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Activity, cost, and durability are the trinity of catalysis research for the electrochemical oxygen reduction reaction (ORR). While studies towards increasing activity and reducing cost of ORR catalysts have been carried out extensively, much effort is needed in durability investigation of highly active ORR catalysts. In this work, we examined the stability of a trimetallic PtPdCu catalyst that has demonstrated high activity and incredible durability during ORR using density functional theory (DFT) based computations. Specifically, we studied the processes of dissolution/deposition and diffusion between the surface and inner layer of Cu species of Pt

There is an increasing need to reduce the silver content in silver-based inks or pastes and achieve low-temperature sintering for scalable and low-cost production of printed wearable electronics. This need depends on the ability to control the metal composition and the surface properties of the nanoinks. Alloying silver with copper provides a pathway for meeting the need in terms of cost reduction, but little is known about the composition controllability and the low-temperature sintering capability. We report herein a scalable wet chemical synthesis of bimetallic silver-copper alloy nanoinks with room temperature sintering properties. The bimetallic alloy nanoparticles with a controllable composition can be formulated as stable nanoinks. The nanoinks printed on paper substrates are shown to sinter under room temperature. In addition to composition dependence, the results reveal an intriguing dependence of sintering on humidity above the printed nanoink films. These findings are assessed based on theoretical simulation of the sintering processes via surface-mediated sintering and interparticle necking mechanisms in terms of nanoscale adsorption, adhesion and diffusion, and surface free energies. Implications of the findings for room temperature fabrication of wearable sensors are also discussed.

The preparation of pH-responsive nanocontainers by typical silane modification of the mesoporous silica nanoparticle (MSN) surface is usually high-cost, complex, and time-consuming, which remains a great challenge for effective corrosion protection of magnesium alloy. Here, a new strategy to construct pH-responsive nanocontainers (MSN-MBT@LDH) is demonstrated. The nanocontainers consist of corrosion inhibitor (2-mercaptobenzothiazole, MBT) loaded MSN core and layered double hydroxide (LDH) nanosheet shell serving as gatekeepers. The successful loading of MBT and encapsulation by LDH nanosheets were confirmed by a series of characterization such as scanning transmission electron microscopy coupled with energy dispersive X-ray spectroscopy (STEM-EDS) and N2 adsorption/desorption isotherms. The pH-responsive feature of the nanocontainers was demonstrated by determination of the MBT concentration in buffer solutions with different pH values. A smart corrosion protection system on Mg alloy is obtained by incorporating the synthesized nanocontainers into a self-assembled nanophase particle (SNAP) coating. The electrochemical tests and visual observations show that the hybrid coating has the best barrier properties and robustness in corrosion protection in NaCl corrosive solutions in comparison with the control coatings. The present method simplifies the synthesis processes of nanocontainers and eliminates the potential detrimental effect of excess gatekeepers on the coating. The findings provide new insights into the preparation of scalable nanocontainers. The self-healing coatings are expected to have widespread applications for corrosion protection of Mg alloy and other metals.

The ability to harness the catalytic oxidation of hydrocarbons is critical for both clean energy production and air pollutant elimination, which requires a detailed understanding of the dynamic role of the nanophase structure and surface reactivity under the reaction conditions. We report here findings of an in situ/operando study of such details of a ternary nanoalloy under the propane oxidation condition using high-energy synchrotron X-ray diffraction coupled to atomic pair distribution function (HE-XRD/PDF) analysis and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The catalysts are derived by alloying Pt with different combinations of second (Pd) and third (Ni) transition metals, showing a strong dependence of the catalytic activity on the Ni content. The evolution of the phase structure of the nanoalloy is characterized by HE-XRD/PDF probing of the lattice strain, whereas the surface activity is monitored by DRIFTS detection of the surface intermediate formation during the oxidation of propane by oxygen. The results reveal the dominance of the surface intermediate species featuring a lower degree of oxygenation upon the first C-C bond cleavage on the lower-Ni-content nanoalloy and a higher degree of oxygenation upon the second C-C bond cleavage on the higher-Ni-content nanoalloy. The face-centered-cubic-type phase structures of the nanoalloys under the oxidation condition are shown to exhibit Ni-content-dependent changes of lattice strains, featuring the strongest strain with little variation for the higher-Ni-content nanoalloy, in contrast to the weaker strains with oscillatory variation for the lower-Ni-content nanoalloys. This process is also accompanied by oxygenation of the metal components in the nanoalloy, showing a higher degree of oxygenation for the higher-Ni-content nanoalloy. These subtle differences in phase structure and surface activity changes correlate with the Ni-composition-dependent catalytic activity of the nanoalloys, which sheds a fresh light on the correlation between the dynamic change of atomic strains and the surface reactivity and has significant implications for the design of oxidation catalysts with enhanced activities.

