The novel anode material for lithium-ion batteries, silicon–oxygen–carbon (Si–O–C) composite, is prepared by a liquid solidification combined with following pyrolysis process, in which silicon dioxide (SiO2) is used as an additive agent to enhance the electrochemical performance of the composite. While the structure of the composite is confirmed by X-ray diffraction (XRD) and Fourier transform infrared spectra (FT-IR), the morphology and microstructure were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), respectively. SEM and TEM observations reveal that the Si–O–C powders are about 1 μm in diameter, and there is a homogenous pyrolyzed carbon layer about 5 nm thick on the surface of the particle. The Si–O–C sample as anode material can deliver a high initial charge capacity of 753.4 mAh g?1, and the capacity keeps above 500.0 mAh g?1 after 40 cycles at 100.0 mA g?1. The electrochemical impedance spectroscopy results show that the composite exhibits lower charge transfer resistance and higher lithium-ion diffusion rate compared with the Si–C anode, which indicates that the composite Si–O–C could be used as a promising anode material for lithium-ion batteries.
A high performing and thermally stable magnesium aluminate (MgAl2O4) coated on both sides of Celgard 2320 for applications in lithium batteries was prepared. The MgAl2O4-coated membrane was thermally stable up to 440 °C and capable of up-taking electrolytes up to 250%. The contact angle of MgAl2O4-coated membrane was lower (21°) than that of uncoated membrane. The MgAl2O4-coated ceramic separator exhibited appreciable ionic conductivity and better compatibility with lithium metal anode. Finally, a 2032-type coin cell comprising Li/MgAl2O4-coated separator/LiFePO4 was assembled and its charge-discharge behavior was analyzed at 0.1, 0.5, and 1 C-rates. A stable discharge capacity was achieved even at 1 C-rate which qualifies this MgAl2O4-coated membrane for lithium battery applications.
The anode material Si/CNTs@C composite is prepared by a spray–drying combined pyrolysis technology. The as–prepared material is characterized by XRD, SEM, TEM, and electrochemical measurements. The composite is composed of nano–Si, CNTs, flake graphite, and amorphous glucose–pyrolyzed carbon, and CNTs provides a good wrapping effect to buffer the volume change of silicon. The composite as anode for LIB shows good electrochemical performance. In the voltage range of 2.00–0.01 V, it delivers initial charge capacity of 630.5 at 100 mA g?1, and 85.14 % of initial capacity is retained even after 50 cycles. The CV and AC impedance analysis indicate that the prepared composite separately shows good electrode stability and low charge- transfer impedance Rct. The results indicate that the Si/CNTs@C composite is a potential alternative to graphite for high energy–density lithium–ion batteries.
In this study, anodic stripping voltammetry was optimized and used for the trace determination of copper ions using modified carbon paste electrode with dicyclohexyl-18-crown-6 and multi-walled carbon nanotubes. The important and critical parameters such as pH, electrolyte type, electrode composition, deposition time, and reduction potential was studied and optimized. Copper shows a sharp peak at +0.095 V that was used for its determination from 4.0 to 200 ng mL?1. With the application of the suggested method, the detection limit and relative standard deviation were obtained as 1.1 ng mL?1 and ±2.3 %, respectively. This electrochemical sensor has several advantages such as simple and low cost preparation, good reproducibility, low LOD, and high speed. The suggested sensor was applied successfully for the determination of copper ions in environmental, biological, and standard samples.
We present a comparative study on the electrocatalytic performance of PtRu/C and PtAu/C nanoparticles for methanol oxidation reaction. The PtRu/C nanoparticles are commercially available, while the PtAu/C nanoparticles were prepared using the conventional sodium borohydride reduction method. The particle size, surface morphology, and crystallinity of the two samples were characterized using transmission electron microscopy (TEM) and X-ray diffraction (XRD). The electrocatalytic activity for MOR and the long-term durability of the PtAu/C and PtRu/C were carefully investigated. The results showed that the PtAu/C exhibited much higher activity for MOR and improved long-term durability in comparison with the PtRu/C. The catalysts before and after accelerated potential cycling test (APCT) were characterized by X-ray photoelectron spectroscopy (XPS). It was found that Ru dissolved and escaped completely from the electrode meanwhile the majority of Au remained after APCT.
