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In this article, we develop a thermodynamic and an electrochemical kinetic model to study the stability of metal nanoparticles (MNPs) supported on an inert substrate and in contact with an electrolyte. Regardless of the model, we find that the redox potential is a property of the entire MNPs' size distribution, which has to be characterized by, at least, its mean and variance. The thermodynamic model, which considers only the excess free energy due to the increased surface-to-volume ratio on MNPs, predicts an increase in surface effects as the size distribution becomes broader. On the other hand, the electrochemical kinetic approach models the MNPs as reactive systems considering the changes in the heterogeneous-rate constants due to surface effects. This allows the use of the mixed potential theory to evaluate the electrode potential, which would be experimentally accessible, showing a tendency contrary to that predicted by the thermodynamic model for closed systems. Then, the electrochemical boundary conditions –i.e., charge conservation- have to be considered rather than just the thermodynamic criteria. Also, it is analyzed under which circumstances the charge-transfer processes control the electrode potential, instead of mass-transfer. Hence, it is shown that the electrochemical kinetic approach is applicable to the study of the electrochemical Ostwald ripening among many other processes. [Display omitted] [ABSTRACT FROM AUTHOR]

To design the highly active, stable electrocatalyst for oxygen evolution is emerging as challenging task for sustainable energy production. Herein, we fabricated the non-noble CuO/NiO/rGO nanocomposite approached by facile chemical co-precipitation method. The successful formation of binary metal oxide nanocomposite with reduced graphene oxide was confirmed with monoclinic CuO and cubic NiO, which is clearly revealed in the XRD diffraction results. By incorporating the CuO and NiO into the rGO sheets results homogeneous tiny nanoparticles morphology decorated on the graphene sheets which improving interaction among metal nanoparticles and carbon based products. The electrocatalytic performance of resultant binary metal oxide nanocomposite with rGO was investigated in alkaline KOH environment towards oxygen evolution reaction. The 200 mV overpotential was attained at 10 mA/cm2 with smaller 165 mV/dec Tafel value. The elevated electrochemical surface area (ECSA) value of 132.5 cm2 was estimated from cyclic voltammetry analysis of optimized CuO/NiO/rGO electrocatalyst. The electrochemical impedance spectrum of the prepared electrocatalyst shows that the low 0.04 Ω charge transfer resistance is highly desirable to the better conductivity. The prepared CuO/NiO/rGO electrocatalyst stability was verified by chronoamperometry test at low 10 mA/cm2 and exhibited stable performance up to 16 h towards OER. Hence, this work contributes innovative synergistic approach for growth of cost effective binary metal-oxide (CuO/NiO) nanocomposite combined with conductive carbon material for oxygen evolution reaction. [ABSTRACT FROM AUTHOR]

An electrochemical sensor was fabricated using tyrosinase functionalized metal oxide nanoparticles that were used to detect dopamine (DA). The copper oxide nanoparticles (Cu 2 O NPs) were synthesized by hydrothermal method using Artemisia absinthium leaf extract. The surface morphology, optical characterization, and elemental composition of synthesized nanoparticles were characterized by various analytical instruments. The Line-weaver relationship was used to estimate the K m and V max values of the tyrosinase enzyme. Differential pulse voltammetry and cyclic voltammetry techniques were used to record the electrochemical responses of DA at Tyr/Cu 2 O NPs/GCE modified electrode. The modified electrode exhibits enhanced electro-catalytic activity towards DA more than the bare electrode that was supported by the lowering of critical voltage in the forward current-voltage characteristics. The Tyr/Cu 2 O NPs/GCE modified electrode exhibits a limit of detection (LOD) of 0.3 µM with a linear range of 10 µM to 70 µM concentration. Further study demonstrated that the modified electrochemical device had excellent repeatability and high selectivity to DA in the presence of various interference molecules. Analyses of real-world samples were demonstrated to estimate the practical applicability of Tyr/Cu 2 O NPs/GCE modified electrode. [Display omitted] [ABSTRACT FROM AUTHOR]

An efficient electrochemical urea oxidation reaction (UOR) could be used in energy production technology. Metallic nickel nano-particles (Ni NPs) are incorporated in cobalt hydroxide layered material to form Ni/Co(OH) 2. The synthesized material is utilized as an electrocatalyst in UOR. It has been revealed that the incorporation of Ni NPs into cobalt hydroxide significantly enhances their electrocatalytic activity toward UOR. Ni/Co(OH) 2 catalyzes UOR at a very low anodic potential of 1.15 V vs RHE with a peak current density of 14.2 mAcm−2 and Tafel slope of 75 mVdec−1. The current work is a step ahead towards use of transition metal hydroxide (TMH) as support in the electrocatalytic oxidation applications especially UOR. [ABSTRACT FROM AUTHOR]

Usually, metallic organic frameworks (MOFs) based electrocatalysts are prepared by pyrolysis of MOFs. And it is improved that the research on direct use of MOFs as electrocatalysts through the development of two-dimensional (2D) shaped MOFs direction is feasible. In this paper, a kind of ultrathin NiFeZn-MOF nanosheets containing few metal oxide nanoparticles grown on nickel foam (NiFeZn-MNS/NF) are successfully synthesized, and they are used as catalyst for the oxygen evolution reaction (OER) and overall water splitting. The NiFeZn-MNS/NF catalyst behaves the most excellent electrocatalytic performance with the best overpotential of 350 mV at 50 mA cm−2 and has the best current density stability with the 5% drop of the initial polarization current density at the end of 120 h. The voltage of NiFeZn-MNS/NF as a bifunctional overall water-splitting catalyst is 1.52 V at the current density of 10 mA cm−2, which is superior to commercial noble metal electrocatalytic combination of RuO 2 /NF(+)//Pt-C/NF(−)(1.63 V). The structure and morphology of the nanosheets and the synergistic effect of nickel, iron and zinc ions enhance the catalytic activity. While the addition of zinc ion promotes the rapid growth of nanosheets on nickel foams, which further improves the stability of nanosheets. [ABSTRACT FROM AUTHOR]

The use of DNA to assembly metal nanoparticles into specific crystalline lattices is a topic of high interest in the moment. Due to the DNA self-assembly it is possible not only to control the crystal symmetry, but also control the distance between particles, rigidity, dynamics and actuation of these systems. In this way, those nanoparticles superlattices are interesting for a broad range of applications, including plasmonics, catalysis and electronics. Herein, we used DNA to self-assembly 20 nm gold nanoparticles into body centered cubic (bcc) films with two different orientations and studied the contribution of DNA to the conduction using methylene blue as electrochemical probe. Our results showed that methylene blue intercalated into the DNA double helix, and the obtained films presented high k ET values, reaching ∼230 s−1, moreover we showed that the (110) orientation have a higher k ET compared to the (100). It indicates that not only the DNA and the nanoparticle are important for the conduction, but their organization is also crucial to understand and improve the charge conduction. Image 10750 [ABSTRACT FROM AUTHOR]

