Electrochemical characterization of platinum-based anode catalysts for membraneless fuel cells

In the present work, carbon-supported Pt–Sn, Pt–Ru, and Pt–Sn–Ru electrocatalysts with different atomic ratios were prepared by alcohol-reduction method to study the electro-oxidation of ethanol in membraneless fuel cells. The synthesized electrocatalysts were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD) analyses. The prepared catalysts had similar particle morphology, and their particle sizes were 2–5 nm. The electrocatalytic activities were characterized by cyclic voltammetry (CV) and chronoamperometry (CA). The electrochemical results obtained at room temperature showed that the addition of Sn and Ru to the pure Pt electrocatalyst significantly improved its performance in ethanol electro-oxidation. The onset potential for ethanol electro-oxidation was 0.2 V vs. Ag/AgCl, in the case of the ternary Pt–Sn–Ru/C catalysts, which was lower than that obtained for the pure Pt catalyst (0.4 V vs. Ag/AgCl). During the experiments performed on single membraneless fuel cells, Pt ? Sn ? Ru/C (70:10:20) performed better among all the catalysts prepared with power density of 36 mW/cm². The better performance of ternary Pt–Sn–Ru/C catalysts may be due to the formation of a ternary alloy and the smaller particle size.     

Enhanced electrical properties of polyethylene oxide (PEO) + polyvinylpyrrolidone (PVP):Li<Superscript>+</Superscript> blended polymer electrolyte films with addition of Ag nanofiller

Polymer blended films of polyethylene oxide (PEO)?+?polyvinyl pyrrolidone (PVP):lithium perchlorate (LiClO₄) embedded with silver (Ag) nanofiller in different concentrations have been synthesized by a solution casting method. The semi-crystalline nature of these polymer films has been confirmed from their X-ray diffraction (XRD) profiles. Fourier transform infrared spectroscopy (FTIR) and Raman analysis confirmed the complex formation of the polymer with dopant ions. Dispersed Ag nanofiller size evaluation study has been done using transmission electron microscopy (TEM) analysis. It was observed that the conductivity increases when increasing the Ag nanofiller concentration. On the addition of Ag nanofiller to the polyethylene oxide (PEO)?+?polyvinyl pyrrolidone (PVP):Li⁺ electrolyte system, it was found to result in the enhancement of ionic conductivity. The maximum ionic conductivity has been set up to be 1.14?×?10^?5 S cm^?1 at the optimized concentration of 4 wt% Ag nanofiller-embedded (45 wt%) polyethylene oxide (PEO)?+?(45 wt%) polyvinyl pyrrolidone (PVP):(10 wt%) Li⁺ polymer electrolyte nanocomposite at room temperature. Polyethylene oxide (PEO)?+?polyvinyl pyrrolidone (PVP):Li⁺ +Ag nanofiller (4 wt%) cell exhibited better performance in terms of cell parameters. This is ascribed to the presence of flexible matrix and high ionic conductivity. The applicability of the present 4 wt% Ag nanofiller-dispersed polyethylene oxide (PEO)?+?polyvinyl pyrrolidone (PVP):Li⁺ polymer electrolyte system could be suggested as a potential candidate for solid-state battery applications. Dielectric constants and dielectric loss behaviours have been studied.     

Synthesis of thiol-functionalized MCM-41 mesoporous silicas and its application in Cu(II), Pb(II), Ag(I), and Cr(III) removal

Thiol-functionalized MCM-41 mesoporous silicas were synthesized via evaporation-induced self-assembly. The mesoporous silicas obtained were characterized by X-ray diffraction (XRD), nitrogen adsorption–desorption analysis, Fourier transform infrared spectroscopy (FTIR), elemental analysis (EA), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The products were used as adsorbents to remove heavy metal ions from water. The mesoporous silicas (adsorbent A) with high pore diameter (centered at 5.27 nm) exhibited the largest adsorption capacity, with a BET surface area of 421.9 m² g^?1 and pore volume of 0.556 cm³ g^?1. Different anions influenced the adsorption of Cu(II) in the order NO₃ ^? < OAc^? < SO₄ ^2? < CO₃ ^2? < Cit^? < Cl^?. Analysis of adsorption isotherms showed that Cu²⁺, Pb²⁺, Ag⁺, and Cr³⁺ adsorption fit the Redlich–Peterson nonlinear model. The mesoporous silicas synthesized in the work can be used as adsorbents to remove heavy metal ions from water effectively. The removal rate was high, and the adsorbent could be regenerated by acid treatment without changing its properties.     