Graphical abstract The synthesized PtAu/C exhibits higher electrocatalytic activity of methanol oxidation and improved durability compared to the commercial PtRu/C
The air cathode is the most crucial component for a zinc-air battery (ZAB) system, which inquires fast diffusion of gaseous O2 and decent bifunctional catalytic performance. Herein, based on our previous attempts, we developed a bi-functional electro-catalyst utilizing co-doped manganese dioxide nanotube/carbon nanotube (CNT) composite to improve the catalytic activity toward both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). A simple characterization of the morphology and physicochemical properties of various Co3O4/MnO2/CNT (CMC) composites was performed by employing various techniques (SEM, TEM, and XRD). More importantly, using CMC composite as the bifunctional cathode catalysts, we thoroughly investigated the effects of catalyst loading, bonding layer loading, and spraying area in catalyst layer (CL) on cell performance and charge-discharge cyclic ability for rechargeable zinc-air batteries. The highest peak power density of 400.3 mW cm?2 can be reached when the catalyst loading is 3 mg cm?2, the spraying area is 1 cm2 and the binder content is 80 μL. The rechargeable zinc-air batteries with the air electrodes containing different spraying areas and bonding layer loadings are stably operated for 22 h at a high current density (100 mA cm?2) and show a maximum voltage gap of 1.5 V between charge and discharge voltages. All these optimization efforts are particularly important to future large-scale applications in ZAB.
Tin-based composites are promising high-capacity anode materials for Li-ion batteries, but they usually exhibit poor cycling stability because of their large volume expansion during the Li uptake and release process. We reported a facile solvothermal method to produce nanosheet-assembled SnS microspheres and a rational strategy to improve the electrochemical performance of SnS microspheres by anchoring on reduced graphene oxide (RGO) networks. The as-prepared SnS/RGO nanocomposites were characterized by XRD, SEM, TEM, TGA, and Raman spectra. The electrochemical results show that the SnS/RGO electrode exhibited high reversible capacity and good cycling stability (delivered a capacity of 760 mAh g?1 after 100 cycles at a current density of 100 mA g?1). The superior electrochemical performance can be attributed to the large available surface area, high conductivity, and fast transportation of electrons and Li-ions; these are benefited from the unique hybrid structure and the synergistic effect between SnS and RGO.
Graphical AbstractTOC Anode materials of nanosheet-assembled SnS microspheres anchored with RGO sheets have been simply synthesized via a facile solvothermal route and subsequently RGO anchoring. When used as the anode for Li-ion batteries, they show a high specific capacity of 760 mA h g?1 after 100 cycles at the current density of 100 mA g?1.
A novel approach has been made to tailor Niobium pentoxide (Nb2O5) as a coating material on the surface of lithium iron phosphate (LiFePO4) via a facile polyol technique. The coating content was optimized at 1 wt%. The superficial coating demonstrated superior discharge capacity than the pristine LiFePO4. However, increasing the coating content further would result in a capacity loss. This may be due to the electrochemical inactiveness that increases with the content of the coating material, and 1 wt% of Nb2O5-coated LiFePO4 sample exhibits initial discharge capacity of 163 mAh g?1 at a current of 0.1 C and retains a stable discharge capacity of 143 mAh g?1 up to 400 cycles at 1 C rate with a coulombic efficiency of 98%.
High-potential, eco-friendly LiFePO4 cathode materials were synthesized by polyol, hydrothermal, and solid-state reaction methods. The polyol technique was carried out without any special atmosphere and postheat treatment. The synthesized samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM) with energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectrometry (XPS), and charge-discharge and cyclic voltammetry tests. The LiFePO4 prepared via polyol technique exhibits good electrochemical performance than other method samples do.
