The study of Au/MoS2 anode catalyst for solid oxide fuel cell (SOFC) using H2S-containing syngas fuel

Au/MoS₂ is a promising anode catalyst for conversion of all components of H₂S-containing syngas in solid oxide fuel cell (SOFC). MoS₂-supported nano-Au particles have catalytic activity for conversion of CO when syngas is used as fuel in SOFC systems, thus preventing poisoning of MoS₂ active sites by CO. In contrast to use of MoS₂ as anode catalyst, performance of Au/MoS₂ anode catalyst improves when CO is present in the feed. Current density over 600 mA cm⁻² and maximum power density over 70 mW cm⁻² were obtained at 900 °C, showing that Au/MoS₂ could be potentially used as sulfur-tolerant catalyst in fuel cell applications.     

Effects of roasting temperature and modification on properties of Li2FeSiO4/C cathode

Li₂FeSiO₄/C cathodes were synthesized by combination of wet-process method and solid-state reaction at high temperature, and effects of roasting temperature and modification on properties of the Li₂FeSiO₄/C cathode were investigated. The XRD patterns of the Li₂FeSiO₄/C samples indicate that all the samples are of good crystallinity, and a little Fe₃O₄ impurity was observed in them. The primary particle size rises as the roasting temperature increases from 600 to 750 °C. The Li₂FeSiO₄/C sample synthesized at 650 °C has good electrochemical performances with an initial discharge capacity of 144.9 mAh g⁻¹ and the discharge capacity remains 136.5 mAh g⁻¹ after 10 cycles. The performance of Li₂FeSiO₄/C cathode is further improved by modification of Ni substitution. The Li₂Fe_0.9Ni_0.1SiO₄/C composite cathode has an initial discharge capacity of 160.1 mAh g⁻¹, and the discharge capacity remains 153.9 mAh g⁻¹ after 10 cycles. The diffusion coefficient of lithium in Li₂FeSiO₄/C is 1.38 × 10⁻¹² cm² s⁻¹ while that in Li₂Fe_0.9Ni_0.1SiO₄/C reaches 3.34 × 10⁻¹² cm² s⁻¹.     

Structural and electrochemical properties of Cl-doped LiFePO4/C

Cl-doped LiFePO₄/C cathode materials were synthesized through a carbothermal reduction route, and the microstructure and electrochemical performances were systematically studied. Cl-doped LiFePO₄/C cathode materials presented a high discharge capacity of ∼90 mAh g⁻¹ at the rate of 20 C (3400 mA g⁻¹) at room temperature. Electrochemical impedance spectroscopy and cyclic voltamperometry indicated the optimized electrochemical reaction and Li⁺ diffusion in the bulk of LiFePO₄ due to Cl-doping. The improved Li⁺ diffusion capability is attributed to the microstructure modification of LiFePO₄ via Cl-doping.     

A novel method for synthesis of layered LiNi1/3Mn1/3Co1/3O2 as cathode material for lithium-ion battery

The layered LiNi_1/3Mn_1/3Co_1/3O₂ materials with good crystalline are synthesized by a novel method of hydrothermal method followed by a short calcination process. The crystalline structure and morphology of the synthesized materials are characterized by XRD, SEM. Their electrochemical performances are evaluated by CV, EIS and galvonostatic charge/discharge tests. The material synthesized at 850 °C for 6 h shows the highest initial discharge capacity of 187.7 mAh g⁻¹ at 20 mA g⁻¹. And the capacity retention of 97.9% is maintained at the end of 40 cycles at 1.0 C. CV test reveals almost no shift of anodic and cathodic peaks after first cycle, which indicates good reversible deintercalation and intercalation of Li⁺ ions.     

Preparation of manganese oxide with high density by decomposition of MnCO3 and its application to synthesis of LiMn2O4

Manganese oxide with high tap density was prepared by decomposition of spherical manganese carbonate, and then LiMn₂O₄ cathode materials were synthesized by solid-state reaction between the manganese oxide and lithium carbonate. Structure and properties of the samples were determined by X-ray diffraction, Brunauer–Emmer–Teller surface area analysis, scanning electron microscope and electrochemical measurements. With increase of the decomposition temperature from 350 °C to 900 °C, the tap density of the manganese oxide rises from 0.91 g cm⁻³ to 2.06 g cm⁻³. Compared with the LiMn₂O₄ cathode made from chemical manganese dioxide or electrolytic manganese dioxide, the LiMn₂O₄ made from manganese oxide of this work has a larger tap density (2.53 g cm⁻³), and better electrochemical performances with an initial discharge capacity of 117 mAh g⁻¹, a capacity retention of 93.5% at the 15th cycle and an irreversible capacity loss of 2.24% after storage at room temperature for 28 days.     