The present investigation deals with the development, characterization and application of nanostructured Pd doped Ni electrodes (Pd@Ni), which uses the electrochemical properties of Pd in synergy with the magnetic properties of Ni for biosensors development. The Pd@Ni electrodes have been characterized by X-ray diffraction, scanning electron microscopy with energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. It has been shown that palladium presented spherical assemblies ranging 150–200 nm medium diameter size that covers large areas of the electrode surface while metallic nickel, which confers magnetic properties, showed a uniform granular structure with sizes between 20 and 50 nm. Cyclic voltammetry and electrochemical impedance spectroscopy were performed to understand the electrochemical process at the Pd@Ni electrodes in neutral media. The Pd@Ni electrodes were applied for the electrochemical detection of H 2 O 2. Finally, Ni nanoparticles (NiNP) functionalized with the model enzyme glucose oxidase (GOx-NiNP) have been attached to the Pd@Ni electrode solely through magnetic interactions, and the obtained GOx-NiNP/Pd@Ni biosensor applied for glucose determination in aqueous solutions by fixed potential amperometry at −0.05 V (vs Ag/AgCl) with reduced interferences. Image 10197 • Palladium doped nickel electrodes and nickel nanoparticles. • Benefits from the catalytic effect of Pd and the magnetic properties of Ni. • Oxidase immobilization solely through magnetic interactions. • Palladium doped nickel electrodes for the detection of H 2 O 2. • Biosensor operates at low potential values avoiding interfering compounds. [ABSTRACT FROM AUTHOR]

• Boron-doped diamond electrodes (BDDEs) can be easily modified in different ways. • Various modification procedures have been developed and reviewed. • Modification by metal and metal oxide nanoparticles, biomolecules,carbon materials. • Utilization in biosensing,electroanalysis fuel cell construction, and CO2 reduction. This review presents recent developments in the modification of boron-doped diamond electrodes (BDDEs) and their application in biosensing, electroanalysis, electrosynthesis, fuel cell construction, and CO 2 reduction. The various modification procedures are also described. In addition to the outstanding properties of unmodified BDDEs, they have recently become a highly functional substrate for various modifications. The modifications of BDDEs by metals or metal oxides were aimed at increasing the surface area and promoting electron transfer kinetics or electrocatalytic activity for CO 2 reduction, sensing of oxygen, or stripping voltammetry. Modification by polymers such as Nafion, polypyrrole, or polyaniline was used mostly to fine-tune the specificity of voltammetric analyses and interference suppression. DNA, enzymes, or other biomolecules were used to obtain specific sensing capabilities. These chemical modifications are critically compared to the other strategies used for BDDEs, including varied boron doping levels, the ratio of sp2 to sp3 carbon, and BDDE surface pre-treatment. [Display omitted] [ABSTRACT FROM AUTHOR]

Rational three-dimensional nitrogen doped mesoporous carbon nanostructured surfaced Nickel metal (Ni) nanoparticles (nps), NCNP composites have been developed using nickel organic complex and utilized as an electrocatalyst for oxygen evolution reaction. The NCNP composites of tunable physio-chemical characteristics, such as Ni nps size (∼18–∼42 nm), surface area (∼18–∼43 m2 g−1), pore size (3.23–3.84 nm) and nitrogen doping amount (1.20–3.87 wt%) have been achieved via controlled carbonization temperature. An optimized NCNP composite of favorable physio-chemical properties has delivered good oxygen evolution kinetics such as a lower overpotential value (370 mV) at 10 mA cm−2, a minimum Tafel slope value (55 mV dec−1), and relatively a higher electrochemical surface area (0.6325 cm−2) than the other NCNP composites. Moreover, the best NCNP electrocatalyst has shown a comparable overpotential value with the benchmarking catalyst at 10 mA cm−2, equivalent to ∼10% solar photoelectrical conversion efficiency. In addition, the best NCNP electrocatalyst has exhibited excellent accelerated degradation test for 24 h at a constant current density of 10 mA cm−2 with an increase overpotential value of 0.029 V. Image 1 • N-doped mesoporous NCNP electrocatalyst prepared by a simple cost-effective approach. • NCNP delivers comparable overpotential value with the benchmark electrocatalyst. • NCNP exhibits excellent accelerated degradation test for 24 h at a 10 mA cm−2. [ABSTRACT FROM AUTHOR]

Interconnected graphene aerogels (IC:GA) and their composites with transition metal oxide nanoparticles are attracting increasing research interest for fabrication of supercapacitors. In this study, for the first time, we have incorporated ytterbium oxide nanoparticles (Yb 2 O 3 NPs) to a nitrogen doped-interconnected graphene aerogels (N-IC:GA) matrix through a facial one-step hydrothermal method and by using p-phenylenediamine (PPD) as an interconnector and a source of nitrogen. In this porous network, graphene nanosheets are present with very low thickness of about 5–9 nm. The electrochemical performance of the nanocomposite was investigated by cyclic voltammetry (CV), galvanostatic charge/discharge, electrochemical impedance spectroscopy (EIS) and continuous cyclic voltammetry (CCV). The obtained Yb 2 O 3 /N-IC:GA nanocomposite was tested as a symmetric capacitor which exhibited a specific capacitance of 321 Fg−1 at a current density of 0.5 A g−1, a high energy density of 25 Wh Kg−1, an excellent cycle life for voltage values up to 1.5 V, and a capacitance retention of 98.4% after 4000 cycles in an environment-friendly aqueous electrolyte of 1 M Na 2 SO 4. Moreover, Yb 2 O 3 /N-IC:GA proved to be highly capable because the delivered specific capacitance at a current density of 16 A g−1 retained 53.4% of its value at 0.5 A g−1. Image 1 • For the first time, ytterbium oxide nanoparticles were incorporated to N-IC:GA in a simple synthetic manner. • Due to the utilizing of Yb 2 O 3 and PPD, the performance of graphene aerogel-based supercapacitor was significantly upgraded. • The synthesized nanocomposite exhibits a high energy density of 25 Wh kg−1 at a power density of 375 W kg−1. [ABSTRACT FROM AUTHOR]

Growth of finely dispersed nanocatalysts by exsolution of metal nanoparticles from perovskite oxides under reducing conditions at elevated temperature is a promising approach of producing highly active catalytic materials. An alternative method of exsolution using an applied potential has been recently shown to potentially accelerate the exsolution process of nanoparticles that can be achieved in minutes rather than the hours required in chemical reduction. In the present study, we investigate exsolution of nanoparticles from perovskite oxides of La 0.43 Ca 0.37 Ni 0.06 Ti 0.94 O 3-γ (LCTNi) and La 0.43 Ca 0.37 Ni 0.03 Fe 0.03 Ti 0.94 O 3-γ (LCTNi-Fe) under applied potentials in carbon dioxide atmosphere. The impedance spectra of single cells measured before and after electrochemical poling at varying voltages showed that the onset of exsolution process occurred at 2 V of potential reduction. An average particle size of the exsolved nanoparticles observed after testing using a scanning electron microscopy was about 30–100 nm. The cells with the reduced electrodes exhibited desirable electrochemical performances not only in pure carbon dioxide (current density of 0.37 A cm−2 for LCTNi and 0.48 A cm−2 for LCTNi-Fe at 1.5 V) but also in dry hydrogen (0.36 W cm−2 for LCTNi and 0.43 W cm−2 for LCTNi-Fe). [ABSTRACT FROM AUTHOR]

