Natural antimicrobials synergistically coupled with nanomotors: An innovative strategy for biofilm eradication

Biofilms are one of the most important problems occurring in industrial environments, especially in food industry. The possibility of foodborne disease outbreaks as a result of biofilm-food cross-contamination is a distinct concern, along with the substantial costs associated with food spoilage and biofilm control. Besides, despite daily cleaning and disinfection, many bacteria grow in machines and surfaces in food processing plants, some of them forming biofilms. A promising procedure for disinfection and biofilm elimination could be the use of hybrid antimicrobial nanomaterials endowed with motion (i.e., nanomotors). Herein, we report Janus nanoparticles based on the conjunction of platinum and mesoporous silica nanoparticles, functionalized with a derivative of a natural antimicrobial compound, vanillin. The engineered nanomotors combine H2O2-triggered self-propulsion with the antimicrobial activity of vanillin, allowing enhanced physical penetration into the 3D matrix formed by the exopolymeric substances generated in monospecies (Staphylococcus aureus) and multispecies (S. aureus and Escherichia coli) biofilms and the subsequent elimination of pathogenic cells.

Glucose-Fueled Gated Nanomotors: Enhancing In Vivo Anticancer Efficacy via Deep Drug Penetration into Tumors

Bioinspired nano/micromotors with drug delivery capabilities are emerging tools with the promising potential to treat numerous diseases. However, some major challenges must be overcome before reaching real biomedical applications. Above all, it is necessary to design engines that employ biocompatible and bioavailable fuels to induce efficient propulsion in biological environments. In addition, ideal nanomotors should also be capable of delivering the cargo on-command using selected stimuli. To tackle these challenges, we herein present the design and evaluation (both in vitro and in vivo) of a glucose-driven gated Janus nanomotor that performs on-demand anticancer drug delivery to treat solid tumors. The motor's nanoarchitectonics is based on the anisotropic conjunction of catalytic platinum nanodendrites (PtNds) and a mesoporous silica nanoparticle (acting as a nanocontainer for anticancer drug doxorubicin) capped with enzyme glucose oxidase (GOx). Autonomous nanomotor movement is achieved thanks to two catalytic components, GOx and PtNds, in a hybrid cascade reaction: GOx transforms glucose to give H2O2 that is subsequently catalyzed by PtNds into H2O and O2. Besides, gatekeeper moieties (GOx) respond to the presence of intracellular proteases, which induces doxorubicin delivery. Biological experiments with the nanomotor are carried out in cancer cell cultures, three-dimensional (3D) tumor models (spheroids), in vivo and in patient-derived organoids (PDOs). A strong anticancer effect is found and attributed to the synergistic combination glucose-induced propulsion, controlled drug delivery, elimination of glucose (by GOx), ROS production (H2O2 generation by GOx) and hypoxia reduction (O2 generated by PtNds). Taken together, this study advances the engineering of endogenously fueled nanomotors for in vivo operation and provides insights into the application of active particles in cancer therapy toward clinical application.

Neighboring Effect of Adjacent Nitrogen Sites on Vinylene Linkage in Covalent Organic Frameworks for Regulating Oxygen Reduction Reaction

Vinylene-linked covalent organic frameworks (COFs) are attractive electrocatalysts owing to their corresponding high chemical stability and excellent conjugated frameworks. In this study, for the first time, the methyl group of the pyrimidine ring was used to synthesize conjugated COFs (TB-TFT-COF and TB-TFC-COF) with vinylene linkages, which were employed as catalysts for the oxygen reduction reaction (ORR). In addition, local electronic structures of the vinylene linkages could be regulated by the adjacent nitrogen atomic sites of various functional moieties (triazine, pyridine, and pyrimidine), resulting in tunable electrocatalytic activity and selectivity of the COFs. Notably, the TB-TFT-COF attained a half-wave potential of 0.74 V relative to RHE alongside superior electrochemical stability, matching the performance of metal-free COF-based catalysts for ORR. Furthermore, as evidenced by density functional theory (DFT) calculations, the adjacent nitrogen sites of the pyrimidine unit around the vinylene linkage are crucial for enhancing the utilization of electrocatalytic active sites. This work establishes that the precise modulation of electronic coupling between neighboring active sites enables the development of efficient oxygen reduction reaction catalysts.

Intentional Formation of Persistent Surface Redox Mediators by Adsorption of Polyconjugated Carbonyl Complexes to Pd Nanoparticles

Adsorbing polyconjugated carbonyl and aromatic species to Pd nanoparticles forms persistent intermediates that mediate reactions between hydrogen and oxygen-derived species. These surface redox mediators form in situ and increase selectivities toward H2O2 formation (∼65-85%) compared to unmodified Pd nanoparticles (∼45%). Infrared spectroscopy, temperature-programmed oxidation measurements, and ab initio calculations show that these species adsorb irreversibly to Pd surfaces and persist over extended periods of catalysis. Combined rates and kinetic isotope effect measurements and simulations suggest that carbonyl groups of bound organics react heterolytically with hydrogen to form partially hydrogenated oxygenated complexes. Subsequently, these organic species transfer proton-electron pairs to O2-derived surface species via pathways that favor H2O2 over H2O formation on Pd nanoparticles. Computational and experimental measurements show redox pathways mediated by partially hydrogenated carbonyl species form H2O2 with lower barriers than competing processes while also obstructing O-O bond dissociation during H2O formation. For example, adsorption and hydrogenation of hexaketocyclohexane on Pd forms species that react with oxygen with high H2O2 selectivities (85 ± 8%) for 130 h on stream in flowing water without additional promoters or cosolvents. These paths resemble the anthraquinone auto-oxidation process (AAOP) used for industrial H2O2 production. These surface-bound species form partially hydrogenated intermediates that mediate H2O2 formation with high rates and selectivities, comparable to AAOP but on a single catalytic nanoparticle in pure water without organic solvents or multiunit reaction-separation chains. The molecular insights developed herein provide strategies to avoid organic solvents in selective processes and circumvent their associated process costs and environmental impacts.

Direct Visualization of Temperature-Induced Phase Separation of Completely Miscible Au─Pd Alloy by In Situ TEM

In situ transmission electron microscopy (TEM) studies reveal key insights into the structural and chemical evolution of nanoparticles (NPs) under external stimuli like heating and biasing, which is critical for evaluating their suitability in chemical reactions and their tendency toward forming novel NP systems. In this study, starting from a core@shell Au nanotriangle (AuNT)@Pd nanostructure, the formation of a phase-separated bi-metallic Au─Pd NP system at high temperature is reported, despite the fact that Au and Pd are miscible in the entire composition and temperature range. In situ TEM heating of bare AuNT@Pd core@shell structures up to 1000 °C is performed. Between 400 and 800 °C, an initial alloy formation is observed. Notably, higher initial loading of Pd increases the melting temperature of the bi-metallic system. However, the most important observation is the separation of the nanostructure into Au and Pd phases at temperatures above 850 °C for high Pd doping. The extent of Pd separation depends on the amount of initial Pd loading. A Janus Au─Pd nanostructure is formed at the end of the thermal treatments at 1000 °C. The phase-separated NP is observed to be highly stable and could be clearly beneficial for various applications, particularly in catalytic processes.

Simultaneous Enhancement of the Activity and Durability of the Oxygen Reduction Reaction via Pd3Mo@Pt/C Catalysts

To overcome the limitations of conventional bimetallic catalysts in facilitating the oxygen reduction reaction (ORR), we employed density functional theory (DFT) screening to evaluate ternary Pd3X@Pt core@shell catalysts (X = transition metals), with the objective of increasing both the ORR activity and durability. Among the 25 candidates, Pd3Mo@Pt emerges as the most promising catalyst, showing a combination of a low limiting potential and a high dissolution potential. Experimental validation reveals that the carbon-supported Pd3Mo@Pt/C catalysts clearly exhibit exceptional mass activity (3.76 A mgPt-1) and specific activity (1.67 mA cm-2); these activities significantly surpass those of their Pt/C counterparts by factors of 10.2 and 3.18, respectively. Furthermore, these core@shell catalysts exhibit robust durability, while also exhibiting enhanced CO tolerance, as evidenced by CO stripping voltammetry. DFT calculations show that the superior activity and stability of Pd3Mo@Pt/C are attributed to the optimal modulation of the Pt surface electronic structures by the core elements, particularly Mo.