Electrochemical properties of LiFePO4 prepared via hydrothermal route

LiFePO₄ as a cathode material for rechargeable lithium batteries was prepared by hydrothermal process at 170 °C under inert atmosphere. The starting materials were LiOH, FeSO₄, and (NH₄)₂HPO₄. The particle size of the obtained LiFePO₄ was 0.5 μm. The electrochemical properties of LiFePO₄ were characterized in a mixed solvent of ethylene carbonate and diethyl carbonate (1:1 in volume) containing 1.0 mol dm⁻³ LiClO₄. The hydrothermally synthesized LiFePO₄ exhibited a discharge capacity of 130 mA h g⁻¹, which was smaller than theoretical capacity (170 mA h g⁻¹). The annealing of LiFePO₄ at 400 °C in argon atmosphere was effective in increasing the discharge capacity. The discharge capacity of the annealed LiFePO₄ was 150 mA h g⁻¹.     

Nafion/SiO2 hybrid membrane for vanadium redox flow battery

Sol–gel derived Nafion/SiO₂ hybrid membrane is prepared and employed as the separator for vanadium redox flow battery (VRB) to evaluate the vanadium ions permeability and cell performance. Nafion/SiO₂ hybrid membrane shows nearly the same ion exchange capacity (IEC) and proton conductivity as pristine Nafion 117 membrane. ICP-AES analysis reveals that Nafion/SiO₂ hybrid membrane exhibits dramatically lower vanadium ions permeability compared with Nafion membrane. The VRB with Nafion/SiO₂ hybrid membrane presents a higher coulombic and energy efficiencies over the entire range of current densities (10–80 mA cm⁻²), especially at relative lower current densities (<30 mA cm⁻²), and a lower self-discharge rate compared with the Nafion system. The performance of VRB with Nafion/SiO₂ hybrid membrane can be maintained after more than 100 cycles at a charge–discharge current density of 60 mA cm⁻². The experimental results suggest that the Nafion/SiO₂ hybrid membrane approach is a promising strategy to overcome the vanadium ions crossover in VRB.     

La1−xSrxCoO3 (x = 0.1-0.5) as the cathode catalyst for a direct borohydride fuel cell

Direct borohydride fuel cells (DBFCs), with a series of perovskite-type oxides La_1−xSr_xCoO₃ (x = 0.1-0.5) as the cathode catalysts and a hydrogen storage alloy as the anode catalyst, are studied in this paper. The structures of the perovskite-type catalysts are mainly La_1−xSr_xCoO₃ (_x = 0.1-0.5) oxides phases. However, with the increase of strontium content, the intensities of the X-ray diffraction peaks of the impure phases La₂Sr₂O₅ and SrLaCoO₄ are gradually enhanced. Without using any precious metals or expensive ion exchange membranes, a maximum current density of 275 mA cm⁻² and a power density of 109 mW cm⁻² are obtained with the Sr content of x = 0.2 at 60 °C for this novel type of fuel cell.     

Ni sulfide/Ti50Ni50 electrode with the superelasticity

Ni sulfides layers were formed on the surface of a Ti₅₀Ni₅₀ alloy by reacting sulfur with a Ni film deposited on the alloy, and then microstructures, transformation behavior, shape memory characteristics, superelasticity and electrochemical properties were investigated. When a Ni film deposited on a Ti₅₀Ni₅₀ alloy was annealed under the sulfur pressure of 100 kPa at 623 K, sulfides layers consisted of NiS and NiS₂ were formed. When annealing was made at 648 K with annealing time less than 0.9 ks, sulfides layers with a mixture of NiS and NiS₂ were formed, while only NiS₂ was formed when it was made for 1.8 ks. When annealing was made at 673 K with annealing time longer than 0.9 ks, only NiS₂ was formed. With raising annealing temperature and prolong annealing time, NiS changed into NiS₂ accompanied with a morphological change from a particulate-like to a dense film-like. A Ti₅₀Ni₅₀ alloy with surface NiS₂ layer showed the two-stage B2–R–B19′ transformation behavior, the shape memory effect and a partial superelasticity with a superelastic recovery ratio of 78%. NiS₂ cathode showed a clear discharge behavior with multivoltage plateaus induced by intermediate reaction products; NiS and Ni₃S₂. The initial discharge capacity was 743 mA h g⁻¹ corresponding to 85% of theoretical capacity and 65% of capacity duration is obtained at 20th discharge.     