Abstract In this study, an efficient and cheap electrocatalysts are prepared by a simple synthetic method for oxygen evolution reaction (OER) hydrogen evolution reaction (HER). Nickel/nickel oxide@3dimensional hierarchical porous graphene (Ni-NiO@3DHPG) and cobalt/cobalt oxide@3dimensional hierarchical porous graphene (Co-CoO@3DHPG) electrocatalysts were obtained from cation exchange resin, nickel acetate and cobalt nitrate as a source of carbon, Ni and Co respectively. In Ni-NiO@3DHPG and Co-CoO@3DHPG, metal and metal oxide nanoparticles embedded in the graphene layers, were confirmed by different techniques. The 3-D graphene in Ni-NiO@3DHPG and Co-CoO@3DHPG were thinned wall and highly porous structure and large specific surface area. The Ni-NiO@3DHPG composite displays onset potential, overpotential (10 mA cm−2) and Tafel value of are 1.53 V, 1.64 V and 55 mV dec−1 for OER and −0.18 V, −0.31 V and 78 mV dec−1 for HER respectively. Similarly, Co-CoO@3DHPG catalyst show onset potential, overpotential (10 mA cm−2) and Tafel are 1.59 V, 1.68 V and 65 mV dec−1 for OER and −0.26 V, −0.40 V and 85 mV dec−1 for HER respectively. Electrocatalysts show good stability after 4 h continuously. This simple synthetic method will open a new way for cheap and efficient electrocatalysts of other types of non-precious metals for OER and HER. Graphical abstract A simple method was used to in situ grown Ni-NiO and Co-CoO in three dimensional hierarchical porous graphene by ion exchange/activation method. The obtained Ni-NiO@3DHPG and Co-CoO@3DHPG show efficient performance for OER and HER. the better performance of Ni-NiO@3DHPG and Co-CoO@3DHPG are due to well dispersion of Ni-NiO and Co-CoO particle in graphene layers and high conductivity of graphene layer which facilitate fast transport of electron. Image 1 Highlights • - A novel and less toxic alternative precursor to synthesize 3DHPG. • Ni-NiO@3DHPG and Co-CoO@3DHPG active and stable electrocatalyst for OER and HER. • The efficient activities attributed to Ni-NiO and Co-CoO and condutive graphene. [ABSTRACT FROM AUTHOR]

Abstract We describe a facile and simple solid-state thermolysis route for the preparation of Co, Ni, and Fe phosphide nanoparticles embedded in amorphous carbon using an organometallic complex. This was achieved by using a suitable organometallic complex in a single step synthetic route without using any solvent or catalyst. The advantage of using such precursor was to offer a source for metal, phosphorus and carbon without using any additional sources. The morphology of products was characterized by transmission electron microscopy, scanning electron microscopy and nature of carbon was analyzed using the Raman microscope and X-ray diffraction. The electrocatalytic oxygen evolution reaction (OER) activity and stability of the metal phosphide nanostructure was evaluated using the rotating disk electrode technique. The CoP, NiP and FeP exhibit the OER overpotential of 370, 380 and 550 mV at 10 mA cm−2, respectively in 0.1 M KOH electrolyte. Among prepared phosphide catalysts, cobalt phosphide shows a lowest Tafel slope indicate favorable kinetics for the OER activity than nickel and iron phosphide catalysts. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

Abstract An assembly of hemispherical particles continuously nucleating on a planar electrode and growing under mixed kinetic-diffusion control is here considered. A model is derived, from the exact boundary integral formulation of the diffusion equation, to predict the overall current evolution, and the radii distribution of particles nucleating within any prescribed time interval. Iso-nucleation-time classes are introduced in the model, grouping particles (almost) simultaneously nucleating over the underlying substrate. The dynamics of particles belonging to a given iso-nucleation-time class are assumed to be identical. By this approximation, hereby referred to as Averaged Class Approximation (ACA), the computation of the average radius of any iso-nucleation-time class is reduced to the solution of an integro-differential equation, parameterized by the nucleation time. An effective computational method is also presented to solve the model equations, giving predictions that fairly well agree with the results of direct multi-particle numerical simulations. [ABSTRACT FROM AUTHOR]

Abstract A unique interconnected porous Mn 2 O 3 /C@Co 3 O 4 cubic composite, as efficient electro-active electrode for supercapacitors, was successfully synthesized via a facile two-step hydrothermal method. Novel cube-like Mn 2 O 3 /C@Co 3 O 4 composite, with a high specific surface area (S BET) and conductivity, could promote charge transfer and improve the overall electrochemical performance. The as-prepared Mn 2 O 3 /C@Co 3 O 4 composite exhibited the excellent reversible specific capacitance (523.8 F g−1 at a current density of 0.3 A g−1, much higher than Mn 2 O 3 /C), good rate performance (57.2% capacitance retention) and superior cycling stability (90.6% capacitance retention after 3000 cycles). In addition, an asymmetric supercapacitor (Mn-Co//AC) with Mn 2 O 3 /C@Co 3 O 4 as the positive electrode and activated carbon (AC) as the negative electrode delivered a maximum energy density of 45.8 Wh kg−1 at a power density of 0.3 kW kg−1. Graphical abstract The unique interconnected porous Mn 2 O 3 /C@Co 3 O 4 cubic composite was synthesized through a facile two-step hydrothermal method and calcination treatment for high performance asymmetric supercapacitors. Image 1 Highlights • The Mn 2 O 3 /C@Co 3 O 4 cubic composite was prepared via a facile two-step hydrothermal route and a calcination process. • The novel porous cubic-like Mn 2 O 3 /C@Co 3 O 4 displays the maximum C m of 523.8 F g−1 at 0.3 A g−1. • The Mn-Co//AC delivers high energy density of 45.8 Wh kg−1 at a power density of 0.3 kW kg−1. • A structural advantage of Mn 2 O 3 /C@Co 3 O 4 materials is proposed. [ABSTRACT FROM AUTHOR]

Abstract TiO 2 -doped RuO 2 nanoparticles, obtained through wet milling and sol-gel process, are coated on thin SnO 2 film covered tantalum substrate by magnetron sputtering to make a composite electrode of sandwiched framework. Phase structure, morphology, specific surface area, pore distribution as well as electrochemical performance of this composite electrode are tested and analyzed. Our results indicate that sample annealed at 260 °C for 4 h has optimal microstructure and electrochemical performance at doping level of 15 wt.% TiO 2 with particles size of 38–43 nm and specific surface area of 22.330 m2 g−1. Specific capacitance of 692 Fg−1 (the highest in this study), good charge-discharge behavior, low equivalent series resistance as well as long cycling life are observed. Integrating into a 50 V 8000 μF electrochemical capacitor, specific energy and specific power reach 31.6 in Wh.Kg−1 and specific power of 2032 W Kg−1, respectively. Meanwhile, composite electrode shows stable capacitance without hydrogen evolution and peeling between TiO 2 -doped RuO 2 nanoparticles and thin SnO 2 film modified tantalum substrate. [ABSTRACT FROM AUTHOR]

Abstract Na-ion battery has been investigated as a potential candidate for Li-ion battery because of its abundant sodium resource. One of the advanced anodes for Na-ion battery is NaTi 2 (PO 4) 3 due to the open 3D framework, good thermal structure and high Na+ conductivity. However, the NaTi 2 (PO 4) 3 material possesses a low electrical conductivity, which hinders its application for large-scale sodium storage. Herein, the nanosized NaTi 2 (PO 4) 3 @C crystals embedded in 2D sulfur-doped graphene sheets are synthesized using a simple method. The 2D sulfur-doped graphene sheets can easily facilitate the transport of electrons/ions and inhibit the volume change during the insertion/extraction of Na+ ions, resulting in superior rate property. The synthesized electrode shows the high discharge capacity (130.1 mAh g−1 at 0.1 C), excellent rate property (112.8 mAh g−1 at 10 C) and stable cycle life (95.8 mAh g−1 over 500 cycles at 20 C), revealing its great application for Na-ion battery. This novel strategy could be applied to synthesize other advanced electrode materials for electrochemical sodium storage. Graphical abstract Image Highlights • Ultrafine NaTi 2 (PO 4) 3 @C embedded in sulfur-doped graphene has been designed and prepared. • 2D sulfur-doped graphene sheet can easily facilitate the transport of electron/ion. • Sulfur-doped graphene can accommodate the volume variation during Na+ insertion/extraction. • The obtained electrode shows a reversible capacity of 95.8 mAh g−1 over 500 cycles at 20 C. [ABSTRACT FROM AUTHOR]

