Effect of carbonaceous materials on electrochemical properties of nano-sized Fe2O3-loaded carbon as a lithium battery negative electrode

Nano-sized Fe₂O₃-loaded carbon material was prepared by loading Fe₂O₃ on carbon using various carbonaceous materials. Carbonaceous materials strongly affected the electrochemical behavior of nano-sized Fe₂O₃-loaded carbon. Among the carbons used, nano-carbons such as acetylene black (AB), tubular carbon nanofibers (CNF), and platelet CNF provided larger capacities than other carbons. This may be due to the greater surface area of nano-carbon, which gives a greater distribution of nano-sized Fe₂O₃ particles than other carbons and delivers a greater capacity than other carbons. Investigation of the first-cycle materials by X-ray photoelectron spectroscopy (XPS) revealed that Fe₂O₃ was reduced to Fe metal in the charge process (reduction of Fe₂O₃), and, conversely, Fe metal was not completely oxidized to Fe₂O₃ during discharge (oxidation of Fe). This result may be due to the covering of non-conductive Li₂O formed during charging.     

Effect of metal-sulfide additives on electrochemical properties of nano-sized Fe2O3-loaded carbon for Fe/air battery anodes

In the present study, K₂S and Bi₂S₃ were used as additives in electrolytes and electrodes, respectively. The effects of these additives on the electrochemical properties of nano-sized Fe₂O₃-loaded carbon electrodes were investigated using cyclic voltammetry (CV), galvanostatic cycling performance and scanning electron microscopy (SEM), along with electron dispersive spectroscopy (EDS). The results showed that both K₂S and Bi₂S₃ significantly reduced hydrogen evolution and benefited the Fe₂O₃-loaded carbon electrode, such as by retarding passivation and improving the discharge capacity. The effects of metal sulfide additives depended on the carbon used. For Bi₂S₃ additive, all carbons provided larger capacities than acetylene black (AB) while AB gave greater capacity than other carbons when K₂S was used.     

Synthesis of nano-Fe3O4-loaded tubular carbon nanofibers and their application as negative electrodes for Fe/air batteries

Nano-Fe₃O₄-loaded tubular carbon nanofibers (nano-Fe₃O₄/TCNFs) were synthesized by adding TCNFs into the high-temperature solution-phase reactions of iron(III) acetylacetonate with 1,2-hexadecanediol in the presence of oleic acid and oleylamine. The morphology and structure of this material were investigated by transmission electron microscopy (TEM) and X-ray diffraction (XRD) measurements. TEM observation clarified that nano-sized Fe₃O₄ particles with a uniform diameter of several nanometers were distributed and loaded tightly on the TCNF surfaces (inside and outside). After being annealed at 500 °C in Ar gas flow, nano-Fe₃O₄/TCNFs were used as the active material of negative electrodes for Fe/air batteries. Using an alkaline aqueous electrolyte with K₂S additive, a high specific capacity of 786 mAh g⁻¹ and cycling efficiency of 76% at the 30th cycle were obtained. The downsizing of the conductive Fe₃O₄ nano-particles was considered to have contributed to the good electrochemical properties of the material.     

Electrochemical performance of In2O3 thin film electrode in lithium cell

Indium oxide (In₂O₃) coating on Pt, as an electrode of thin film lithium battery was carried out by using cathodic electrochemical synthesis in In₂(SO₄)₃ aqueous solution and subsequently annealing at 400 °C. The coated specimens were characterized by X-ray photoelectron spectroscopy (XPS) for chemical bonding, X-ray diffraction (XRD) for crystal structure, scanning electron microscopy (SEM) for surface morphology, cyclic voltammetry (CV) for electrochemical properties, and charging/discharging test for capacity variations. The In₂O₃ coating film composed of nano-sized particles about 40 nm revealing porous structure was used as the anode of a lithium battery. During discharging, six lithium ions were firstly reacted with In₂O₃ to form Li₂O and In, and finally the Li_4.33In phase was formed between 0.7 and 0.2 V, revealing the finer particles size about 15 nm. The reverse reaction was a removal of Li⁺ from Li_4.33In phase at different oxidative potentials, and the rates of which were controlled by the thermodynamics state initially and diffusion rate finally. Therefore, the total capacity was increased with decreasing current density. However, the cell delivering a stable and reversible capacity of 195 mAh g⁻¹ between 1.2 and 0.2 V at 50 μA cm⁻² may provide a choice of negative electrode applied in thin film lithium batteries.     

