Metal Nanoparticles Research Articles

Decrypting Synergy of Alloy & Metal Nanoparticles Within Nitrogen-Doped Carbon Nanosheets for Zn-Air Batteries with Ultralong Cycling Stability.

The exploration of efficient, robust, and low-cost bifunctional electrocatalysts to drive the commercial application of Zn-air batteries (ZABs) is of great significance but still remains a challenge. Herein, a 1D coordination polymer (1D-CP) derived FeNi alloy & Co nanoparticles (NPs) co-implanted N-doped carbon nanosheets (FNC/NCS) is judiciously crafted and employed as a high-performance electrocatalyst for ultralong lifetime ZABs. The key to this strategy is the leveraging of metal-coordinated melamine to direct the pyrolysis of 1D-CP, enabling the in situ formation of well-dispersed FeNi alloy and Co NPs within the carbon matrix. The resulting FNC/NCS exhibits prominent oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activity with a small overall oxygen potential difference (ΔE = 0.68V). Density functional theory (DFT) simulation demonstrates that the synergistic effect between FeNi alloy and Co NPs can reduce energy barriers, promote electron transfer, and optimize the formation of crucial intermediates, thereby largely boost ORR/OER activity of FNC/NCS. The FNC/NCS-assembled ZABs possess high specific capacity, large power density, and ultralong cycling life in both aqueous (> 3300h) and solid-state (150h) electrolytes. This work provides a viable strategy for 1D-CP-derived bifunctional electrocatalysts and dissects the synergistic effect between different metal species, affording significant guidance for the development of renewable energy materials.

Hydrogen generation via NaBH4 hydrolysis over cobalt-modified niobium oxide catalysts

The increasing concentration of CO₂ in the atmosphere, primarily driven by fossil fuel combustion, is a major contributor to global warming and one of the most pressing environmental challenges of the 21st century. In response, the development of sustainable energy technologies, such as hydrogen (H₂) production, has become crucial in the global transition to a low-carbon economy. In this study, we explored the catalytic activity of cobalt-modified niobium-based catalysts for hydrogen generation through the hydrolysis of NaBH₄. The catalysts were characterized using XRD, FTIR, XPS, SEM-EDX, and N₂ adsorption-desorption. XRD analysis revealed that the synthesized Nb₂O₅ (Nb₂O₅ Synt.) and Nb₂O₅/Co (Nb₂O₅/Co Synt.) exhibited amorphous structures, while the commercial Nb₂O₅ (Nb₂O₅ Com.) and its Co-modified composite displayed orthorhombic phases. The Nb₂O₅/Co Synt. catalyst achieved a surface area of 33.1 m2/g, significantly surpassing that of the commercial Nb₂O₅. The Nb₂O₅/Co Synt. catalyst exhibited superior catalytic activity, yielding 250 mL of hydrogen in 60 min, in contrast to other catalysts that showed no activity under identical conditions. This enhanced activity was attributed to the presence of surface hydroxyl groups and metallic Co nanoparticles, following the Langmuir-Hinshelwood bimolecular mechanism. Temperature was identified as a critical factor in the H₂ production rate, with a calculated activation energy of 11.37 kJ/mol. Moreover, the Nb₂O₅/Co Synt. catalyst demonstrated excellent reusability, maintaining stable performance after multiple reaction cycles, highlighting its potential for sustainable hydrogen production.

Impacting the Surface Chemistry of NiAu by Immobilizing on MgO/N-Rich Nanoporous Carbon Heterostructures for Boosting Catalytic Activities.

Tuning the physical and chemical interaction between metal-metal' (M-M') and metal-support is an ideal way to realize enhanced catalytic activity of metal nanoparticles (NPs). As a proof of concept, herein we report the fabrication of nickel-gold (Ni-Au) alloy nanoparticles attached to N-doped nanoporous carbon (NPC) intervened with MgO (Ni73Au27@MgO-NPC), achieved through the impregnation of metal precursors into Schiff-base network polymer (SNP) framework along with Mg(OH)2 and pyrolysis at 800 °C in N2 atmosphere. With high stability and heterogeneity, the nickel rich Ni73Au27@MgO-NPC exhibited higher catalytic activities with turnover frequencies of 29,272 h-1 (hydrogenation of p-nitrophenol), 93,843 h-1 (degradation of methyl orange), and 2,218 h-1 (epoxidation of stilbene), compared to commercial 10 wt % Pd/C. Enhanced catalytic activity is correlated to the synchronized electron density enhancement in Au, by Ni and MgO/N-rich nanoporous carbon heterostructures, as evident from detailed X-ray photoelectron spectroscopic studies.