In this research, the electrochemical properties of a stir cast Al-0.65Mg-0.15Sn-0.05Ga (wt.%) alloy as an anode material in 3 wt.% NaCl solution was examined by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The corrosion behavior of the material was also evaluated using self-corrosion rate, hydrogen evolution, open circuit and closed circuit potentials, and anode efficiency measurements. In addition, the microstructure of the material was studied using scanning electron microscopy (SEM) and the intermetallic particles were analyzed by energy dispersive spectrometer (EDS). The results showed that tin inclusions were formed within the grains and along the grain boundaries and the dissolution of aluminum substrate was occurred preferentially around these particles leading to form round pits. The dissolution of alloy was accompanied by hydrogen gas evolution from cathodic tin particles. Polarization measurements showed active behavior with considerably negative corrosion potential value without any passive region. The obtained impedance results showed an increase in the impedance values due to the coverage of anode surface by reaction products during immersion. A sample of the alloy which was subjected to homogenizing annealing at 570 °C showed more active behavior by providing more negative open and closed circuit potential values and improved anode efficiencies at higher impressed currents, but evolved higher amounts of hydrogen compared to the as-cast anode.
Graphical abstract This paper aims at evaluating the electrochemical and microstructural characteristics of an as-cast and solution-annealed Al-0.65Mg-0.15Sn-0.05Ga alloy anode which was fabricated by stir casting. The polarization and EIS results indicate negative corrosion potential and OCP values without passive region. The activity and anodic efficiency of the solution-annealed anode was higher in high impressed current densities but evolves more hydrogen
Morphologies and structures of M-N-C catalysts are the key factor for controlling the formation of catalytic active sites, which are directly connected with the electrocatalytic activities for oxygen reduction reaction (ORR). By combining different metal sources (metal-free, Co, and Fe) with polyaniline (PANI) and para-phenylenediamine functionalized GO (PGO), morphologies and structures are tuned to accelerate the ORR activity. Compared with metal-free catalyst, metal-containing catalysts show better ORR performance because of the possible synergistic effect between metal and N atoms. In particular, the improved ORR activity of Fe-PANI-PGO catalyst is obtained by rotating disc electrode (RDE) at 1600 rpm in 0.1 M KOH electrolyte. The Fe-PANI-PGO electrocatalyst has the enhanced half-wave potential of 0.89 V and the high stability with only decreasing 7 mV of half-wave potential after 10,000 cycles, implying increased number and strengthened structures of active sites. Combined with various means of characterization, advantageous morphologies and structures including large electrochemically active surface area, high graphitization degree, and thick carbon structure with more pyridinic nitrogen boned with metal atoms can greatly enhance the ORR activity and stability of the catalyst.
As a key component of alkali anion exchange membrane fuel cells, the anion exchange membrane (AEM) needs to have high ionic conductivity and good stability. Herein, highly branched side chain grafted polysulfone AEMs are designed and fabricated via macromolecule-initiated atom transfer radical polymerization of chloromethyl styrene. The highly branched side chain results in increased free volume in the AEM. As a result, the membrane shows significantly improved hydroxide conductivity relative to its un-branched counterpart membrane. Furthermore, the highly branched side chain renders the membrane with better anti-swelling property and improved alkaline stability. These results demonstrate that constructing highly branched side chain architecture is an effective strategy for fabricating AEMs with high conductivity and stability.
Graphical abstract Highly branched side chain grafted AEMs were designed and fabricated. The highly branched side chain provides more free volume for facile hydroxide ion transport. It also provides space for water storage and shielding effect for the interior cations, and thus leads to lower swelling and better alkali stability than the linear polymer AEM at a similar IEC.
With the growth of new energy economy, proton exchange membrane fuel cell (PEMFC) has great potential to be success. However, the lack of high-performance catalyst layer (CL) especially at cathode limits its applications. It is becoming increasingly important to understand interface property during electrocatalytic oxygen reduction reaction (ORR). Here, the rotating disk electrode (RDE) method is developed to study the temperature and Nafion ionomer content effects on interface formed between Nafion and Pt/C. The results show that the temperature has the significant influence on electrochemical active sites, charging double capacitance, and reaction polarization resistance at low Nafion content region. Excess Nafion loaded in CLs will turn to self-reunion and increase the exposed active sites. We find that the optimum Nafion loading is in the range of 30 to 40 wt.%. The highest specific activity we achieve is 107.8 μA/cm2.Pt at 60 °C with 0.4 of ionomer/catalyst weight ratio, corresponding to the kinetic current 283.5 μA at 0.9 V. This finding provides new insights into enhancing the Pt utilization and designing high-efficiency catalysts for ORR.
