Preparation and enhanced capacitance of core–shell polypyrrole/polyaniline composite electrode for supercapacitors

Polypyrrole (PPy) nanotubes were synthesized by using the complex of methyl orange (MO)/FeCl₃ as a template. Then the core–shell polypyrrole/polyaniline (PPy/PANI) composite was prepared by in situ chemical oxidation polymerization of aniline on the surface of PPy nanotubes. The morphology and molecular structure were characterized by transmission electron microscopy (TEM), infrared spectroscopy (IR) and X-ray diffraction (XRD). TEM images confirmed that the composite was core–shell nanotubes. The electrochemical properties of the PPy/PANI composite electrode were investigated by cyclic voltammetry (CV), galvanostatic charge–discharge and electrochemical impedance spectroscopy (EIS). The electrochemical experiments showed that the specific capacitance of the PPy/PANI composite was 416 F g⁻¹ in 1 M H₂SO₄ electrolyte and 291 F g⁻¹ in 1 M KCl electrolyte. Furthermore, the composite electrode exhibited a good rate capability and maintained 91% of initial capacity at a current density of 15 mA cm⁻² in 1 M H₂SO₄ electrolyte.     

Electrochemical characterization of activated carbon–ruthenium oxide nanoparticles composites for supercapacitors

The high specific capacitance of ruthenium oxide (denoted as RuO_x) nanoparticles prepared by a modified sol–gel method with annealing in air for supercapacitors was demonstrated in this work. The specific capacitance of activated carbon (denoted as AC) measured at 5 mA/cm² is significantly increased from 26.8 to 38.7 F/g by the adsorption of RuO_x nanoparticles with ultrasonic weltering in 1 M NaOH for 30 min. This method is a promising tool in improving the performance of carbon-based double-layer capacitors. The total specific capacitance of a composite composed of 90 wt.% AC and 10 wt.% RuO_x measured at 25 mV/s is about 62.8 F/g, which is increased up to ca. 111.7 F/g when RuO_x has been previously annealed in air at 200 °C for 2 h. The specific capacitance of RuO_x nanoparticles was promoted from 470 to 980 F/g by annealing in air at 200 °C for 2 h. The nanostructure of RuO_x was examined from the transmission electron microscopic (TEM) morphology.     

Homogeneous core–shell NiCo2S4 nanorods as flexible electrode for overall water splitting

Exploring low-cost and highly efficient Water splitting electrocatalyst has been recognized as one of the most challenging and promising ways. NiCo₂S₄ core-shell nanorods supported on nickel foam (NF) have been fabricated by a facile hydrothermal method. The electrochemical performance of NiCo₂S₄@NiCo₂S₄ for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is studied. NiCo₂S₄@NiCo₂S₄/NF exhibits a significantly improved OER and HER performance with an overpotential of 200 mV at 40 mA/cm² and an overpotential of 190 mV at 10 mA/cm². The combination of low charge-transfer resistance, enhanced interaction and charge transport as well as large electrochemical double-layer capacitance enables superior OER and HER. The NiCo₂S₄@NiCo₂S₄/NF nanorod electrode shows excellent electrocatalytic activity with a low voltage 1.57 V and stability with long hour electrolysis, which is highly satisfactory for a prospective bifunctional electrocatalyst.     

Fe2O3-filled carbon nanotubes as a negative electrode for an Fe–air battery

Fe₂O₃-filled carbon nanotube material was prepared by filling carbon nanotubes (CNTs) with iron nitrate and then heating in an argon flow. The morphology and structure of this material were investigated by transmission electron microscopy (TEM), scanning electron microscopy (SEM) coupled with X-ray energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) measurements. The morphology, particle size and amount of iron oxide that filled CNTs depended on the amount of iron nitrate precursor. When Fe:C = 1:17 wt%, almost all of the iron oxide particles resided inside CNTs and their particle size was smaller than that at Fe:C = 1:8 wt%. The electrochemical properties of this material were investigated using cyclic voltammetry (CV) and galvanostatic cycling.     

CNTs@γ-Fe2O3@C composite electrode for high capacity lithium ion storage

Electrode materials with high specific capacity and cycle stability are the key factors that determine the overall performance of lithium ion batteries (LIBs) for new smart electronic device, and such materials with high performance are still challenging. Here, we report a composite material Carbon nanotube @ Iron oxide @ Carbon (γ-CNTs@γ-Fe₂O₃@C) with coaxial cable structure in hydrothermal method with the assistance of glucose. The as-prepared composite materials show superior electrochemical properties with good rate capability and excellent cycling performance, which show the great potential of CNTs@γ-Fe₂O₃@C for practical production and application in energy devices.     

