Green synthesis and characterization of SnO2, CuO,Fe2O3/activated carbon nanocomposites and their application in electrochemical hydrogen storage

The goal of this study is to produce environmentally friendly nanomaterials that have a high hydrogen storage capacity. The researchers in this study used inexpensive natural bitumen to produce activated carbon (substratum) and a green solution synthesis combustion method to produce CuO, Fe₂O₃, and SnO₂ nanoparticles using a Mint extract as the source material. Metal oxides such as CuO, Fe₂O₃ and SnO₂ are used to increase hydrogen storage capacity and Columbic efficiency. AC and AC/SnO₂, AC/CuO, and AC/Fe₂O₃ nanocomposites have been confirmed via XRD (X-ray diffraction), TEM (transmission electron microscopy), EDX (energy-dispersive X-rays), FT-IR (fourier transform infrared), scanning electron microscope (SEM), and adsorption and desorption analysis of N₂ (BET). In terms of discharge capacity, AC/CuO, AC/Fe₂O₃, and AC/SnO₂ display respective capacities of 2250, 2500, and 3600 mAh/g after 20 cycles, respectively. Of all the sample materials, the AC/SnO₂ nanocomposite with the highest hydrogen storage capacity has the lowest Columbic efficiency. This implies that a sample with 54% Columbic efficiency, such as AC/CuO nanocomposite, is a more suitable specimen.     

Synthesis,characterization and investigation of the electrochemical hydrogen storage properties of CuO–CeO2 nanocomposites synthesized by green method

Pure CuO–CeO₂ nanocomposites were synthesized by simple thermal decomposition method in presence of various Cu salts as a copper source and fructose as a green capping agent. In this study, the effect of various parameters such as the type of copper sources, temperature and time of reaction on the morphology and the particles size were studied. The products were characterized via X-ray diffraction (XRD) pattern, scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), transmission electron microscopy (TEM), N2 adsorption (BET), vibrating sample magnetometer (VSM), and infrared spectrum (FT-IR). The optical property of the nanocomposite was examined via UV–vis (DRS) spectroscopy and the band gap was calculated to 3 eV. Also, the hydrogen storage capacity of CuO–CeO₂ nanocomposites and CeO₂ nanoparticles were investigated via chronopotentiometry method for the first time. The discharge capacity of CeO₂ nanoparticles and CuO–CeO₂ nanocomposites in 1 mA current and 20 cycles obtained 2150 and 2450 mAh/g, respectively.     

Enhanced lithium-ion intercalation properties of coherent hydrous vanadium pentoxide-carbon cryogel nanocomposites

Coherent hydrous vanadium pentoxide (V₂O₅·nH₂O)-carbon cryogel (CC) nanocomposites were synthesized by electrodeposition of vanadium pentoxide onto the porous carbon scaffold which was derived from resorcinol (R) and formaldehyde (F) organic hydrogels. As-fabricated nanocomposites were characterized by scanning electron microscopy (SEM), along with EDAX and nitrogen sorption isotherms which suggested vanadium pentoxide incorporated in the pores of carbon cryogels. The nanocomposites showed much improved discharge capacity and better cyclic stability as compared to hydrous vanadium pentoxide films deposited on platinum foil. The discharge capacity of the nanocomposites reached 280 mAh g⁻¹ based on the mass of the vandium pentoxide at a current density of 100 mA g⁻¹ and it possessed good cycle stability at different discharge rates. The results demonstrated that electrochemical performances, such as specific discharge capacitance and reversibility of the composite electrode, could be greatly enhanced by the introduction of carbon cryogels (CCs) scaffold with three-dimensionally interconnected porous structure in which V₂O₅·nH₂O homogeneously dispersed.     

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.     

Preparation of copper oxide/oak-based biomass nanocomposite for electrochemical hydrogen storage

In this study, oak fruit as a biomass was used to prepare CuO/OBM nanocomposite and the electrochemical hydrogen storage (EHS) capacity of this nanocomposite was investigated. The product was characterized via energy dispersive X-ray analysis (EDX), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET), Fourier-transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM) and X-ray diffraction (XRD). Then, the effect of CuO/OBM ratio on the electrochemical hydrogen storage was investigated via chronopotentiometry method. After 20 cycles, the discharge capacities of OBM and CuO/OBM nanocomposite under 1 mA current were achieved from 3490 to 5950 mAh/g, respectively. Results show that coating of CuO on the OBM leads to improve the discharge capacity, but by increasing the CuO/OBM ratio, the discharge capacity has been decreased. Results of this study show that produced nanocomposite can be hopeful in replacing of fossil fuel.     

