Nanodendrites Research Articles

Electrochemical Reduction of CO2 at Coinage Metal Nanodendrites in Aqueous Ethanolamine.

Electrocatalytic reduction of CO2 into usable chemicals is a promising path to address climate change and energy challenges. Herein, we demonstrate the synthesis of unique coinage metal (Cu, Ag, and Au) nanodendrites (NDs) via a facile galvanic replacement reaction (GRR), which can be effective electrocatalysts for the reduction of CO2 in an ethanolamine (EA) solution. Each metal ND surface was directly grown on glassy-carbon (GC) substrates from a mixture of Zn dust and the respective precursor solution. The electrocatalytic activities of the synthesized ND surfaces were optimized for CO2 reduction in EA solution by varying their composition. It was determined that a 0.05 mol fraction of EA exhibited the highest catalytic activity for all metal NDs. Linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) techniques showed that metal-ND electrodes possessed higher current densities, lower onset potentials and lower charge-transfer resistances for CO2 reduction than their smooth polycrystalline electrode counterparts, indicating improved CO2 reduction catalytic activity. It was determined, using FTIR and NMR spectroscopy, that formate was produced as a result of the CO2 reduction.

Boosting Pd-catalysis for electrochemical CO2 reduction to CO on Bi-Pd single atom alloy nanodendrites

Pd is a catalyst for electrochemical CO2 reduction to CO but often disturbed by H2 and formate formation at low overpotentials due to its strong affinity to H atoms. Herein, guided by density functional theory (DFT) calculations, Bi-Pd single atom alloy (SAA) nanodendrites (NDs) with Bi atomically dispersed in Pd matrices have been developed for efficient CO2 reduction to CO. The Faradic efficiencies (FEs) of CO on the Bi6Pd94-SAA ND catalyst reach 90.5 % and 91.8 % in H-type and gas diffusion flow cells with overpotentials of only 290 and 200 mV, respectively, which are among the best of the reported Pd-based electrocatalysts. The greatly enhanced CO formation on the Bi6Pd94-SAA NDs can be attributed to the increased reaction barriers for H2 formation due to a lower H coverage resulted from Bi doping, and the decreased free energy for *COOH generation which is a key intermediate for CO production.

Synthesis and electrochemical study of coinage metal nanodendrites for hydrogen evolution reaction

Herein, we report a facile one-step synthesis route to fabricate the coinage metal nanodendrites (NDs) via a tailored galvanic replacement reaction (GRR). Cu, Ag and Au NDs are directly grown on glassy carbon plate (GCP) from the mixture of their precursor solutions and Zn dust. The formed NDs are uniformly distributed to the substrate and obtained the unique structures with sharp tips and tertiary branches. The electrocatalytic activity of the synthesized NDs towards the hydrogen evolution reaction (HER) is further investigated in 0.5 M H2SO4 using linear sweep voltammetry (LSV) and the Tafel slope. The results demonstrate that the nanodendrites formed through the GRR process exhibit greater catalytical activity towards HER in comparison to the polycrystalline Cu, Ag and Au. The prepared Au NDs exhibits the highest catalytic performance with a current density of −10.68 mA cm−2 at overpotential of 67 mV and a low Tafel slope of 65 mV dec−1. The simple and easy synthesis approach, the unique morphology and high electrocatalytic activity and excellent stability make the developed Cu, Ag and Au NDs highly efficient catalysts for green energy and electrochemical applications.

