Novel synthesis of Zn2GeO4/graphene nanocomposite for enhanced electrochemical hydrogen storage performance

For the first time, a novel technique of preparing Zn₂GeO₄ nanostructures has been developed by using chemical precipitation method of GeCl₄ as a Ge precursor and acacen as a capping agent. Uniform and fine Zn₂GeO₄ nanoparticle was synthesized. The optimized Zn₂GeO₄ nanostructures anchored onto graphene sheets and Zn₂GeO₄/graphene nanocomposite synthesized through pre-graphenization, successfully. Hydrogen storage capacities of Zn₂GeO₄ nanoparticle and Zn₂GeO₄/graphene nanocomposite were compared, for the first time. Obtained results represent that Zn₂GeO₄/graphene nanocomposites have higher electrochemical hydrogen storage capacity than Zn₂GeO₄ nanoparticles. It was found that the synergistic effect between Zn₂GeO₄ nanoparticles and graphene sheets can improve the electrochemical performance of this hybrid composite electrode. After 29 cycles, the discharging capacities of the electrode reached to 2695 mAh/g. These results indicate that the Zn₂GeO₄/graphene nanocomposite can be potentially applied for electrochemical hydrogen storage.     

Growth of polyaniline on rGO-Co3S4 nanocomposite for high-performance supercapacitor energy storage

Recently, since the supercapacitors have drawn considerable attention, a vast study have been triggered in order to develop efficient electrodes for responding to the increasing demand of supercapacitors. In this report, a possible approach have been used to prepare a ternary nanocomposite, polyaniline/reduced graphene oxide-cobalt sulfide (PANI/rGO-Co₃S₄). At first, a simple and inexpensive hydrothermal route has been used for the preparation of cobalt sulfide (Co₃S₄) on the surface of graphene oxide sheets (rGO-Co₃S₄). Then, the polyaniline nanorods have been flourished on the surface of rGO-Co₃S₄ sheets via in situ chemical polymerization of aniline which was synergistically adjoined to the graphene surface. Polyaniline has uniformly covered the surface of the rGO-Co₃S₄ due to the rational combination of two components. Combining of PANI with rGO-Co₃S₄ electrode material amplify its electrochemical efficiency in terms of a high specific capacitance of 767 F g^?1 at 1 A g^?1 and 81.7% of specific capacitance maintenance after 5000 cycles due to the creation of synergistic effect. Therefore, the ternary nanocomposite of PANI/rGO-Co₃S₄ provides a new promising pathway for the expanding of high-performance electrode materials for supercapacitors.     

Synthesis of Co2SnO4@C core-shell nanostructures with reversible lithium storage

This paper reports the synthesis of Co₂SnO₄@C core-shell nanostructures through a simple glucose hydrothermal and subsequent carbonization approach. The as-synthesized Co₂SnO₄@C core-shell nanostructures have been applied as anode materials for lithium-ion batteries, which exhibit improved cyclic performance compared to pure Co₂SnO₄ nanocrystals. The carbon matrix has good volume buffering effect and high electronic conductivity, which may be responsible for the improved cyclic performance.     

Hydrothermal synthesis of Co2SnO4 nanocrystals as anode materials for Li-ion batteries

Cubic spinel Co₂SnO₄ nanocrystals are successfully synthesized via a simple hydrothermal reaction in alkaline solution. The effect of alkaline concentration, hydrothermal temperature, and hydrothermal time on the structure and morphology of the resultant products were investigated based on X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It is demonstrated that pure Co₂SnO₄ nanocrystals with good crystallinity can be obtained in NaOH solution (2.0 M) at 240 °C for 48 h. The galvanostatic charge/discharge and cyclic voltammetry were conducted to measure the electrochemical performance of the Co₂SnO₄ nanocrystals. It is shown that Co₂SnO₄ nanocrystals exhibit good electrochemical activity with high reversible capacity (charge capacity) of 1088.8 mAh g⁻¹ and good capacity retention as anode materials for Li-ion batteries, much better than that of bulk Co₂SnO₄ prepared by high temperature solid-state reaction.     