Carbon-supported manganese oxide nanocatalysts for rechargeable lithium-air batteries

Manganese oxide based catalysts were synthesised in the form of nano-particles using a redox reaction of MnSO₄ and KMnO₄, housed into the pores of a carbon matrix and followed by a thermal treatment. Particle sizes of the manganese oxide nanocatalysts were around 50 nm, based on the tunnelling electron microscope measurement. They were uniformly distributed in the carbon matrix, which contributed to an improved electrical connection among the catalyst and current collectors. The charge/discharge tests using this material as the cathode material in a rechargeable lithium-air battery showed high discharge capacities up to 4750 mAh (g carbon)⁻¹. The cycle ability of the composite electrode was superior to those of the commercial electrolytic manganese dioxide electrodes.     

Improving hydrogen production via water splitting over Pt/TiO2/activated carbon nanocomposite

Mesoporous TiO₂/AC, Pt/TiO₂ and Pt/TiO₂/AC (AC = activated carbon) nanocomposites were synthesized by functionalizing the activated carbon using acid treatment and sol–gel method. Photochemical deposition method was used for Pt loading. The nano-photocatalysts were characterized using XRD, SEM, DRS, BET, FTIR, XPS, CHN and ICP methods. The hydrogen production, under UV light irradiation in an aqueous suspension containing methanol has been studied. The effect of Pt, methanol and activated carbon were investigated. The results show that the activated carbon and Pt together improve the hydrogen production via water splitting. Also methanol acts as a good hole scavenger. Mesoporous Pt/TiO₂/AC nanocomposite is the most efficient photocatalyst for hydrogen production compared to TiO₂/AC, Pt/TiO₂ and the commercial photocatalyst P25 under the same photoreaction conditions. Using Pt/TiO₂/AC, the rate of hydrogen production is 7490 μmol (h g catal.)⁻¹ that is about 75 times higher than that of the P25 photocatalyst.     

A comparative study of the electrochemical hydrogen storage properties of activated carbon and well-aligned carbon nanotubes mixed with copper

We studied the electrochemical hydrogen storage properties of activated carbon (AC) material mixed with copper. The discharge capacity of AC–Cu electrode which reached 510 mAh/g after 384 cycles, is much higher than that of the CNT–Cu electrodes. The plateau of discharge potential for AC–Cu electrode was very long and flat and reached −0.88 V vs. Hg/HgO, which was far from the potential of copper oxidation. The discharge plateau gradually appeared and continually lengthened with the increase of cycle number. Cyclic voltammetric experiments showed that the adsorption and desorption of hydrogen occurred on the surface of activated carbon and the active site increased with the increase of cycle number. The mechanism for electrochemical storage of hydrogen in AC–Cu electrode may be mainly physisorption.     

Two dimensional MAX supported copper oxide/nickel Oxide/MAX as an efficient and novel photocatalyst for hydrogen evolution

An innovative 2D MAX structure comprising of Ti₃AlC₂ multilayers and copper oxide (CuO)/nickel oxide (NiO) (CN) composite was fabricated via a facile chemical route for improving photocatalytic hydrogen evolution activity. The physicochemical properties of the synthesized nanocomposites were analyzed through various structural, morphological, and elemental techniques. The 2D Ti₃AlC₂/CuO/NiO composite showed a maximum H₂ generation rate of 20.7 mmol g^?1 h^?1, which is greater than that of the CN nanocomposite. This improved activity can be attributed to the presence of Ti₃AlC₂ multilayers on CuO/NiO, which showed excellent photoinduced charge carrier separation via the s-scheme mechanism. As an electron-bridge, CN NC can support the photoelectrons to transfer from the CB of CN to the CB of MAX, from where the photoelectrons respond with hydrogen ion to release hydrogen. The time-resolved photoluminescence measurement results showed that the CuO/NiO/MAX (CNM) composite had a charge carrier lifetime of 3 ns. The outcomes of this study will be beneficial in realizing the industrial applications of Ti₃AlC₂ MAX-based structured catalysts for hydrogen evolution and other ecological energy systems.     