Quasi-solid-state dye-sensitized solar cells (QS-DSSCs) using polymer electrolytes display excellent long-term stability with comparable light to electricity conversion efficiency (PCE). In this paper, poly(methyl methacrylate) (PMMA) is chosen as the template polymer, and polymer viscosity and its weight percentage of PMMA in the I3?/I? electrolyte system are optimized considering the competitive factors of the ionic conductivity (σ) and gel dimension stability. A systematic study is carried out to study the environmental factors on the ionic conductivity of quasi-solid electrolytes in terms of storage time, thermal stress, and light soaking. In the different temperature range, the polymer presents different aggregation states and molecular motion forms, which results in different conductive mechanism of the gel electrolyte. It could be described by the Arrhenius equation in the sol state and the Vogel–Tammann–Fulcher (VFT) equation on the gel state, respectively. Both the cyclic voltammetry curve and the Tafel polarization curve indicate that the quasi-solid electrolyte exhibits a lower ion diffusion and transport capacity (1.83?×?10?6 cm2/s) than that of the liquid electrolyte (9.15?×?10?6 cm2/s). This work provides new insights about the degradation mechanism of polymer electrolytes for QS-DSSC application.
Mesoporous Ni(OH)2/Co(OH)2 electrode materials were synthesized via a simple one-pot procedure by combining homogeneous precipitation and stepwise precipitation method. The configuration of the porous Ni(OH)2/Co(OH)2 electrode materials synthesized provides 3D electron transmission channels through a high conductive Co(OH)2 distributed in the peripheral nanolayer of the composites, which is beneficial to rate capability and cycle stability. The Ni(OH)2/Co(OH)2 electrode materials have a specific surface area of 229 m2 g?1, which is approximately 40% higher than that of Ni(OH)2 (163 m2 g?1). Their specific capacitance is up to 1202 and 1022 F g?1 at the current densities of 10 and 20 A g?1, respectively. Furthermore, the capacitance retention of the electrode materials at the current density of 10 A g?1 is 98% after 5000 cycles. The synthesis method provides a novel simple route to fabricate heterostructure materials for capacitors with high electrochemical performance.
Layered zinc-based metal-organic framework ([Zn(4,4′-bpy)(tfbdc)(H2O)2], Zn-LMOF) nanosheets were synthesized by a facile hydrothermal method (4,4′-bpy = 4,4′-bipyridine, H2tfbdc = tetrafluoroterephthalic acid). The materials were characterized by IR spectrum, elemental analysis, thermogravimetric analysis, powder X-ray diffraction, transmission electron microscope (TEM), scanning electron microscope (SEM), and the Brunauer–Emmett–Teller (BET) surface. When the Zn-LMOF nanosheets with the thickness of about 24 ± 8 nm were used as an anode material of lithium-ion batteries, not only the Zn-LMOF electrode shows a high reversible capacity, retaining 623 mAh g?1 after 100 cycles at a current density of 50 mA g?1 but also exhibits an excellent cyclic stability and a higher rate performance.
Graphical abstract Zinc-based layered metal-organic framework ([Zn(4,4′-bpy)(tfbdc)(H2O)2], Zn-LMOF) nanosheets have been synthesized, displaying a high capacity as anode materials for lithium-ion batteries.
Dendritic Pt–Cu nanoparticles were synthesized by a facile one-step method with the help of surfactant Brij58 at room temperature, and we also studied the effects of different Pt–Cu ratios on the morphology and size of nanoparticles. In addition, we further tuned the morphology of the Pt–Cu nanostructures by introducing bromide ions, eventually leading to the appearance of some tripod-like structures. Compared with dendritic Pt–Cu and commercial Pt black, these tripod-like Pt–Cu nanostructures exhibited higher electrocatalytic activity and CO tolerance for catalyzing methanol oxidation.