Fabrication and electrochemical investigation of MWO<Subscript>4</Subscript> (M = Co,Ni) nanoparticles as high-performance anode materials for lithium-ion batteries

In this work, the MWO₄ (M = Co, Ni) nanoparticles were successfully synthesized by a facile one-step hydrothermal method and used as novel anode materials for LIBs. The micromorphology of obtained CoWO₄ and NiWO₄ was uniform nanoparticles with the size of ~60 and ~40 nm, respectively, by structural characterization including X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). When tested as lithium-ion battery anode, CoWO₄ nanoparticles exhibited a stabilized reversible capacity of 980 mA h g^?1 at 200 mA g^?1 after 120 cycles and 632 mA h g^?1 at 1000 mA g^?1 even after 400 cycles. And, the discharge capacity was as high as 550 mA h g^?1 at the 400th cycle for NiWO₄ nanoparticles. The excellent electrochemical performance could be attributed to the unique nanoparticles structure of the materials, which can not only shorten the diffusion length for electrons and lithium ions but also provide a large specific surface area for lithium storage.     

Preparation and Properties of Novel Modified Humidity Control Composite Materials

Montmorillonite /polyacrylamide (MMT/PAM) humidity control materials, with the MMT modified separatly by argent-ammonium complex ions ([Ag(NH₃)₂]⁺) and copper ions (Cu²⁺) (Ag-MMT/PAM, Cu-MMT/PAM) were prepared. The structures of the Ag-MMT/PAM and Cu-MMT/PAM were characterized with X-ray diffraction (XRD), Fourier transform infrared spectra (FTIR) and scanning electron microscopy (SEM). The humidity control property was examined by a desiccator method. Antibacterial properties were tested with an inhibition zone method. The results showed that the structures of Ag-MMT/PAM and Cu-MMT/PAM were loose and porous. Polyacrylamide was intercalated into the layers of the MMT. The increasing interlayer spacings of Ag-MMT/PAM and Cu-MMT/PAM were from 1.51 nm for the original MMT to 2.04 nm and 2.11 nm, respectively. Both Ag-MMT/PAM and Cu-MMT/PAM presented good humidity control and antibacterial properties.     

Synthesis,characterization and excellent photocatalytic activity of Ag/AgBr/MoO3 composite photocatalyst

A novel composite photocatalyst Ag/AgBr/MoO₃ was successfully synthesized via a simple precipitation method at room temperature. The obtained products were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, high-resolution transmission electron microscopy and UV–vis diffuse reflectance spectroscopy in detail. The photocatalytic activity of the samples was evaluated by monitoring the degradation of rhodamine B (RhB) solution under visible-light irradiation. The results showed that the photocatalytic activity of Ag/AgBr/MoO₃ composite significantly enhanced and the degradation ratio of RhB reached 97.7 % after 15 min only. The excellent photocatalytic activity might be closely related to the large surface area, porosity structure and efficient separation of photoinduced electron–hole pairs. The possible reaction mechanism was also discussed.     

Three-dimensional macroporous Sn–Ag thin film anode prepared by electro-less reduction method: effect of micro-structure

A three-dimensional Sn–Ag thin film with open interconnected walls consisting of active small grains of Sn and Ag was fabricated by electro-less reduction method as anode for lithium-ion batteries application. The morphologies and electrochemical performance of the macroporous Sn–Ag thin films were investigated by using scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, cyclic voltammetry, and galvanostatical charge–discharge measurement. The results demonstrated that through controlling the plating time, the electrode with optimized microstructure exhibited the largest reversible capacities, maintaining a capacity of 583 mAh g^?1 after 100 cycles, due to the well-preserved micro-porous structure after extended cycling.     

Simple method for synthesizing few-layer graphene as cathodes in surface-enabled lithium ion-exchanging cells

In order to realize a wider application for graphene materials specifically in the field of energy storage, a simple and mass-scalable method described as “the atmospheric, low-temperature, shock-heating process” is proposed in this work. During this low-temperature process, the graphite oxide without pre-treatment is completely exfoliated to form the few-layer graphene materials at atmospheric conditions. The Brunauer-Emmett-Teller (BET)-specific surface area of acquired material at 350 °C can reach 487 m² g^?1. The acquired few-layer graphene materials are also confirmed by X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and high-resolution transmission electron microscopy (HRTEM). The results demonstrate that this simple method is feasible for synthesizing the few-layer graphene materials. Besides that, the acquired graphene is also used as the cathode material in the surface-enabled lithium ion-exchanging cell. The galvanostatic charge/discharge tests show that the graphene prepared from this method is suitable for this system and displays a satisfactory electrochemical performance. The acquired graphene sample exhibits the reversible capacities of around 187, 107, 84, 58, and 45 mAh g^?1 at 0.1, 2, 5, 10, and 15 A g^?1, respectively. At the current density of 0.5 A g^?1, the capacity retention can reach 75 % after 2000 cycles.     