Nanostructured Fe2O3 and CuO composite electrodes for Li ion batteries synthesized and deposited in one step

Nanostructured composite electrodes based on iron and copper oxides for applications in Li-ion batteries are produced by Electrostatic spray pyrolysis (ESP). The electrodes are directly formed by electrospraying precursor solutions containing either iron or copper salts dissolved in N-methylpyrrolidone (NMP) together with polyvinylidene fluoride (PVdF) as binder. The morphology and the structure of the deposited electrodes are investigated by X-ray diffraction (XRD) and Transmission electron microscopy (TEM), which show that sub-micrometric deposits are formed as a composite of oxide nanoparticles of a few nanometers in a PVdF polymer matrix. Electrochemical characterization by cyclic voltammetry (CV) and galvanostatic charge-discharge tests demonstrate that the conversion reactions in these electrodes enable initial discharge capacities of about 800 mAh g⁻¹ and 1550 mAh g⁻¹ for CuO and Fe₂O₃, respectively. The capacity retention in both cases needs further improvements.     

Preparation of LiCoPO4/C nanocomposite cathode of lithium batteries with high rate performance

LiCoPO₄/C nanocomposites could be successfully prepared by a combination of spray pyrolysis and wet ball-milling followed by heat treatment. X-ray diffraction analysis confirmed that the LiCoPO₄/C nanocomposites were well crystallized in an orthorhombic structure with Pmna space group. Scanning electron microscopy and transmission electron microscopy with equipped energy dispersive spectroscopy verified that the LiCoPO₄/C nanocomposites were the agglomerates of LiCoPO₄ primary particles with a geometric mean diameter of 87 nm, and the carbon was well distributed on the surface of the agglomerates. The LiCoPO₄/C nanocomposites were used as cathode active materials for lithium batteries, and the electrochemical tests were carried out for the cell Li|1 M LiPF₆ in EC:DMC = 1:1|LiCoPO₄/C at various charge-discharge rates. The cells delivered first discharge capacities of 142 and 109 mAh g⁻¹ at 0.05 and 20 C, respectively. Furthermore, the discharge capacity after 40 cycles corresponded to 87% of initial one at 0.1 C rate. The excellent rate capability of the cells is mainly due to the well distributed carbon on the LiCoPO₄ agglomerates, and a much smaller lithium ion diffusion distance in the electrode.     

CuOx dispersion and reducibility on TiO2 and its impact on photocatalytic hydrogen evolution

Nanostructured CuO_x/TiO₂ (a mixture of Cu/Cu₂O/CuO) was prepared by impregnation for enhancing photocatalytic hydrogen generation from an aqueous solution containing 10 v/v% methanol. At an optimum Cu loading of 0.5 wt% and a calcination temperature of 500 °C, the CuO_x was present as relatively highly dispersed (0.90), fine deposits. At Cu loadings beyond 0.5 wt% a bimodal distribution of CuO_x deposits appeared with the prevalence of larger Cu deposits increasing with increasing Cu content. A corresponding decrease in H₂ generation was observed as Cu loading increased which was attributed to the increasing presence of the larger CuO_x deposits. The particle calcination temperature (in air) was also found to affect CuO_x/TiO₂ activity with an optimum performance achieved at a temperature of 300 °C. Calcining the CuO_x/TiO₂ at 500 °C led to greater oxidation of the CuO_x deposits (∼40%) to form more Cu²⁺ which corresponded to an almost proportional (42%) decrease in H₂ generation. The findings demonstrate the importance of Cu dispersion and oxidation state in governing photocatalytic H₂ generation by CuO_x/TiO₂.     