Facile synthesis of platinum-rhodium alloy nanodendrites as an advanced electrocatalyst for ethylene glycol oxidation and hydrogen evolution reactions

Direct ethylene glycol fuel cells (DEGFCs) and water splitting devices have received intensive interest during the past few decades. However, the commonly used Pt catalysts are seriously restricted by the high cost and very low resistance to CO-like intermediates during the catalysis. Herein, a general and simple solvothermal method was developed to synthesize three-dimensional (3D) bimetallic alloyed PtRh nanodendrites (NDs) for ethylene glycol oxidation reaction (EGOR) and hydrogen evolution reaction (HER). Citric acid (CA) and cetyltrimethylammonium chloride (CTAC) played important roles in formation of such dendritic structures. The optimized Pt56Rh44 NDs displayed the greatest mass activity (MA) for EGOR in 0.5 M KOH, which was 2.6-fold higher than commercial Pt black, coupled with the remarkable increase in the HER activity with a decayed overpotential of 20.0 mV to drive a current density of 10 mA cm−2 relative to the homemade Pt41Rh59 NDs (26.2 mV), Pt81Rh19 NDs (26.2 mV), Pt black (44.3 mV), Pt/C (44.4 mV) and Rh NFs (37.3 mV). This work offers some constructive guidelines for synthesis of advanced Pt-based catalysts in such energy devices.

Facile construction of 3D hyperbranched PtRh nanoassemblies: A bifunctional electrocatalyst for hydrogen evolution and polyhydric alcohol oxidation reactions

Development of highly effective and stable electrocatalysts is urgent for various energy conversion applications. Herein, a facile co-reduction approach was developed to fabricate three-dimensional (3D) hyperbranched PtRh nanoassemblies (NAs) under solvothermal conditions, where creatinine and cetyltrimethylammonium chloride (CTAC) were employed as the structure-directing agents. The as-synthesized nanocatalyst exhibited intriguing catalytic characters for hydrogen evolution reduction (HER) with a low overpotential (20 mV) at 10 mA cm−2 and a small Tafel slope (49.01 mV dec−1). Meanwhile, the catalyst showed remarkably enlarged mass activity (MA: 2.16/2.02 A mg−1) and specific activity (SA: 4.16/3.88 mA cm−2) towards ethylene glycol and glycerol oxidation reactions (EGOR and GOR) alternative to commercial Pt black and homemade Pt3Rh nanodendrites (NDs), PtRh3 NDs and Pt nanoparticles (NPs). This method offers a feasible platform to fabricate bifunctional, efficient, durable and cost-effective nanocatalysts with finely engineered structures and morphologies for renewable energy devices.

Highly porous PtPd nanoclusters synthesized via selective chemical etching as efficient catalyst for ethanol electro-oxidation

Direct ethanol fuel cells (DEFCs) have received great interest owing to their high power density and environmental friendness. Nevertheless, the designing of active, durable, and efficient anode for DEFCs is a profound challenge. In this context, we reported the synthesis of PtPd porous nanoclusters (PtPd PNCs) as electrocatalyst for ethanol oxidation reaction (EOR). This was implemented through two-step synthesis. Firstly, ternary AgPtPd nanodendrites (NDs) were synthesized via ultrasound-assisted co-reduction of the metal precursors using ascorbic acid (AA) as a mild reductant and Pluronic F127 as structure-directing agent. Thereafter, PtPd PNCs were created by selective chemical etching of AgPtPd nanocrystals in 1 M HNO3. The textural properties, morphology, and elemental composition of the studied electrocatalysts were investigated, and their catalytic activities towards ethanol electrooxidation were examined. PtPd PNCs revealed a high surface area of 83.0 m2 g−1 and high porosity compared to its counterparts. Additionally, it depicted enhanced catalytic performance towards ethanol electrooxidation in 1 M KOH with mass activity of 1.8 A mg−1 compared to PtPd NDs (0.97 A mg−1), Pt NDs (0.51 A mg−1), and Pt/C (0.33 A mg−1). The enhanced catalytic performance of PtPd PNCs was ascribed to high surface area, high porosity, and increased active sites.