Enhanced electrochemical performance of LiFePO4/C prepared by sol–gel synthesis with dry ball-milling

LiFePO₄/C was prepared by a modified aqueous sol–gel route developed by incorporating an additional ball-milling step where the dry gel was milled with the additives of synthetic graphite and carbon black. The materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET), transmission electron microscopy (TEM), high resolution TEM (HRTEM) and elemental analysis. Results showed that the LiFePO₄/C synthesized by suitable ball-milling process had pure, fine and homogenous LiFePO₄ particles. Results of cyclic voltammetry and charge/discharge plateaus demonstrated that the LiFePO₄/C composite synthesized by milling for 2 h had much better electrochemical kinetics. High performances were achieved with its discharge capacities of 157 mA h g^?1 at 0.1?C and 133 mA h g^?1 at 1?C between 2.5 and 4.2 V (1?C?=?170 mA g^?1). And no obvious capacity fading was observed upon cycling. The simple and convenient synthesis route is promising for large-scale production of LiFePO₄/C.     

A novel synthesis of size-controllable mesoporous NiMoO<Subscript>4</Subscript> nanospheres for supercapacitor applications

A novel hydrothermal emulsion method is proposed to synthesize mesoporous NiMoO₄ nanosphere electrode material. The size of sphere-shaped NiMoO₄ nanostructure is controlled by the mass ratio of water and oil phases. Nickel acetate tetrahydrate and ammonium heptamolybdate were used as nickel and molybdate precursors, respectively. The resultant mesoporous NiMoO₄ nanospheres were characterized by X-ray diffraction, N₂ adsorption and desorption, scanning electron microscopy, and transmission electron microscopy. The electrochemical performances were evaluated by cyclic voltammetry (CV), cyclic chronopotentiometry (CP), and electrochemical impedance spectroscopy (EIS) in 6 M KOH solution. The typical mesoporous NiMoO₄ nanospheres exhibit the large specific surface area of 113 m² g^?1 and high specific capacitance of 1443 F g^?1 at 1 A g^?1, an outstanding cyclic stability with a capacitance retention of 90 % after 3000 cycles of charge-discharge at a current density of 10 A g^?1, and a low resistance.     

Hollow polypyrrole nanosphere embedded in nitrogen-doped graphene layers to obtain a three-dimensional nanostructure as electrode material for electrochemical supercapacitor

A novel approach was developed to prepare hollow polypyrrole (PPy) nanospheres and nitrogen-doped graphene/hollow PPy nanospheres (NG/H-PPy) composites. In this process, uniform poly (methyl methacrylate-butyl methacrylate-methacrylic acid) (PMMA-PBMA-PMAA) latex microspheres as sacrificial templates were synthesized by using an emulsion polymerization method. Then, hollow PPy nanospheres were obtained on the surface of PMMA-PBMA-PMAA microspheres by in situ chemical oxidative polymerization. Finally, H-PPy was embedded in NG layers successfully through a simple approach. The nanobeads have been characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectra, and Fourier transform infrared spectra (FTIR). Different electrochemical methods including cyclic voltammetry (CV), galvanostatic charge–discharge (GCD), and electrochemical impedance spectroscopy (EIS) have been applied to study the electrochemical properties. The specific capacitance of NG/H-PPy composites based on the three-electrode system is as high as 575 F g^?1 at a current density of 1 A g^?1 and enhanced stability about 90.1 % after 500 cycles, indicating that the composite has an impressive capacitance and excellent cycling performance.     

Effect of milling time on the performance of bowl-like LiFePO4/C prepared by wet milling-assisted spray drying

LiFePO₄/C was prepared by wet milling-assisted spray drying. The effects of ball-milling time on the characteristics of LiFePO₄/C were investigated by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Brunauer-Emmett-Teller analysis, cyclic voltammograms, electrochemical impedance spectra, and galvanostatic charge–discharge testing. Bowl-like material was obtained, surrounded by a network of carbon, which display larger specific surface area. The specific surface area of particle first increased and then decreased, as the increasing of ball-milling time; when ball-milling time reach 2.5 h, it showed the largest specific surface area of 29.350 m² g^?1, primary particles with size of ～50 nm, delivered a discharge capacity of 162 mAh g^?1 at 0.5 C and 123 mAh g^?1 at 10 C, and with no capacity loss.     