Enhancement of discharge performance of Li/CFx cell by thermal treatment of CFx cathode material

In this work we demonstrate that the thermal treatment of CF_x cathode material just below the decomposition temperature can enhance discharge performance of Li/CF_x cells. The performance enhancement becomes more effective when heating a mixture of CF_x and citric acid (CA) since CA serves as an extra carbon source. Discharge experiments show that the thermal treatment not only reduces initial voltage delay, but also raises discharge voltage. Whereas the measurement of powder impedance indicates the thermal treatment does not increase electronic conductivity of CF_x material. Based on these facts, we propose that the thermal treatment results in a limited decomposition of CF_x, which yields a subfluorinated carbon (CF_x−δ), instead of a highly conductive carbon. In the case of CF_x/AC mixture, the AC provides extra carbon that reacts with F₂ and fluorocarbon radicals generated by the thermal decomposition of CF_x to form subfluorinated carbon. The process of thermal treatment is studied by thermogravimetric analysis and X-ray diffraction, and the effect of treatment conditions such as heating temperature, heating time and CF_x/CA ratio on the discharge performance of CF_x cathode is discussed. As an example, a Li/CF_x cell using CF_x treated with CA at 500 °C under nitrogen for 2 h achieved theretical specific capacity when being discharged at C/5. Impedance analysis indicates that the enhanced performance is attributed to a significant reduction in the cell reaction resistance.     

Fabrication of high-power electric double-layer capacitors

The electrochemical behavior of activated carbon/carbon (AC/C) composite electrodes was investigated for high-power electric doublelayer capacitors (EDLCs). It was found that high-rate charge/discharge characteristics are affected by the resistance of the electrolyte phase in the pores of the electrode. The charge/discharge characteristics were improved by optimizing the pore-size distribution of the electrodes. The size and total volume of the macro-pores in the electrodes were controlled by mixing and burning out polymer spheres. A high-power EDLC (15V, 470 F), which can discharge as much as 500 A, was fabricated by using improved AC/C composite electrodes.     

Magnetic field influence on CuO–H2O nanofluid convective flow in a permeable cavity considering various shapes for nanoparticles

In this paper, CuO–H₂O nanofluid forced convection in a lid driven porous cavity is investigated under the impact of magnetic field. Shape effect of nanoparticles and Brownian motion impact on nanofluid properties are taken into consideration. Vorticity stream function formulation is utilized. The solutions of final equations are obtained by CVFEM. Graphs are shown for different values of Darcy number (Da), CuO–H₂O volume fraction (?), Reynolds (Ra) and Hartmann (Ha) numbers. Outputs indicate that selecting Platelet shaped nanoparticles results the highest heat transfer rate. Nusselt number augments with rise of Darcy and Reynolds number while it decreases with augment of Lorentz forces.     

Mesoscopic simulation of CuOH2O nanofluid in a porous enclosure with elliptic heat source

In this article, mesoscopic approach has been utilized to investigate magnetic field impact on CuOH₂O nanofluid free convection inside a porous cavity with elliptic heat source. Simulations have been done via LBM. KKL model is employed to consider Brownian motion impact on nanofluid properties. Influences of Rayleigh number (Ra), nanofluid volume fraction (?), Hartmann number (Ha), Darcy number (Da) on heat transfer treatment are demonstrated. Outputs demonstrate that temperature gradient reduces with increase of Ha while it increases with augment of Da,Ra.     

Optical,structural and phase transition properties of Cu2O,CuO and Cu2O/CuO: Their photoelectrochemical sensor applications

Cu₂O and CuO provide a unique possibility to tune the band gap into the middle of the efficiency maximum for photoelectrochemical (PEC) and solar cell applications. Photoactive materials containing Cu₂O, CuO and Cu₂O/CuO have been prepared with high quality and stability in various compositions by an economic, simple and reliable electrodeposition (ED) method. These materials based on copper oxide have been characterized and compared using XRD, SEM, EDX, UV–Vis, PL, FTIR, Raman spectroscopy and electrochemical techniques. Based on the electrochemical production conditions; phase changes of photoactive materials and, at which conditions which phase or phases are present, were evaluated in detail. It was carried out that a full phase change from single-phase Cu₂O to single-phase CuO. The crystal dimensions expand as the cube-shaped Cu₂O transforms into CuO, crystal surface areas increase, crystal shapes change and turn gradually into flower-shaped crystals. Here, the band gap of copper oxide material can be altered within a broad scale by adjusting the element ratios. The semiconductors have been found to have direct band gap that is more preferred for solar energy applications. PEC performances of the copper oxide electrodes containing a different phase structure were determined, and the changes of PEC activities were examined comparatively. Copper oxide semiconductors have p-type conductivity and they act as photocathodes.     