The structural and electronic properties of small Cu clusters were studied using density functional theory (DFT) calculations. The Cu clusters consist of up to fifty-five atoms with linear, planar, and three-dimensional structures. Five functionals, the Perdew-Wang 91 form of the generalized gradient approximation (PW91), Perdew-Burk-Ernzerhof functional (PBE), and three Minnesota functionals (M05, M06, and M06-L) were used. The dispersion correction in the format of DFT-D3 was also taken into account to the results of the PBE. The binding energy, average bond length, magnetic moment, and the HOMO-LUMO gap of each cluster were obtained and compared. DFT results for PBE and PW91 are very similar and agree with experimental data well. DFT-D3 corrections have no effect on the stable sequence. The copper clusters are more stable in the planar structure for clusters with n≤6, which agrees with other theoretical studies. In the case of bigger clusters, different DFT methods predicted different most stable structures. As cluster size increases, there was a monotonic decrease in magnetic moment for the odd number of clusters. As the linear cluster size increases, the bond distances between the atoms begin to alternate.

Intermolecular interactions play a critical role in the binding strength of molecular assemblies on surfaces. The ability to harness them enables molecularly-tunable interfacial structures and properties. Herein we report the tuning of the intermolecular interactions in monolayer assemblies derived from organothiols of different structures for the creation of nanoelectrode arrays or ensembles with effective mass transport by a molecular-level perforation strategy. The homo- and hetero-intermolecular interactions can be fully controlled, which is demonstrated not only by thermodynamic analysis of the fractional coverage but also by surface infrared reflection absorption and X-ray photoelectron spectroscopic characterizations. This understanding enables controllable electrochemical perforation for the creation of ensembles or arrays of channels across the monolayer thickness with molecular and nanoscale dimensions. Redox reactions on the nanoelectrode array display molecular tunability with a radial diffusion characteristic in good agreement with theoretical simulation results. These findings have implications for designing membrane-type ion-gating, electrochemical sensing, and electrochemical energy storage devices with molecular level tunability., Intermolecular interactions in monolayer assembly are harnessed for creating molecularly-tunable nanoelectrode arrays or ensembles.

Catalysis plays a significant role in most processes of the chemical industry, especially in the emerging areas of sustainable energy and clean environment. A major challenge is the design of catalysts with the desired synergies in terms of activity, selectivity, stability, and cost. New insights into many fundamental questions related to the challenge have sparked a surge of interest in recent years in the area of exploring copper-based alloy catalysts. In this review, the most recent progress in the explorations of copper-alloy catalysts will be highlighted, with a focus on the structural and mechanistic characterizations of the catalysts in different catalytic reactions. The fundamental understanding of the detailed catalytic synergies of the catalysts for the targeted heterogeneous catalytic reactions depends strongly on the utilization of various analytical techniques for the characterization. Significant progress has been made in utilizing advanced techniques, both ex situ and in situ/operando characterizations, demonstrating the abilities to gain atomic/molecular level insights into the morphological, structural, electronic and catalytic properties of copper alloy catalysts, especially the dynamic surface active sites under the reaction conditions or during the catalytic processes. The focus on structural characterization in this review serves as a forum for discussions on structural and mechanistic details, which should provide useful information for identifying challenges and opportunities in future research and development of copper-alloy catalysts.

The need for active and stable oxidation catalysts is driven by the demands in production of valuable chemicals, remediation of hydrocarbon pollutants and energy sustainability. Traditional approaches focus on oxygen-activating oxides as support which provides the oxygen activation at the catalyst-support peripheral interface. Here we report a new approach to oxidation catalysts for total oxidation of hydrocarbons (e.g., propane) by surface oxygenation of platinum (Pt)-alloyed multicomponent nanoparticles (e.g., platinum-nickel cobalt (Pt–NiCo)). The in-situ/operando time-resolved studies, including high-energy synchrotron X-ray diffraction and diffuse reflectance infrared Fourier transform spectroscopy, demonstrate the formation of oxygenated Pt–NiOCoO surface layer and disordered ternary alloy core. The results reveal largely-irregular oscillatory kinetics associated with the dynamic lattice expansion/shrinking, ordering/disordering, and formation of surface-oxygenated sites and intermediates. The catalytic synergy is responsible for reduction of the oxidation temperature by ~100 °C and the high stability under 800 °C hydrothermal aging in comparison with Pt, and may represent a paradigm shift in the design of self-supported catalysts., Traditional approach to oxidation catalysts relies on metal/oxide supported peripheral interfacial oxygen activity. Here the authors show surface oxygenation of platinum-alloyed multicomponent nanoparticles, and reveals irregular oscillatory kinetics associated with the surface oxygenated sites.