Screening of single-atomic catalysts loaded on two-dimensional transition metal dichalcogenides for electrocatalytic oxygen reduction via high throughput ab initio calculations

The design and screening of low cost and high efficiency oxygen reduction reaction (ORR) electrocatalysts is vital in the realms of fuel cells and metal-air batteries. Existing studies largely rely on the calculation of absorption free energy, a method established 20 years ago by Jens K. Nørskov. However, the study of electrocatalysts grounded solely on free energy calculation often lacks in-depth analysis, particularly overlooking the influence of solvent and electrode potential. In this regard, we here present a novel approach using constant-potential and ab initio molecular dynamics (AIMD) simulation to screen single-atom catalysts loaded on transition metal dichalcogenides (SA@TMDs) for ORR. An extensive investigation of 1584 SA@TMDs results in 20 high performing ORR catalysts with overpotential less than 0.33 V and high working stability. In addition, our study shows that the electrode potential has different effects on the adsorption energy of *OOH, *O and *OH, which leads to a reversal of the rate-determining step (RDS) of the ORR. This work presents not only credible, high-performance catalyst candidates for experimental exploration, but also significantly improves our understanding on the reaction mechanism of ORR under realistic reaction conditions.

Enhancing the oxygen evolution reaction by tuning the electrode-electrolyte interface in nickel-based electrocatalysts

A comprehensive understanding of the electrode-electrolyte interface in energy conversion systems remains challenging due to the complex and multifaceted nature of interfacial processes. This complexity hinders the development of more efficient electrocatalysts. In this work, we propose a hybrid approach to the theoretical description of the OER process on nickel-iron-based oxyhydroxides (γ-Ni1-xFexOOH) electrodes in alkaline media as a model system. Multiple reaction pathways represented by the single- and dual-site mechanisms were investigated by taking into account the realistic structure of the catalyst, the doping, and the solvation effects using a simple and computationally feasible strategy. Accounting for the variable solvation effects considerably affects the predicted overpotential in a roughly linear relationship between overpotential and dielectric constant. By incorporating quantum chemical simulations with kinetic modeling, we demonstrate that tuning the local solvation environment can significantly enhance the OER activity, opening new routine ways for elucidation of the emerging issues of OER processes on transition metal oxide surfaces and design of cost-effective, efficient electrocatalytic systems.

Enhanced Catalytic Activity of Pt Nanostructured Electrodes Deposited by Spark Ablation for Proton Exchange Membrane Fuel Cells

Catalyst layers play a crucial role in determining the performance of proton exchange membrane fuel cells (PEMFCs). However, the deposition of catalyst layers poses challenges in PEMFC stack production due to the complexity of the fabrication steps. Herein, we present a simplified approach to synthesize Pt nanostructures via spark ablation and simultaneously deposit them onto gas diffusion layers (GDL). The in situ deposited catalyst layers on GDL serve as electrodes for membrane electrode assembly (MEA) fabrication. Moreover, the carrier gas in the spark ablation process significantly influences the nucleation and growth of the Pt nanostructures. Pt nanostructures produced in forming gas (Pt_FG, 95% nitrogen, and 5% hydrogen) exhibit dendritic morphology distinct from those obtained in pure N2 (Pt_N2). Investigating the catalytic activity of Pt synthesized in different carrier gases reveals that the Pt_FG catalyst demonstrates enhanced half-wave potential, mass activity, and durability compared to those of Pt_N2 and commercial Pt-black catalysts. Single-cell measurements evaluate the electrocatalytic activity of the ionomer-free, in situ deposited catalyst layers. The Pt_FG MEA (0.2 mgPt cm-2) achieves a power density of 1285 mW cm-2 at 70 °C, 200 kPa, approximately 1.8 and 2 times higher than Pt_N2 and Pt-black MEAs, respectively. Further reduction of the catalyst loading to 0.1 mgPt cm-2 results in the Pt_FG MEA delivering 961 mW cm-2, indicating enhanced catalytic activity and Pt utilization efficiency. This study provides insights into fabricating catalytic layers using a facile strategy, circumventing the need for catalyst synthesis, ink formation, and electrode coating techniques.

Direct control of electron spin at an intrinsically chiral surface for highly efficient oxygen reduction reaction

The oxygen reduction reaction (ORR) in acidic media suffers from sluggish kinetics, primarily due to the spin-dependent electron transfer involved. The direct generation of spin-polarized electrons at catalytic surfaces remains elusive, and the underlying mechanisms are still controversial due to the lack of intrinsically chiral catalysts. To address this challenge, we investigate topological homochiral PdGa (TH PdGa) crystals with intrinsically chiral catalytic surfaces for ORR. Through spin-resolved photoemission spectroscopy and theoretical simulations, we show that both structural chirality and spin-orbit coupling are critical for inducing spin polarization at the surface of TH PdGa. As a result, TH PdGa achieves a kinetic current density over 100 times higher than the achiral PdGa (AC PdGa) at 0.85 V versus the reversible hydrogen electrode. This work underscores the pivotal role of spin polarization in enhancing acidic ORR activity and lays the groundwork for the rational design of chiral catalysts for spin-dependent catalysis.

Ultrasmall High-Entropy-Alloy Nanozyme Catalyzed In Vivo ROS and NO Scavenging for Anti-Inflammatory Therapy

High-entropy alloy (HEA) nanoparticles possess finely tunable and multifunctional catalytic activity due to their extremely diverse adsorption sites. Their unique properties enable HEA nanoparticles to mimic the complex interactions of the redox homeostasis system, which is composed of cascade and multiple enzymatic reactions. The application of HEAs in mimicking complex enzymatic systems remains relatively unexplored, despite the importance of regulating biological redox reactions. Here, it is reported that ultra-small (<10 nm in a diameter) HEA nanozymes consisting of five platinum-group metals with tunable morphologies from planar to dendritic structures are synthesized. The synthesized HEA nanozymes exhibited higher peroxidase-like activity compared to monometallic platinum-group nanoparticles. Additionally, HEA nanoparticles effectively mimicked RONS-regulation metabolism in cascade reactions involving superoxide dismutase and catalase, as well as in multiple reactions including HORAC and NO scavenging. As a result, the HEA nanozyme exhibited superior anti-inflammatory efficacy both in vitro and in vivo. The findings underscore the effectiveness of the high-entropy alloy structure in restoring in vivo enzymatic systems through intrinsic activity enhancements and cascade reaction mechanisms.

Modulation in Spin State of Co3O4 Decorated Fe Single Atom Enables a Superior Rechargeable Zinc-Air Battery Performance

High-performance bifunctional electrocatalyst for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is the keystone for the industrialization of rechargeable zinc-air battery (ZAB). In this work, the modulation in the spin state of Fe single atom on nitrogen doped carbon (Fe1-NC) is devised by Co3O4 (Co3O4@Fe1-NC), and a mediate spin state is recorded. Besides, the d band center of Fe is downshifted associated with the increment in eg filling revealing the weakened interaction with OH* moiety, resulting in a boosted ORR performance. The ORR kinetic current density of Co3O4@Fe1-NC is 2.0- and 5.6 times higher than Fe1-NC and commercial Pt/C, respectively. Moreover, high spin state is found for Co in Co3O4@Fe1-NC contributing to the accelerated surface reconstruction of Co3O4 witnessed by operando Raman and electrochemical impedance spectroscopies. A robust OER activity with overpotential of 352 mV at 50 mA cm-2 is achieved, decreased by 18 and 60 mV by comparison with Co3O4@NC and IrO2. The operando Raman reveals a balanced adsorption of OH* species and its deprotonation leading to robust stability. The ZAB performance of Co3O4@Fe1-NC is 193.2 mW cm-2 and maintains for 200 h. Furthermore, the all-solid-state ZAB shows a promising battery performance of 163.1 mW cm-2.