Two chromite spinel-based composite materials, Mn II Cr III 2 O 4 /Mn II Mn III 2 O 4 /C and CoCr 2 O 4 /C are successfully synthesized by a solid-state conversion process via annealing Mn Cr-coordination compound and Co Cr-coordination compound at 350 °C in air for 1 h, respectively. The two composite materials both show the morphology of nanoparticles, in which the spinels are embedded in carbon matrix into a continuous phase. The as-prepared composite materials are used as supercapacitor electrodes in basic electrolyte. The Mn II Cr III 2 O 4 /Mn II Mn III 2 O 4 /C composite material possesses a high specific capacity of 184.0 mAh g −1 at a current density of 0.5 A g −1 with a superior rate capability of 138.3 mAh g −1 (75.2% retention) at 20 A g −1 . Meanwhile, CoCr 2 O 4 /C nanoparticles also deliver a high specific capacity of 158.8 mAh g −1 at a current density of 0.5 A g −1 with a superior rate capability of 125.0 mAh g −1 (78.7% retention) at 20 A g −1 . The good supercapacitive behaviors of the two composite materials are probably attributed to the characteristics of bimetallic compound and the presence of multiple valence states in the samples, giving rise to obvious redox responses. And the Mn II Cr III 2 O 4 /Mn II Mn III 2 O 4 /C and CoCr 2 O 4 /C composites possess reversible electrochromism. [ABSTRACT FROM AUTHOR]

Hierarchical iron sulfide nanocubes consisting of multiple iron sulfide-carbon core-shell nanoparticles coated with few-layer graphene (Fe 1-x S@C/rGO) were prepared by a two-step in-situ transformation strategy employing Prussian blue (PB) as a starting material. The hierarchical nanocubes delivered an outstanding rate capability of 323 mAh g −1 at the current density of 10 A g −1 when used as the anode of sodium ion half cells. An iron-based sodium-ion full cell composed of a hierarchical Fe 1-x S@C/rGO anode and PB cathode had a capacity of 323 mAh g −1 for 150 cycles. We attributed the good sodium ion storage properties of the Fe 1-x S@C/rGO nanocubes to the stable hierarchical building structures and the high graphitization degree of carbon obtained during the transformation process. The graphene-coated nanocube structures inhibited the agglomeration of iron sulfide-carbon core-shell nanoparticles and accommodated the huge volume expansion that occurred during cycling. The high graphitization degree of carbon endowed Fe 1-x S@C/rGO nanocubes with high electronic conductivity, facilitated sodium ion accessibility, and increased mechanical durability. [ABSTRACT FROM AUTHOR]

In this work, highly ordered nickel oxide nanoparticles were electrochemically synthesized on nickel foam (NiO x NPs/Ni foam) via the formation and subsequent heat treatment of nickel hydroxide. The synthesized NiO x NPs were characterized using Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) with elemental analysis and high resolution transmission electron microscopy (HR-TEM). The XRD results revealed the presence of two different oxide phases with high crystallinity. The synthesized NiO x NPs were highly ordered spherical morphology with average size of 7 nm, identified from the FE-SEM images. Further, the electrochemical performance of synthesized NiO x NPs/Ni foam was evaluated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge discharge (GCD) methods. The calculated specific capacity of NiO x NPs/Ni foam was found to be 219 C/g (60.7 mAh/g) at scan rate of 5 mV/s. This present work implies that the electro-synthesized NiO x NPs/Ni foam as a good binder-free, highly stable battery-type material and it can be used as a positive electrode for hybrid-capacitors. [ABSTRACT FROM AUTHOR]

Constructing semiconductor heterojunction with optimal structure and composition is highly desired to maximize the solar light utilization for photoelectrochemical (PEC) water splitting. Here, we reported the fabrication of BiVO 4 @ZnO heterojunction with a novel nanostructure for PEC water splitting via foaming-assisted electrospinning and subsequent atomic layer deposition (ALD) techniques. In such BiVO 4 @ZnO heterojunction, the isolated BiVO 4 nanoparticles were packaged within the ZnO microbelt matrix. During PEC water splitting, the BiVO 4 acts as the primary light absorber for wider solar spectral harvesting, and the ZnO prompts the transfer of the photo-excited high-energy electrons, which would render them with prolonged lifetime and enhanced separation of the photogenerated charge carriers. In addition, the microbelts architecture with a hollow channel can also effectively improve the interfacial charge separation and transportation. Accordingly, the PEC performances of BiVO 4 @ZnO hybrid microbelts were significantly enhanced with a photocurrent density up to ∼0.46 mA cm −2 (at 1.23 V vs. reversible hydrogen electrode (RHE) under simulated sunlight illumination), which is 15.3 times to that of pure BiVO 4 counterpart (∼0.03 mA cm −2 ). The photocurrent density of the BiVO 4 @ZnO electrode can be further increased to 1.07 mA cm −2 at 1.2 V vs. RHE by adding hole scavenger (NaSO 3 ) in the electrolyte solution under AM 1.5 G irradiation. [ABSTRACT FROM AUTHOR]

Metallic antimony with high capacity, abundant and a very appropriate reaction potential is considered as a promising anode material for LIBs. But poor cycle performance due to the huge volume expansion during cycling process seriously hinders its practical application. Here, Sb nanoparticles encapsulated into carbon nanosheets were prepared by a facile and scalable method. And the carbon nanosheets can effectively buffer the volume expansion and inhibit the aggregation of Sb nanoparticles during the lithiation/delithiation process. Finally, the as-prepared Sb@C nanosheets display superior rate capability (418 mAh g −1 can be observed even at 5.0 A g −1 ) and long cycle stability (449 mAh g −1 can be maintained after 1000 cycle at 2.0 A g −1 ). Furthermore, when coupled with LiFePO 4 /C cathode, the Sb@C//LiFePO 4 /C full cell also exhibits outstanding electrochemical performance. [ABSTRACT FROM AUTHOR]

Electrochemical performance of MoS 2 /graphene materials in Li-ion batteries is strongly dependent on the structure of individual components and their coupling in the hybrid. We present a comparative study of the materials produced by annealing of amorphous MoS 3 deposited on the surface of multilayer graphene flakes at 500 °C, 800 °C, and 1000 °C in vacuum. X-ray photoelectron spectroscopy confirmed a transformation of MoS 3 to MoS 2 at these conditions. High-resolution transmission electron microscopy and Raman scattering showed a growth of in-plane size of MoS 2 nanocrystals with a raise of annealing temperature. Electrochemical tests detected a gradual decrease of the specific capacity of the MoS 2 /graphene materials prepared at 500 and 800 °C and a stable performance for the material synthesized at 1000 °C even at high current densities. Based on the initial discharge-charge profiles, we associate this effect with in-plane size of MoS 2 nanocrystals, which should decompose more easily when the size is small, due to the interaction of lithium with edge sulfur atoms. [ABSTRACT FROM AUTHOR]

Herein, we report a simple approach to synthesize high-performance and structurally stable CuO nanoparticles catalyst embedded in TiO 2 nanotube arrays for CO 2 reduction. To summarize, anodic TiO 2 nanotube arrays (TNTs) were electrochemical reductive doped in 1 mol/L (NH 4 ) 2 SO 4 solution to form an activated surface. Then CuO nanoparticles were successfully filled into the pores pace of TNTs by electrodeposition and heat treatment. The effects of Ti(Ⅲ) reduction doping were discussed by means of electrochemical impedance spectroscopy (EIS) and X ray photoelectron spectroscopy (XPS). Results show that partial Ti(Ⅳ) in TNTs can be reduced to Ti(Ⅲ) by electrochemical reduction, which leads to a significant improvement in TNTs surfactivity and then benefits the deposition of Cu nanoparticles to form a stable embedded structure. As a consequence, the composite electrodes showed higher photoelectrocatalytic performance for CO 2 reduction. The maximum current of CuO-TNTs composite electrodes is up to −1.37 mA/cm 2 at −0.5 V and high selectivity for methanol synthesis is also obtained in this case. At the same time, the amount of methanol produced by the CuO/self-doped TNTs composite electrode is about 15% higher than that by the CuO/TNTs electrode without reductive doping. [ABSTRACT FROM AUTHOR]