Electrocatalytic activity of alloy nanocatalytsts can be manipulated effectively by tuning their physical properties (ensemble, geometric, and ligand effects) to afford optimal surface structure and compositions for proton exchange membrane fuel cell (PEMFC) application. Herein, highly catalytic platinum-palladium nanowires (PtnPd100-n NWs) with a subtle lattice strain and Boerdijk-Coxeter helix type morphology are synthesized through a surfactant-free, thermal single phase solvent method. X-ray diffraction results show that PtnPd100-n NWs are exposed through the (111) facets and their shrinking or expanding lattice parameters can be modulated by the alloy compositions. Electrochemical results reveal that their high catalytic activity correlates with the lattice shrinking, facets, and bimetallic compositions, showing higher activity when the ratio of Pt and Pd is ∼78:22, which is further supported by DFT results. Compared to the nanoparticle type platinum-palladium alloyed catalysts with similar metal compositions (PtnPd100-n NPs), the PtnPd100-n NWs exhibit significantly improved electrocatalytic activity and stability for the oxygen reduction reaction. These findings open new strategies to design the highly active and stable alloy nanocatalysts with controllable compositions.

A key challenge to the creation of chemically responsive electro-functionality of nonconductive, hydrophobic, and free-contacted textile or fibrous network materials is how to impart the 3D structure with functional filaments to enable responsive structure sensitivity, which is critical in establishing the fibrous platform technology for sensor applications. We demonstrate this capability using an electrospun polymeric fibrous substrate embedded with nano-filaments defined by size-tunable gold nanoparticles and structurally sensitive dendrons as crosslinkers. The resulting interparticle properties strongly depend on the assembly of the nano-filaments, enabling an interface with high structure sensitivity to molecular interactions. This is demonstrated with chemiresistive responses to vaporous alcohol molecules with different chain lengths and isomers, which is critical in breath and sweat sensing involving a high-moisture or -humidity background. The sensitivity scales with the chain length and varies with their isomers. This approach harnesses the multifunctional tunability of the nano-filaments in a sensor array format, showing high structure sensitivity to the alcohol molecules with different chain lengths and isomers. The high structure sensitivity and its implications for a paradigm shift in the design of textile sensor arrays for multiplexing human performance monitoring via breath or sweat sensing and environmental monitoring of air quality are also discussed.

Understanding how the catalyst morphology influences surface sites is crucial for designing active and stable catalysts and electrocatalysts. We here report a new approach to this understanding by decorating gold (Au) nanoparticles on the surface of cuprous oxides (Cu2O) with three different shape morphologies (spheres, cubes, and petals). The Au-Cu2O particles are dispersed onto carbon nanotube (CNT) matrix with high surface area, stability, and conductivity for oxygen reduction reaction. A clear morphology-dependent enhancement of the electrocatalytic activity is revealed. Oxygenated gold species (AuO-) are found to coexist with Au0 on the cube and petal catalysts, whereas only Au0 species are present on the sphere catalyst. The AuO- species function effectively as active sites, resulting in the improved catalytic performance by changing the reaction mechanism. The enhanced catalytic performance of the petal-shaped catalyst in terms of onset potential, half-wave potential, diffusion-limited current density, and stability is closely associated with the presence of the most abundant AuO- species on its surface. Highly active AuO- species are identified on the surface of the catalysts as a result of the unique structural characteristics, which is attributed to the structural origin of high activity and stability. This insight constitutes the basis for assessing the detailed correlation between the morphology and the electrocatalytic properties of the nanocomposite catalysts, which has implications for the design of surface-active sites on metal/metal oxide electrocatalysts.

The ability to control the surface composition and morphology of alloy catalysts is critical for achieving high activity and durability of catalysts for oxygen reduction reaction (ORR) and fuel cells. This report describes an efficient surfactant-free synthesis route for producing a twisty nanowire (TNW) shaped platinum-iron (PtFe) alloy catalyst (denoted as PtFe TNWs) with controllable bimetallic compositions. PtFe TNWs with an optimal initial composition of ∼24% Pt are shown to exhibit the highest mass activity (3.4 A/mg

Direct ethanol fuel cell technology suffers from a lack of effective anode catalysts for complete ethanol oxidation reaction (EOR). Pd and Pd-based catalysts showed some promise, but only a trace a...