Iron (Magnetite) Nanoparticle-Assisted Dark Fermentation Process for Continuous Hydrogen Production from Rice Straw Hydrolysate

The use of metal nanoparticles (NPs) to enhance hydrogen production in dark fermentation (DF) has become a pioneering field of interest. In particular, iron-based nanoparticles (FeNPs) play a pivotal role in enhancing the activity of metalloenzymes and optimizing feedstock utilization, resulting in improved hydrogen production. This study investigated the effect of FeNPs (magnetite) supplementation at three different concentrations of 50, 100, and 200 ppm in a continuous dark fermenter for the production of hydrogen from rice straw acid hydrolysate. The highest hydrogen production rate of 2.6 ± 0.3 NL H2/L-d was achieved with the addition of 100 ppm of nanoparticles, representing a 53% increase compared to the condition without FeNPs addition. This improvement was driven by a microbial community in which Clostridium was the major dominant genus. In addition, increasing the nanoparticle concentration to 100 ppm resulted in an increase in butyrate concentration to 2.0 ± 0.1 g/L, which is 43% higher than the butyrate concentration without FeNPs. However, when the NP concentration was increased to 200 ppm, the hydrogen production rate decreased to 1.6 ± 0.2 NL H2/L-d. This study can serve as a guideline for future research aimed at evaluating the effects of FeNPs in continuous dark fermentation systems. This work highlights the potential benefits and challenges associated with the use of FeNPs, paving the way for future studies to optimize their application and improve the efficiency of dark fermentation processes.

Catalytically Active Gold Nanoparticles on Star Block Co-polymer Matrix: Synthesis of Nanocomposite Film Exploring the Langmuir-Blodgett Technique.

Nanocomposites with metal nanoparticles and block copolymers distributed in a stable and robust thin film are preferred for various applications. Here, synthesis of such a nanocomposite is reported, which is composed of gold nanoparticles (AuNPs) embedded in a tetronic 701 (T701) and 90R4 (T90R4) thin film matrix generated using the Langmuir-Blodgett (LB) thin film technique. Tetronics contain a monoprotonated central ethylenediamine group at pH 5 due to the presence of chloroauric acid (HAuCl4) in the subphase, along with poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) blocks, both of which have the capacity to serve as the reducing agent toward chloroaurate anion (AuCl4-). Calorimetric experiments have shown that T90R4 has a better interaction with AuCl4-, probably due to its better electrostatic interaction with AuCl4- ions due to the higher % of the hydrophilic PEO group. On the other hand, the T701-AuNP interaction turned out to be more spontaneous due to the higher hydrophobicity of T701 (higher PPO/PEO ratio). The optical properties and structure/morphology of these nanocomposites are characterized by UV-vis spectroscopy, FTIR spectroscopy, XRD, and TEM. The composite thin film has the ability to catalyze the organic electron transfer process between p-nitrophenol and p-aminophenol in the presence of sodium borohydride. A clear correlation has been found between the reaction rates and the kind of tetronic present in the nanocomposite, which acted as a matrix and stabilizer toward AuNPs.

Highly interweaved carbonaceous interlayer synchronously decorated by foreign atoms and metals for adsorbing and catalyzing polysulfides in lithium-sulfur batteries

A highly interweaved carbonized bacterial cellulose (CBC) decorated by heteroatoms and metallic nanoparticles was fabricated through initial coating of a metallic coordination polymer onto BC nanofibers followed by carbonization. The carbonaceous CBC networks not only efficiently transfer electrons but also entrap the soluble polysulfides by physical interception. Moreover, the polar ingredients of foreign atoms and metals on CBC networks enable a favorable chemisorption toward polysulfides, and meanwhile the embedded metallic nanoparticles promote the conversion kinetics via electrocatalysis. Theoretical simulation and experimental investigation co-confirm that the decorated Ni species greatly enhance the adsorption capability towards polysulfides, as well as reduce the energy barrier of the rate-determining step via electrocatalysis. As a consequence, the lithium-sulfur batteries equipped with the optimal Ni-NCBC interlayer exhibited relatively high specific capacity (1245 mAh g−1 at 0.2 A g−1), superior rate capability (820 mAh g−1 at 4.0 A g−1), and stable cycling performance (73.2 % capacity retention after 1000 cycles). This work proposes a facile strategy to synchronously incorporate heteroatoms and metallic decorations into highly conductive nanofibrous networks for alleviating the shuttling effects of polysulfides effectively.