Effect of Ag additive on the performance of LiNi1/3Co1/3Mn1/3O2 cathode material for lithium ion battery

The LiNi_1/3Co_1/3Mn_1/3O₂/Ag composite used for cathode material of lithium ion battery was prepared by thermal decomposition of AgNO₃ added to commercial LiNi_1/3Co_1/3Mn_1/3O₂ powders to improve the electrochemical performance of LiNi_1/3Mn_1/3Co_1/3O₂. Structure and morphology analysis showed that Ag particles were dispersed on the surface of LiNi_1/3Co_1/3Mn_1/3O₂ instead of entering the crystal structure. The results of charge–discharge tests showed that Ag additive could improve the cycle performance and high-rate discharge capability of LiNi_1/3Mn_1/3Co_1/3O₂. Extended analysis indicated that Ag was unstable in the commercial electrolyte at high potential. The improved electrochemical performance caused by Ag additive was associated not only with the enhancement of electrical conductivity of the material and the lower polarization of the cell, but also with the increased “c” parameter of LiNi_1/3Mn_1/3Co_1/3O₂ after repeated charge/discharge cycles and the compact and protective SEI layer formed on the surface of LiNi_1/3Mn_1/3Co_1/3O₂.     

Synthesis of LiNi1/3Co1/3Mn1/3O2 as a cathode material for lithium battery by the rheological phase method

LiNi_1/3Co_1/3Mn_1/3O₂ is prepared by a rheological phase method. Homogeneous precursor derived from this method is calcined at 800 °C for 20 h in air, which results in the impressive differences in the morphology properties and electrochemical behaviors of LiNi_1/3Co_1/3Mn_1/3O₂ in contrast to that obtained by a solid-state method. The microscopic structural features of LiNi_1/3Co_1/3Mn_1/3O₂ are investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD). The electrochemical properties of LiNi_1/3Co_1/3Mn_1/3O₂ are carried out by charge–discharge cycling test. All experiments show that the microscopic structural features and the morphology properties are deeply related with the electrochemical performances. The obtained results suggest that the rheological phase method may become an effective route to prepare LiNi_1/3Co_1/3Mn_1/3O₂ cathode materials for lithium battery.     

Mesoporous nano-Co3O4: A potential negative electrode material for alkaline secondary battery

A potential negative electrode material (mesoporous nano-Co₃O₄) is synthesized via a simple thermal decomposition of precursor Co(OH)₂ hexagonal nanosheets in the air. The structure and morphology of the samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It is found that the nano-Co₃O₄ is present in mesoporous hexagonal nanoparticles. The average size of holes is about 5-15 nm. The electrochemical performances of mesoporous nano-Co₃O₄ as the active starting negative electrode material for alkaline secondary battery are investigated by galvanostatic charge-discharge and cyclic voltammetry (CV) technique. The results demonstrate that the prepared mesoporous nano-Co₃O₄ electrode displays excellent electrochemical performance. The discharge capacity of the mesoporous nano-Co₃O₄ electrode can reach 436.5 mAh g⁻¹ and retain about 351.5 mAh g⁻¹ after 100 cycles at discharge current of 100 mA g⁻¹. A properly electrochemical reaction mechanism of mesoporous nano-Co₃O₄ electrode is also constructed in detail.     

Hybrid supercapacitor with nano-TiP2O7 as intercalation electrode

Nano-size (≤100 nm) TiP₂O₇ is prepared by the urea assisted combustion synthesis, at 450 and 900 °C. The compound is characterized by powder X-ray diffraction, Rietveld refinement, high resolution transmission electron microscopy and surface area methods. Lithium cycling properties by way of galvanostatic cycling and cyclic voltammetry (CV) showed a reversible and stable capacity of 60 (±3) mAh g⁻¹ (0.5 mole of Li) up to 100 cycles, when cycled at 15 mA g⁻¹ between 2-3.4 V vs. Li. Non-aqueous hybrid supercapacitor, TiP₂O₇ (as anode) and activated carbon (AC) (as cathode) has been studied by galvanostatic cycling and CV in the range, 0-3 V at 31 mA g⁻¹ and exhibited a specific discharge capacitance of 29 (±1) F g⁻¹stable in the range, 100-500 cycles. The Ragone plot shows a deliverable maximum of 13 Wh kg⁻¹ and 371 W kg⁻¹ energy and power density, respectively.     