Cucurbit[n]uril-Derived Electrocatalysts for Oxygen Evolution, Oxygen Reduction, and Hydrogen Evolution Reactions

Various sustainable energy conversion techniques like water electrolyzers, fuel cells, and metal-air battery devices are promising to alleviate the issues in fossil fuel consumption. However, their broad employment has been mainly inhibited by the lack of advanced electrocatalysts to accelerate the sluggish kinetics of the three involved half-reactions including oxygen evolution reaction (OER), oxygen reduction reaction (ORR), and hydrogen evolution reaction (HER). Recent advances have witnessed the cucurbit[n]uril (CB[n])-directed strategy as a prominent tool to develop high performance electrocatalysts with either OER, ORR, or HER activities. In this review, the recent progress on CB[n]-derived electrocatalysts ranging from molecular complexes to heterogeneous nanostructures and single-atoms for the three half-reactions are reviewed, and future opportunities are discussed. A concise introduction to the fundamentals of CB[n]s regarding their synthesis, structure, and chemistry is given first. Subsequently, the systematic summary of CB[n]-derived electrocatalysts and their performance for the OER/ORR/HER are discussed in detail, with a specific emphasis on correlating their structure and activities by combining diverse physiochemical characterizations, electrochemical experiments, and theory simulations. Finally, a brief conclusion and perspective for future opportunities regarding CB[n]-derived electrocatalysts for many other electrocatalytic applications are proposed.

Application of Hydrogenated Graphitic Supports in Electrocatalysts: Effects on Carbon Support Surface Chemistry, Nanoparticle Growth, and Electrocatalytic Activity

One of the key technical challenges before the widespread adoption of proton exchange membrane fuel cells (PEMFCs) is increasing the durability of the platinum catalyst layer to meet a target of 8000 operating hours with only a 10% loss of performance. Carbon corrosion, one of the primary mechanisms of degradation in fuel cells, has attracted attention from researchers interested in solving the durability problem. As such, the development of catalyst supports to avoid this issue has been a focus in recent years, with interest in hydrophobic supports such as highly graphitized carbons. In this research, we propose a method to increase the durability of carbon supports by way of exploiting hydrogenated graphene's hydrophobic properties. By performing a Birch reduction on graphene nanoplatelets, we were able to synthesize hydrogenated graphene nanoplatelets which were used as support for hollow porous PtNi nanoparticles. The structure of these nanoparticle-carbon composites was characterized by transmission electron microscopy (TEM), energy dispersive spectroscopy coupled with scanning transmission electron microscopy (STEM-EDS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). We found that hydrogenation can strongly affect the morphology of nanoparticles formed as well as increase the electrochemical stability of the composites. Accelerated stress tests for 6000 cycles between 1.0 and 1.6 V vs RHE at 25 °C demonstrated that a hydrogenated support for PtNi increased the retained electrochemical surface from 36.8% to 61.9% when compared to the pristine graphene nanoplatelets. Moreover, the retained activity was increased from 26.6% to 53.0% by use of the hydrogenated carbon support. To confirm that hydrogenation enhanced durability, stress tests combined with Raman spectroscopy showed minimal change in the ID/IG ratio of the hydrogenated composite. Finally, identical location transmission electron microscopy (IL-TEM) was used to support the results of the electrochemical stress tests.

Precisely designing asymmetrical selenium-based dual-atom sites for efficient oxygen reduction

Owing to their synergistic interactions, dual-atom catalysts (DACs) with well-defined active sites are attracting increasing attention. However, more experimental research and theoretical investigations are needed to further construct explicit dual-atom sites and understand the synergy that facilitates multistep catalytic reactions. Herein, we precisely design a series of asymmetric selenium-based dual-atom catalysts that comprise heteronuclear SeN2-MN2 (M = Fe, Mn, Co, Ni, Cu, Mo, etc.) active sites for the efficient oxygen reduction reaction (ORR). Spectroscopic characterisation and theoretical calculations revealed that heteronuclear selenium atoms can efficiently polarise the charge distribution of other metal atoms through short-range regulation. In addition, compared with the Se or Fe single-atom sites, the SeFe dual-atom sites facilitate a reduction in the conversion energy barrier from *O to *OH via the coadsorption of *O intermediates. Among these designed selenium-based dual-atom catalysts, selenium-iron dual-atom catalysts achieves superior alkaline ORR performance, with a half-wave potential of 0.926 V vs. a reversible hydrogen electrode. In addition, the SeN2-FeN2-based Zn-air battery has a high specific capacity (764.8 mAh g-1) and a maximum power density (287.2 mW cm-2). This work may provide a good perspective for designing heteronuclear DACs to improve ORR efficiency.

Boosting the oxygen reduction activity on metal surfaces by fine-tuning interfacial water with midinfrared stimulation

Heterogeneous catalysis at the metal surface generally involves the transport of molecules through the interfacial water layer to access the surface, which is a rate-determining step at the nanoscale. In this study, taking the oxygen reduction reaction on a metal electrode in aqueous solution as an example, using accurate molecular dynamic simulations, we propose a novel long-range regulation strategy in which midinfrared stimulation (MIRS) with a frequency of approximately 1,000 cm-1 is applied to nonthermally induce the structural transition of interfacial water from an ordered to disordered state, facilitating the access of oxygen molecules to metal surfaces at room temperature and increasing the oxygen reduction activity 50-fold. Impressively, the theoretical prediction is confirmed by the experimental observation of a significant discharge voltage increase in zinc-air batteries under MIRS. This MIRS approach can be seamlessly integrated into existing strategies, offering a new approach for accelerating heterogeneous reactions and gas sensing within the interfacial water system.

A review on Pd-M bimetallic electrochemical sensors: Techniques, performance, and applications

Environmental pollution, food safety, and medical diagnostics pose severe threats to human health, making the development of effective detection technologies crucial. Electrochemical sensors, as an efficient detection method, are extensively employed in detecting environmental pollutants, food additives, and biomolecules. Pd-M bimetallic materials, known for their excellent electrocatalytic performance, are extensively utilized as electrode modification materials. Although earlier reviews have covered the sensing applications of bimetallic materials, they have not targeted discussed Pd-based bimetallic materials. This paper systematically summarizes the preparation methods of Pd-M bimetallic materials, explores their structural and morphological regulation, and elaborates on their recent applications in pesticide detection, environmental pollutant detection, food additive detection, drug detection, and biosensing. It enumerates the detection performance of various Pd-M bimetallic material-modified electrochemical sensors for the aforementioned analytes in detail, including specific modification materials, linear range, detection limits, and sensitivity parameters.

High Oxygen Reduction Efficiency and Durability of Nano-Honeycomb Pt3(NiFeCo) Replenished by High-Entropy Metallic Glass Support

Developing low-Pt oxygen reduction reaction (ORR) catalysts with high efficiency and robustness is critical for practical fuel cells. The most advanced ORR catalysts either feature high percentages of Pt (>70 at.%) or exhibit poor durability when reducing Pt loading. Herein, a multicomponent solid-solution Pt3(FeCoNi) honeycomb nano-framework supported by the specially designed high-entropy metallic glass (MG) is reported for efficient ORR. This hybrid catalyst with a low surface Pt loading of 5.79 µg cm-2 displays exceptional mass and specific activities of 7.02 A mgpt -1 and 8.15 mA cmPt -2 at 0.9 V, respectively, which are ≈15 and 22 times higher compared with commercial Pt/C. The analyses reveal the weakened chemisorption of oxygenated species, which is induced by the strong strain and ligand effects originating from the synergistic multicomponent alloying. This in turn enhances the intrinsic ORR activity. Moreover, benefiting from a unique replenishment behavior, the hybrid catalyst delivers ultra-high durability with negligible activity decay even after 50 000 potential cycles. This mechanism is achieved by sacrificing the interior MG supplementary support to dynamically compensate for the loss of catalytically active surface. The work provides an alternative way to design more efficient and durable low-Pt electrocatalysts for electrochemical devices.