ZnO-coated LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> cathode material for lithium-ion batteries synthesized by a combustion method

ZnO-coated LiMn₂O₄ cathode materials were prepared by a combustion method using glucose as fuel. The phase structures, size of particles, morphology, and electrochemical performance of pristine and ZnO-coated LiMn₂O₄ powders are studied in detail by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), galvanostatic charge-discharge test, and X-ray photoelectron spectroscopy (XPS). XRD patterns indicated that surface-modified ZnO have no obvious effect on the bulk structure of the LiMn₂O₄. TEM and XPS proved ZnO formation on the surface of the LiMn₂O₄ particles. Galvanostatic charge/discharge test and rate performance showed that the ZnO coating could improve the capacity and cycling performance of LiMn₂O₄. The 2 wt% ZnO-coated LiMn₂O₄ sample exhibited an initial discharge capacity of 112.8 mAh g^?1 with a capacity retention of 84.1 % after 500 cycles at 0.5 C. Besides, a good rate capability at different current densities from 0.5 to 5.0 C can be acquired. CV and EIS measurements showed that the ZnO coating effectively reduced the impacts of polarization and charge transfer resistance upon cycling.     

Roles of Al-doped ZnO (AZO) modification layer on improving electrochemical performance of LiNi<Subscript>1/3</Subscript>Co<Subscript>1/3</Subscript>Mn<Subscript>1/3</Subscript>O<Subscript>2</Subscript> thin film cathode

Al-doped ZnO (AZO) was sputtered on the surface of LiNi_1/3Co_1/3Mn_1/3O₂ (NCM) thin film electrode via radio frequency magnetron sputtering, which was demonstrated to be a useful approach to enhance electrochemical performance of thin film electrode. The structure and morphology of the prepared electrodes were characterized by X-ray diffraction, scanning electron microscopy, energy dispersive spectrometer, and transmission electron microscopy techniques. The results clearly demonstrated that NCM thin film showed a strong (104) preferred orientation and AZO was uniformly covered on the surface of NCM electrode. After 200 cycles at 50 μA μm^?1 cm^?2, the NCM/AZO-60s electrode delivered highest discharge capacity (78.1 μAh μm^?1 cm^?2) compared with that of the NCM/AZO-120s electrode (62.4 μAh μm^?1 cm^?2) and the bare NCM electrode (22.3 μAh μm^?1 cm^?2). In addition, the rate capability of the NCM/AZO-60s electrode was superior to the NCM/AZO-120s and bare NCM electrodes. The improved electrochemical performance can be ascribed to the appropriate thickness of the AZO coating layer, which not only acted as HF scavenger to keep a stable electrode/electrolyte interface but also reduced the charge transfer resistance during cycling.     

Chitosan: A N-doped carbon source of silicon-based anode material for lithium ion batteries

Silicon/graphite/carbon (Si/G/CTS-C) composite, based on nano-silicon, flake graphite, and chitosan-derived carbon (CTS-C), was prepared by spray drying and subsequent pyrolysis. The results of X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy illustrate that chitosan is a good dispersion agent and chitosan-derived carbon is N-doped. The results indicate that the initial charge capacity of Si/G/CTS-C composite is 613.9 mAh g^?1 at a current density of 100 mA g^?1 corresponding to an initial coulombic efficiency of 81.89%. Besides, the Si/G/CTS-C composite exhibits higher specific capacity, more superior rate capability, better cycling performance, and lower impedance than that of silicon/graphite/phenolic resin-derived carbon (Si/G/P-C) composite.     

Structural,electrical and dielectric studies of nanocrystalline LiMnPO4 particles

Olivine-structured LiMnPO₄ nanoparticles were prepared by microwave-assisted solvothermal method. The as obtained LiMnPO₄ sample was characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM) and impedance spectroscopy techniques. The XRD pattern confirms the formation of LiMnPO₄ phase with an orthorhombic structure. The electrical conductivity of the sample at room temperature is found to be 1.2654?×?10^?7 S cm^?1. Dielectric spectra show an increase in dielectric constant with increase of temperature. The dielectric loss spectra reveal the predomination of DC conduction in the sample. The modulus studies indicate the non-Debye nature of the sample which corresponds to the distribution of elements in the sample. Galvanostatic battery testing showed that LiMnPO₄ nanoparticles displayed good cycleability in 30 cycles.     