The present chain of five papers considers the concept of defect engineering in processing TiO2-based photosensitive semiconductors for solar-to-chemical energy conversion. The papers report the effect of chromium on the key performance-related properties of polycrystalline TiO2 (rutile), including (i) electronic structure, (ii) chromium-related photocatalytic properties, (iii) oxygen-related photocatalytic properties, (iv) electrochemical coupling and (v) surface versus bulk properties. The present work reports the effect of chromium on defect disorder and the related electronic structure of TiO2, including the band gap and mid-gap energy levels. It is shown that chromium incorporation into the TiO2 lattice results in a decrease of the band gap from 3.04 eV for pure TiO2 to 1.4 and 1.3 eV, for Cr-doped TiO2 (1.365 at% Cr) after annealing at 1373 K in the gas phase of controlled oxygen activity, 21 kPa and 10?10 Pa, respectively. The optical properties determined using the ultraviolet-vis spectroscopy (in the reflectance mode) indicate that chromium incorporation results in the formation of mid-band energy levels. In this work, we show that chromium at and above the concentrations levels of 0.04 and 0.376 at% results in the formation of acceptor-type energy levels at 0.57 and 1.16 eV (above the valence band), respectively, which are related to tri-valent chromium in titanium sites and titanium vacancies, respectively. Application of well-defined protocol leads to the determination of data that are well reproducible. The new insight involves the determination of the band gap of TiO2 processed in the gas phase of controlled oxygen activity.
The optical properties of diphosphate LiCrP2O7 compound prepared by the classic ceramic method were recorded at room temperature. Absorption spectrum shows the presence of five characteristics bands related to the octahedral transitions of Cr3+ from ground term 4A2g to excited terms. Crystal field strength and inter electronic repulsion Racah parameters were deduced. The calculated value of direct \( {E}_g^{\mathrm{direct}} \)=1.62 eV energy gap has been found using Tauc’s procedure. Besides, the dielectric properties were carried out by impedance spectroscopy at different temperatures (460–700 K). The frequency and temperature dependent of the real ε′ and imaginary ε″ parts of the dielectric constant were discussed. The variation of the frequency power law of the imaginary part of dielectric constant was analyzed in terms of two different conduction mechanisms. Furthermore, the modulus plots can be characterized by the empirical Kohlrausch–Williams–Watts (K.W.W.) function and the obtained values of activation energies deduced from relaxation frequency are in order of Ea (I) = 0.49 eV and Ea (II) = 0.87 eV.
A novel ascorbic acid (AA) electrochemical biosensor based on ferrocene dicarboxylic acid (Fc(COOH)2)/zeolitic imidazolate framework-8 (ZIF-8)/three-dimensional (3D) kenaf stem-derived macroporous carbon (3D-KSCs) was proposed for the first time. The formation and properties of Fc(COOH)2/ZIF-8/3D-KCSs nanocomposites were characterized by scanning electron microscopy, Fourier transform-infrared spectroscopy, N2 adsorption/desorption isotherms, X-ray powder diffraction, and energy dispersive X-ray spectroscopy. The results showed that a large number of short rod-like ZIF-8/Fc(COOH)2 was arrayed on the 3D-KSCs surface via a simple one-step hydrothermal method. Fc(COOH)2 was firmly encapsulated into the pores of ZIF-8 simultaneously during the synthesis process of ZIF-8. The Fc(COOH)2/ZIF-8/3D-KCSs nanocomposites were employed to prepare integrated Fc(COOH)2/ZIF-8/3D-KSCs electrode directly for electrochemical AA sensing, and the integrated electrode showed better performance for AA detection than traditional enzyme-based biosensors and nonenzymatic sensors. A wide detection range of 0.06 μM~5.01 mM and a low detection limit of 0.017 μM were obtained with good stability and selectivity. The work also sheds new light on developing ZIF-8-based nanocomposites for electrochemical sensing.