Improved separation efficiency of photogenerated carriers for Fe2O3/SrTiO3 heterojunction semiconductor

To investigate the mechanisms of the improvement on separation efficiency of photogenerated carriers, a Fe₂O₃/SrTiO₃ heterojunction semiconductor with an improved separation efficiency was successfully prepared. The heterojunction semiconductor was characterized with X-ray diffraction (XRD), UV–vis absorption spectrum, scanning electron microscope (SEM) and surface photovoltage (SPV) spectroscopy. The energy band diagrams of Fe₂O₃ and SrTiO₃ were determined with X-ray photoelectron spectroscopy (XPS), based on which the conduction band offset (CBO) between Fe₂O₃ and SrTiO₃ was quantified to be 1.26 ± 0.03 eV. The recombination of photogenerated carriers was investigated with photoluminescence (PL) spectrum, which indicates that the formation of Fe₂O₃/SrTiO₃ decreases the recombination. Thus the improved separation efficiency is mainly due to the energy difference between the conduction band edges of Fe₂O₃ and SrTiO₃, and the decreased electron-hole recombination for Fe₂O₃/SrTiO₃.     

Influence of surfactants on Fe2O3 nanostructure photoanode

Fe₂O₃ nanostructures photoanodes were prepared via sol–gel spin-coating method onto fluorine-doped tin oxide glass substrates using six different surfactants: polyethylene glycol (PEG-300), Triton X-100, pluronic F127, cetyltrimethylammonium bromide (CTAB), octadecyltrimethylammonium bromide (OTAB) and tetradecyltrimethylammonium bromide (TTAB). The resulting films have thickness from 520 ± 10 to 980 ± 10 nm after calcinations at 450 °C in the air. A comparative study of photocatalytic activity of thin films was performed. The photo-generated samples were determined by measuring the currents and voltages under illumination of UV–vis light. The highest photocurrent density of 1.77 mA/cm² at 1 V/SCE, under illumination intensity of 100 mW cm⁻² from a solar simulator with a global AM 1.5 filter, were produced by TTAB treated sample. The optical properties, morphology, surface roughness and structure of the films were also characterized by UV–visible spectroscopy, SEM, AFM and XRD. The results are consistent with photocatalytic performance: TTAB treated sample has the highest grain size and optical absorption. The improved performance of this sample can be attributed to the crystallinity process of TTAB, which leads to the larger grain size and highest photocatalytic activity. The study demonstrates that photoelectrochemical performance of metal oxide can be improved by simply changing surfactant. The results highlighted the superior performance of cationic surfactants over non-ionic surfactants in preparing Fe₂O₃ photoanodes by sol–gel method. Moreover, the study showed that decreasing hydrocarbon tail of cationic surfactants can increase the crystallite size and improve photocatalytic activity.     

Morphological, optical and photocatalytic properties of TiO2–Fe2O3 multilayers

Morphological, optical and photocatalytic properties of TiO₂, Fe₂O₃ and TiO₂–Fe₂O₃ samples (formed by 1, 3 and 5 coatings) were studied. The layers were deposited on glass substrate by the sol–gel method. The catalytic activity of the samples was studied by the photodecomposition of methylene blue (MB) under visible light illumination. The FTIR results indicate that all samples present surface OH radicals that are bound either to the Ti or Fe atoms. This effect is better visualized at larger number of coatings in the TiO₂–Fe₂O₃/glass systems. Also, two mechanisms are observed during the photodecomposition of the MB.     

Photoelectrochemical study on charge transfer properties of nanostructured Fe2O3 modified by g-C3N4

Novel photocatalysts, which consist of two visible light responsive semiconductors including graphite-like carbon nitride (g-C₃N₄) and Fe₂O₃, were successfully synthesized via electrodeposition followed by chemical vapor deposition. The morphology of the g-C₃N₄/Fe₂O₃ can be tuned from regular nanosheets to porous cross-linked nanostructures. Remarkably, the optimum activity of the g-C₃N₄/Fe₂O₃ is almost 70 times higher than that of individual Fe₂O₃ for photoelectrochemical water splitting. The enhancement of photoelectrochemical activity could be assigned to the morphology change of the photocatalysts and the effective separation and transfer of photogenerated electrons and holes originated from the intimately contacted interfaces. The g-C₃N₄/Fe₂O₃ composites could be developed as high performance photocatalysts for water splitting and other optoelectric devices.     