The ability to tune the surface partial charge of noble metal catalysts at the nanoscale size dimension is essential for harnessing the activity of nanocatalysts in many important environmental cat...

The architecture of catalyst particles plays an important role in determining the catalytic properties. However, the challenge is the ability to tune the architecture on a nanoscale. Herein, we report the design and construction of hollow CuO/CeO2 microspheres with controllable shells, which exhibit significantly enhanced catalytic performance. The hollow CuO/CeO2 microspheres with single and multiple shells were synthesized by a self-templating method. The catalytic activity of the catalysts for preferential CO oxidation is shown to increase with increasing the number of the spherical shells. A maximum performance is observed for the triple-shelled catalyst, reaching a CO conversion of 100% and CO2 selectivity of 91% at 95 °C. The triple-shelled catalyst also displays a broad temperature window for CO total conversion from 95 °C to 195 °C. The findings are attributed to the enhanced exposure of the active sites on the surface of the triple-shelled architecture, fine-tunable geometric and electronic interactions, and increased space inside the catalyst, which together amplify the reactant access and interaction.

Background Previous studies have demonstrated that exposure to nickel nanoparticles (Nano-Ni) causes oxidative stress and severe, persistent lung inflammation, which are strongly associated with pulmonary toxicity. However, few studies have investigated whether surface modification of Nano-Ni could alter Nano-Ni-induced lung injury, inflammation, and fibrosis in vivo. Here, we propose that alteration of physicochemical properties of Nano-Ni through modification of Nano-Ni surface may change Nano-Ni-induced lung injury, inflammation, and fibrosis. Methods At first, dose–response and time-response studies were performed to observe lung inflammation and injury caused by Nano-Ni. In the dose–response studies, mice were intratracheally instilled with 0, 10, 20, 50, and 100 μg per mouse of Nano-Ni and sacrificed at day 3 post-exposure. In the time-response studies, mice were intratracheally instilled with 50 µg per mouse of Nano-Ni and sacrificed at days 1, 3, 7, 14, 28, and 42 post-instillation. At the end of the experiment, mice were bronchoalveolar lavaged (BAL) and the neutrophil count, CXCL1/KC level, LDH activity, and concentration of total protein in the BAL fluid (BALF) were determined. In the comparative studies, mice were intratracheally instilled with 50 μg per mouse of Nano-Ni or with the same molar concentration of Ni as Nano-Ni of either partially [O]-passivated Nano-Ni (Nano-Ni–P) or carbon-coated Nano-Ni (Nano-Ni–C). At day 3 post-exposure, BAL was performed and the above cellular and biochemical parameters in the BALF were analyzed. The MMP-2/9 protein levels and activities in the BALF and mouse lung tissues were also determined. Mouse lung tissues were also collected for H&E staining, and measurement of thiobarbituric acid reactive substances (TBARS) and 8-hydroxy-2′-deoxyguanosine (8-OHdG) in the genomic DNA. At day 42 post-exposure, mouse right lung tissues were collected for H&E and Trichrome stainings, and left lung tissues were collected to determine the hydroxyproline content. Results Exposure of mice to Nano-Ni resulted in a dose–response increase in acute lung inflammation and injury reflected by increased neutrophil count, CXCL1/KC level, LDH activity, and concentration of total protein in the BALF. The time-response study showed that Nano-Ni-induced acute lung inflammation and injury appeared as early as day 1, peaked at day 3, and attenuated at day 7 post-instillation. Although the neutrophil count, CXCL1/KC level, LDH activity, and concentration of total protein in the BALF dramatically decreased over the time, their levels were still higher than those of the controls even at day 42 post-exposure. Based on the results of the dose- and time-response studies, we chose a dose of 50 µg per mouse of Nano-Ni, and day 3 post-exposure as short-term and day 42 post-exposure as long-term to compare the effects of Nano-Ni, Nano-Ni–P, and Nano-Ni–C on mouse lungs. At day 3 post-exposure, 50 μg per mouse of Nano-Ni caused acute lung inflammation and injury that were reflected by increased neutrophil count, CXCL1/KC level, LDH activity, concentration of total protein, and MMP-2/9 protein levels and activities in the BALF. Nano-Ni exposure also caused increased MMP-2/9 activities in the mouse lung tissues. Histologically, infiltration of large numbers of neutrophils and macrophages in the alveolar space and interstitial tissues was observed in mouse lungs exposed to Nano-Ni. Nano-Ni–P exposure caused similar acute lung inflammation and injury as Nano-Ni. However, exposure to Nano-Ni–C only caused mild acute lung inflammation and injury. At day 42 post-exposure, Nano-Ni caused extensive interstitial fibrosis and proliferation of interstitial cells with inflammatory cells infiltrating the alveolar septa and alveolar space. Lung fibrosis was also observed in Nano-Ni–P-exposed lungs, but to a much lesser degree. Only slight or no lung fibrosis was observed in Nano-Ni–C-exposed lungs. Nano-Ni and Nano-Ni–P, but not Nano-Ni–C, caused significantly elevated levels of TBARS in mouse lung tissues and 8-OHdG in mouse lung tissue genomic DNA, suggesting that Nano-Ni and Nano-Ni–P induce lipid peroxidation and oxidative DNA damage in mouse lung tissues, while Nano-Ni–C does not. Conclusion Our results demonstrate that short-term Nano-Ni exposure causes acute lung inflammation and injury, while long-term Nano-Ni exposure causes chronic lung inflammation and fibrosis. Surface modification of Nano-Ni alleviates Nano-Ni-induced pulmonary effects; partially passivated Nano-Ni causes similar effects as Nano-Ni, but the chronic inflammation and fibrosis were at a much lesser degree. Carbon coating significantly alleviates Nano-Ni-induced acute and chronic lung inflammation and injury.