Oxygen Vacancy-Mediated Synthesis of Inter-Atomically Ordered Ultrafine Pt-Alloy Nanoparticles for Enhanced Fuel Cell Performance

Pt-based intermetallics are expected to be the highly active catalysts for oxygen reduction reaction (ORR) in proton-exchange membrane fuel cells but still face great challenges in controllable synthesis of interatomically ordered and ultrafine intermetallic nanoparticles. Here, we propose an oxygen vacancy-mediated atomic diffusion strategy by mechanical alloying to reduce the energy barrier of the transition from interatomic disordering to ordering, and to resist interparticulate sintering via strong M-O-C bonding. This synthesis results in a nanosized core/shell structure featuring an interatomically ordered PtM core and a Pt shell of two to three atomic layers in thickness and can be extended to the multicomponent PtM (M = Co, FeCo, FeCoNi, FeCoNiGa) systems. The electron enrichment in the Pt outer shell induced by the compressive strain leads to the enhanced antibonding orbital occupation below the Fermi level and accelerated OH* desorption kinetics. The optimized PtCo-O/C-6 catalyst presents excellent ORR activity (mass activity = 1.28 A mgPt-1 at 0.9 ViR-free, peak power densities = 2.38/1.25 W cm-2 in H2-O2/-air) and durability (∼1% activity loss in over 50 h in air condition) in fuel cells at a total Pt loading of 0.1 mgPt cm-2. Furthermore, we establish a systematic correlation to elucidate the formation mechanisms of highly ordered intermetallic catalysts underlying oxygen vacancies. This study provides a general approach for the large-scale production of highly ordered and nanosized Pt-dispersed intermetallic catalysts.

Unprecedented selectivity behavior in the direct dehydrogenation of n-butane to n-butenes with similar active Pt nanoparticle size: unveiling structural and electronic characteristics of supported monometallic catalysts

In this work, supported Pt monometallic catalysts were prepared using oxide and carbon supports by conventional impregnation methods. Similar Pt metallic nanoparticle sizes (mean sizes about 1.8-2 nm) have been obtained using different Pt precursor loadings (0.3 to 5 wt%). For comparison, catalysts with larger nanoparticle sizes were prepared using the liquid phase reduction method. Characterization results indicate different electronic and structural characteristics for the Pt nanoparticles, comparing nanoparticles with similar and different sizes, implying that both the Pt loading and the preparation method affect the formation of different metallic phases. We used the direct dehydrogenation of n-butane to n-butenes reaction as a test reaction to study the catalytic behavior of the Pt nanoparticles obtained at different Pt atomic concentrations. Surprisingly, Pt catalysts with the lowest metallic loading show the highest selectivities to olefins. Besides, Pt catalysts supported on carbon materials showed higher selectivity to butenes than those supported on oxide materials, this was attributed to a higher electron density in the Pt active sites. Likewise, at low Pt loadings, the CNP-supported Pt nanoparticles could be confined at the defect in the nanotube structure as crystalline agglomerates of atoms with few layers or monolayers with very few surface adatom or stepped adatom nanostructures or simply as a group of atoms, thus creating active Pt sites that favor the dehydrogenation reaction over secondary reactions.

Magnetic Field Enhanced Oxygen Reduction Reaction via Oxygen Diffusion Speedup

The mass-transfer of oxygen in liquid phases (including in the bulk electrolyte and near the electrode surface) is a critical step to deliver oxygen to catalyst sites (especially immersed catalyst sites) and use the full capacity of oxygen reduction reaction (ORR). Despite the extensive efforts of optimizing the complex three-phase reaction interfaces to enhance the gaseous oxygen transfer, strong limitations remain due to oxygen's poor solubility and slow diffusion in electrolytes. Herein, a magnetic method for boosting the directional hydrodynamic pumping of oxygen toward immersed catalyst sites is demonstrated which allows the ORR to reach otherwise inaccessible catalytic regions where high currents normally would have depleted oxygen. For Pt foil electrodes without forced oxygen saturation in KOH electrolytes, the mass-transfer-limited current densities can be improved by 60% under an external magnetic field of 435 mT due to the synergistic effect between bulk- and surface-magnetohydrodynamic (MHD) flows induced by Lorentz forces. The residual magnetic fields are further used at the surface of magnetic materials (such as CoPt alloys and Pt/FeCo heterostructures) to enhance the surface-MHD effect, which helps to retain part of the ORR enhancement permanently without applying external magnetic fields.

Design of Multifunctional Electrocatalysts for ORR/OER/HER/HOR: Janus Makes Difference

Multifunctional electrocatalysts for hydrogen evolution reaction (HER), hydrogen oxidation reaction (HOR), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR) have broad application prospects; However, realization of such kinds of materials remain difficulties because it requires the materials to have not only unique electronic properties, but multiple active centers to deal with different reactions. Here, employing density functional theory (DFT) computations, it is demonstrated that by decorating the Janus-type 2D transition metal dichalcogenide (TMD) of TaSSe with the single atoms, the materials can achieve multifunctionality to catalyze the ORR/OER/HER/HOR. Out of sixteen catalytic systems, Pt-VS (i.e., Pt atom embedded in the sulfur vacancy), Pd-VSe, and Pt-VSe@TaSSe are promising multifunctional catalysts with superior stability. Among them, the Pt-VS@TaSSe catalyst exhibits the highest activity with theoretical overpotentials ηORR = 0.40 V, ηOER = 0.39 V, and ηHER/HOR = 0.07 V, respectively, better than the traditional Pt (111), IrO2 (110). The interplays between the catalyst and the reaction intermediate over the course of the reaction are then systematically investigated. Generally, this study presents a viable approach for the design and development of advanced multifunctional electrocatalysts. It enriches the application of Janus, a new 2D material, in electrochemical energy storage and conversion technology.

Enhanced catalytic performance through a single-atom preparation approach: a review on ruthenium-based catalysts

The outstanding catalytic properties of single-atom catalysts (SACs) stem from the maximum atom utilization and unique quantum size effects, leading to ever-increasing research interest in SACs in recent years. Ru-based SACs, which have shown excellent catalytic activity and selectivity, have been brought to the frontier of the research field due to their lower cost compared with other noble catalysts. The synthetic approaches for preparing Ru SACs are rather diverse in the open literature, covering a wide range of applications. In this review paper, we attempt to disclose the synthetic approaches for Ru-based SACs developed in the most recent years, such as defect engineering, coordination design, ion exchange, the dipping method, and electrochemical deposition etc., and discuss their representative applications in both electrochemical and organic reaction fields, with typical application examples given of: Li-CO2 batteries, N2 reduction, water splitting and oxidation of benzyl alcohols. The mechanisms behind their enhanced catalytic performance are discussed and their structure-property relationships are revealed in this review. Finally, future prospects and remaining unsolved issues with Ru SACs are also discussed so that a roadmap for the further development of Ru SACs is established.

Opportunities and Challenges in the Synthesis of Noble Metal Nanoparticles via the Chemical Route in Microreactor Systems

The process of noble metal nanoparticle synthesis is complex and consists of at least two steps: slow nucleation and fast autocatalytic growth. The kinetics of these two processes depends on the reductant "power" and the addition of stabilizers, as well as other factors (e.g., temperature, pH, ionic strength). Knowing these parameters, it is possible to synthesize materials with appropriate physicochemical properties, which can be simply adjusted by the type of the used metal, particle morphology and surface property. This, in turn, affects the possibility of their applications in various areas of life, including medicine, catalysis, engineering, fuel cells, etc. However, in some cases, the standard route, i.e., the chemical reduction of a metal precursor carried out in the batch reactor, is not sufficient due to problems with temperature control, properties of reagents, unstable or dangerous intermediates and products, etc. Therefore, in this review, we focused on an alternative approach to their chemical synthesis provided by microreactor systems. The use of microreactors for the synthesis of noble metal nanomaterials (e.g., Ag, Au, Pt, Pd), obtained by chemical reduction, is analyzed, taking into account investigations carried out in recent years. A particular emphasis is placed on the processes in which the use of microreactors removed the limitations associated with synthesis in a batch reactor. Moreover, the opportunities and challenges related to the synthesis of noble nanomaterials in the microreactor system are underlined. This review discusses the advantages as well as the problems of nanoparticle synthesis in microreactors.