Sulphur–carbon composites for Li/S batteries

Abstract

Structural and electrochemical properties of various types of sulphur–carbon composites were reviewed to propose approaching ways for the development of lithium/sulphur battery with high energy density and good cycle performance. To improve the electrochemical properties of a sulphur cathode, carbon and polymer materials are applied to sulphur composites: multiwalled nanotube (MWNT), graphene, CMK-3 and activated carbon; and polyaniline (PANi), polyacrylonitrile and polythiophene (PTh). These can serve conducting paths and a polysulphide reservoir to enhance the electrical conductivity of the sulphur cathode and effectively prevent dissolution of polysulphides. And the composites are categorised in two parts such as mixed type sulphur composites and embedded type sulphur composites. Among the sulphur–carbon composites, the hollow carbon capsule/S composite prepared by a geometric control and an infusion method of sulphur in sulphur carbon composite electrode, demonstrated the best electrochemical properties.     

Impregnated carbon–ionic liquid as innovative adsorbent for H2/CO2 separation from biohydrogen

Currently, purification is a considerably important technology for biohydrogen (bioH₂) production as a renewable energy resource. Adsorption methods are promising techniques for separation of CO₂ from the H₂/CO₂ mixture of bioH₂. In this study, the adsorbent is synthesized by impregnating activated carbon (AC) with ionic liquid (IL). The ILs were prepared using choline chloride and zinc chloride at different wt% with the AC, i.e., 0.5 wt%–3 wt%. The physical and chemical properties of the synthesized adsorbents, such as surface morphology, porosity, and structures, were investigated and characterized by using scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and Brunauer–Emmett–Teller analysis (BET). To investigate the actual adsorption performances, the effects of different synthesized adsorbent types and feed gas flow rates, i.e., 0.1–1.0 L min⁻¹, were observed. Hence, a commercial gas composed of CO₂ and H₂ mixture with different compositions, i.e., 40, 50, and 60 vol%, was used as synthetic bioH₂ gas. The adsorption capacity of CO₂, i.e., adsorption capacity, were determined using single adsorber column (0.6 L) at a temperature of 300 K and pressure of 1 bar. Results showed that adsorption capacity decreased with the increased feed gas flow rate. Moreover, the carbon impregnated with 1 wt% of IL showed the most excellent adsorption capacity at 84.89 mg of CO₂/g of adsorbent. The present results are the initial findings generated for the bioH₂ separation technology for future high-purity hydrogen production.     

High-performance Ni–SiO2 for pressurized carbon dioxide reforming of methane

The SiO₂ and Ni–SiO₂ were synthesized via the complex-decomposition method by using different organic acids as the complexing agent and fuel. The Ni-supported SiO₂ from different sources was prepared by the incipient impregnation method. The Ni–SiO₂ and Ni/SiO₂ were comparatively evaluated for carbon dioxide reforming of methane (CDR) under severe conditions of CH₄/CO₂ = 1.0, T = 750 °C, GHSV = 53200 mL g⁻¹ h⁻¹, and P = 0.1–1.0 MPa. The materials were fully characterized by XRD, XPS, TEM, TG-DSC, H₂-TPR, and N₂ adsorption-desorption at −196 °C. It was found that the complexing agent and preparation method of the catalyst significantly affected its surface area, the size and dispersion of Ni, the reduction behavior, and the coking and sintering properties, which determine the activity and stability of the catalyst for CDR. As a result, a highly active and stable Ni–SiO₂ for pressurized CDR was obtained by optimizing the complexing agent.     