Hydrogen purification for fuel cell using CuO/CeO2-Al2O3 catalyst

CuO/CeO₂, CuO/Al₂O₃ and CuO/CeO₂-Al₂O₃ catalysts, with CuO loading varying from 1 to 5 wt.%, were prepared by the citrate method and applied to the preferential oxidation of carbon monoxide in a reaction medium containing large amounts of hydrogen (PROX-CO). The compounds were characterized ex situ by X-ray diffraction, specific surface area measurements, temperature-programmed reduction and temperature-programmed reduction of oxidized surfaces; XANES-PROX in situ experiments were also carried out to study the copper oxidation state under PROX-CO conditions. These analyses showed that in the reaction medium the Cu⁰ is present as dispersed particles. On the ceria, these metallic particles are smaller and more finely dispersed, resulting in a stronger metal-support interaction than in CuO/Al₂O₃ or CuO/CeO₂-Al₂O₃ catalysts, providing higher PROX-CO activity and better selectivity in the conversion of CO to CO₂ despite the greater BET area presented by samples supported on alumina. It is also shown that the lower CuO content, the higher metal dispersion and consequently the catalytic activity. The redox properties of the ceria support also contributed to catalytic performance.     

CuO-TiO2 nanostructures prepared by chemical and electrochemical methods as photo electrode for hydrogen production

In present study, copper (II) oxide (CuO) nanostructures were separately synthesized via chemical and electrochemical methods. CuO were coated with chemically synthesized titanium dioxide (TiO₂). Morphological and structural properties of CuO and TiO₂ coated CuO (CuO-TiO₂) materials were examined via field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD). FESEM images showed that nanowire like CuO formed at both chemical and electrochemical techniques. TiO₂ nanoparticles were homogenously distributed all over CuO surfaces. XRD pattern revealed CuO has monoclinic crystal structure with metallic Cu. Moreover, rutile TiO₂ crystallized in the tetragonal crystal structure. Electrochemical impedance spectroscopy (EIS) and potentiodynamic (PD) polarization measurements were utilized to study electro catalytic performance of the materials towards hydrogen evolution reaction (HER). The values of both energy consumption, and energy efficiency were determined as 329.43 kJ mol^?1 and 86.0% at ?50 mA cm^?2 current density for HER on electrochemically synthesized CuO-TiO₂ at 25 °C.     

The effect of Copper(II) oxide loading and precursor on the cyclic stability of combined mayenite based materials for calciumcopper looping technology

Combined CO₂ sorbents and O₂ carrier materials have been prepared, characterized and tested over 40 TGA cycles under relevant operating conditions for the CaCu Looping process. Materials were prepared using two different loadings of calcium and copper with a CuO/CaO [wt/wt] of 2, and mayenite (Ca₁₂Al₁₄O₃₃) as support, to produce powders with composition 20/40/40 wt% and 25/50/25 wt% CaO/CuO/Ca₁₂Al₁₄O₃₃. Three different copper precursors, CuO, Cu(OH)₂ and Cu(NO₃)₂·3H₂O were used. Materials were characterized by powder X-ray diffraction (PXD), scanning electron microscopy (SEM), Brunauer–Emmett–Teller surface analysis (BET). Mixed calcium-copper phases, CaCu₂O₃ and Ca₂CuO₃, were found in the calcined materials when Cu(OH)₂ and Cu(NO₃)₂·3H₂O were used as precursors. The mixed phases were not observed after TGA testing and did not hinder the activity of the materials. CO₂ carrying capacity of the synthesized powders was found to be more stable than O₂ carrying capacity. The latter decreased during 40 TGA cycles for all materials with 50 wt% CuO, while it exhibited an enhanced cyclic stability for copper loading of 40 wt%. This behaviour has been assigned to severe copper migration and sintering in the 50 wt% CuO containing material.