Advances in Noble Metal Electrocatalysts for Acidic Oxygen Evolution Reaction: Construction of Under-Coordinated Active Sites

Renewable energy-driven proton exchange membrane water electrolyzer (PEMWE) attracts widespread attention as a zero-emission and sustainable technology. Oxygen evolution reaction (OER) catalysts with sluggish OER kinetics and rapid deactivation are major obstacles to the widespread commercialization of PEMWE. To date, although various advanced electrocatalysts have been reported to enhance acidic OER performance, Ru/Ir-based nanomaterials remain the most promising catalysts for PEMWE applications. Therefore, there is an urgent need to develop efficient, stable, and cost-effective Ru/Ir catalysts. Since the structure-performance relationship is one of the most important tools for studying the reaction mechanism and constructing the optimal catalytic system. In this review, the recent research progress from the construction of unsaturated sites to gain a deeper understanding of the reaction and deactivation mechanism of catalysts is summarized. First, a general understanding of OER reaction mechanism, catalyst dissolution mechanism, and active site structure is provided. Then, advances in the design and synthesis of advanced acidic OER catalysts are reviewed in terms of the classification of unsaturated active site design, i.e., alloy, core-shell, single-atom, and framework structures. Finally, challenges and perspectives are presented for the future development of OER catalysts and renewable energy technologies for hydrogen production.

Palladium/Platinum/Ruthenium Trimetallic Dendritic Nanozymes Exhibiting Enhanced Peroxidase-like Activity for Signal Amplification of Lateral Flow Immunoassays

Developing ultrasensitive lateral flow immunoassays (LFIAs) has garnered significant attention in the field of point-of-care testing. In this study, a trimetallic dendritic nanozyme (Pd@Pt-Ru) was synthesized through Ru deposition on a Pd@Pt core and utilized to enhancing the sensitivity of LFIAs. Pd@Pt-Ru exhibited a Km value of 5.23 mM for detecting H2O2, which indicates an H2O2 affinity comparable with that of horseradish peroxidase. The Ru surface layer reduces the activation energy barrier, which increases the maximum reaction rate. As a proof of concept, the proposed Pd@Pt-Ru nanozyme was incorporated into LFIAs (A-Pd@Pt-Ru-LFIAs) for detecting human chorionic gonadotropin (hCG). Compared with conventional gold nanoparticle (AuNP)-LFIAs, A-Pd@Pt-Ru-LFIAs demonstrated 250-fold increased sensitivity, thereby enabling a visible detection limit as low as 0.1 IU/L. True positive and negative rates both reached 100%, which renders the proposed Pd@Pt-Ru nanozyme suitable for detecting hCG in clinical samples.

Synergistic Modulating Interlayer Space and Electron-Transfer of Covalent Organic Frameworks for Oxygen Reduction Reaction

Covalent organic frameworks (COFs) are an ideal template to construct high-efficiency catalysts for oxygen reduction reaction (ORR) due to their predictable properties. However, the closely parallel-stacking manner and lacking intramolecular electron transfer ability of COFs limit atomic utilization efficiency and intrinsic activity. Herein, COFs are constructed with large interlayer distances and enhanced electronic transfer ability by side-chain functionalization. Long chains with electron-donating features not only enlarge interlayer distance, but also narrow the bandgap. The resulting DPPS-COF displays higher electrochemical surface areas to provide more exposed active sites, despite <1/10 surface areas. DPPS-COF exhibits excellent electrocatalytic ORR activity with half-wave potential of 0.85 V, which is 30 and 60 mV positive than those of Pt/C and DPP-COF, and is the record among the reported COFs. DPPS-COF is employed as cathode electrocatalyst for zinc-air battery with a maximum power density of 185.2 mW cm-2, which is superior to Pt/C. Theoretical calculation further reveals that longer electronic-donating chains not only facilitate the formation of intermediate OOH* from O2, but also promote intermediates desorption , and thus leading to higher activity.

Single Transition-Metal Atom Anchored on a Rhenium Disulfide Monolayer: An Efficient Bifunctional Electrocatalyst for the Oxygen Evolution and Oxygen Reduction Reactions

Developing efficient oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) bifunctional electrocatalysts is attractive for rechargeable metal-air batteries. Meanwhile, single metal atoms embedded in 2D layered transition metal chalcogenides (TMDs) have become a very promising catalyst. Recently, many attentions have been paid to the 2D ReS2 electrocatalyst due to its unique distorted octahedral 1T' crystal structure and thickness-independent electronic properties. Here, the catalytic activity of different transition metal (TM) atoms embedded in ReS2 using the density functional theory is investigated. The results indicate that TM@ReS2 exhibits outstanding thermal stability, good electrical conductivity, and electron transfer for electrochemical reactions. And the Ir@ReS2 and Pd@ReS2 can be used as OER/ORR bifunctional electrocatalysts with a lower overpotential for OER (ηOER) of 0.44 V and overpotentials for ORR (ηORR) of 0.26 V and 0.27 V, respectively. The excellent catalytic activity is attributed to the optimal adsorption strength for oxygen intermediates coming from the effective modulation of the electronic structure of ReS2 after Ir/Pd doping. The results can help to deeply understand the catalytic activity of TM@ReS2 and develop novel and highly efficient OER/ORR electrocatalysts.

Controllable synthesis of high-entropy alloys

High-entropy alloys (HEAs) involving more than four elements, as emerging alloys, have brought about a paradigm shift in material design. The unprecedented compositional diversities and structural complexities of HEAs endow multidimensional exploration space and great potential for practical benefits, as well as a formidable challenge for synthesis. To further optimize performance and promote advanced applications, it is essential to synthesize HEAs with desired characteristics to satisfy the requirements in the application scenarios. The properties of HEAs are highly related to their chemical compositions, microstructure, and morphology. In this review, a comprehensive overview of the controllable synthesis of HEAs is provided, ranging from composition design to morphology control, structure construction, and surface/interface engineering. The fundamental parameters and advanced characterization related to HEAs are introduced. We also propose several critical directions for future development. This review can provide insight and an in-depth understanding of HEAs, accelerating the synthesis of the desired HEAs.

A Theoretical Benchmark of the Geometric and Optical Properties for 3d Transition Metal Nanoclusters via Density Functional Theory

Understanding structure-property relationships in atomically precise metal nanoclusters is vital in finding selective and tunable catalysts. In this study, density functional theory (DFT) was used to benchmark seven exchange correlation functionals at different basis sets for 17 atomically precise nanoclusters against experimentally determined geometries, band gaps, and optical gaps. The set contains both monometallic and bimetallic clusters that possess at least two types of 3d transition metals (specifically, Cu, Ni, Fe, or Co). The benchmark highlights that PBE0 is a good functional to use regardless of the basis set, and Minnesota functionals do well with respect to specific metals. Further, while long-range corrected functionals overestimate band and optical gaps, they model absorption features better than the other considered functionals. The study additionally looks at the photoinduced hydrogen evolution reaction (HER) and the CO2 reduction mechanism on nanoclusters reported from the literature.