Facile precipitation synthesis and electrochemical evaluation of Zn2SnO4 nanostructure as a hydrogen storage material

A facile precipitation method with the subsequent thermal treatment has been developed for the synthesis of Zn₂SnO₄ nanostructures in presence of tetraethylenepentamine (TEPA) with long chain as a capping and basic agent. The effects of different parameters such as precursor of Zn, solvent, reaction time and temperature were studied to reach optimum size and morphology conditions. More importantly, through controlling the experimental conditions, three different morphologies of nanoparticle, nanorod and nanoplate Zn₂SnO₄ mesoporous through one reaction were successfully obtained. In this paper, hydrogen storage capacity of Zn₂SnO₄ nanoparticle reported for the first time. Furthermore, the mesoporous of Zn₂SnO₄ nanoparticle showed high electrochemical hydrogen storage capacities at room temperature. After 13 cycles, the discharging capacities of the electrode still remain above 4650 mAh/g. These results indicate that the mesoporous Zn₂SnO₄ nanoparticle may be potentially applied for electrochemical hydrogen storage.     

SnO2 nanoparticles@polypyrrole nanowires composite as anode materials for rechargeable lithium-ion batteries

The SnO₂@polypyrrole (PPy) nanocomposites have been synthesized by a one-pot oxidative chemical polymerization method. The structure, composition, and morphology of the as-prepared SnO₂@PPy nanocomposites are characterized by XRD, FTIR, TG, SEM, and TEM. Electrochemical investigations show that the obtained SnO₂@PPy nanocomposites exhibit high discharge/charge capacities and favorable cycling when they are employed as anode materials for rechargeable lithium-ion batteries. For the SnO₂@PPy nanocomposite with 79 wt% SnO₂, the electrode reaction kinetics is demonstrated to be controlled by the diffusion of Li⁺ ions in the nanocomposite. The calculated diffusion coefficiency of lithium ions in the SnO₂@PPy nanocomposite with 79 wt% SnO₂ is 6.7 × 10⁻⁸ cm² s⁻¹, while the lithium-alloying activation energy at 0.5 V is 47.3 kJ mol⁻¹, which is obviously lower than that for the bare SnO₂. The enhanced electrode performance with the SnO₂@PPy nanocomposite is proposed to derive from the advantageous nanostructures that allow better structural flexibility, shorter diffusion length, and easier interaction with lithium.     

Facile microwave-assisted synthesized reduced graphene oxide/tin oxide nanocomposite and using as anode material of microbial fuel cell to improve power generation

A new nanocomposite material was fabricated by a facile and reliable method for microbial fuel cell (MFC) anode. Tin oxide (SnO₂) nanoparticles were anchored on the surface of reduced graphene oxide (RGO/SnO₂) in two steps. The hydrothermal method was used for the modification of GO and then microwave-assisted method was used for coating of SnO₂ on the modified GO. Nanohybrids of RGO/SnO₂ achieved a maximum power density of 1624 mW m⁻², when used as the MFC anode. The obtained power density was 2.8 and 4.8 times larger than that of RGO coated and bare anodes, respectively. The electrodes were characterized by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The electrochemical characteristics were also studied by cyclic voltammetry (CV), linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS). The high conductivity and large specific surface of the nanocomposite were greatly improved the bacterial biofilm formation and increased the electron transfer. The results demonstrate that the RGO/SnO₂ nanocomposite was advantageous material for the modification of anode and enhanced electricity generation of MFC.     

Dual gas sensing properties of graphene-Pd/SnO2 composites for H2 and ethanol: Role of nanoparticles-graphene interface

In the present work, role of palladium (Pd) and tin oxide (SnO₂) nanoparticles (NPs) deposited on graphene has been investigated in terms of dual gas sensing characteristics of ethanol and H₂ between two temperatures. The incorporation of nanoparticles into graphene has been observed which results a large change in the sensing response towards these gases. It is investigated that, incorporation of isolated Pd NPs on the graphene facilitates the room temperature sensing of H₂ gas with fast response and recovery time whereas, isolated SnO₂ NPs on graphene enables the detection of ethanol at 200 °C. However, combination of isolated Pd and SnO₂ NPs on graphene shows improved sensitivity and good selectivity towards H₂ and ethanol, usually not observed in chemiresistive gas sensors. Catalytic PdH interaction and corresponding change in work function of nanoparticles on hydrogenation resulting in modifications in electronic exchange between Pd, SnO₂ and graphene are responsible for the observed behavior. These results are important for developing a new class of chemiresistive type gas sensor based on change in the electronic properties of the graphene and NPs interfaces.     