In silico estimation of polyethylene glycol coating effect on metallic NPs radio-sensitization in kilovoltage energy beams

PurposeNanoparticles (NPs) as radiosensitizers present a promising strategy for enhancing radiotherapy effectiveness, but their potential is significantly influenced by the properties of their surface coating, which can impact treatment outcomes. Most Monte Carlo studies have focused on metallic NPs without considering the impact of coating layers on radiosensitization. In this study, we aim to assess both the physical and radiobiological effects of nanoparticle coatings in nanoparticle-based radiation therapy.Materials and methodsIn this simulation study, we used Geant4 Monte Carlo (MC) toolkit (v10.07.p02) and simulated the bismuth, gold, iridium and gadolinium NPs coated with polyethylene glycol (PEG-400: Density: 1.13 g/cm³, Molar mass: 380–420 g/mol) as radiosensitizer for photon beams of 30, 60 and 100 keV. Secondary electron number and reactive oxygen species enhancement factor were estimated. Also, dose enhancement factor (DEF) was determined in spherical shells with logarithmic scale thickness from the nanoparticle surface to 4 mm.ResultsSecondary electron emission was highest at 30 keV for gold, bismuth, and iridium NPs, while gadolinium NPs peaked at 60 keV. Coating reduced electron emissions across all energies, with thicker coatings leading to a more significant decrease. DEF values declined with increasing radial distance from the NP surface and were lower with thicker coatings. For gadolinium NPs, DEF behavior differed due to K-edge energy effects. Reactive species generation varied, showing maximum production at 30 keV for gold, bismuth, and iridium NPs, while gadolinium NPs showed peak activity at 60 keV. PEG coatings enhanced reactive species formation at 100 keV.ConclusionThe findings indicate that the coating layer thickness and material not only influence the emission of secondary particles and DEF but also affect the generation of reactive species from water radiolysis. Specifically, thicker coatings reduce secondary particle emission and DEF, while PEG coatings demonstrate a dual behavior, offering both protective and enhancing effects depending on photon energy. These insights underscore the importance of optimizing NP design and coating in future studies to maximize therapeutic efficacy in nanoparticle-based radiation therapy.

A Novel Method for Rapid and High-Performance SERS Substrate Fabrication by Combination of Cold Plasma and Laser Treatment

In this paper, we report a simple yet efficient method for rapid and high-performance SERS substrate fabrication by a combination of cold plasma and laser treatment. Our analysis reveals that cold plasma pre-treatment significantly reduced surface roughness, transforming 200 nm spikes into an almost perfectly uniform surface, while enhancing the substrate’s surface energy by lowering the water contact angle from 59° to 0°, all achieved within just 30 s of 0.9-mW plasma treatment, while 15-min green-laser treatment facilitated more uniform deposition of AuNPs across the entire treated area, effectively creating the SERS substrates. The combined treatments result in enhancement of the Raman intensity (11 times) and consistency over the whole area of the SERS substrates, and their reusability (up to 10 times). The fabricated SERS substrates exhibit a significant enhancement factor of approximately 3 × 10⁸ with R6G, allowing detection down to a concentration of 10−12 M. We demonstrate the application of these SERS substrates by detecting amoxicillin—an antibiotic used worldwide to treat a diversity of bacterial infections—in a dynamic expanded linear range of seven orders (from 10−3 to 10−9 M) with high reliability (R2 = 0.98), and a detection limit of 9 × 10−10 M. Our approach to high-performance SERS substrate fabrication holds potential for further expansion to other metallic NPs like Ag, or magnetic NPs (Fe3O4).