Enhanced Mass Activity and Durability of Bimetallic Pt-Pd Nanoparticles on Sulfated-Zirconia-Doped Graphene Nanoplates for Oxygen Reduction Reaction in Proton Exchange Membrane Fuel Cell Applications

Developing highly active and durable Pt-based electrocatalysts is crucial for polymer electrolyte membrane fuel cells. This study focuses on the performance of oxygen reduction reaction (ORR) electrocatalysts composed of Pt-Pd alloy nanoparticles on graphene nanoplates (GNPs) anchored with sulfated zirconia nanoparticles. The results of field emission scanning electron microscopy and transmission electron microscopy showed that Pt-Pd and S-ZrO2 are well dispersed on the surface of the GNPs. X-ray diffraction revealed that the S-ZrO2 and Pt-Pd alloy coexist in the Pt-Pd/S-ZrO2-GNP nanocomposites without affecting the crystalline lattice of Pt and the graphitic structure of the GNPs. To evaluate the electrochemical activity and reaction kinetics for ORR, we performed cyclic voltammetry, rotating disc electrode, and EIS experiments in acidic solutions at room temperature. The findings showed that Pt-Pd/S-ZrO2-GNPs exhibited a better ORR performance than the Pt-Pd catalyst on the unsulfated ZrO2-GNP support and with Pt on S-ZrO2-GNPs and commercial Pt/C.

Rational Electrochemical Design of Cuprous Oxide Hierarchical Microarchitectures and Their Derivatives for SERS Sensing Applications

Rational morphology control of inorganic microarchitectures is important in diverse fields, requiring precise regulation of nucleation and growth processes. While wet chemical methods have achieved success regarding the shape-controlled synthesis of micro/nanostructures, accurately controlling the growth behavior in real time remains challenging. Comparatively, the electrodeposition technique can immediately control the growth behavior by tuning the overpotential, whereas it is rarely used to design complex microarchitectures. Here, the electrochemical design of complex Cu2O microarchitectures step-by-step by precisely controlling the growth behavior is demonstrated. The growth modes can be switched between the thermodynamic and kinetic modes by varying the overpotential. Cl- ions preferably adhered to {100} facets to modulate growth rates of these facets is proved. The discovered growth modes to prepare Cu2O microarchitectures composed of multiple building units inaccessible with existing methods are employed. Polyvinyl alcohol (PVA) additives can guarantee all pre-electrodeposits simultaneously evolve into uniform microarchitectures, instead of forming undesired microstructures on bare electrode surfaces in following electrodeposition processes is discovered. The designed Cu2O microarchitectures can be converted into noble metal microstructures with shapes unchanged, which can be used as surface-enhanced Raman scattering substrates. An electrochemical avenue toward rational design of complex inorganic microarchitectures is opened up.

Photochemical engineering unsaturated Pt islands on supported Pd nanocrystals for a robust pH-universal hydrogen evolution reaction

The rational design of heterostructured nanocrystals (HNCs) is of great significance for developing highly efficient hydrogen evolution reaction (HER) electrocatalysts. However, a significant challenge still lies in realizing the controllable synthesis of desired HNCs directly onto a support and exploring their structure-activity-dependent HER performance. Herein, we reported various controllable Pd7@Ptx core-shell HNCs with optimal hybrid structures via a photochemical deposition strategy. The growth patterns of a Pt shell can be finely controlled by adjusting the growth kinetics, resulting in a varying deposition rate. In particular, the as-prepared Pd7@Pt3 HNCs with a Pt shell in the Stranski-Krastanov mode showed the best performances over a wide pH range media, delivering low overpotentials of 33, 18 and 49 mV, resulting in a catalytic current density of 10 mA cm-2 at a low effective catalyst loading of 0.021 mg cm-2. The resulting Tafel slopes were 23.1, 52.6 and 42.7 mV dec-1 in 0.5 M H2SO4, 1.0 M phosphate-buffered saline (PBS) and 1.0 M KOH electrolyte, respectively. It was found that the increased fraction of unsaturated coordination of Pt islands in the resultant material is the key to the enhanced and robust HER activity, which has been confirmed through density functional theory (DFT) calculations. This strategy could be extended to the rational design and synthesis of other heterostructured catalysts for energy conversion and storage.

Trace Amount of Bi-Doped Core-Shell Pd@Pt Mesoporous Nanospheres with Specifically Enhanced Peroxidase-Like Activity Enable Sensitive and Accurate Detection of Acetylcholinesterase and Organophosphorus Nerve Agents

The urgent need for sensitive and accurate assays to monitor acetylcholinesterase (AChE) activity and organophosphorus pesticides (OPs) arises from the imperative to safeguard human health and protect the ecosystem. Due to its cost-effectiveness, ease of operation, and rapid response, nanozyme-based colorimetry has been widely utilized in the determination of AChE activity and OPs. However, the rational design of nanozymes with high activity and specificity remains a great challenge. Herein, trace amount of Bi-doped core-shell Pd@Pt mesoporous nanospheres (Pd@PtBi2) have been successfully synthesized, exhibiting good peroxidase-like activity and specificity. With the incorporation of trace bismuth, there is a more than 4-fold enhancement in the peroxidase-like performance of Pd@PtBi2 compared to that of Pd@Pt. Besides, no significant improvement of oxidase-like and catalase-like activities of Pd@PtBi2 was found, which prevents interference from O2 and undesirable consumption of substrate H2O2. Based on the blocking impact of thiocholine, a colorimetric detection platform utilizing Pd@PtBi2 was constructed to monitor AChE activity with sensitivity and selectivity. Given the inhibition of OPs on AChE activity, a biosensor was further developed by integrating Pd@PtBi2 with AChE to detect OPs, capitalizing on the cascade amplification strategy. The OP biosensor achieved a detection limit as low as 0.06 ng mL-1, exhibiting high sensitivity and anti-interference ability. This work is promising for the construction of nanozymes with high activity and specificity, as well as the development of nanozyme-based colorimetric biosensors.

Boosted Oxygen Kinetics of Hierarchically Mesoporous Mo2C/C for High-current-density Zn-air Battery

The high-current-density Zn-air battery shows big prospects in next-generation energy technologies, while sluggish O2 reaction and diffusion kinetics barricade the applications. Herein, the sequential assembly is innovatively demonstrated for hierarchically mesoporous molybdenum carbides/carbon microspheres with a tunable thickness of mesoporous carbon layers (Meso-Mo2C/C-x, where x represents the thickness). The optimum Meso-Mo2C/C-14 composites (≈2 µm in diameter) are composed of mesoporous nanosheets (≈38 nm in thickness), which possess bilateral mesoporous carbon layers (≈14 nm in thickness), inner Mo2C/C layers (≈8 nm in thickness) with orthorhombic Mo2C nanoparticles (≈2 nm in diameter), a high surface area of ≈426 m2 g-1, and open mesopores (≈6.9 nm in size). Experiments and calculations corroborate the hierarchically mesoporous Mo2C/C can enhance hydrophilicity for supplying sufficient O2, accelerate oxygen reduction kinetics by highly-active Mo2C and N-doped carbon sites, and facilitate O2 diffusion kinetics over hierarchically mesopores. Therefore, Meso-Mo2C/C-14 outputs a high half-wave potential (0.88 V vs RHE) with a low Tafel slope (51 mV dec-1) for oxygen reduction. More significantly, the Zn-air battery delivers an ultrahigh power density (272 mW cm-2), and an unprecedented 100 h stability at a high-current-density condition (100 mA cm-2), which is one of the best performances.

Plasmonic Alloys Enhanced Metabolic Fingerprints for the Diagnosis of COPD and Exacerbations

Accurate diagnosis of chronic obstructive pulmonary disease (COPD) and exacerbations by metabolic biomarkers enables individualized treatment. Advanced metabolic detection platforms rely on designed materials. Here, we design mesoporous PdPt alloys to characterize metabolic fingerprints for diagnosing COPD and exacerbations. As a result, the optimized PdPt alloys enable the acquisition of metabolic fingerprints within seconds, requiring only 0.5 μL of native plasma by laser desorption/ionization mass spectrometry owing to the enhanced electric field, photothermal conversion, and photocurrent response. Machine learning decodes metabolic profiles acquired from 431 individuals, achieving a precise diagnosis of COPD with an area under the curve (AUC) of 0.904 and an accurate distinction between stable COPD and acute exacerbations of COPD (AECOPD) with an AUC of 0.951. Notably, eight metabolic biomarkers identified accurately discriminate AECOPD from stable COPD while providing valuable information on disease progress. Our platform will offer an advanced nanoplatform for the management of COPD, complementing standard clinical techniques.