Hollow NiCo 2 Se 4 microspheres composed of nanoparticles are prepared using NiCo-glycerate microsphere as the sacrificial template. The NiCo 2 Se 4 electrode has multiple functions, which can electrocatalyze both the reduction of triiodide in quasi-solid-state dye-sensitized solar cells (QSSDSSCs) and the overall water splitting. The hollow NiCo 2 Se 4 microspheres as the electrocatalyst achieves power conversion efficiency of 8.26% for QSSDSSCs and 10 mA cm −2 of current density at 1.85 V for the two-electrode water-splitting reaction of 0.1 mol dm −3 KOH aqueous solution. Three single QSSDSSCs connected in series, under 1-sun illumination, can drive the overall water-splitting device efficiently with solar-to-hydrogen efficiency of 5.18% and good stability, where the unassisted artificial photosynthesis employs only one kind of electrocatalyst. [ABSTRACT FROM AUTHOR]

A novel composite, polydopamine-modified Mo 2 C/MoO 2 nanoparticles (HD-Mo 2 C/MoO 2 ), as anode electrocatalyst for microbial fuel cells (MFCs), is synthesized via carbon thermal reduction and following in situ polydopamine modification. The physical and electrochemical characterizations show that Mo 2 C/MoO 2 nanoparticles can be well dispersed through polydopamine modification and the resulting HD-Mo 2 C/MoO 2 exhibits excellent electrocatalytic activity compared with unmodified Mo 2 C/MoO 2 . The MFC using HD-Mo 2 C/MoO 2 as anode electrocatalyst achieves a maximum output power density of 1.64 ± 0.09 W m −2 , which is 39% higher than that using Mo 2 C/MoO 2 (1.18 ± 0.08 W m −2 ) as anode electrocatalyst. This excellent performance is attributed to modification of PDA, HD-Mo 2 C/MoO 2 shows better hydrophilicity and electrocatalytic activity toward the direct oxidation of bacterial metabolites than unmodified Mo 2 C/MoO 2 . [ABSTRACT FROM AUTHOR]

Pristine Na 3 Fe 0.5 V 1.5 (PO 4 ) 3 and carbon-coated Na 3 Fe 0.5 V 1.5 (PO 4 ) 3 nano-particles are synthesized by one-step solid-phase reaction method. The full battery based on Na 3 Fe 0.5 V 1.5 (PO 4 ) 3 @C nano-particles as cathode and commercial hard carbon as anode outputs a high working voltage about 3.3 V and exhibits superior-rate performance. While the rate increases from 0.5 to 1, 2 and 5 C, the discharge capacity of full battery slightly decreases from 110 to 94, 88, 79 mA h g −1 gradually. Moreover, it shows excellent cycle stability with a capacity retention of 93.8% after 200 cycles at 0.5 C. [ABSTRACT FROM AUTHOR]

This work reports the application of the microwave-assisted solvothermal process to synthesize Pt-Ni alloy polyhedral nanoparticles for oxygen reduction reaction (ORR). Well-faceted nanoparticles, mainly octahedral and tetrahedral ones were generated. All the as-prepared Pt-Ni nanocrystals are uniformly dispersed on the carbon support. HR-TEM images confirm that the polyhedral nanoparticles are exposed by (111) facets. When the number of pulses is 12, rotating disk electrode (RDE) demonstrate ORR activities of the as-prepared catalysts with the highest mass activity of 1.217 A·mg Pt −1 and specific activity of 4.41 mA cm −2 Pt at 0.9V iR-free , which is over 11 and 25 times than that of Pt/C catalyst, respectively. Even after being prepared into MEA, the catalyst prepared by 12 microwave pulses still possesses higher performance than commercial Pt/C. Thus, this method can greatly shorten the preparation time to expand the scale of production of the high-performance electrocatalyst. [ABSTRACT FROM AUTHOR]

This work presents a physical-statistical model of platinum degradation as well as a modelling-based algorithm for the analysis of experimental degradation data. The modelling framework encompasses the main processes at the level of catalyst nanoparticles, namely dissolution, redeposition, coagulation, and detachment, and it accounts for the effluence of platinum ions into the polymer electrolyte membrane. Data sets analyzed include changes in electrochemically active surface area, particle radius distribution, platinum mass distribution, and thickness of the catalyst layer. The proposed algorithm processes experimental input and generates output information on kinetic parameters. The model-based data treatment proceeds in two stages: (i) statistical exploration of the parameter space using Monte Carlo techniques and (ii) optimization routine to explicate degradation contributions and determine the pertinent set of parameters. Model outcomes contribute to fuel cell performance and lifetime evaluation, development of strategies for degradation mitigation, and refinement of efforts in design and fabrication of catalyst materials and catalyst layers. [ABSTRACT FROM AUTHOR]

High concentration of polyvinylpyrrolidone (PVP) favored the growth of cobalt hexacyanoferrate (CoHCF) nanocubes with sharp corners and small particle size during synthesis. The cobalt-iron (CoFe) alloy nanoparticles were embedded in the carbon matrix through pyrolysis of the CoHCF powder. The presence of PVP in CoHCF also changed the morphology and microstructure of the resultant carbon-CoFe composite. Bare CoHCF formed bamboo-like hollow nanotubes, while CoHCF nanoparticles capped with large and small amounts of PVP tended to form porous nanocubes and aggregated nanoparticles, respectively. Cyclic voltammetry and electrochemical impedance measurements indicated that the carbon-CoFe nanocube electrode exhibited better catalytic performance than the nanotube, nanoparticle, and Pt electrodes, mostly due to its higher surface area and suitable pore size distribution for facilitating the iodide/triiodide couple. Dye-sensitized solar cells (DSSCs) employing the nanocube counter electrode (CE) exhibited a high photovoltaic conversion efficiency of 9.20%, which was greater than those obtained using Pt (8.94%), nanotube (8.48%), and nanoparticle (8.40%) CEs. The enhanced performance of the DSSC using the nanocube CE was due to the low charge-transfer resistance of the porous nanocubes with embedded CoFe nanoparticles compared to the other CEs. [ABSTRACT FROM AUTHOR]

We propose a new perovskite/carbon composite of LaMnO 3 nanoparticles anchored on N and P co-doped porous carbon as an efficient electrocatalyst for oxygen reduction reaction (ORR) in alkaline solution. A facile two-step method is applied for the synthesis of such composite, involving the pyrolysis of cheap, abundant and renewable natural okara with the formation of N and P co-doped porous carbon for the first step, and the deposition of LaMnO 3 nanoparticles on the carbon surface by sol-gel synthesis at the second step. A synergistic effect is built between the LaMnO 3 nanoparticles and the porous carbon substrate, resulting in obviously improved ORR activity as compared with the individual N, P co-doped carbon and the nanosized LaMnO 3 electrocatalysts, in terms of onset potential, limiting current density, and stability. The LaMnO 3 /N, P co-doped carbon composites further evaluated as an air electrode in a Zn-air battery, demonstrating attractive performance, including high discharge voltage plateau (∼1.2 V) and excellent stability with negligible degradation in voltage at 25 mA cm −1 discharge current for 24 h. The present results highly promise the LaMnO 3 /biocarbon nanocomposite as a potential metal-free ORR electrocatalyst, which may find a wide use in metal-air batteries or fuel cells. [ABSTRACT FROM AUTHOR]

