copolymer (BCP) directed inorganic materials self-assembly and macroscale spinodal decomposition can be employed in multicomponent BCP/hydrophilic inorganic precursor blends with homopolymers to prepare mesoporous inorganic particles with controlled meso- and macrostructures. The homogeneous multicomponent blend solution undergoes dual phase separation upon solvent evaporation. Microphase-separated (BCP/inorganic precursor)-domains are confined within the macrophase-separated majority homopolymer matrix, being self-organized toward particle shapes that minimize the total interfacial area/energy. The pore orientation and particle shape (solid spheres, oblate ellipsoids, hollow spheres) are tailored by changing the kind of homopolymer matrix and associated enthalpic interactions. Furthermore, the sizes of particle and hollow inner cavity are tailored by changing the relative amount of homopolymer matrix and the rates of solvent evaporation. Pyrolysis yields discrete mesoporous inorganic particles and hollow spheres. The present approach enables a high degree of control over pore structure, orientation, and size (15-44 nm), particle shape, particle size (0.6-3 µm), inner cavity size (120-700 nm), and chemical composition (e.g., aluminosilicates, carbon, and metal oxides).

Biofouling-Resistant Platinum Bimetallic Alloys

A new electrosynthetic approach for the fabrication of three-dimensional bicontinuous nanoporous platinum-based (3D-BC-NP-Pt(Au)) electrodes is described. Binary Pt-Ag alloys are first electrodeposited on gold substrates from appropriately formulated plating solutions. Following annealing and dealloying, a new family of nanoporous platinum-based electrodes emerges whose morphology, porosity, and chemical compositions depend on electrodeposition parameters and plating solution composition. Scanning electron microscopy images reveal an interesting and distinctive nanoporous gold-like microstructure with pores and ligaments in the 10-30 nm range arranged in a bicontinuous fashion throughout the thickness of the film. X-ray photoelectron spectroscopy (XPS) confirms that the as-formed electrodeposited films are silver-rich platinum binary alloys. Interestingly, XPS also reveals that after annealing and dealloying, the electrodes are actually ternary alloys containing platinum, gold, and a small amount of residual silver that remains after dealloying. Electrochemical measurements are consistent with this result and disclose a high surface area with roughness factors of 15-24. The ability to successfully conduct electrochemical measurements in biofouling solutions via a unique biosieving-like mechanism is demonstrated by exposure of the unique 3D bicontinuous nanoporous platinum-based electrode to fibrinogen in phosphate buffer and in a solution containing red blood cells. The work described herein has the potential to enrich the fields of electrochemical sensing and biosensing via the introduction of new 3D bicontinuous nanostructured porous platinum-based electrodes that can be easily and reliably fabricated.

Highly Ordered Hierarchical Pt and PtNi Nanowire Arrays for Enhanced Electrocatalytic Activity toward Methanol Oxidation

Highly ordered hierarchical Pt and PtNi nanowire arrays were prepared using CdS hierarchical nanowire arrays (HNWAs) as sacrificial templates and demonstrated high electrochemical active surface areas. For the resulting Pt HNWAs sample, the peak current for methanol oxidation at +0.74 V was almost 1 order of magnitude higher than that of Pt solid nanowire arrays prepared in a similar manner but without the use of CdS template, and the addition of a Ni cocatalyst effectively enhanced the tolerance against CO poisoning. The results demonstrated that highly ordered Pt and PtNi HNWAs may be exploited as promising anode catalysts in the application of direct methanol fuel cells.