Atomic Ordering Engineering of Precious Metal Alloys in Liquid Phase Synthesis

Atomic ordering of noble metal alloys is an effective strategy for improving catalytic performance, yet the low-temperature synthesis of ordered alloys still faces significant challenges. The low-temperature liquid phase method has enormous potential for the synthesis of alloys; however, the atomic ordering mechanism of this process has not been thoroughly studied. Herein, we investigate the mechanism of the influence of metal precursors, reducing agents, solvents, and mixing modes of reactant regulating strategies on precious metal alloy ordering using this method. These regulating strategies are designed to change the coordination structure of metal complexes, affect the reduction potential of metals, and thus change the reduction order of metals and their arrangement in the alloy products. Notably, the reduction potential differences between metal complexes can be used to predict the ordering of the synthetic products (Pd-Cu, Pd-Cd, Pd-Sn, Pd-Pb, and Pt-Sn). This work provides an excellent platform for investigating atomic arrangement engineering.

Controlled Sequential Doping of Metal Nanocluster

Atomically precise doping of metal nanoclusters provides excellent opportunities not only for subtly tailoring their properties but also for in-depth understanding of composition (structure)-property correlation of metal nanoclusters and has attracted increasing interest partly due to its significance for fundamental research and practical applications. Although single and multiple metal atom doping of metal nanoclusters (NCs) has been achieved, sequential single-to-multiple metal atom doping is still a big challenge and has not yet been reported. Herein, by introducing a second ligand, a novel multistep synthesis method was developed, controlled sequential single-to-multiple metal atom doping was successfully achieved for the first time, and three doped NCs Au25Cd1(p-MBT)17(PPh3)2, Au18Cd2(p-MBT)14(PPh3)2, and [Au19Cd3(p-MBT)18]- (p-MBTH: para-methylbenzenethiol) were obtained, including two novel NCs that were precisely characterized via mass spectrometry, single-crystal X-ray crystallography, and so forth. Furthermore, sequential doping-induced evolutions in the atomic and crystallographic structures and optical and catalytic properties of NCs were revealed.

Low-Electronegativity Mn-Contraction of PtMn Nanodendrites Boosts Oxygen Reduction Durability

Platinum metal (PtM, M=Ni, Fe, Co) alloys catalysts show high oxygen reduction reaction (ORR) activity due to their well-known strain and ligand effects. However, these PtM alloys usually suffer from a deficient ORR durability in acidic environment as the alloyed metal is prone to be dissolved due to its high electronegativity. Herein, we report a new class of PtMn alloy nanodendrite catalyst with low-electronegativity Mn-contraction for boosting the oxygen reduction durability of fuel cells. The moderate strain in PtMn, induced by Mn contraction, yields optimal oxygen reduction activity at 0.53 A mg-1 at 0.9 V versus reversible hydrogen electrode (RHE). Most importantly, we show that relative to well-known high-electronegativity Ni-based Pt alloy counterpart, the PtMn nanodendrite catalyst experiences less transition metals' dissolution in acidic solution and achieves an outstanding mass activity retention of 96 % after 10,000 degradation cycles. Density functional theory calculation reveals that PtMn alloys are thermodynamically more stable than PtNi alloys in terms of formation enthalpy and cohesive energy. The PtMn nanodendrite-based membrane electrode assembly delivers an outstanding peak power density of 1.36 W cm-2 at a low Pt loading and high-performance retention over 50 h operations at 0.6 V in H2 -O2 hydrogen fuel cells.

Continuous production of bimetallic nanoparticles on carbon nanotubes based on 3D-printed microfluidics

Nanoparticle-functionalized carbon nanotubes are promising in many research fields, especially in sensing, due to their intriguing performance in catalysis. However, these nanomaterials are mainly produced through batch processes under harsh conditions, thus encountering inherent limitations of low throughput and uncontrollable morphology of functional nanoparticles (NPs). In this work, we propose a method for high-yield and continuous production of bimetallic (Pt-Pd) NPs on multi-walled carbon nanotubes (MWCNTs) at room temperature through a custom 3D-printed microfluidic platform. A homogenous particle nucleation and growth environment could be created on the microfluidic platform that was equipped with two 3D-printed micromixers. Pt-Pd NPs loaded on MWCNTs were prepared in the microfluidic platform with high throughput and controlled size, dispersity and composition. The synthetic parameters for these nanocomposites were investigated to optimize their electrocatalytic performance. The optimized nanocomposites exhibited excellent electrocatalytic activity with exceptional sensitivity and wide detection range, superior to their counterparts prepared via conventional approaches. This method proposed here could be further adapted for manufacturing other catalyst support materials, opening more avenues for future large-scale production and catalytic investigation of functional nanomaterials.

A universal strategy for green and surfactant-free synthesis of noble metal nanoparticles

We propose a universal, green, and surfactant-free strategy to synthesize noble metal particles with high monodispersity using gaseous H2 as a reducing agent in a solution at 60 °C. The prepared Pt nanoparticles have a 24 mV more positive half-wave potential than the commercially available Pt/C in the oxygen reduction reaction, while showing high durability with negligible half-wave potential decay after 10 000 cycles of testing.

Tetrahedral Clusters Stabilized by Alloying

A family of nanoclusters of tetrahedral symmetry is proposed. These clusters consist of symmetrically truncated tetrahedra with additional hexagonal islands on the four facets of the starting tetrahedron. The islands are placed in stacking fault positions. The geometric magic numbers of these clusters are derived. Global optimization searches within an atomistic potential model of Pt-Pd show that the tetrahedral structures can be stabilized for intermediate compositions of these nanoalloys, even when they are not the most stable structures of the elemental clusters. These results are also confirmed by density functional theory calculations for the magic sizes 59, 100, and 180. A thermodynamic analysis by the harmonic superposition approximation shows that Pt-Pd tetrahedral nanoalloys can be stable even above room temperature.

Tuning Pd-to-Ag Ratio to Enhance the Synergistic Activity of Fly Ash-Supported PdxAgy Bimetallic Nanoparticles

Fly ash (FA)-supported bimetallic nanoparticles (PdxAgy/FA) with varying Pd:Ag ratios were prepared by coprecipitation of Pd and Ag involving in situ reduction of Pd(II) and Ag(I) salts in aqueous medium. All the supported nanoparticles were thoroughly characterized with the aid of powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), electron microscopy (field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM)), and elemental analyses, which include inductively coupled plasma-optical emission spectroscopy (ICP-OES) and energy-dispersive X-ray spectroscopy (EDS). A gradual broadening and shifting of PXRD peaks, ascribable to Ag, to higher angles with an increase in the Pd:Ag ratio affirms the alloying of interface between Pd and Ag nanoparticles. The coexistence of Pd and Ag was further confirmed by EDS elemental mapping as well as by the presence of bimetallic lattices on the FA surface, as evident from the high-resolution TEM analysis. The dependency of crystallite size and average size of bimetallic nanoparticles on Ag loading (mol %) was elucidated with the help of a combination of PXRD and TEM studies. Based on XPS analysis, the charge transfer phenomenon between contacting Pd-Ag sites could be evident from the shifting of 3d core electron binding energy for both Pd and Ag compared with monometallic Pd and Ag nanoparticles. Following a pseudo-first-order reaction kinetics, all the nanocatalysts were able to efficiently reduce 4-nitrophenol into 4-aminophenol in aqueous NaBH4. The superior catalytic performance of the bimetallic nanocatalysts (PdxAgy/FA) over their monometallic (Pd100/FA and Ag100/FA) analogues has been demonstrated. Moreover, the tunable synergistic effect of the bimetallic systems has been explored in detail by varying the Pd:Ag mol ratio in a systematic manner which in turn allowed us to achieve an optimum reaction rate (k = 1.050 min-1) for the nitrophenol reduction using a Pd25Ag75/FA system. Most importantly, all the bimetallic nanocatalysts explored here exhibited excellent normalized rate constants (K ≈ 6000-15,000 min-1 mmol-1) compared with other supported bimetallic Pd-Ag nanocatalysts reported in the literature.