Catalysts for energy related applications, in particular metallic nanoalloys, readily undergo atomic-level changes during electrochemical reactions. The origin, dynamics and implications of the changes for the catalysts' activity inside fuel cells though are not well understood. This is largely because they are studied on model nanoalloy structures under controlled laboratory conditions. Here we use combined synchrotron X-ray spectroscopy and total scattering to study the dynamic behaviour of nanoalloys of Pt with 3d-transition metals as they function at the cathode of an operating proton exchange membrane fuel cell. Results show that the composition and atomic structure of the nanoalloys change profoundly, from the initial state to the active form and further along the cell operation. The electrocatalytic activity of the nanoalloys also changes. The rate and magnitude of the changes may be rationalized when the limits of traditional relationships used to connect the composition and structure of nanoalloys with their electrocatalytic activity and stability, such as Vegard's law, are recognized. In particular, deviations from the law inherent for Pt-3d metal nanoalloys can well explain their behaviour under operating conditions. Moreover, it appears that factors behind the remarkable electrocatalytic activity of Pt-3d metal nanoalloys, such as the large surface to unit volume ratio and "size misfit" of the constituent Pt and 3d-transition metal atoms, also contribute to their instability inside fuel cells. The new insight into the atomic-level evolution of nanoalloy electrocatalysts during their lifetime is likely to inspire new efforts to stabilize transient structure states beneficial to their activity and stability under operating conditions, if not synthesize them directly.

Understanding the structural ordering and orientation of interfacial molecular assemblies requires an insight into the penetration depth of the probe molecules which determines the interfacial reactivity. In contrast to the conventional liquid probe-based contact angle measurement in which penetration depth is complicated by the liquid cohesive interaction, we report here a new approach that features a simple combination of vaporous hexane, which involves only van der Waals interaction, and quartz crystal microbalance operated at the third harmonic resonance, which is sensitive to sub-monolayer (0.2%) adsorption. Using this combination, we demonstrated the ability of probing the structural ordering and orientation of the self-assembled monolayers with a sensitivity from penetrating the top portion of the monolayers to interacting with the very top atomic structure at the interface. The determination of the dependence of the adsorption energy of vaporous hexane on the penetration depth in the molecular assembly allowed us to further reveal the atomic-scale origin of the odd–even oscillation, which is also substantiated by density functional theory calculations. The findings have broader implications for designing interfacial reactivities of molecular assemblies with atomic-scale depth precision.

Safe administration of highly cytotoxic chemotherapeutic drugs is a challenging problem in cancer treatment due to the adverse side effects and collateral damage to non-tumorigenic cells. To mitigate these problems, new promising approaches, based on the paradigm of controlled targeted drug delivery (TDD), utilizing drug nanocarriers with biorecognition ability to selectively target neoplastic cells, are being considered in cancer therapy. Herein, we report on the design and testing of a nanoparticle-grid based biosensing platform to aid in the development of new targeted drug nanocarriers. The proposed sensor grid consists of superparamagnetic gold-coated core-shell Fe2Ni@Au nanoparticles, further functionalized with folic acid targeting ligand, model thiolated chemotherapeutic drug doxorubicin (DOX), and a biocompatibility agent, 3,6,-dioxa-octanethiol (DOOT). The employed dual transduction based on electrochemical and enhanced Raman scattering detection have enabled efficient monitoring of the drug loading onto the nanocarriers, attached to the sensor surface, as well as the drug release under simulated intracellular conditions. The grid’s nanoparticles serve here as the model nanocarriers for new TDD systems under design and optimization. The superparamagnetic properties of the Fe2Ni@Au NPs aid in nanoparticles’ handling and constructing a dense sensor grid with high plasmonic enhancement of the Raman signals due to the minimal interparticle distance.