High-rate performance of all-solid-state lithium secondary batteries using Li4Ti5O12 electrode

The all-solid-state Li–In/Li₄Ti₅O₁₂ cell using the 80Li₂S·20P₂S₅ (mol%) solid electrolyte was assembled to investigate rate performances. It was difficult to obtain the stable performance at the charge current density of 3.8 mA cm⁻² in the all-solid-state cell. In order to improve the rate performance, the pulverized Li₄Ti₅O₁₂ particles were applied to the all-solid-state cell, which retained the reversible capacity of about 90 mAh g⁻¹ at 3.8 mA cm⁻². The 70Li₂S·27P₂S₅·3P₂O₅ glass–ceramic, which exhibits the higher lithium ion conductivity than the 80Li₂S·20P₂S₅ solid electrolyte, was also used. The Li–In/70Li₂S·27P₂S₅·3P₂O₅ glass–ceramic/pulverized Li₄Ti₅O₁₂ cell was charged at a current density higher than 3.8 mA cm⁻² and showed the reversible capacity of about 30 mAh g⁻¹ even at 10 mA cm⁻² at room temperature.     

Improved high temperature performance of La0.8Sr0.2MnO3 cathode by addition of CeO2

Ceria is proposed as an additive for La_0.8Sr_0.2MnO₃ (LSM) cathodes in order to increase both their thermal stability and electrochemical properties after co-sintering with an yttria-stabilized zirconia (YSZ) electrolyte at 1350 °C. Results show that LSM without CeO₂ addition is unstable at 1350 °C, whereas the thermal stability of LSM is drastically improved after addition of CeO₂. In addition, results show a correlation between CeO₂ addition and the maximum power density obtained in 300 μm thick electrolyte-supported single cells in which the anode and modified cathode have been co-sintered at 1350 °C. Single cells with cathodes not containing CeO₂ produce only 7 mW cm⁻² at 800 °C, whereas the power density increases to 117 mW cm⁻² for a CeO₂ addition of 12 mol%. Preliminary results suggest that CeO₂ could increase the power density by at least two mechanisms: (1) incorporation of cerium into the LSM crystal structure, and (2) by modification or reduction of La₂Zr₂O₇ formation at high temperature. This approach permits the highest LSM-YSZ co-sintering temperature so far reported, providing power densities of hundreds of mW cm⁻² without the need for a buffer layer between the LSM cathode and YSZ electrolyte. Therefore, this method simplifies the co-sintering of SOFC cells at high temperature and improves their electrochemical performance.     

Electrochemical supercapacitor behavior of Ni3(Fe(CN)6)2(H2O) nanoparticles

Nanosized Ni₃(Fe(CN)₆)₂(H₂O) was prepared by a simple co-precipitation method. The electrochemical properties of the sample as the electrode material for supercapacitor were studied by cyclic voltammetry (CV), constant charge/discharge tests and electrochemical impedance spectroscopy (EIS). A specific capacitance of 574.7 F g⁻¹ was obtained at the current density of 0.2 A g⁻¹ in the potential range from 0.3 V to 0.6 V in 1 M KNO₃ electrolyte. Approximately 87.46% of specific discharge capacitance was remained at the current density of 1.4 A g⁻¹ after 1000 cycles.     