Most high capacity anode materials expand significantly during charging, such anodes must contain sufficient porosity or tough protective layer in the discharged state to enable the expansion, yet not excess porosity or low mobility of mass, which lowers the overall energy density. Here, we present a high capacity anode consisting of hierarchical mesoporous carbon nanospheres without any additives, which are derived from lignosulfonate and can be used as an excellent support for in-situ embedding NiO nanoparticles of 11 wt%. The as-prepared hybrid nanospheres have an integrated architecture with micropore-to-mesopore distribution and a surface area of 852 m 2  g −1 . As a result, the hybrid nanosphere anode exhibit a high discharging capacity of 863 mAh·g −1 at 0.1 A g −1 is retained after 100 cycles for a Li-ion battery. When evaluated as an electrode material for supercapacitors, the as-prepared hybrid nanospheres manifest exceptional performance with a high pseudocapacitance of 508 F g −1 . Remarkably, about 92% of the initial capacitance can be retained after 2000 charge/discharge cycles. This approach generates a strategy to combine metal oxide nanoparticles with nanostructured carbon derived from biomass, which is expected for a broad set of possible electrode chemistries. [ABSTRACT FROM AUTHOR]

3D-ordered porous nitrogen and sulfur co-doped carbon (NS/C) is synthesized from the functionalized fluidic acrylonitrile telomer (ANT) as C, N and S source. The dispersed PdCuW nanoparticles with an average size of 5.25 nm are supported on the walls of the NS/C by a glycol reduction method. Compared with 20%Pd black (Pd/C), NS/C and 20%Pd-NS/C, it is found that PdCuW-NS/C composite with 11.4 wt% Pd exhibits superior catalytic activity for oxygen reduction reaction (ORR) in alkaline solution. Moreover, PdCuW-NS/C possesses higher capacities, lower overpotentials and better cyclic stability as cathode materials for Li-O 2 batteries; the cyclic retention of more than 70 cycles are achieved at 300 mA g −1 with the restricted capacity at 500 mAh g −1 . [ABSTRACT FROM AUTHOR]

Manganese oxide (MnO x )-based hybrid electrode materials have been designed by electrochemical deposition on carbon cloth preliminary activated by palladium (Pd) nanoparticles. The synthesis conditions (current density, deposition time) were chosen in such a way as to achieve a stable structure of MnO x with a large surface area. The structural parameters and surface morphology of materials obtained are characterized by Scanning Electron and Transmission Electron Microscopy (SEM, TEM), Raman spectroscopy, X-ray Photoelectron Spectroscopy (XPS), etc. The electrochemical behavior was investigated by cyclic voltammetry, galvanostatic charge/discharge and impedance spectroscopy. The attained results indicate that MnO x deposits reviled birnessite-type structural feature. Apart from that, the morphology of MnO x transformed with increasing of current density from needlelike structure to loosely-packed thin sheets and then to closed-packed thicker sheets structures. Different morphology exhibits different specific surface area and electrochemical efficiency. Hence electrochemical analysis reviled the highest specific capacitance (186 F g −1 ) and cyclic stability for MnO x PdCC with obtained at current density of 1 mA cm −2 . It can be explained by the formation of a less dense structure of MnOx (loosely-packed thin sheets) with large specific surface area and thus better permeability for Na + and SO 4 −2 ions. As to the role of Pd, its nanoparticles deposited on CC can play a dual role, namely electron conducting passway between CC and MnO x and structure–guiding agent of manganese oxides nucleation and grows. [ABSTRACT FROM AUTHOR]

Monodispersed metal (Cu, Pd, Pt, Rh) nanoparticles have been anchored on reduced graphene oxide (rGO) by a facile electrochemical co-deposition method. Scanning electron microscopic images reveal the presence of homogeneously dispersed metal nanoparticles on the rGO nanosheets. The as-prepared nanocomposites demonstrate excellent electrocatalytic activity for electroreduction of NO 3 − and NO 2 − . The mechanisms associated with the best performed Rh-rGO were studied in detail by cyclic voltammetry, X-ray photoelectron spectroscopic (XPS) and Fourier transformed ac voltammetry. It is proposed that the electrocatalytic reduction of NO 3 − on Rh-rGO is catalyzed by an adsorbed H* (H + aq + e − → H*) species to form NO 2 − which is further catalyzed by H* to form a surface confined NO* intermediate. Rh-rGO displays high electrochemical stability for NO 3 − reduction over the pH range of 4–9, which could be a suitable candidate for applications in remediation of NO 3 − contamination. [ABSTRACT FROM AUTHOR]

Studying electrocatalytic metal nanoparticles (NPs) at the single particle level is highly desirable to unfold their structure-function correlation. In this report, we present the fabrication and spectroelectrochemistry characteristics of light-scattering single Au NP at the tip of an electrochemically etched sharp tungsten (W)electrode. Au NPs with a tunable particle size (≥60 nm) can be obtained at the W tips by adjusting the Au electrodeposition conditions. Catalyzed electrogenerated chemiluminescence (ECL) from Tris(2,2′-bipyridine) ruthenium (II) (Ru(bpy) 3 2+ )/Tri- n -propylamine (TPrA) system at single Au NP electrode shows an increase in its intensity with Au NP particle size in the range of 300 nm–500 nm. The potential application of these single Au NP electrodes in the studies of electrocatalytic reaction and spectroelectrochemistry at the nanometer scale is demonstrated using dark-field scattering (DFS) spectroelectrochemistry method. The decrease in DFS intensity upon oxidation of hydrazine at the single Au NP electrode is attributed to the formation of low-refraction-index N 2 near the surface of the Au NP to decrease its light scattering cross-section. Single Au NP electrode presented in this work would help improve instrument capability of scanning electrochemical microscope (SECM) and near-field scanning optical microscope (NSOM) techniques for ultrasensitive electrochemical analysis. [ABSTRACT FROM AUTHOR]

Bimetallic nanoparticles (NPs) show interesting synergy to enhance the activity and durability in electrocatalytic alcohol oxidation compared to single-component metal NPs. The synthesis of bimetallic NPs often carried out in solution brings challenges in separating, loading and dispersing these NPs on conductive carbon supports. We herein report the direct growth of well-defined AuPd bimetallic NPs in the size range of 2–5 nm on nitrided carbon support. Our method is based on a seed-mediated growth method using Au seeds (1.8 ± 0.3 nm) supported on nitrided carbon. We show that the sizes and surface compositions of bimetallic NPs are precisely controllable. The resultant core-shell AuPd bimetallic NPs are thermally stable and they can be converted to alloyed AuPd NPs when subjected to thermal activation at 250 °C for 1 h. The chemical compositions of the AuPd alloyed NPs have been investigated by combining electron microscopy dispersive X-ray analysis, X-ray photoelectron spectroscopy and surface oxygen desorption using electrochemical reduction of catalysts. The catalytic activity, stability, poisoning tolerance and charge transfer resistance of AuPd alloyed NPs for the ethanol electrooxidation are largely enhanced compared to single-component NPs. Au 0.45 Pd 0.55 -5 nm exhibited the superior specific activity of 1.11 mA/cm 2 and mass activity of >0.4 A/mg metal toward ethanol oxidation, approximately 5 times more active than commercial Pd/C. We expect that this synthetic method will be of interest to prepare metallic electrocatalysts having defined nanostructures and compositions directly on conductive carbon for applications in fuel cells and batteries. [ABSTRACT FROM AUTHOR]