Harnessing interparticle spatial properties of surface assembly of nanoparticles (SAN) on flexible substrates is a rapidly emerging front of research in the design and fabrication of highly-sensitive strain sensors. It has recently shown promising potentials for applications in wearable sensors and skin electronics. SANs feature 3D structural tunability of the interparticle spatial properties at both molecular and nanoscale levels, which is transformative for the design of intriguing strain sensors. This review will present a comprehensive overview of the recent research development in exploring SAN-structured strain sensors for wearable applications. It starts from the basic principle governing the strain sensing characteristics of SANs on flexible substrates in terms of thermally-activated interparticle electron tunneling and conductive percolation. This discussion is followed by descriptions of the fabrication of the sensors and the proof-of-concept demonstrations of the strain sensing characteristics. The nanoparticles in the SANs are controllable in terms of size, shape, and composition, whereas the interparticle molecules enable the tunability of the electrical properties in terms of interparticle spatial properties. The design of SAN-derived strain sensors is further highlighted by describing several recent examples in the explorations of their applications in wearable biosensor and bioelectronics. Fundamental understanding of the role of interparticle spatial properties within SANs at both molecular and device levels is the focal point. The future direction of the SAN-derived wearable sensors will also be discussed, shining lights on a potential paradigm shift in materials design in exploring the emerging opportunities in wearable sensors and skin electronics.

As a promising substitute for fossil fuels, hydrogen has emerged as a clean and renewable energy. A key challenge is the efficient production of hydrogen to meet the commercial-scale demand of hydrogen. Water splitting electrolysis is a promising pathway to achieve the efficient hydrogen production in terms of energy conversion and storage in which catalysis or electrocatalysis plays a critical role. The development of active, stable, and low-cost catalysts or electrocatalysts is an essential prerequisite for achieving the desired electrocatalytic hydrogen production from water splitting for practical use, which constitutes the central focus of this review. It will start with an introduction of the water splitting performance evaluation of various electrocatalysts in terms of activity, stability, and efficiency. This will be followed by outlining current knowledge on the two half-cell reactions, hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), in terms of reaction mechanisms in alkaline and acidic media. Recent advances in the design and preparation of nanostructured noble-metal and non-noble metal-based electrocatalysts will be discussed. New strategies and insights in exploring the synergistic structure, morphology, composition, and active sites of the nanostructured electrocatalysts for increasing the electrocatalytic activity and stability in HER and OER will be highlighted. Finally, future challenges and perspectives in the design of active and robust electrocatalysts for HER and OER towards efficient production of hydrogen from water splitting electrolysis will also be outlined.

Alloying noble metals with non-noble metals enables high activity while reducing the cost of electrocatalysts in fuel cells. However, under fuel cell operating conditions, state-of-the-art oxygen reduction reaction alloy catalysts either feature high atomic percentages of noble metals (>70%) with limited durability or show poor durability when lower percentages of noble metals (, Durability of catalysts under fuel cell reaction conditions is challenging for active nanoalloy electrocatalysts derived from platinum group metals and other transition metals. Here, the authors show that realloying in certain multimetallic nanoalloys plays a major role in enabling the high durability.

The ability to tune the synergistic properties of heterogeneous catalysts by manipulating the surface composition, structure, and morphology is critical for achieving the desired catalytic performance, especially for metal and alloy catalysts at the nanoscale sizes. However, the control of the surface composition, structure, and morphology of nanocatalysts is challenging due to the highly dynamic nature of atoms on the surface or in the bulk phase of the metal or alloy nanomaterials. This chapter focuses on discussing recent findings of the investigations of the composition, structure, and morphology of metal and alloy nanoparticle catalysts, especially those involving dynamic core–shell and alloy structures. Insights into the structural synergies of their catalytic and electrocatalytic properties in reactions such as oxygen reduction reaction and hydrocarbon oxidation reaction. The development of active, stable, and low-cost heterogeneous catalysts for these reactions will contribute to the global drive to sustainable energy and environment.