Optical Study of Desmodium Elegan Mediated Silver Nanoparticles Using Tauc’s Equation

Green synthesis of metallic nanoparticles is more eco-friendly, simpler, and nontoxic as compared to chemical synthesis. Due to their thermal stability and good electrical conduction silver nanoparticles have significant importance these days. In the present work, the stable silver nanoparticles were prepared from the aqueous solution of AgNO3 by green synthesis technique in which the Desmodium elegan plant extract was used as a reducing and capping agent to convert Ag+ to Ag0. A UV-visible spectrometer is used in the range of 200 nm to 800 nm with a scanning speed of 200 nm per minute, the absorption band is found at a 450 nm peak that indicates the synthesis of silver nanoparticles. The particle size of the nanoparticles was in the range of 11 nm to 70 nm with an average of 45 nm and a spherical shape. Further confirmation of nano size, scanning electron microscopy (SEM) was also utilized for the size distribution and shape of the synthesized nanoparticles. The synthesized nanoparticles SEM studies show irregular spherical morphology with polydispersed trend and the average particle size was found at 45 nm. The absorption band for the synthesized sample was found at 450 nm peak. The bandgap energy was 2.84 eV estimated by Tauc’s equation. This indicates that the synthesized nanoparticles electrically lie in the range of semiconductors and can be used as a biosensor. This synthesis technique is a nontoxic technique so these particles may be used for water treatment.

Secondary electron emission measurements from imidazolium-based ionic liquids

Abstract The electron-induced secondary electron emission (SEE) yields of imidazolium-based ionic liquids are presented for primary electron beam energies between 30 and 1000 eV. These results are important for understanding plasma synthesis of nanoparticles in plasma discharges with an ionic liquid electrode. Due to their low vapor pressure and high conductivity, ionic liquids can produce metal nanoparticles in low-pressure plasmas through reduction of dissolved metal salts. In this work, the low vapor pressure of ionic liquids is exploited to directly measure SEE yields by bombarding the liquid with electrons and measuring the resulting currents. The ionic liquids studied are [BMIM][Ac], [EMIM][Ac], and [BMIM][BF4]. The SEE yields vary significantly over the energy range, with maximum yields of around 2 at 200 eV for [BMIM][Ac] and [EMIM][Ac], and 1.8 at 250 eV for [BMIM][BF4]. Molecular orbital calculations indicate that the acetate anion is the likely electron donor for [BMIM][Ac] and [EMIM][Ac], while in [BMIM][BF4], the electrons likely originate from the [BMIM]$^+$ cation. The differences in SEE yields are attributed to varying ionization potentials and molecular structures of the ionic liquids. These findings are essential for accurate modeling of plasma discharges and understanding SEE mechanisms in ionic liquids.

Immobilization of Metal Nanoparticles to an Ultrathin Two-Dimensional Conjugated Metal-Organic Framework for Synergistic Electrocatalysis.

Metal-organic frameworks (MOFs) have been considered as promising hosts for immobilizing ultrafine metal nanoparticles (MNPs) due to their high surface area and porosity. However, electrochemical applications of such emerging composites are severely limited by the poor electrical conductivity and large size of the MOFs. Herein, we report the general synthesis of incorporating various MNPs into a conjugated MOF ultrathin nanosheet (Cu-TCPP UNS) matrix, which not only prevents agglomeration and restricts the growth of MNPs but also benefits the exposure of active sites and the transport of electrons. Specifically, the obtained PtCu@Cu-TCPP UNSs exhibited nearly two times higher mass activity for the methanol oxidation reaction (MOR) than the commercial Pt/C catalyst. Mechanistic studies reveal that the strong interaction between MNPs and Cu-TCPP promotes the oxidation of the CO intermediate. Moreover, the PtCu@Cu-TCPP UNSs can be employed as bifunctional electrocatalysts to couple MOR with the hydrogen evolution reaction for highly efficient hydrogen production.