Study on photocurrent of bilayers photoanodes using different combination of WO3 and Fe2O3

Bilayer photoanodes were prepared onto glass substrates (FTO) in order to improve generated photocurrents using UV-vis light by water splitting process. A comparative study of photocatalytic was performed over the films surface using Fe₂O_3, WO₃ and mixture of bicomponents (Fe₂O₃:WO₃). Different types of films were prepared using Fe₂O_3, WO₃ and bicomponents (mixture) on FTO substrates. The films were grown by sol gel method with the PEG-300 as the structure-directing agent. The photo-generated of the samples were determined by measuring the currents and voltages under illumination of UV-vis light. The morphology, structure and related composition distribution of the films have been characterized by SEM, XRD and EDX respectively. Photocurrent measurements indicated surface roughness as the effective parameter in this study. The deposited surfaces by bicomponents or mixture are flat without any feature on the surface while the deposited surfaces by WO₃ appears rough surface as small round (egg-shaped particles) and cauliflower-like. The surface deposited by Fe₂O₃ show rough no as well as WO₃ surface. The deposited surfaces by WO₃ reveal the higher value of photocurrent measurement due to surface roughness. Indeed, the roughness can be effective in increasing contact surface area between film and electrolyte and diffuse reflection (light scattering effect). The solution (Fe₂O₃:WO₃) shows the low photocurrent value in compare to WO₃ and Fe₂O₃ hat it may be due to decomposition the compound at 450 ± 1 °C to iron-tungstate Fe₂(WO₄)₃.     

Effects of dopant on the electrochemical performance of Li4Ti5O12 as electrode material for lithium ion batteries

The effects of dopant on the electrochemical properties of spinel-type Li_3.95M_0.15Ti_4.9O₁₂ (M = Al, Ga, Co) and Li_3.9Mg_0.1Al_0.15Ti_4.85O₁₂ were systematically investigated. Charge–discharge cycling were performed at a constant current density of 0.15 mA cm⁻² between the cut-off voltages of 2.3 and 0.5 V, the experimental results showed that Al³⁺ dopant greatly improved the reversible capacity and cycling stability over the pristine Li₄Ti₅O₁₂. The substitution of the Ga³⁺ slightly increased the capacity of the Li₄Ti₅O₁₂, but did not essentially alleviate the degradation of cycling stability. Dopants such as Co³⁺ and Mg²⁺ to some extent worsened the electrochemical performance of the Li₄Ti₅O₁₂.     

Cathodic shift and improved photocurrent performance of cost-effective Fe2O3 photoanodes

We successfully fabricated cost-effective and efficient pulse electrodeposited Fe₂O₃ photoanodes for PEC water splitting application. Surface modifications of Fe₂O₃ by oxygen evolution catalysts like cobalt phosphate (Co–Pi), a monoclinic BiVO₄ or both showed cathodic/anodic shift in photocurrent with significantly improved photo-response.     

Electrochemical evaluation of rutile TiO2 nanoparticles as negative electrode for Li-ion batteries

Nanosized rutile TiO₂ has been prepared by sol–gel chemistry from a glycerol-modified titanium precursor in the presence of an anionic surfactant. The sample has been characterized by X-ray diffraction, nitrogen sorption, scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM) and electrochemical tests. Nanosized rutile TiO₂ has been electrochemically investigated using two potential windows: 1.2–3 V and 1–3 V. It exhibits excellent high rates capabilities and good cycling stability.     

Effect of Al2O3 content on the adsorptive properties of Cu/ZnO/Al2O3 for removal of odorant sulfur compounds

Cu/ZnO/Al₂O₃ adsorbents for removal of odorant sulfur compounds were prepared with various Al/Cu molar ratios by co-precipitation method. The sulfur removing ability as a function of Al/Cu molar ratio of the adsorbents for t-butyl mercaptan (TBM), tetrahydro thiophene (THT), dimethyl disulfide (DMS) and H₂S were investigated at 250 °C and 6000 h⁻¹ space velocity. Based on the results of adsorption capacity and characterization by various techniques, the optimum Al/Cu ratio for maximum sulfur removal capacity is found to be at Al/Cu molar ratio of 0.15 which possesses the well-dispersed Cu species with high reducibility. The adsorption capacity is highest for H₂S followed by TBM, DMS and THT. The main role of Al₂O₃ component is to provide the dispersion of CuO species homogeneously with small particle formation and high reducibility.     