Preparation of Co<Subscript>3</Subscript>O<Subscript>4</Subscript> hollow microsphere/graphene/carbon nanotube flexible film as a binder-free anode material for lithium-ion batteries

A flexible Co₃O₄ hollow microsphere/graphene/carbon nanotube hybrid film is successfully prepared through a facile filtration strategy and a subsequent thermally treated process. The composition, morphology, and structure of the as-prepared film are characterized by X-ray diffraction, X-ray photoelectron spectrometer, scanning electron microscopy, and transmission electron microscopy. Based on the morphology characterizations on the hybrid film, the Co₃O₄ hollow microspheres are uniformly and closely attached on three-dimensional (3D) graphene/carbon nanotubes (GR/CNTs) network, which decreases the agglomeration of Co₃O₄ microspheres effectively. In this hybrid film, the 3D GR/CNT network which enhances conductance as well as prevents aggregation is a benefit to help Co₃O₄ to exert its lithium storage capabilities sufficiently. When used as a binder-free anode material for lithium-ion batteries, the hybrid film delivers excellent electrochemical properties involving reversible capacity (863 mAh g^?1 at a current density of 100 mA g^?1) and rate performance (185 mAh g^?1 at a current density of 1600 mA g^?1).     

Preparation and characterization of zirconium sulfophenyl phosphate-doped sulfonated poly(phthalazinone ether sulfone) composite proton exchange membrane

Polymer composite membranes based on sulfonated poly(phthalazinone ether sulfone) (SPPES) and zirconium sulfophenyl phosphate (ZrSPP) were prepared. Three ZrSPP concentrations were used: 10, 20, and 30 wt%. The membranes were characterized by infrared spectroscopy (IR), X-ray diffraction spectroscopy, thermal gravimetric analysis, and scanning electron microscopy (SEM). The IR results indicated the formation of intense hydrogen bonds between ZrSPP and SPPES molecules. The SEM micrographs showed that ZrSPP well dispersed with SPPES and form a lattice structure. The proton conductivity of the SPPES (degree of sulfonation (DS) 64 %)/ZrSPP (10 wt%) composite membrane reached 0.39 S/cm at 120 °C 100 % relative humidity and that of the 30 wt% of SPPES (DS 16.1 %)/ZrSPP composite membrane reached 0.18 S/cm at 150 °C. The methanol permeabilities of the SPPES/ZrSPP composite membranes were in the range of 2.1?×?10^?8 to 0.13?×?10^?8?cm²/s, much lower than that of Nafion®117 (10^?6?cm²/s). The composite membranes exhibited good thermal stabilities, proton conductivities, and good methanol resistance properties.     

ZnO nanoparticles anchored on nitrogen and sulfur co-doped graphene sheets for lithium-ion batteries applications

Herein, we demonstrate a facile one-step hydrothermal synthesis route to anchor ZnO nanoparticles on nitrogen and sulfur co-doped graphene sheets. The detailed material and electrochemical characterization have been carried out to demonstrate the potential of novel ZnO/NSG nanocomposite in Li-ion battery (LIBs) applications. The structure and morphology of nanocomposite were assessed by X-ray diffraction (XRD), Fourier transform infrared (FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The as-synthesized ZnO/NSG nanocomposite has been studied as anode material in LIBs and delivered a high initial discharge capacity of 1723 mAh g^?1, at the current density of 200 mA g^?1. After 100 cycles, the ZnO/NSG nanocomposites demonstrated a high reversible capacity of 720 mAh g^?1 and coulombic efficiency of 99.8%, which can be attributed to the porous three-dimensional network, constructed by ZnO nanoparticles and nitrogen and sulfur co-doped graphene. Moreover, the designed nanocomposite has shown excellent rate capability and lower charge transfer resistance. These results are promising and encourage further research in the area of ZnO-based anodes for next-generation LIBs.     

Urea-assisted solvothermal synthesis of monodisperse multiporous hierarchical micro/nanostructured ZnCo<Subscript>2</Subscript>O<Subscript>4</Subscript> microspheres and their lithium storage properties

High-quality monodisperse multiporous hierarchical micro/nanostructured ZnCo₂O₄ microspheres have been fabricated by calcinating the Zn_1/3Co_2/3CO₃ precursor prepared by urea-assisted solvothermal method. The as-prepared products are characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), and Brunauer-Emmett-Teller (BET) measurement to study the crystal phase and morphology. When tested as anode material for lithium ion batteries, the multiporous ZnCo₂O₄ microspheres exhibit an initial discharge capacity of 1,369 mAh g^?1 (3,244.5 F cm^?3) and retain stable capacity of 800 mAh g^?1 (1,896 F cm^?3) after 30 cycles. It should be noted that the good electrochemical performances can be attributed to the porous structure composed of interconnected nanoscale particles, which can promote electrolyte diffusion and reduce volume change during discharge/charge processes. More importantly, this ZnCo₂O₄ 3D hierarchical structures provide a large number of active surface position for Li⁺ diffusion, which may contribute to the improved electrochemical performance towards lithium storage.