Synthesis of Fe0.3Co0.7/rGO nanoparticles as a high performance catalyst for the hydrolytic dehydrogenation of ammonia borane

Well-dispersed Fe_0.3Co_0.7/rGO nanocatalysts have been synthesized utilizing the two-step reduction method and successfully employed in the hydrolysis of ammonia borane (NH₃BH₃ AB) at room temperature. The mass percent of the supported Fe_0.3Co_0.7 nanoparticles (NPs) on graphene (rGO) sheets can reach to the maximum value of 50 wt%. The as-synthesized catalysts exerted satisfying activity and reusability for the hydrolytic dehydrogenation of AB at 298 K, especially for the specimen of 50 wt% Fe_0.3Co_0.7/rGO NPs. The catalytic hydrolysis reaction was rapidly completed within 1 min.     

Electrocatalytic hydrogen production on GCE/RGO/Au hybrid electrode

We have prepared a nanocomposite hybrid film to produce a collaborative network of gold (Au) nanoparticles that are highly dispersed on reduced graphene oxide (RGO) sheets, and tested it for electrocatalytic hydrogen production. The RGO/Au nanocomposite film synthesized on glassy carbon electrode (GCE) allows significant improvements to the electron-transfer process. The Au nanoparticles decorated on the surface of graphene increases the electron density, which synergistically promote the adsorption of hydrogen atoms on the graphene sheets and consequently enhance the hydrogen evolution reaction (HER) activity. The surface properties of the composite was characterized by field-emission scanning electron microscopy (FE-SEM) and the electrocatalytical performances evaluated as-prepared electrocatalyst toward (HER) by linear sweep voltammetry (LSV), Tafel polarization curves and electrochemical impedance spectroscopy (EIS) analyses. The GCE/RGO/Au nanohybrid electrode exhibited good catalytic activity for HER with an onset potential of ?0.3 V and a Tafel slope of 136 mV dec^?1, achieving a current density of 10 mA cm^?2 at an overpotential of ?0.43 V.     

Pt support of multidimensional active sites and radial channels formed by SnO2 flower-like crystals for methanol and ethanol oxidation

SnO₂ nanoflowers and nanorods have been synthesized by the hydrothermal method without using any capping agent. Both types of SnO₂ nanostructures are selected as a support of Pt catalyst for methanol and ethanol electrooxidation. The synthesized SnO₂ nanostructures and SnO₂ supported platinum (Pt/SnO₂) catalysts are characterized by X-ray diffraction, scanning electron microscope and high resolution transmission electron microscope. The electrocatalytic properties of the Pt/SnO₂ and Pt/C catalysts for methanol and ethanol oxidation have been investigated systematically by typical electrochemical methods. The influence of SnO₂ morphology on its electrocatalytic activity is comparatively investigated. The Pt/SnO₂ flower-shaped catalyst shows higher electrocatalytic activity and better long-term cycle stability compared with other electrocatalysts owing to the multidimensional active sites and radial channels of liquid diffusion.     