Plasma‐Enhanced Magnetron Sputtering: A Novel Approach for Biofunctional Metal Nanoparticle Coatings on Reverse Osmosis Composite Membranes

AbstractReverse osmosis (RO) is the most common method for treating salt and brackish water. As a membrane‐driven process, a key challenge for RO systems is their susceptibility to scaling and biofouling. To address these issues, functional coatings utilizing metal nanoparticles (MNPs) are developed. In this study, silver, gold, and copper nanoparticles are applied onto thin‐film composite (TFC) membranes using plasma‐enhanced magnetron sputtering. The elemental composition, surface morphology, and hydrophilicity of the coatings are analyzed using X‐ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and contact angle measurements. The antimicrobial properties and the filtration efficiency of the coated membranes are assessed through application‐specific experimental setups. Silver and copper nanoparticles exhibit superior antimicrobial properties, reducing microorganism adhesion by a factor of 103 compared to uncoated membranes. Under appropriate coating conditions, no deterioration in filtration performance is observed. Enhancing the adhesion of MNPs is necessary for achieving sustained release of metal ions.

Synthesis of concave Au NRs-Pt-CdS plasmonic photocatalyst with efficient hydrogen production rate

Light-driven water photolysis for hydrogen (H2) generation has been proven to be exceptionally efficient in the field of energy transformation. Nevertheless, the practical applications of many single-component semiconductors still suffer from a relatively low energy conversion efficiency. In this work, concave gold nanorods (Au NRs) with three plasmon resonance modes were synthesized using a one-step method in an aqueous solution. Pt nanoparticles and CdS nanocrystals were rational grown onto Au NRs to design the plasmonic photocatalysts with specific morphology and structure characteristic. Photocatalytic test indicated that concave Au NRs-Pt-CdS hetero-nanostructure possess efficient H2 production rate under visible and near-infrared regions. These findings offer a blueprint for creating a novel group of hetero-nanostructures that combine faceted noble metal nanoparticles with semiconductor materials, demonstrating promise for applications across fields such as photocatalysis and energy storage.

In Vitro Assessment of Gallium Nanoalloy Hydrogels for Antimicrobial and Wound Healing Applications.

Chronic and recurring wounds pose a significant challenge in modern healthcare, leading to substantial morbidity. These wounds allow pathogens to colonize, potentially resulting in local and systemic infections. Current interventions need to be revised and become increasingly less reliable due to the emergence of antibiotic resistance. In the present study, we aim to address these issues by fabricating hydrogels impregnated with gallium-based nanoalloys for their antimicrobial activity. Gallium liquid metal nanoparticles (approximately 100 nm in diameter) were alloyed in different combinations with bismuth and silver ions through a galvanic replacement reaction. These multimetallic hydrogels showed favorable antibacterial activity against the Gram-positive Staphylococcus aureus and the Gram-negative Pseudomonas aeruginosa, as observed with fluorescence microscopy and inhibition assays. The multimetallic hydrogels showed no toxicity against murine macrophages or human dermal fibroblasts and enhanced in vitro wound healing. The development of these innovative gallium-based hydrogels represents a promising strategy to combat chronic wounds and their associated complications, offering an effective alternative to current antimicrobial treatments amidst rising antibiotic resistance.

Electronic effect in bromide-modified noble metal catalysts promotes highly stable and selective hydrogenation

Halides with strong affiliation to metals are traditionally viewed as positions in heterogeneous catalysis. This study introduces a method to enhance the selective hydrogenation performance of noble metal nanoparticle catalysts (Pd, Pt, and Rh hosted on N-doped carbon, SiO2, and Al2O3) by gas-phase bromination with 1-bromooctane. Brominated Pd catalysts, particularly those supported on N-doped carbon, show significant improvements in total butene selectivity and stability in butadiene hydrogenation reactions, displaying >97.5 % selectivity to total butenes at complete conversion with 50 h stable performance even at excessive H2 (H2:butadiene = 50) and a high temperature of 473 K. Comprehensive characterizations coupled with density functional theory calculations reveal that bromide species enhance selective hydrogenation by preferentially adsorbing at stepped Pd sites, altering reaction kinetics and preventing over-hydrogenation. Bromination influences reactant and intermediate adsorption, leading to increased competitive adsorption compared to pristine catalysts. Chemisorption studies on butadiene and 1-butene support altered kinetic behaviors post-bromination. X-ray photoelectron spectroscopy analysis demonstrate an increase in surface Pdδ+ species, owing to the electron-pulling character of nearby adsorbed bromide. In situ diffuse reflection infrared Fourier transform spectroscopy with CO probe molecules confirms Br species adsorption at unsaturated Pd sites. Overall, the study provides an effective approach to tuning the electronic properties of metal catalysts and highlights the positive impact of bromination on improving the hydrogenation performance.