Interface modulation of twinned PtFe nanoplates branched 3D architecture for oxygen reduction catalysis

Highly-branched dendritic Pt-based nanocrystals possess great potential in catalyzing the oxygen reduction reaction (ORR), but encounter performance ceiling due to their poor thermal and electrochemical stability. Here, we present a novel PtFe nanodendrites (NDs) branched with two-dimensional (2D) twinned nanoplates rather than conventional 1D nanowires, which breaks the ORR performance ceiling of dendritic catalysts by inducing the unique Pt-skin configuration via rationally thermal treatment. By further hybridizing the Pt-skin PtFe NDs/C with amino-functionalized ionic liquids (ILs), we achieve an unprecedented mass activity of 3.15 A/mgPt at 0.9 V versus reversible hydrogen electrode (RHE) in the PtFe-based ORR electrocatalytic system. They also show excellent electrocatalytic durability for ORR with negligible activity decay and no apparent structural change after 20,000 cycles, in sharp contrast to the nanowires branched PtFe NDs counterpart. The remarkable catalytic performance is attributed to a combination of several structural features, including 2D morphology, twin boundary, partially ordered phase and strong coordination with amino group. This work highlights the significance of stabilizing electrocatalytic structures via morphology tuning, which thus enables further surface and interface modification for performance breakthrough in ORR electrocatalysis.

Core-shell Au@Ag nanodendrites supported on TiO2 nanowires for blue laser beam-excited SERS-based pH sensing

The blue laser beam-excited surface-enhanced Raman scattering (SERS)-based pH sensing holds great promise for avoiding undesired thermal heating effect on some special temperature-vulnerable molecules, as compared to the vast majority studies by exciting in the red or near-infrared (NIR). Herein, we report an ingenious approach to support core-shell Au@Ag nanodendrites (NDs) on TiO2 nanowires, which can possess enhanced SERS activity under 473 nm laser excitation, owing to the improved charge-transfer effect on modified TiO2 support by inserting plasmonic Au@Ag. By using pH-indicating 4-mercaptobenzoic acid (4-MBA), the obtained TiO2/Au@Ag NDs can not only exhibit high sensitive linear-responses of pH changes ranging from pH 4.0 to 9.0 in different solutions (deionized water, NaCl, CaCl2, and MgCl2) but also provide excellent temperature stability under 4°C, 25°C and 37°C temperatures as well as good time stability after storage for 10 days. The established SERS-pH sensing by using shorter wavelength laser excitation is highly desirable for understanding physiological process in temperature-vulnerable microenvironment.

Trimetallic hybrid nanodendrites and magnetic nanocomposites-based electrochemical immunosensor for ultrasensitive detection of serum human epididymis protein 4

Alloy nanomaterials with various morphologies have showed their potential application in electrochemical signal amplification. However, it is still challenging to fabricate stable multimetallic nanomaterials with large surface area and strong electrochemical activity for the further enhancement of electrochemical sensors’ performance. Here, the trimetallic AgPtCo nanodendrites (NDs) were synthesized as powerful redox probe and highly efficient signal amplifier for electrochemical signal readout. A robust and ultrasensitive electrochemical immunosensor, based on AgPtCo NDs and magnetic nanocomposites (Fe3O4@SiO2@Au MNCs), was successfully developed to detect serum human epididymis protein 4 (HE4). The established method, drawing upon the strong electrochemical activity of AgPtCo NDs and the enrichment and separation effect of MNCs, exhibited a wide linear range (0.001–50 ng mL−1) and a low detection limit (0.487 pg mL−1). Besides, the developed sensor was applied to analyze the concentration of HE4 in real samples and the results achieved were consistent with those of clinical methods. Thus, this AgPtCo NDs and MNCs based electrochemical immunosensor might become a powerful alternative approach for ultrasensitive detection of various serum biomarkers associated with early diagnosis and treatment of diseases.

Trimetallic Hollow Pt–Ni–Co Nanodendrites as Efficient Anodic Electrocatalysts

A hollow nanostructure represents an emerging class of efficient catalysts for advanced catalytic applications due to their intrinsic surface area and high catalytic activity. Here, we report the design and synthesis of hollow Pt–Ni–Co nanodendrites (NDs) through selectively etching the Ni-rich core of solid core–shell Pt–Ni–Co NDs used as starting material. Moreover, the formation mechanism of solid core–shell Pt–Ni–Co NDs was investigated in detail by tracing the growth stages at different reaction timed. Impressively, hollow Pt–Ni–Co NDs exhibit 4.2- and 6.7-times higher mass activity for methanol and formic acid oxidation than that of commercial Pt/C, respectively.