Improved high-rate charge/discharge performances of LiFePO4/C via V-doping

V-doped LiFePO₄/C cathode materials were prepared through a carbothermal reduction route. The microstructure was characterized by X-ray diffraction, X-ray photoelectron spectroscopy and scanning electron microscopy. The electrochemical Li⁺ intercalation performances of V-doped LiFePO₄/C were compared with those of undoped one through galvanostatic intermittent titration technique, cyclic voltamperometry, and electrochemical impedance spectrum. V-doped LiFePO₄/C showed a high discharge capacity of ∼70 mAh g⁻¹ at the rate of 20 C (3400 mA g⁻¹) at room temperature. The significantly improved high-rate charge/discharge capacity is attributed to the increase of Li⁺ ion “effective” diffusion capability.     

Electrochemical capacitance of NiO/Ru0.35V0.65O2 asymmetric electrochemical capacitor

A designed asymmetric hybrid electrochemical capacitor was presented where NiO and Ru_0.35V_0.65O₂ as the positive and negative electrode, respectively, both stored charge through reversible faradic pseudocapacitive reactions of the anions (OH⁻) with electroactive materials. And the two electrodes had been individually tested in 1 M KOH aqueous electrolyte to define the adequate balance of the active materials in the hybrid system as well as the working voltage of the capacitor based on them. The electrochemical tests demonstrated that the maximum specific capacitance and energy density of the asymmetric hybrid electrochemical capacitor were 102.6 F g⁻¹ and 41.2 Wh kg⁻¹, respectively, delivered at a current density of 7.5 A cm⁻². And the specific energy density decreased to 23.0 Wh kg⁻¹ when the specific power density increased up to 1416.7 W kg⁻¹. The hybrid electrochemical capacitor also exhibited a good electrochemical stability with 83.5% of the initial capacitance over consecutive 1500 cycle numbers.     

Morphology and electrochemical performance of Li[Ni1/3Co1/3Mn1/3]O2 cathode material by a slurry spray drying method

The spherical Li[Ni_1/3Co_1/3Mn_1/3]O₂ powders with appropriate porosity, small particle size and good particle size distribution were successfully prepared by a slurry spray drying method. The Li[Ni_1/3Co_1/3Mn_1/3]O₂ powders were characterized by XRD, SEM, ICP, BET, EIS and galvanostatic charge/discharge testing. The material calcined at 950 °C had the best electrochemical performance. Its initial discharge capacity was 188.9 mAh g⁻¹ at the discharge rate of 0.2 C (32 mA g⁻¹), and retained 91.4% of the capacity on going from 0.2 to 4 C rate. From the EIS result, it was found that the favorable electrochemical performance of the Li[Ni_1/3Co_1/3Mn_1/3]O₂ cathode material was primarily attributed to the particular morphology formed by the spray drying process which was favorable for the charge transfer during the deintercalation and intercalation cycling.     

Effect of nano-silica filler in polymer electrolyte on Li dendrite formation in Li/poly(ethylene oxide)-Li(CF3SO2)2N/Li

Lithium dendrite growth in Li/poly(ethylene oxide) (PEO)-Li(CF₃SO₂)₂N (LiTFSI)-nano-SiO₂/Li was examined using direct in situ observation under galvanostatic conditions at 60 °C. Both the onset time of dendrite formation and the short-circuit time of the cells were extended by the addition of nano-SiO₂ filler into the polymer electrolyte, of which an acid-modified nano-SiO₂ filler was the most effective. The onset time was dependent on the current density in the range from 0.1 to 1.0 mA cm⁻². Li dendrite growth in Li/PEO₁₈LiTFSI/Li at 60 °C for current densities of 0.1 and 0.5 mA cm⁻² started at 125 and 15 h, respectively. PEO₁₈ LiTFSI with addition of 10 wt% acid-modified 50 nm SiO₂ showed extended dendrite formation onset times of 250 h at 0.1 mA cm⁻² and 32 h at 0.5 mA cm⁻². The suppression of dendrite formation at the Li/PEO₁₈ LiTFSI interface could be explained by enhancement of the conductivity and suppression of the interface resistance between lithium and the polymer electrolyte by addition of the nano-SiO₂ filler. The electrical conductivity of 4.1 × 10⁻⁴ S cm⁻¹ and interface resistance of 405 Ω cm² for PEO₁₈ LiTFSI at 60 °C were respectively increased to 7.2 × 10⁻⁴ S cm⁻¹ and decreased to 77 Ω cm² by the addition of 10 wt% acid-modified nano-SiO₂.     