Surface-structure tailoring of Dendritic PtCo nanowires for efficient oxygen reduction reaction

Platinum-based alloy nanowire catalysts demonstrates great promise as electrocatalysts to facilitate the cathodic oxygen reduction reaction (ORR) of proton exchange membrane fuel cells (PEMFCs). However, it is still challenge to further improve the Pt atom utilization of Pt based nanowires featuring inherent structural stability. Herein, a new structure of PtCo nanowire with nanodendrites was developed using CO-assistance solvent thermal method. The dendrite structure with an average length of about 7 nm are characterized by a Pt-rich surface and the high-index facets of {533}, {331} and {311}, and grows from the ultra-fine wire structure with an average diameter of about 3 nm. PtCo nanowires with nanodendrites developed in this work shows outstanding performance for ORR, in which its mass activity of 1.036 A/mgPt is 5.76 times, 1.74 times higher than that of commercial Pt/C (0.180 A/mgPt) and PtCo nanowires without nanodendrites (0.595 A/mgPt), and its mass activity loss is only 18% under the accelerated durability tests (ADTs) for 5k cycles. The significant improvement is attributed to high exposure of active sites induced by the dendrite structure with Pt-rich surface with the high-index facets and Pt-rich surface. This structure may provide a new idea for developing novel 1D Pt based electrocatalysts.

Precise solid-phase synthesis of CoFe@FeOx nanoparticles for efficient polysulfide regulation in lithium/sodium-sulfur batteries

Complex metal nanoparticles distributed uniformly on supports demonstrate distinctive physicochemical properties and thus attract a wide attention for applications. The commonly used wet chemistry methods display limitations to achieve the nanoparticle structure design and uniform dispersion simultaneously. Solid-phase synthesis serves as an interesting strategy which can achieve the fabrication of complex metal nanoparticles on supports. Herein, the solid-phase synthesis strategy is developed to precisely synthesize uniformly distributed CoFe@FeOx core@shell nanoparticles. Fe atoms are preferentially exsolved from CoFe alloy bulk to the surface and then be carburized into a FexC shell under thermal syngas atmosphere, subsequently the formed FexC shell is passivated by air, obtaining CoFe@FeOx with a CoFe alloy core and a FeOx shell. This strategy is universal for the synthesis of MFe@FeOx (M = Co, Ni, Mn). The CoFe@FeOx exhibits bifunctional effect on regulating polysulfides as the separator coating layer for Li-S and Na-S batteries. This method could be developed into solid-phase synthetic systems to construct well distributed complex metal nanoparticles.

Capping Layer Determined Self-assembly of Au-Ag Bimetallic Janus Nanoparticles at An Oil/Water Interface by Molecular Dynamics Simulations

Bimetallic Janus nanoparticles (BJNPs) have gained more attention due to their unique catalytic and optical properties. The self-assembly of BJNPs is expected as an effective way to fabricate metamaterials suitable for different potential applications. However, the self-assembly dynamic process of BJNPs, which is key to achieving a controllable synthesis, is limited in both experimental and theoretical investigations. Herein, all-atom molecular dynamics (MD) simulations were employed to investigate the self-assembly process of 1-dodecanethiol (DDT)-decorated Au-Ag BJNPs at an oil-water interface. We demonstrate that DDT's van der Waals (vdW) interaction dominates the self-assembly process. BJNPs form close-packed structures at both fast and slow evaporation rates. Au-Ag BJNPs exhibit relatively larger rotations at a low evaporation rate than those at a high evaporation rate, suggesting that the evaporation rate influences the orientation of the Au-Ag BJNPs. BJNPs tend to orient their electric dipole moments toward the external electric field, according to the ab initio MD simulation results. Based on the energy comparison and model analysis, it is found that the parallel array is more stable than the antiparallel one for the Au-Ag BJNP arrays. The dipole-dipole interaction difference between the parallel and antiparallel BJNP arrays obtained according to dipole moment obtained from ab initio calculation is qualitatively consistent with that obtained from MD simulations, indicating that the dipole plays a decisive role in determining the orientation of the BJNP array. This work uncovers the self-assembly dynamic process of BJNPs, paving the way for future applications.

Production of Metallic Alloy Nanowires and Particles Templated Using Tomato Mosaic Virus (ToMV)

We demonstrate a simple, low-energy method whereby tomato mosaic virus (ToMV) particles can be used to template the production of nanowires and particles consisting of alloys of gold (Au), platinum (Pt) and palladium (Pd) in various combinations. Selective nanowire growth within the inner channel of the particles was achieved using the polymeric capping agent polyvinylpyrrolidone (PVPK30) and the reducing agent ascorbic acid. The reaction conditions also resulted in the deposition of alloy nanoparticles on the external surface of the rods in addition to the nanowire structures within the internal cavity. The resulting materials were characterized using a variety of electron microscopic and spectroscopic techniques, which revealed both the structural and chemical composition of the alloys within the nanomaterials.

Highly efficient and continuous activation of O2 by a novel FexP-FeCu composite for water purification and insights into the activation mechanisms through DFT calculation

Degradation of organic pollutants through O2 activation catalyzed by transitional metals is challenging without addition of external chemicals and input of energy. We prepare a novel Fe based catalyst by compositing carbon, iron phosphide (FexP), iron carbide (FexC), Fe0 and Cu NPs, which can continuously activate O2 to produce high amount of 1O2,·O2- and·OH radicals in a wide pH range. DFT calculation discloses that O2 molecules are dissociated into *O or exist as O-O in various configurations. The Fe-O2, Cu-O2 and FeP-O2 surfaces can react with H2O molecules to generate *OOH, *OH and/or OH-. The sorbed-O2 intermediates on FexC surface might be released as 1O2 or·O2-. The oxidative O2-sorbed surfaces and in-situ produced oxygen reactive species contribute to the efficient and pH-indenpendent degradation of organic pollutants. Cu NPs accelerate Fe2+/Fe3+ cycles and offer impetus to initiate O2 activation due to the potential difference between Fe and Cu. The recycling test and XPS results confirm that the mutual electron transferring among carbon, FexC, FexP, Fe and Cu maintains reactivity and stability of the catalysts.

Extended-Surface Thin-Film Platinum Electrocatalysts with Tunable Nanostructured Morphologies

Reducing platinum group metal (PGM) loadings in fuel cells and electrolyzers is paramount for cost reductions and getting hydrogen to scale to help decarbonize the global economy. Conventional PGM nanoparticle-based ink-cast electrocatalysts lose performance at high current densities owing to mass transport resistances that arise due to the use of ionomer binders. Herein, we report the development of binder-free extended-surface thin-film platinum electrocatalysts with tunable nanoscale morphology and periodic spacing. The electrocatalysts are prepared by sputtering various loadings of platinum on Al2O3 nanostructures templated from self-assembled block copolymer (BCP) thin films on glassy carbon substrates. Testing for oxygen reduction on a rotating disk electrode setup with ultralow PGM loadings (5.8 μgPt cm-2) demonstrates electrocatalyst performance that rivals commercial platinum electrocatalysts in terms of mass activity (380 mA mgPt-1 at 0.9 V vs RHE) while surpassing commercial catalysts in terms of stability (mass activity loss: 11-13% after 20,000 potential cycles). Moreover, catalyst performance probed as a function of nanoscale feature size and morphology reveals an inverse correlation between feature size and electroactivity, as well as the superiority of cylindrical morphologies over lamellae, presenting BCP templating as a fabrication pathway toward stable, tunable catalyst geometries.