One-pot wet-chemical synthesis of uniform AuPtPd nanodendrites as efficient electrocatalyst for boosting hydrogen evolution and oxygen reduction reactions

Uniform trimetallic AuPtPd nanodendrites (NDs) were synthesized by a simple and quick method, using l-proline and ascorbic acid (AA) as eco-friendly structure-guiding agent and reducing agent, respectively. The obtained AuPtPd NDs displayed greatly enlarged electrochemically active surface area (27.65 m2 g−1metal) relative to home-made AuPt nanocrystals (NCs, 21.76 m2 g−1metal), AuPd NCs (3.91 m2 g−1metal), Pt black (20.88 m2 g−1metal) and Pd black (8.30 m2 g−1metal). For hydrogen evolution and oxygen reduction reactions, AuPtPd NDs showed excellent catalytic performances relative to the referenced catalysts. These results reveal the practical applications of the as-obtained catalyst in energy storage and conversion.

Facile solvothermal synthesis of Pt71Co29 lamellar nanoflowers as an efficient catalyst for oxygen reduction and methanol oxidation reactions

The research for highly efficient and stable electrocatalysts in fuel cells has attracted substantial interest. Herein, bimetallic alloyed Pt71Co29 lamellar nanoflowers (LNFs) with abundant active sites were obtained by a one-pot solvothermal method, where cetyltrimethylammonium chloride (CTAC) and 1-nitroso-2-naphthol (1-N-2-N) served as co-structure-directors, while oleylamine (OAm) as the solvent and reducing agent. The fabricated Pt71Co29 LNFs exhibited the higher mass activity (MA, 128.29 mA mg−1) for oxygen reduction reaction (ORR) than those of home-made Pt48Co52 nanodendrites (NDs), Pt79Co21 NDs and commercial Pt black with the values of 39.46, 49.42 and 22.91 mA mg−1, respectively. Meanwhile, the MA (666.23 mA mg−1) and specific activity (SA, 2.51 mA cm−2) of the constructed Pt71Co29 LNFs for methanol oxidation reaction (MOR) are superior than those of Pt48Co52 NDs (213.91 mA mg−1, 1.99 mA cm−2), Pt79Co21 NDs (210.09 mA mg−1, 1.12 mA cm−2) and Pt black (57.03 mA mg−1, 0.25 mA cm−2). Also, the Pt71Co29 LNFs catalyst exhibited the best durable ability relative to the references. This work demonstrates that the developed strategy provides a facile platform for synthesis of high-performance, low-cost and robust catalysts in practical catalysis, energy storage and conversion.

Facile Fabrication of Radial PtCo Nanodendrites for Enhanced Methanol Oxidation Electrocatalysis

To improve the catalytic performances of Pt-based catalysts toward the methanol oxidation reaction (MOR) and reduce the consumption of Pt, we report one-step facile fabrication of radial PtCo nanodendrites (NDs) by a modified solvothermal method. It is noticeable that the radial PtCo NDs have a Pt-rich surface, and the radial PtCo NDs possess more tip areas due to unique first level NDs and more interconnected second level NDs, which can facilitate electronic transmission and mass exchange. Compared with commercial Pt/C, the radial PtCo NDs catalyst shows enhanced catalytic performance and stability toward the MOR. More importantly, this study offers more opportunities to prepare bimetallic NDs with enhanced catalytic performance.

A palladium-platinum bimetal nanodendritic melamine network for signal amplification in voltammetric sensing of DNA.