Facile nanofabrication and simultaneous color-and-Raman hybrid mechanism of economic SERS substrate with tunable structure color for high enhancement factor

The conventional SERS technique utilizing metal nanoparticles (MNPs) is a powerful optical sensing method, relying on the inelastic collision between incident light and the analyte. However, the development of traditional color-tunable MNP-SERS substrates remains limited to two separate components of the color supporter for generating structure color and followed by the MNPs coating to generate the localized surface plasmonic resonance for SERS sensing. Here, a novel color-tunable SERS substrate without MNPs based on the economic one-step anodic aluminum oxide (AAO) coated with nanoporous Pt films was proposed to generate the color-and-Raman hybrid effect for high enhancement factor. This novel SERS substrate employs an economic method, that is a facile and low-cost one-step anodization process to fabricate the AAO with tunable structure color, enabling adaptation to excitation of laser sources. The substrate with the lowest reflectance to laser light exhibits the highest enhancement factor due to the coupling between the laser and the substrate. The resultant SERS substrate demonstrates a high enhancement factor (EF) of 5.27x105 to methylene blue with a good uniformity of the relative standard deviation (RSD) of 6.35 %. In a practical application, one of preservative, benzoic acid, was detected with a low concentration of 1 ppm in the extraction solution of tapioca balls. This innovative approach promotes limitations associated with traditional color-tunable SERS substrates and offers a promising path for sensitive and versatile trace substance detection.

Design, Synthesis, and Evaluation of Noble Metal Nanoparticles and In Situ-Decorated Carbon-Supported Nanoparticle Electrocatalysts Using Hypergolic Reactions

Design, Synthesis, and Evaluation of Noble Metal Nanoparticles and In Situ-Decorated Carbon-Supported Nanoparticle Electrocatalysts Using Hypergolic Reactions

Enhancing the Lithium Storage Performance of Phosphorus–Carbon Composites by Reinforcing P–C Bonding with High-Strength Metal Nanoparticles

Enhancing the Lithium Storage Performance of Phosphorus–Carbon Composites by Reinforcing P–C Bonding with High-Strength Metal Nanoparticles

Metallization of leaf-derived lignocellulose scaffolds for high-performance flexible electronics and oligodynamic disinfection

Vascular tubules in natural leaves form quasi-fractal networks that can be metallized. Traditional metallization techniques for these lignocellulose structures are complex, involving metal sputtering, nanoparticle solutions, or multiple chemical pretreatments. Here we present a novel, facile, and reliable method for metallizing leaf-derived lignocellulose scaffolds using silver microparticles. The method achieves properties on-par with the state-of-the-art, such as broadband optical transmittance of over 80%, sheet resistances below 1 Ω/sq., and a current-carrying capacity exceeding 6 A over a 2.5 × 2.5 cm² quasi-fractal electrode. We also demonstrate copper electrodeposition as a cost-effective approach towards fabricating such conductive, biomimetic quasi-fractals. Additionally, we show that these metallized structures can effectively eliminate pathogenic microorganisms like fecal coliforms and E. coli, which are bacterial indicators of microbiological contamination of water. We finally show that these oligodynamic properties can be significantly enhanced with a small externally applied voltage, indicating the noteworthy potential of such structures for water purification and pollution control.

Glassy Carbon Electrodes Modified with Ru nanoparticles Loaded in B-Doped Imidazolium Porous Organic Polymers for Hydrogen Evolution Reaction.

Porous organic polymers (POPs) are a type of porous material composed of organic structural units connected by covalent bonds and POPs have been used as efficient electrocatalysts for hydrogen evolution reaction (HER). Herein, glassy carbon electrode (GCE) is chemically modified by B-doped imidazolium-based porous organic polymers loaded with Ru nanoparticles on the GCE surface. The incorporation of B in the POPs regulates the electronic structure of electrocatalysts to enhance their inherent electrocatalytic activity for HER. The optimized modified electrode GCE-Ru/PIM-Br2 exhibits a low overpotential of 271 mV at a current density of 10 mA cm-2 with a small Tafel slope (80 mV dec-1) in acidic solutions, and shows long-term stability for up to 22 h. This work presents a strategy to develop B-doped porous electrodes with loaded metal nanoparticles to strengthen the catalytic performance of electrocatalysts.