Nonwoven Ni–NiO/carbon fibers for electrochemical water oxidation

The development of technologically efficient anodes for water oxidation is crucial to improve hydrogen production via water splitting. Electrodes based on metallic active sites dispersed in carbon matrices have been shown to be an attractive way to attain this goal. However, challenges remain to prevent catalyst agglomeration that otherwise can result in a decrease of performance over time.In this work, we report an alternative and efficient method to produce nickel-nickel oxide nanoparticles-embedded in carbon nanofibers (Ni–NiO/C), by the solution blow spinning (SBS) process. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses show the carbon nanofibrillar matrix as a robust support, with well-dispersed nickel nanoparticles on the surface. The responses of the linear scanning voltammetry, cyclic voltammetry and electrochemical impedance spectroscopy demonstrate how a small fraction of nickel on the fiber surface (≈1.2–5.3%) is enough to promote substantial improvement in performance (η = 278 and 309 mV vs RHE for 10 mA cm^?2) and a significant turnover frequency (TOF) values of 1.38 (η = 278) and 1.30 s^?1 (η = 309). These promising results are correlated with a large amount of Ni³⁺ present on the fiber surfaces, as identified by X-ray Photoelectron Spectroscopy (XPS). This work provides a low-cost and rapid preparation technique that can be extended for the manufacture of a wide variety of electrodes based on metals supported on carbon nanofibers.     

Ni–P alloy@carbon nanotubes immobilized on the framework of Ni foam as a 3D hierarchical porous self-supporting electrode for hydrogen evolution reaction

The development of self-supporting electrodes that exhibited both high efficiency and good durability remained a challenge in the field of hydrogen energy utilisation. Here, we designed a self-supporting 3D hierarchical porous electrode by filling carbon nanotubes (CNTs) loaded with Ni–P alloy into the framework of nickel foam (NF). Firstly, CNTs were decorated with a catalytically active Ni–P alloy via electroless plating (Ni–P@CNTs). Then, the Ni–P@CNTs were filled and anchored onto the framework of NF via electroplating to synthesise a self-supporting electrode (Ni–P@CNTs/NF). The Ni–P@CNTs/NF exhibited an excellent catalytic performance toward the hydrogen evolution reaction (HER) in 1 M KOH electrolyte, with an overpotential of 53 mV at 10 mA cm^?2, a small Tafel slope of 101.56 mV dec^?1 and excellent long-term durability. This facile and effective strategy might provide a new path to the design of self-supporting electrodes with enhanced HER catalytic.     

ZnCl2- and NH4Cl-hydroponics gel electrolytes for zinc–carbon batteries

Absorbency testing is used to determine the percentage of ZnCl₂ or NH₄Cl solution absorbed by a hydroponics gel (HPG). It is found that the absorbency of ZnCl₂ or NH₄Cl solution decreases with increasing solution concentration. The conductivity of ZnCl₂- and NH₄Cl-HPG electrolytes is dependent on the solution concentration. A mixture of salt solution with HPG yields excellent gel polymer electrolytes with conductivities of 0.026 and 0.104 S cm⁻¹ at 3 M ZnCl₂ and 7 M NH₄Cl, respectively. These gel electrolytes are then used to produce zinc–carbon cells. The fabricated cells give capacities of 8.8 and 10.0 mAh, have an internal resistance of 25.4 and 19.8 Ω, a maximum power density of 12.7 and 12.2 mW cm⁻², and a short-circuit current density of 29.1 and 33.9 mA cm⁻² for ZnCl₂- and NH₄Cl-HPG electrolytes, respectively.     

Sol–gel processed thin-layer ruthenium oxide/carbon black supercapacitors: A revelation of the energy storage issues

Hydrous ruthenium oxide/carbon black nanocomposites were prepared by impregnation of the carbon blacks by differently aged inorganic RuO₂ sols, i.e. of different particle size. Commercial Black Pearls 2000^® (BP) and Vulcan^® XC-72 R (XC) carbon blacks were used. Capacitive properties of BP/RuO₂ and XC/RuO₂ composites were investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) in H₂SO₄ solution. Capacitance values and capacitance distribution through the composite porous layer were found different if high- (BP) and low- (XC) surface-area carbons are used as supports. The aging time (particle size) of Ru oxide sol as well as the concentration of the oxide solid phase in the impregnating medium influenced the capacitive performance of prepared composites. While the capacitance of BP-supported oxide decreases with the aging time, the capacitive ability of XC-supported oxide is promoted with increasing oxide particle size. The increase in concentration of the oxide solid phase in the impregnating medium caused an improvement of charging/discharging characteristics due to pronounced pseudocapacitance contribution of the increasing amount of inserted oxide. The effects of these variables in the impregnation process on the energy storage capabilities of prepared nanocomposites are envisaged as a result of intrinsic way of population of the pores of carbon material by hydrous Ru oxide particle.     