A sandwich-type electrochemical DNA sensor is described for the detection of oligonucleotides typical for MECP2 gene mutations. Palladium nanoparticles (PdNPs) and platinum nanoparticles (PtNPs) were used to synthesize flower-like PdPt nanodendrites (NDs) by a one-pot method. The PdPt NDs possess a high specific surface area and excellent catalytic capabilities. They served as the carrier for the signal DNA probe (SP) and simultaneously catalyze the reduction of hydrogen peroxide (H2O2). The PdPt NDs were modified with melamine, and this results in the formation of a PdPt-melamine network through stable interactions between the PdPt NDs and the three amino groups of each melamine molecule. The network exhibits excellent catalytic ability in enhancing the current signal response in the voltammetric detection of MECP2 gene mutation, best measured at -0.4V vs. SCE and using H2O2 as the electrochemical probe. In addition, gold nanoflowers were electrodeposited on the electrode interface in order to accelerate electron transfer and to capture the capture probe. The sensor is stable and can detect MECP2 gene mutations in the 1 fmol·L-1 to 1nmol·L-1 concentration range, with a 0.33 fmol·L-1 lower detection limit at an S/N ratio of 3. Graphical abstract Schematic presentation of electrodes for the determination of the X-linked gene methyl-CpG-binding protein 2 (MECP2). The sensor is based on the electrooxidation of added H2O2 by using the melamine modified palladium platinum bimetal nanodendrites as network signal amplification strategy. This versatile platform expands studies on the detection of monogenic disease.

Sonochemical fabrication of reduced graphene oxide supported Au nano dendrites for ethanol electrooxidation in alkaline medium

In this report, the experimental characterization of reduced graphene oxide (RGO) nanosheets supported highly branched Au nano dendrites were successfully synthesized by using simple two-step method, such as co-precipitation followed by sonochemical irradiation method. The as-prepared nano dendrites catalysts have open surface structures with enhanced catalytic activity. Both RGO supported Au nano dendrites with high index (411) surface and unsupported Au nano dendrites with a surface facet of (211) were characterized using electrochemical techniques, such as cyclic voltammetry (CV), chronoamperometry (CA), CO-Stripping voltammetry, electrochemical impedance spectroscopy (EIS), and rotating disk electrode (RDE) to quantitatively obtained ethanol oxidation and oxygen reduction mechanism. The RGO supported Au nano dendrites possess small size with improved electrocatalytic activity than pure Au nano dendrites, suggesting that RGO nanosheets are a necessary material for catalyst activity improvement.

Synthesis of hierarchical platinum-palladium-copper nanodendrites for efficient methanol oxidation

Tuning the architecture and composition of platinum (Pt)-based nanostructures for enhancing the electrocatalytic activity and stability towards methanol oxidation reaction (MOR) is pivotal for the commercialization of direct methanol fuel cells (DMFCs), but still remains great challenge. Here, hierarchical platinum-palladium-copper (PtPdCu) nanodendrites (NDs) with tip-cracked defects have been developed with tailored morphology and dopants. We firstly electrodeposited PtPdCu nanowires (NWs) inside the channels of aluminum anodic oxide (AAO) template, and then wet-chemically transformed the as-synthesized NWs into NDs. Benefiting from the synergetic effect between the tip-cracked defects and dopants, firstly, the MOR mass activity and specific activity of PtPdCu NDs are ∼1.78 times and ∼2.14 times higher than those of commercial Pt/C, respectively; secondly, after 2000s stability test, the electrocatalytic activity of PtPdCu NDs is ∼5.02 times higher than commercial Pt/C; finally, the PtPdCu NDs also show better CO tolerance as well. Our PtPdCu NDs are promising anode electrocatalysts in next-generation DMFCs.

PEGylated Au@Pt Nanodendrites as Novel Theranostic Agents for Computed Tomography Imaging and Photothermal/Radiation Synergistic Therapy.