Enhanced electrocatalytic performance of Cu0.02S0.01/rGO hybrid for oxygen reduction reaction in alkaline medium at low temperature

Graphene, is a carbon allotrope, which is widely used as a substrate for various catalysts due to its interesting physicochemical properties. In the present study, graphene oxide sheets were prepared from graphite, then, the graphene oxide surface was modified by a low-temperature method using sulfur and copper atoms to obtain pseudo-enzyme Cu/S/Graphene prosthetic group. The current density passing through Cu/S/Graphene catalyst was four times higher than that passing through graphite. The novel copper-based catalyst had an extraordinary performance for oxygen reduction reaction (ORR) due to the unique bio-inspired and stoichiometric structure. The results of Raman and Dispersive X-ray spectroscopy confirmed the presence of ultra-low content of copper (2%) and sulfur (1%) atoms on the graphene surface. Thermogravimetric analysis indicated a strong interaction between nanoparticles and graphene layers. The number of electrons transferred for ORR varied from 3.98 to 4.16 in a wide range of over-potentials indicating an effective 4-electron pathway form O₂ to H₂O. The Tafel slopes indicated insignificant amount of formed copper oxide on the catalyst surface. The catalyst showed excellent electrochemical durability and its half-wave potential (E_1/2) was exhibited a negative shift only 8.2 mV after 10000 cycles.     

Enhancement of the energy storage properties of supercapacitors using graphene nanosheets dispersed with metal oxide-loaded carbon nanotubes

Graphene nanosheets (GNs) dispersed with SnO₂ nanoparticles loaded multiwalled carbon nanotubes (SnO₂-MWCNTs) were investigated as electrode materials for supercapacitors. SnO₂-MWCNTs were obtained by a chemical method followed by calcination. GNs/SnO₂-MWCNTs nanocomposites were prepared by ultrasonication of the GNs and SnO₂-MWCNTs. Electrochemical double layer capacitors were fabricated using the composite as the electrode material and aqueous KOH as the electrolyte. Electrochemical performance of the composite electrodes were compared to that of pure GNs electrodes and the results are discussed. Electrochemical measurements show that the maximum specific capacitance, power density and energy density obtained for supercapacitor using GNs/SnO₂-MWCNTs nanocomposite electrodes were respectively 224 F g⁻¹, 17.6 kW kg⁻¹ and 31 Wh kg⁻¹. The fabricated supercapacitor device exhibited excellent cycle life with ∼81% of the initial specific capacitance retained after 6000 cycles. The results suggest that the hybrid composite is a promising supercapacitor electrode material.     

Electrochemical deposition of porous Co3O4 nanostructured thin film for lithium-ion battery

Porous Co₃O₄ nanostructured thin films are electrodeposited by controlling the concentration of Co(NO₃)₂ aqueous solution on nickel sheets, and then sintered at 300 °C for 3 h. The as-prepared thin films are characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The electrochemical measurements show that the highly porous Co₃O₄ thin film with the highest electrochemically active specific surface area (68.64 m² g⁻¹) yields the best electrochemical performance compared with another, less-porous film and with a non-porous film. The highest specific capacity (513 mAh g⁻¹ after 50 cycles) is obtained from the thinnest film with Co₃O₄ loaded at rate of 0.05 mg cm⁻². The present research demonstrates that electrode morphology is one of the crucial factors that affect the electrochemical properties of electrodes.     

Designed synthesis of hierarchical Mn3O4@SnO2/Co3O4 core-shell nanocomposite for efficient electrocatalytic water splitting

The hierarchical Mn₃O₄@SnO₂/Co₃O₄ core-shell nanocomposite has been successfully synthesized via a facile structural construction strategy. The SnO₂/Co₃O₄ nanosheets (SnO₂/Co₃O₄ NSs) were enclosed on the surface of Mn₃O₄ nanorods (Mn₃O₄ NRs). The prepared materials were investigated as the catalyst toward oxygen evolution reaction (OER) performance in alkaline. By contrast, the design of core-shell hierarchical nanocomposite of Mn₃O₄@SnO₂/Co₃O₄ possesses the obvious electrocatalytic OER performance than others, showing the overpotential of approximately 420 mV at a current density of 10 mA cm⁻² with a low Tafel slope of 70.1 mV dec⁻¹, in which the interesting structure can provide the interfacial and cooperative effect between core (hierarchical SnO₂/Co₃O₄ NSs) and shell (1D Mn₃O₄ NRs) that 1D Mn₃O₄ NRs can act as an electron acceptor and accelerates electron transfer, and that hierarchical SnO₂/Co₃O₄ NSs provide a large specific surface area and multiple exposed surface active sites between electrode material and electrolyte.     