The use of Ionic Liquids (ILs) to enhance the electrocatalytic activity of metal nanoparticles has garnered sustained research interest. However, current strategies involving ionic liquids do not exploit their use and advantages in chemical synthesis of metal nanoparticles. Herein, we demonstrate a straightforward method, which combines the advantages of ILs in nanoparticle synthesis with the potentials of ILs in electrocatalysis, for the synthesis of Pd nanoclusters for electrochemical oxidation of formaldehyde. This method relies on the use of 1-(2′-aminoethyl)-3-methyl-imidazolum tetrafluoroborate ionic liquid as stabilizers to directly generate Pd nanoclusters with average sizes of 1.8 ± 0.3 nm in a reaction medium consisting of water and methanol at room temperature. The electrochemical measurements prove that the ionic liquid-assisted Pd nanoclusters have mass-normalized activity approximately 7 times than that of commercial Pd/C catalysts for the oxidation of formaldehyde. [ABSTRACT FROM AUTHOR]

Coconut leaf sheath-derived nitrogen doped carbon framework is developed and incorporated with nickel and cobalt metal nanoparticles in the carbon matrix by a facile process of growing ZIF-67 metal organic framework particles on the graphitised carbon, followed by annealing it in inert atmosphere. Various parameters are modified to obtain three different samples. These samples are tested for high performance supercapacitors and oxygen evolution reaction (OER) catalysts. The optimised sample NiCo C-1 gave a high specific capacity of 308 mAh g −1 at a current density of 1 A g −1 in a 2 M KOH electrolyte. An asymmetric supercapacitor assembly prepared from NiCo C-1 as the positive electrode and the nitrogen-doped carbon as the negative electrode, exhibited an energy density of up to 31.8 Wh Kg −1 for a high power density of 6.2 kW kg −1 over a potential window of 0–1.55 V. Two of our best samples were also tested for OER, giving good water oxidation kinetics, revealed by their lower Tafel slopes of around 107 mV and a low over potential (η) of around 420 mV at a current density of 10 mA cm −2 . Hence, this work opens great avenues for biomass-derived materials for high performance supercapacitors and catalysis. [ABSTRACT FROM AUTHOR]

To promote the improvement of the hydrogen evolution reaction (HER) performance, it is critical to expose as many active sites of Ni 0.85 Se as possible. In this study, we prepared well-dispersed Ni 0.85 Se nanoparticles on nitrogen-doped graphene oxide (NGO) assisted by the ethylenediamine treatment of NGO before selenylation reaction during hydrothermal process. The NGO nanosheets decorated by uniformly distributed Ni 0.85 Se nanoparticles was confirmed to be the optimal morphology with maximum catalytic active sites. Moreover, optimized structure control resulted in strong interaction between Ni 0.85 Se and NGO, which contributes to effective electron delivery, thus leading to excellent HER activity evidenced from the small overpotential of 104 mV at 10 mA cm −2 , the low Tafel slope of 50.7 mV dec −1 . Moreover, the catalyst exhibits outstanding stability which accelerates the electrochemical measurement. This work provides a general approach to the synthesis of highly dispersed nanoparticles grown on the two-dimensional carbon substrate materials for catalytic reactions. [ABSTRACT FROM AUTHOR]

Manganese oxide and carbon hybrid materials have attracted intensive research attention as advanced electrode materials for energy storage. Herein, starting form metal-organic frameworks (MOFs), the nanocomposites of mixed-valent manganese oxide nanoparticles in-situ grown on ultrathin carbon sheets (MnO x -CSs nanocomposites) have been synthesized via a simple method. Benefiting from the unique structural merits, the nanocomposite obtained at 600 °C (MnO x -CSs-600) exhibits excellent performance for both supercapacitors (SCs) and lithium-ion batteries (LIBs). A high specific capacitance of 220 F g −1 is achieved at the current density of 1 A g −1 . An asymmetric supercapacitor (ASC) based on the MnO x -CSs-600 nanocomposite cathode and activated carbon anode exhibits a high energy density of 27.5 W h kg −1 at the power density of 225 W kg −1 . Moreover, the MnO x -CSs-600 nanocomposite displays a high reversible capacity of 1217.7 mA h g −1 at 200 mA g −1 after 160 cycles as an anode material for LIBs. Remarkably, the discharge capacity is still as high as 612.1 mA h g −1 even at high current density of 2000 mA g −1 , indicating good rate capability. This synthetic strategy is quite simple, cost-effective and environmental friendly, which is highly promising for scaled-up production. [ABSTRACT FROM AUTHOR]

It has been recently reported that engineering the pores within alloy nanoparticles leads to improvement in the electrochemical activity of nanoparticle catalysts due to the enhanced electrochemical active surface areas. However, to date, few works have reported the tailoring intraporosity within alloy nanoparticle networks. In this study, a different and innovative approach was adopted to yield a network-like PtCo catalyst composed of intraporous nanoparticles used a cotton-like PtCo precursor material. It was found that the network-like structure and intrapores within the nanoparticles could co-evolve after careful controlled electrochemical dealloying, whereby Pt-rich surface was formed during the leaching out of Co in the first 13th potentiostatic cyclic voltammetry cycles from +0.056 to +1.256 V vs. RHE. Electrochemical data also showed that the mass and area activity of the obtained PtCo networks toward methanol oxidation reaction (MOR) was nearly 3.9, 2.0 and 2.1 times higher than that of commercial Pt/C, PtRu/C catalyst respectively, and much higher than that of Pt 3 Co networks made of only solid nanoparticles. Moreover, it was observed that such networks exhibited high CO oxidation ability whilst maintaining high catalytic durability under an applied potential of +0.756 V vs. RHE. It was found that developing network-like catalysts composed of porous nanoparticles can be an efficient strategy to improve the catalytic activity and durability of fuel cell catalysts. [ABSTRACT FROM AUTHOR]

Pd electroless deposition is carried out at the expense of oxidation of pre-reduced poly(3,4-ethylene dioxythiophene) (PEDOT)-coated electrodes. Two largely differing potentials for deep and mild pre-reduction of PEDOT are chosen and correspond to initial low (deep pre-reduction) and, correspondingly, high (mild pre-reduction) conductive states of the polymer material. The role of organic doping ions (polysterene sulfonate, PSS or dodecyl sulfate, SDS) used in the course of PEDOT synthesis for the electroless deposition of Pd is also investigated. PEDOT-supported Pd catalysts with high-density homogeneous distribution of Pd nanoparticles (NPs) with sizes ranging between 4 and 12 nm are obtained. The amount of deposited metal depends significantly on the pre-reduction potential of PEDOT whereas the surface density of the metal NPs is largely influenced by the doping ions used to obtain the PEDOT material. Evidence for irreversible structural transformation obtained upon deep pre-reduction of PEDOT:SDS is obtained. [ABSTRACT FROM AUTHOR]

In this work, for the first time, carbon self-repairing porous g-C 3 N 4 nanosheets (CPCN-NSs) with high surface area (220.7 m 2 g −1 ) are prepared by a solvothermal process coupled with post multistep thermal treatment in air. Then a facile hydrothermal method is developed to synthesize carbon self-repairing porous g-C 3 N 4 nanosheets/NiCo 2 S 4 nanoparticles (CPCN-NSs/NCS-NPs) hybrid composite for supercapacitor electrode. With large surface area as well as ultrathin thickness and porous structure, the as-prepared CPCN-NSs could be served as an excellent scaffold to combine with NiCo 2 S 4 nanoparticles (NCS-NPs), while the NCS-NPs with high conductivity could function as conductive linkers between CPCN-NSs and improve the electrical conductivity of the hybrid composite. Electrochemical characterizations indicate that the as-prepared hybrid composite delivers excellent electrochemical properties, exhibiting a high capacitance (1557 F g −1 at current density of 1 A g −1 ) and excellent cycling stability (only 7.4% loss after 10000 cycles). These results clearly demonstrate that the combination of CPCN-NSs with NCS-NPs can substantially improve the capacitive performance of materials and ultimately increase the cycling stability of supercapacitor electrode. [ABSTRACT FROM AUTHOR]