The integration of photothermal therapy (PTT) with radiation therapy (RT) in a single nanoscale platform is believed to have considerable potential for cancer therapy. In this work, the rationally designed PEGylated Au@Pt nanodendrites (NDs) have been developed as a novel X-ray computed tomography (CT) and PTT/RT enhanced theranostic agent for cancer therapy. The absorption of Au@Pt NDs was turned to the near-infrared region with the growth of Pt nanobranches and thus enhances the efficacy of PTT. Furthermore, because of the high atomic number (high Z) of Au as well as Pt, Au@Pt NDs significantly enhanced lethal effects of RT by inducing a highly localized radiation dose within cancer cells. More importantly, the combination of Au@Pt ND-enhanced RT with PTT suppressed cancer cell growth more efficiently than that RT or PTT alone did, indicating a synergistic effect. Meanwhile, the Au@Pt NDs also possess significant CT imaging signal enhancement that has the potential to guide PTT/RT for cancers. The integrated strategy significantly improved CT and PTT/RT of cancer cells with mild laser and radiation. Because of these advantages, Au@Pt NDs have become appealing and effective agents for cancer theranostic.

Ultrasonication-assisted wet-chemical fabrication of uniform AuPt nanodendrites as efficient electrocatalyst for oxygen reduction and hydrogen evolution reactions

Herein, we present an ultrasonication-assisted wet-chemical method for facile synthesis of uniform bimetallic AuPt alloy nanodendrites (NDs), using 4-amino-2,6-dihydroxypyrimidine as the structure-directing and dispersing agents, without any template, seed, organic solvent or polymer. The structure, morphology, size, and composition of the as-obtained nanocrystals are examined by a series of characterization techniques. The architectures display remarkable catalytic performances toward oxygen reduction and hydrogen generation in comparison with commercial Pt black and Pt/C catalysts, through the polarization, chronoamperometry, and durability measurements. This is due to the special dendritic nanostructures with rich surface defects, porous features and the synergistic effects between Pt and Au in the alloy. In combination with the simple, easily controllable, and time-saving synthetic strategy, AuPt NDs may find potential applications and shed some light on the construction of other bimetallic nanocatalysts in fuel cells.

Ultrafast self-assembly of silver nanostructures on carbon-coated copper grids for surface-enhanced Raman scattering detection of trace melamine

Structurally well-defined assemblies of silver nanoparticles, including the dendritic nano-flowers (NFs), planar nano-spheres (NSs) and nano-dendrites (NDs) were obtained by a surfactant-free and ultrafast (≈15min) self-assembly process on as-purchased carbon-coated copper TEM grids. The silver nano-assemblies, especially the NFs modified TEM grids, when serving as surface-enhanced Raman spectroscopy (SERS) substrates for detecting melamine molecules, demonstrated a long-lived limit of detection (LOD) of as low as 10−11M, suggesting the potential of these silver-assemblies modified carbon-coated copper grids as novel potable and cost-effective SERS substrates for trace detection toward various food contaminants like melamine.

Folic acid bio-inspired route for facile synthesis of AuPt nanodendrites as enhanced electrocatalysts for methanol and ethanol oxidation reactions

Abstract Folic acid (FA), as an important biomolecule in cell division and growth, is firstly employed as the structure director and stabilizing agent for controlled synthesis of uniform Au 65 Pt 35 nanodendrites (NDs) by a one-pot wet-chemical bio-inspired route at room temperature. No pre-seed, template, organic solvent, polymer, surfactant or complex instrument is involved. The products are mainly characterized by transmission electron microscopy (TEM), high angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), X-ray diffraction (XRD), and X-Ray photoelectron spectroscopy (XPS). The architectures have enlarged electrochemically active surface area (60.6 m 2 g Pt −1 ), enhanced catalytic activity and durability for methanol and ethanol oxidation in contrast with commercial Pt black and the other AuPt alloys by tuning the molar ratios of Au to Pt (e.g., Au 31 Pt 69 and Au 82 Pt 18 nanoparticles). This strategy would be applied to fabricate other bimetallic nanocatalysts in fuel cells.