Effect of synthesis temperature on the properties of LiFePO4/C composites prepared by carbothermal reduction

LiFePO₄/C composite cathode materials were synthesized by carbothermal reduction method using inexpensive FePO₄ as raw materials and glucose as conductive additive and reducing agent. The precursor of LiFePO₄/C was characterized by differential thermal analysis and thermogravimetry. The microstructure and morphology of the samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM) and particle size analysis. Cyclic voltammetry (CV) and charge/discharge cycling performance were used to characterize their electrochemical properties. The results showed that the LiFePO₄/C composite synthesized at 650 °C for 9 h exhibited the most homogeneous particle size distribution. Residual carbon during processing was coated on LiFePO₄, resulting in the enhancement of the material's electronic properties. Electrochemical measurements showed that the discharge capacity first increased and then decreased with the increase of synthesis temperature. The optimal sample synthesized at 650 °C for 9 h exhibited a highest initial discharge capacity of 151.2 mA h g⁻¹ at 0.2 C rate and 144.1 mA h g⁻¹ at 1 C rate with satisfactory capacity retention rate.     

A new low-temperature synthesis and electrochemical properties of LiV3O8 hydrate as cathode material for lithium-ion batteries

LiV₃O₈, synthesized from V₂O₅ and LiOH, by heating of a suspension of V₂O₅ in a LiOH solution at a low-temperature (100-200 °C), exhibits a high discharge capacity and excellent cyclic stability at a high current density as a cathode material of lithium-ion battery. The charge-discharge curve shows a maximum discharge capacity of 228.6 mAh g⁻¹ at a current density of 150 mA g⁻¹ (0.5 C rate) and the 100 cycles discharge capacity remains 215 mAh g⁻¹. X-ray diffraction indicates the low degree of crystallinity and expanding of inter-plane distance of the LiV₃O₈ phase, and scanning electronic microscopy reveals the formation of nano-domain structures in the products, which account for the enhanced electrochemical performance. In contrast, the LiV₃O₈ phase formed at a higher temperature (300 °C) consists of well-developed crystal phases, and coherently, results in a distinct reduction of discharge capacity with cycle numbers. Thus, an enhanced electrochemical performance has been achieved for LiV₃O₈ by the soft chemical method via a low-temperature heating process.     

Preparation and electrochemical properties of Li[Ni1/3Co1/3Mn1−x/3Zrx/3]O2 cathode materials for Li-ion batteries

Layer-structured Zr doped Li[Ni_1/3Co_1/3Mn_1−x/3Zr_x/3]O₂ (0 ≤ x ≤ 0.05) were synthesized via slurry spray drying method. The powders were characterized by XRD, SEM and galvanostatic charge/discharge tests. The products remained single-phase within the range of 0 ≤ x ≤ 0.03. The charge and discharge cycling of the cells showed that Zr doping enhanced cycle life compared to the bare one, while did not cause the reduction of the discharge capacity of Li[Ni_1/3Co_1/3Mn_1/3]O₂. The unchanged peak shape in the differential capacity versus voltage curve suggested that the Zr had the effect to stabilize the structure during cycling. More interestingly, the rate capability was greatly improved. The sample with x = 0.01 presented a capacity of 160.2 mAh g⁻¹ at current density of 640 mA g⁻¹(4 C), corresponding to 92.4% of its capacity at 32 mA g⁻¹(0.2 C). The favorable performance of the doped sample could be attributed to its increased lattice parameter.     

Improvement of the high rate capability of hierarchical structured Li4Ti5O12 induced by the pseudocapacitive effect

Hierarchical structured Li₄Ti₅O₁₂, assembling from randomly oriented nanosheets with a thickness of about 10-16 nm, is fabricated by a facile hydrothermal route and following calcination. It is demonstrated that the as-prepared sample has good cycle stability and excellent high rate performance. In particular, the discharge capacity of 128 mAh g⁻¹ can be obtained at the high current density of 2000 mA g⁻¹, which is about 87% of that at the low current density of 200 mA g⁻¹ upon cycling, indicating that the as-prepared sample can endure great changes of various discharge current densities to retain a good stability. In addition, the pseudocapacitive effect based on the hierarchical structure, also contributes to the high rate capability of Li₄Ti₅O₁₂, which can be confirmed in cyclic voltammograms.