Ni–SiO2 and Ni–Fe–SiO2 catalysts for methane decomposition to prepare hydrogen and carbon filaments

Active and stable Ni–Fe–SiO₂ catalysts prepared by sol–gel method were employed for direct decomposition of undiluted methane to produce hydrogen and carbon filaments at 823 K and 923 K. The results indicated that the lifetime of Ni–Fe–SiO₂ catalysts was much longer than Ni–SiO₂ catalyst at a higher reaction temperature such as 923 K, however, a reverse trend was shown when methane decomposition took place at a lower reaction temperature such as 823 K. XRD studies suggested that iron atoms had entered into the Ni lattice and Ni–Fe alloy was formed in Ni–Fe–SiO₂ catalysts. The structure of the carbon filaments generated over Ni–SiO₂ and Ni–Fe–SiO₂ was quite different. TEM studies showed that “multi-walled” carbon filaments were formed over 75%Ni–25%SiO₂ catalyst, while “bamboo-shaped” carbon filaments generated over 35%Ni–40%Fe–25%SiO₂ catalysts at 923 K. Raman spectra of the generated carbons demonstrated that the graphitic order of the “multi-walled” carbon filaments was lower than that of the “bamboo-shaped” carbon filaments.     

Nanoconfined 2LiBH4–MgH2–TiCl3 in carbon aerogel scaffold for reversible hydrogen storage

Nanoconfinement of 2LiBH₄–MgH₂–TiCl₃ in resorcinol–formaldehyde carbon aerogel scaffold (RF–CAS) for reversible hydrogen storage applications is proposed. RF–CAS is encapsulated with approximately 1.6 wt. % TiCl₃ by solution impregnation technique, and it is further nanoconfined with bulk 2LiBH₄–MgH₂ via melt infiltration. Faster dehydrogenation kinetics is obtained after TiCl₃ impregnation, for example, nanoconfined 2LiBH₄–MgH₂–TiCl₃ requires ∼1 and 4.5 h, respectively, to release 95% of the total hydrogen content during the 1st and 2nd cycles, while nanoconfined 2LiBH₄–MgH₂ (∼2.5 and 7 h, respectively) and bulk material (∼23 and 22 h, respectively) take considerably longer. Moreover, 95–98.6% of the theoretical H₂ storage capacity (3.6–3.75 wt. % H₂) is reproduced after four hydrogen release and uptake cycles of the nanoconfined 2LiBH₄–MgH₂–TiCl₃. The reversibility of this hydrogen storage material is confirmed by the formation of LiBH₄ and MgH₂ after rehydrogenation using FTIR and SR-PXD techniques, respectively.     

Amorphous NiFe–OH/Ni–Cu–P supported on self-supporting expanded graphite sheet as efficient bifunctional electrocatalysts for overall water splitting

With the serious intensification of energy shortage and greenhouse effect, people begin to look for the sustainable energy sources to replace fossil energy sources. Herein, self-supporting expanded graphite sheet (SSEGS) was developed as an ideal catalyst support through electrochemically intercalating flexible graphite sheet in alkaline solution. Electroless deposition was employed to synthesize Ni–Cu–P alloy on SSEGS and then an amorphous NiFe hydroxide/Ni–Cu–P/SSEGS (NiFe–OH/Ni–Cu–P/SSEGS) composite catalyst was further constructed through electrodeposition. Benefitting from the unique structural advantage of SSEGS and the synergistic effect between two amorphous Ni-based materials (Ni–Cu–P alloy and NiFe–OH), the resulting electrode exhibited superior bifunctional electrocatalytic performance in 1 M KOH. For H₂ evolution reaction and O₂ evolution reaction, the NiFe–OH/Ni–Cu–P/SSEGS composite catalyst could reach 10 mA cm⁻² at low overpotentials of 75 and 240 mV, respectively. Remarkably, the two-electrode system driven by NiFe–OH/Ni–Cu–P/SSEGS as the anode and cathode could afford 10 mA cm⁻² at a low cell voltage of 1.56 V vs. RHE. And after the 12 h stability test, the cell voltage at 10 mA cm⁻² increased by only 7 mV, indicating that the two-electrode system had excellent stability. The preparation of NiFe–OH/Ni–Cu–P/SSEGS material with superior bifunctional electrocatalytic performance has a significance influence to the development and expansion of hydrogen production technology.     