Preparation and photoelectrochemical properties of functional carbon nanotubes and Ti co-doped Fe2O3 thin films

Functional carbon nanotubes (CNTs) were incorporated into Ti-doped Fe₂O₃ thin films by a facile, one-step co-electrodeposition method. The films were characterized by X-ray diffraction, scanning electron microscopy, UV–visible absorption, and X-ray photoelectron spectroscopy. The introduction of CNTs results in a better absorption in visible region and greatly enhances the photoelectrochemical properties of the Ti–Fe₂O₃ films. The improved photoelectrochemical properties of the CNTs and Ti co-doped Fe₂O₃ films are due to the charge equilibration which interplays between the Ti–Fe₂O₃ and CNTs. The effect of CNTs to mediate fast charge transfer and to retard charge recombination rate in the composites is also demonstrated by kinetics analysis and electrochemical impedance spectroscopy. The influence of different groups-modified CNTs and different content of CNTs was also studied. The highest photocurrent is 4.5 mA/cm² at 1.23 V (vs. RHE) obtained by incorporating 0.10 mg/mL amino-group modified CNTs in the Ti–Fe₂O₃ film. The amino-functionalized CNTs doped film exhibits the highest photoelectric response compared with those doped by the pristine and acid-treated CNTs under the same conditions, which can be ascribed to the better hydrophilicity and dispersibility of the amino-functionalized CNTs.     

Effect of protecting metal oxide (Co3O4) layer on electrochemical properties of spinel Li1.1Mn1.9O4 as a cathode material for lithium battery applications

Metal oxide (Co₃O₄) was coated on spinel Li_1.1Mn_1.9O₄ using glutamic acid. Powder X-ray diffraction pattern of Co₃O₄-coated spinel Li_1.1Mn_1.9O₄ showed that the Co₃O₄ coating medium was not incorporated in the spinel bulk structure. Morphology of the Co₃O₄-coated spinel Li_1.1Mn_1.9O₄ was observed by scanning electron microscopy and transmission electron microscopy. The cycling performance of the Co₃O₄-coated spinel Li_1.1Mn_1.9O₄ was obviously improved, compared to the pristine Li_1.1Mn_1.9O₄ at elevated temperature (55 °C). Improvement of rate capability was also achieved at high C-rates.     

Cycle life improvement of ZrO2-coated spherical LiNi1/3Co1/3Mn1/3O2 cathode material for lithium ion batteries

A modified synthesis process was developed based on co-precipitation method followed by spray drying process. In this process, a spherical shaped (Co_1/3Ni_1/3Mn_1/3)(OH)₂ precursor was synthesized by co-precipitation and pre-heated at 500 °C to form a high structural stability spinel (CoNiMn)O₄ to maintain its shape for further processing. The spherical LiNi_1/3Co_1/3Mn_1/3O₂ was then prepared by spray drying process using spherical spinel (CoNiMn)O₄. LiNi_1/3Co_1/3Mn_1/3O₂ powders were then modified by coating their surface with a uniform and nano-sized layer of ZrO₂. The ZrO₂-coated LiNi_1/3Co_1/3Mn_1/3O₂ material exhibited an improved rate capability and cycling stability under a high cut-off voltage of 4.5 V. X-ray diffraction (XRD) measurements revealed that the material had a well-ordered layered structure and Zr was not doped into the LiNi_1/3Co_1/3Mn_1/3O₂. Electrochemical impedance spectroscopy measurements showed that the coated material has stable cell resistance regardless of cycle number. The interrupt charging/discharging test indicated that the ZrO₂ coating can suppress the polarization effects during the charging and discharging process. From these results, it is believed that the improved cycling performance of ZrO₂-coated LiNi_1/3Co_1/3Mn_1/3O₂ is attributed to the ability of ZrO₂ layer in preventing direct contact of the active material with the electrolyte resulting in a decrease of electrolyte decomposition reactions.