Novel thin layer graphite encapsulated α-Fe 2 O 3 nanoparticles were fabricated via a facile molecular self-assembly approach. This α-Fe 2 O 3 @graphite composite, used as anode in LIBs, exhibited a stable specific capacity of 518.5 mAhg −1 at the current density of 1000 mAg −1 with 88.2% of retention up to 1000 cycles and delivered a reversible capacity of 374 mAhg −1 even at 5C rate. The high cyclic stability and superior rate performance may be addressed to the formed graphite coating layer, which can buffer the volume expansion, enhance the structural stability and increase the electrical conductivity of the Fe 2 O 3 . Moreover, the thin layer graphite coating structure can provide high specific surface area, sufficient void space to shorten the pathway of Li ions, improve the electrolyte penetration and accelerate the electrochemical Li ion storage. [ABSTRACT FROM AUTHOR]

For the first time, the interwoven CoSe 2 /CNTs hybrid with ultra-small CoSe 2 nanoparticles on highly conductive CNTs has been synthesized by a facile one-pot hydrothermal method. The CoSe 2 /CNTs hybrid has been investigated as electrocatalysts for the Hydrogen evolution reaction (HER) in acidic media. The physicochemical characterizations of CoSe 2 /CNTs have been performed by X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The HER performances have been evaluated by linear sweep voltammetry (LSV), cyclic voltammetry (CV), chronoamperometry, and electrochemical impedance spectroscopy (EIS). The CNT content in the CoSe 2 /CNTs hybrids has been optimized and CoSe 2 /CNTs (14.7 wt%) exhibits the best HER performance. It delivers a very small Tafel slope of −32 mV/dec, a low onset potential of −150 mV vs RHE and overpotential of −186 mV at −10 mA/cm 2 , which are much better than those of bare CoSe 2 with a Tafel slope of −52 mV/dec, an onset potential of −234 mV vs RHE and overpotential of −293 mV vs RHE at −10 mA/cm 2 . Furthermore, the CoSe 2 /CNTs hybrid also demonstrates good long-term stability even after 1000 cycles. The excellent HER performance of CoSe 2 /CNTs can be attributed to its unique and conductive interwoven structure. This work provides insights into rational design and facile synthesis of non-precious electrocatalysts with high efficiency and good stability for HER. [ABSTRACT FROM AUTHOR]

Newly three-dimensional graphene nanosheets/transition metal sulfide nanoparticles (i.e. 3-D GNs/Ni 3 S 2 NPs) composite was synthesized by an efficient quasi chemical vapor deposition (Q-CVD) technique in one-pot high temperature growth process. The as-prepared composite materials were investigated by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and X-ray photoelectric spectroscopy. The supercapacitive performances of electrodes were evaluated by cyclic voltammetry charging, discharging and electrochemical impedance spectroscopy. The 3-D GNs/Ni 3 S 2 NPs composite synthesized by the Q-CVD technique possesses favourable three-dimensional porous network of graphene and reasonable arrangement of Ni 3 S 2 NPs on the surface of graphene nanosheets. As a promising supercapacitor electrode, a relatively high specific capacitance of 652.5 F g −1 at current density of 1 A g −1 in 1 mol L −1 KOH aqueous solution, along with good cycling stability (with a 93% retention rate after 2000 cycles) were demonstrated for the 3-D GNs/Ni 3 S 2 NPs composite electrode. In addition, excellent electrochemical performances were also demonstrated for the asymmetric supercapacitor by using 3-D GNs/Ni 3 S 2 NPs as the cathode and 3-D GNs as the anode. [ABSTRACT FROM AUTHOR]

In this work, the electrochemical activity of carbon felt (CF) for the V 2+ /V 3+ redox reaction is improved by combining KOH-etched pretreatment with uniform Bi nanoparticles deposition. CF is functionalized by the KOH activated pretreatment, resulting in micropores structure on the surface and an increase of oxygen-containing functional groups up to 16.49%. The micropores structure and high content of oxygen-containing functional groups of KOH-etched carbon felt (CFE) promote the uniform distribution of Bi nanoparticles on the surface of CFE with an average particle size of 45 nm. The resulting carbon felt (CFE-Bi) significantly enhances the electrochemical activity for V 2+ /V 3+ redox couple because of the synergistic catalysis between the CFE and the Bi nanoparticles. The peak potential separation (ΔE p ) and the charge transfer resistance of CFE-Bi is 182 mV and 0.160 Ω cm 2 , which are much lower than that of CF (427 mV and 3.238 Ω cm 2 ) under the same conditions. Moreover, the energy efficiency of VRFB based on the CFE-Bi as negative electrode achieves 79.3% at 160 mA cm −2 , which is 36.2% higher than that of the VRFB with raw carbon felt. Overall, CFE-Bi is a promising electrode for the V 2+ /V 3+ redox couple reaction in VRFB. [ABSTRACT FROM AUTHOR]

Antimony metal nanoparticles wrapped with a-few-layer graphene coat (Sb@Gn) were fabricated from their oxide form (Sb 2 O 3 ) in a micrometer dimension using a novel two-step ball-milling process. The first mechanochemical process was designed to decrease the particle size of Sb 2 O 3 microparticles for ensuring advantages of nano size and to subsequently coat the Sb 2 O 3 nanoparticles with a-few-layer graphene (Sb 2 O 3 @Gn). The second metallomechanical ball-milling process reduced the oxide to its metal form (Sb@Gn) by the help of Zn as a metallic reductant. The graphene layer (@Gn) blocked the alloying reaction between Sb and Zn, limiting the size of Sb particles during the metallomechanical reduction step. During reduction, oxygen species were transferred from of Sb 2 O 3 through @Gn to Zn along redox transfer pathways rather than direct mass transfer via unsaturated vacancies in the @Gn. the redox transfer involving oxidation of @Gn by O 2− is plausible routes for O 2− transfer in the metallomechanical reduction. The Sb@Gn anode exhibited outstanding capacity retention along charge/discharge cycles and improved rate capability in sodium-ion batteries. The @Gn provided conductive pathways to the Sb core and limited size expansion during sodium-lithium alloying. [ABSTRACT FROM AUTHOR]

Considering the importance of the oxygen reduction reaction (ORR) for many energy conversion technologies, the design of cost-effective and active electrocatalysts is quite important for the future energy economy. In this investigation, we report the preparation of hybrid biocathodes containing multi-walled carbon nanotubes (MWCNTs) decorated with both enzymes and Ni 90 Pd 10 metallic nanoparticles, targeting the bioelectrocatalytic reduction of oxygen in buffered solutions. The electrochemical characterization showed that the presence of the hydrophobic moieties did not affect the metal nanoparticle synthesis protocol, attesting to the possibility of obtaining a bifunctional material containing both the metallic nanoparticles and the aromatic moieties employed for enzyme orientation. Based on the electrochemical data obtained with the hybrid biocathodes, enhanced direct bioelectrocatalytic reduction of oxygen could be clearly observed at both laccase and bilirubin-based biocathodes, with a larger improvement for the hybrid bioelectrode prepared with laccase. In the laccase bioelectrode, the targeted reaction required a lower overpotential and provided about 50% higher current density, thus, demonstrating the benefit of incorporating small amounts of Ni 90 Pd 10 metallic nanoparticles into enzymatic cathodes for the oxygen reduction reaction. [ABSTRACT FROM AUTHOR]