Performance evaluation of carbon/PrBaCo2O5+δ composite electrodes for Li–O2 batteries

Herein, a new type of perovskite oxide PrBaCo₂O_5+δ (PBCO) was synthesized and optimized by cooperating with carbon nanotubes (CNT) or carbon nanoparticles (BP2000), which was further applied into Li–O₂ battery cathode as a bi-functional cathode catalyst, achieving a high discharge capacity of 15.1 mA h, the number of which is over four times than that of single PBCO or CNT cathode, and seven times than single BP2000 cathode. Furthermore, a significantly enhanced stability was achieved as sustained more than 290 cycles at a fixed capacity, the number of which exceeds most carbon-based and even other perovskite catalytic Li–O₂ batteries. The charge transfer resistance (R_ct) of PBCO was reduced 46.6% after cooperating with carbon materials, which is almost half of single PBCO. All these results demonstrated that the big defect of PBCO can be remedied through the surface decorating with electronic conductors, such as, carbon nano-materials, and thus resulting in a substantially enhanced cathodic performance.     

New three-dimensional electrode structure for the lithium battery: Nano-sized γ-Fe2O3 in a mesoporous carbon matrix

A new electrode structure based on a three-dimensional mesoporous matrix was developed. Nanoparticles of γ-iron oxide (Fe₂O₃) were introduced into the mesopores of a carbon matrix (mesoporous carbon, CMK-3) by oxidizing metallic iron, which was electroplated in the matrix. The resulting structure was found to have a high charge-discharge capacity when used as the positive electrode of a lithium battery. The iron oxide nanoparticles bonded tightly to the electrically conductive electrode framework, and showed a high activity for the electrochemical reaction: Fe₂O₃ + 6Li → 3Li₂O + 2Fe.     

Study of bimetallic Cu–Ni/γ-Al2O3 catalysts for carbon dioxide hydrogenation

The effect of the Cu/Ni ratio on CO₂ hydrogenation at 773 K and 873 K was studied by XRD, TPR, H₂ and CO₂–TPD. There exists strong interaction between Cu and Ni components. At high temperature (773 K and 873 K), the products are CO, CH₄ and H₂O without CH₃OH formation. The Cu/Ni ratio has a significant effect on the conversion and selectivity. Cu favors CO formation while Ni is of benefit in CH₄ formation.     

Carbon-resistant Ni-YSZ/Cu–CeO2-YSZ dual-layer hollow fiber anode for micro tubular solid oxide fuel cell

A NiO-YSZ/porous YSZ dual-layer hollow fiber with an asymmetric structure was fabricated by a co-spinning-sintering method. A dense YSZ electrolyte film was prepared on NiO-YSZ layer by dip-coating method and calcined at 1450 °C; subsequently a porous cathode was dip-coated on the dense YSZ electrolyte film using LSM-YSZ (in the weight ratio 4:1) ink to fabricate a micro tubular solid oxide fuel cell (MT-SOFC). Cu–CeO₂ catalyst was impregnated into the porous YSZ layer to form the second anode composition. The power output of the MT-SOFC with Ni-YSZ/Cu–CeO₂-YSZ graded anode was up to 242 mW cm⁻² operated at 850 °C using CH₄ as fuel and air as oxidant. Little carbon deposition was observed on the double anode using methane as the fuel after 60 h' stable operation.     

Effects of Pt loading in the anode on the durability of a membrane–electrode assembly for polymer electrolyte membrane fuel cells during startup/shutdown cycling

A polymer electrolyte membrane fuel cell (PEMFC) stack of a fuel cell vehicle (FCV) is inevitably exposed to reverse current conditions, which are formed by the oxygen reduction reaction (ORR) induced at the anode with a hydrogen/air boundary during startup/shutdown processes. With an increase in the reverse current, the degradation rate of the cathode that experiences a highly corrosive condition (locally high potential) increases. In this work, the anode Pt loading is decreased from 0.4 to 0.1 mg cm⁻² to decrease the reverse current. The decrease in the anode Pt loading is found to decrease the hydrogen oxidation rates (HOR) during normal operation, but this loading decrease barely affected the cell performance. However, a decrease in the anode Pt loading can significantly decrease the reverse current, leading to a diminished cathode degradation rate during startup/shutdown cycling. It is revealed by slow decreases in the cell performance (i–V curves) and electrochemical active surface area (EAS), and a slow increase in the charge-transfer resistance (R_ct), which can be attributed to corrosion of the carbon support and dissolution/migration/agglomeration of the platinum catalyst.