Simple size-controlled fabrication of Zn2SnO4 nanostructures and study of their behavior in dye sensitized solar cells

Zn₂SnO₄ nanostructures were obtained via facile and rapid co-precipitation approach in presence of amines with different long chain as a novel basic and capping agents. The effect of different amines such as NH₃, ethylenediamine, triethylenetetramine, tetraethylenepentamine on the size of Zn₂SnO₄ nanostructures were investigated. The results demonstrated that applying the appropriate amount of organic amine could be effective in particle size control. The obtained nanostructure products were specified by powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectra, scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX) and ultraviolet–visible (UV–vis) spectroscopy. Dye sensitized solar cells (DSSC) were created by the constructed electrodes as working electrode and then were studied by current density–voltage (J–V) curve. It was found that incorporating of TiO₂ nanoparticles to optimized Zn₂SnO₄ nanostructures has significant role on the constructed DSSCs photovoltaic properties.     

Porous Co3O4 decorated nitrogen-doped graphene electrocatalysts for efficient bioelectricity generation in MFCs

High-performance, low-cost, and robust oxygen reduction reaction (ORR) catalysts have played a very crucial role in the development of microbial fuel cells (MFCs). Herein, A novel in-situ Co₃O₄ nanoparticles (NPs) modified nitrogen-doped graphene with three-dimensional porous structure (3D GN-Co₃O₄) has been successfully synthesized and employed as an efficient ORR catalyst in MFCs. Benefiting from 3D porous architecture feature, highly intrinsic conductivity and synergistic effect between nitrogen-doped graphene and Co₃O₄ NPs, the 3D GN-Co₃O₄ as a cathode catalyst in alkaline condition realizes significantly enhanced electrochemical performance and outstanding cycling stability. Furthermore, the self-assembly of MFCs based on the 3D GN-Co₃O₄ cathode offers a high power density of 578 ± 10 mW m^?2, which is even comparable to the commercial Pt/C.     

Mechanical alloying preparation of fullerene-like Co3C nanoparticles with high hydrogen storage ability

Fullerene-like orthorhombic-structured Co₃C nanoparticles have been synthesized by direct ball-milling of Co and graphene (GE) powders with different Co/GE weight ratios. Electrochemical measurements showed that the Co₃C nanoparticles displayed excellent electrochemical hydrogen storage capacities and the maximum capacity reached 1415 mA h/g (5.176 wt% hydrogen) at room temperature and ambient pressure. The reaction mechanism and the reasons for the differences of the Co₃C electrodes were also investigated. It was found that the quasi-reversible Co₃CH_x/Co₃C reaction was dominant for all the Co₃C electrodes.     

Composite oxygen electrode LSM-BCZYZ impregnated with Co3O4 nanoparticles for steam electrolysis in a proton-conducting solid oxide electrolyzer

A composite oxygen electrode based on Co₃O₄-loaded La_0.8Sr_0.2MnO₃ (LSM)-BaCe_0.5Zr_0.3Y_0.16Zn_0.04O_3−δ (BCZYZ) is investigated for steam electrolysis in a proton-conducting solid oxide electrolyzer. The conductivity of LSM is studied with respect to temperature and oxygen partial pressure and correlated to the electrochemical properties of the composite oxygen electrodes in symmetric cells and solid oxide electrolyzers at 800 °C. The optimal Co₃O₄ loading in the composite oxygen electrode is systematically investigated in symmetric cells; loading catalytically active Co₃O₄ significantly enhances the electrode performance, unlike the bare LSM-BCZYZ electrode. Steam electrolysis was then performed using LSM-BCZYZ and 6 wt.% Co₃O₄-loaded LSM-BCZYZ oxygen electrodes, respectively. The Co₃O₄-loaded catalyst significantly improves the electrode process and enhances the current density below a certain applied voltage. The current efficiencies reach approximately 46% with a 10% H₂O/air feed for the oxygen electrode.