ConspectusMultimetallic nanomaterials containing noble metals (NM) and non-noble 3d-transition metals (3d-TMs) exhibit unique catalytic properties as a result of the synergistic combination of NMs and 3d-TMs in the nanostructure. The exploration of such a synergy depends heavily on the understanding of the atomic-scale structural details of NMs and 3d-TMs in the nanomaterials. This has attracted a great deal of recent interest in the field of catalysis science, especially concerning the core-shell and alloy nanostructures. A rarely asked question of fundamental significance is how the core-shell and alloy structural arrangements of atoms in the multimetallic nanomaterials dynamically change under reaction conditions, including reaction temperature, surface adsorbate, chemical environment, applied electrochemical potential, etc. The dynamic evolution of the core-shell/alloy structures under the reaction conditions plays a crucial role in the catalytic performance of the multimetallic nanocatalysts.This Account focuses on the dynamic structure characteristics for several different types of composition-tunable alloy and core-shell nanomaterials, including phase-segregated, elemental-enriched, dynamically evolved, and structurally different core-shell structures. In addition to outlining core-shell/alloy structure formation via processes such as seed-mediated growth, thermochemical calcination, adsorbate-induced evolution, chemical dealloying, underpotential deposition/galvanic displacement, etc., this Account will highlight the progress in understanding the dynamic core-shell/alloy structures under chemical or catalytic reaction conditions, which has become an important focal point of the research fronts in catalysis and electrocatalysis. The employment of advanced techniques, especially in situ/operando synchrotron high-energy X-ray diffraction and pair distribution function analyses, has provided significant insights into the dynamic evolution processes of NM/3d-TM nanocatalysts under electrocatalytic or fuel cell operating conditions. Examples will highlight Pt- or Pd-based nanoparticles and nanowires alloyed with various 3d-TMs with a focus on their structural evolution under reaction conditions. While the dynamic process is complex, the ability to gain an insight into the evolution of core-shell and alloy structures under the catalytic reaction condition is essential for advancing the design of multimetallic nanocatalysts. This Account serves as a springboard from fundamental understanding of the core-shell and alloy structural dynamics to the various applications of nanostructured catalysts/electrocatalysts, especially in the fronts of energy and environmental sustainability.

Here, a new strategy is reported for the preparation of a new class of nanocomposite anode materials consisting of ppm-level phosphorus-doped Si nanoparticles (P-Si) wrapped in a network of poly-γ-glutamate and graphene. The network produces not only a conductivity-enhanced conduit but also a mechanical stress buffer. The incorporation of poly-γ-glutamate in the nanocomposite enables self-healing capability and maintains the electrode structural integrity. This multifunctionality has significant implications for advancing the design of stable Si-based nanomaterials as high-performance anodes in Li-ion batteries.

Alloying noble metals with non-noble metals enables high activity while reducing the cost of electrocatalysts in fuel cells. However, under fuel cell operating conditions, state-of-the-art oxygen reduction reaction alloy catalysts either feature high atomic percentages of noble metals (>70%) with limited durability or show poor durability when lower percentages of noble metals (

Metal nanoparticles, especially gold and its alloy, core–shell, or nanocomposites function as theranostic probes or vehicles with amplified optical, spectroscopic, electrical and magnetic signals, or unique bio-functional, bio-compatible properties upon the desired bio-conjugation. Exploration of these functions is inherently linked to the ability to control the size, shape, composition, and surface properties, which depends to a large degree on the understanding of the controllability of these nanostructure parameters in the synthesis and processing. Aggregative growth constitutes an important pathway for the control of size, shape and composition in synthesis and processing of nanoparticles. This article highlights recent progress in the exploration of aggregative growth for the control of size, shape, and composition of metal nanoparticles. Examples such as thermally-activated aggregative growth of gold, copper, copper sulfide, alloy nanoparticles, and core–shell nanoparticles with magnetic cores and gold shells are discussed. The focus is to highlight the significance of understanding the mechanistic aspects in establishing the controllability over size, shape, and composition for further harnessing the unique nanoscale properties toward desired bioapplications.

The ability to harness the nanoscale structural properties is essential for the exploration of functional properties of nanomaterials. This report demonstrates a novel strategy exploring bifunctional nanoparticles for spectroscopic detection and magnetic intervention of DNA assembly, disassembly, and enzyme cutting processes in a solution phase. In contrast to existing single-function based approaches, this strategy exploits magnetic MnZn ferrite nanoparticles decorated with gold or silver on the surface to retain adequate magnetization while producing sufficient plasmonic resonance features to impart surface-enhanced Raman scattering (SERS) functions. The decoration of MnZn ferrite nanoparticles with Au or Ag (MZF/Au or MZF/Ag) was achieved by thermally activated deposition of Au or Ag atoms/nanoparticles on MZF nanoparticles. Upon interparticle double-stranded DNA linkage of the MZF/Au (or MZF/Ag) nanoparticles with gold nanoparticles labeled with a Raman reporter, the resulting interparticle “hot spots” are shown to enable real time SERS monitoring of the DNA assembly, disassembly, or enzyme cutting processes, where the magnetic component provides an effective means for intervention of the biomolecular processes in the solution. The unique bifunctional combination of the SERS “hot spots” and the magnetic separation capability serves as the first example of bifunctional nanoprobes for biomolecular recognition and intervention.

Fibrous materials serve as an intriguing class of 3D materials to meet the growing demands for flexible, foldable, biocompatible, biodegradable, disposable, inexpensive, and wearable sensors and the rising desires for higher sensitivity, greater miniaturization, lower cost, and better wearability. The use of such materials for the creation of a fibrous sensor substrate that interfaces with a sensing film in 3D with the transducing electronics is however difficult by conventional photolithographic methods. Here, a highly effective pathway featuring surface-mediated interconnection (SMI) of metal nanoclusters (NCs) and nanoparticles (NPs) in fibrous materials at ambient conditions is demonstrated for fabricating fibrous sensor substrates or platforms. Bimodally distributed gold-copper alloy NCs and NPs are used as a model system to demonstrate the semiconductive-to-metallic conductivity transition, quantized capacitive charging, and anisotropic conductivity characteristics. Upon coupling SMI of NCs/NPs as electrically conductive microelectrodes and surface-mediated assembly (SMA) of the NCs/NPs as chemically sensitive interfaces, the resulting fibrous chemiresistors function as sensitive and selective sensors for gaseous and vaporous analytes. This new SMI-SMA strategy has significant implications for manufacturing high-performance fibrous platforms to meet the growing demands of the advanced multifunctional sensors and biosensors.

To obtain high corrosion protection and break the bottleneck arising from galvanic corrosion between Ni layer and Mg alloy substrate, we report herein a triple-layer composite coating approach, consisting of Ni (ENP) underlayer, NiAl-layered double hydroxide (LDH) middle layer, and silane (PFDTMS) toplayer, i.e., ENP/LDH/PFDTMS. This nanocomposite coating was prepared on the Mg alloy surface by a combination of simple electroless plating, hydrothermal-assisted in situ growth, and condensation reaction. The surface morphology, structure, and chemical composition of the resulting composite coating are characterized using several techniques, including scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The corrosion protection performance of the composite coating in a saline solution is evaluated by electrochemical impedance spectroscopy (EIS), Tafel curve, and immersion measurements. The results indicated that the ENP/LDH/PFDTMS composite coating possesses a much higher corrosion resistance than the single Ni coating and the LDH-grown Ni (ENP/LDH) coating. In contrast to the severe galvanic corrosion the Mg alloy with single Ni coating observed in two days of exposure, the substrate with either ENP/LDH/PFDTMS coating or ENP/LDH coating is shown to exbibit no galvanic corrosion phenomenon even after 30 days of exposure. Moreover, the result from tests including contact angle measurement of the ENP/DLH/PFDTMS coating demonstrates the superhydrophobic function to several typical liquids in daily life and the good self-cleaning capability after contamination by graphite powder. These findings provide a fresh insight into the design of advanced coatings for inhibiting galvanic corrosion between Ni layer and Mg alloy.

Understanding how the shape of a nanocatalyst alters its catalytic performance is essential for the design of active catalysts at the nanoscale. This report describes novel findings of an investigation of CuO/CeO2 nanocatalysts with different shapes for preferential CO oxidation (CO-PROX), aiming at unraveling the structural origin of the high catalytic activity. CuO/CeO2 catalysts with a series of shapes, including octahedron, rod, cube, sphere and spindle morphologies, were synthesized by a combination of hydrothermal and impregnation methods. By probing the structure, elementary valence and reductivity of the catalysts using an array of techniques, an intriguing structure-activity synergy is revealed, pinning the origin of the highest catalytic activity to the intersection of the nanocrystal planes. The CuO/CeO2 catalysts with spheres and spindles featuring exposed {111} and {002} crystal planes of CeO2 were found to exhibit the lowest reaction temperature in terms of 50% CO conversion and a wider temperature window for the complete CO conversion in CO-PROX. The catalytic synergy reflects a combination of high surface area, reduced state of copper sites, high oxygen vacancies, as well as stronger interaction between CuO and CeO2. This synergy was further substantiated by analysis of the results based on DFT calculation, showing that the oxygen vacancies were the highest at the intersection of {111} and {002} facets, but the lowest on CeO2 {111} surface. The finding of {111} and {002} facets with an increased oxygen vacancy and a stronger metal-support interaction for improving the catalytic performance has important implications for designing facet-tunable nanocatalysts for efficient PROX.