Chitosan/polyaniline/MWCNT nanocomposite fibers as an electrode material for electrical double layer capacitors

Polyaniline–MWCNT nanocomposite has successfully been synthesized on the surface of chitosan wet-spun fibers by chemical oxidative polymerization. Morphological characterization of the nanocomposite fibers was performed by scanning electron microscopy (SEM). Electrochemical properties of the nanocomposite fibers as electrode material for electrical double layer capacitors (supercapacitors) in 0.5 M H₂SO₄ were studied by cyclic voltammetry (CV), galvanostatic charge/discharge, and electrochemical impedance spectroscopy (EIS) methods. The results showed that the nanocomposite fibers possess a specific capacitance of 14.48 F cm⁻² and a specific energy of 0.0013 Wh cm⁻² corresponding to a specific power of 0.011 W cm⁻². Total capacitance of the nanocomposite fiber consists of pseudocapacitance produced by the polyaniline and electrical double-layer capacitance produced by fiber|electrolyte interface and chitosan.     

Preparation and performance of thin-layered PdAu/ceramic composite membranes

Preparation of 3–5 μm thick, hydrogen-selective PdAu layers via sequential electroless plating of Pd and Au onto ceramic microfiltration membranes was investigated employing a cyanide-free Au plating bath. The Au deposition rate was strongly dependent on bath temperature and alkalinity reaching an optimum at 333 K and pH 10. Homogenous alloying of the separate metal layers under atmospheric H₂ proved to be a protracted process and required approximately a week at 873 K for a PdAu layer as thin as 3 μm. After 300 h annealing at 823 K the 5 μm thick PdAu layer of a composite membrane still exhibited a Au gradient declining from 7.4 at.% at the top surface to 5.5 at.% at the support interface despite that the H₂ permeation rate had become stable. Nonetheless, the membrane exhibited a very high H₂ permeability of e.g. 1.3 × 10⁻⁸ mol m m⁻² s⁻¹ Pa^−0.5 at 673 K, but it decreased much faster with temperature below 573 K than above, likely due to a change from bulk H diffusion-controlled to H₂ adsorption or desorption-limited transport. The composite membrane withstood cycling between 523 and 723 K in H₂ well showing that differing thermal expansion of the joined metallic and ceramic materials stayed within the tolerance range up to 723 K.     

Identification of oxygen reduction processes at (La,Sr)MnO3 electrode/La9.5Si6O26.25 apatite electrolyte interface of solid oxide fuel cells

Oxygen reduction reaction of (La,Sr)MnO₃ (LSM) cathode on La_9.5Si₆O_26.25 apatite (LSO) electrolyte is studied over the temperature range 750–900 °C and the oxygen partial pressure range 0.01–1 atm by electrochemical impedance spectroscopy. The impedance responses show two separable arcs and are analyzed in terms of two different equivalent circuits with comparable information on the electrode processes at high and low frequencies. The electrode process associated with the high frequency arc (σ₁) is basically independent of oxygen partial pressure. The activation energy of σ₁ is 188 ± 15 kJ mol⁻¹ for the O₂ reduction reaction on the LSM electrode sintered at 1150 °C, and decreases to 120 kJ mol⁻¹ for the O₂ reduction reaction on the LSM electrode sintered at 850 °C, which is close to 80–110 kJ mol⁻¹ observed for the same electrode process at LSM/YSZ interface. The reaction order with respect to PO₂$P_{{\text{O}}_2}$ and the activation energy of the electrode process associated with low frequency arc (σ₂) are generally close to that of σ₂ at the LSM/YSZ interface. The activation process of the cathodic polarization treatment is noticeably slower for the reaction at LSM/LSO interface as compared to that at LSM/YSZ interface. The impedance responses of O₂ reduction reaction at the LSM/LSO interface are significantly higher than that at the LSM/YSZ interface due to the silicon spreading. The impedance responses decrease with the decrease of the sintering temperature of LSM electrode on LSO electrolyte. At the sintering temperature of 1000 °C, the impedance responses of O₂ reduction reaction is 1.74 Ω cm² at 900 °C, which is significantly smaller than that of LSM electrode sintered at 1150 °C.     

Electrochemical characterization of Pr2CuO4 cathode for IT-SOFC

The electrochemical properties of Pr₂CuO₄ (PCO) electrode screen-printed on Ce_0.9Gd_0.1O_1.95 (CGO) electrolyte were investigated. PCO was synthesized by a solid-state route from the stoichiometric mixture of oxides at 1273 K, 20 h. Thermogravimetric analysis (TGA) of PCO both in air and Ar demonstrated its stability up to 1173 K. X-ray powder diffraction study of the PCO–CGO mixture annealed in air at 1173 K for 100 h did not reveal chemical interaction between materials. The oxygen reduction on porous PCO electrodes applied on CGO electrolyte was studied in a symmetrical cell configuration by AC impedance spectroscopy at OCV conditions at 773–1173 K and pO₂$p_{{\text{O}}_2}$ = 10⁻⁴–1 atm. Analysis of the data revealed that depending on temperature and oxygen partial pressure different rate-determining steps of the overall oxygen reduction reaction take place. Calculated value of area specific resistance (ASR) of PCO electrode is 1.7 ± 0.2 Ω cm² at 973 K in air and it is constant after 6 subsequent thermocycles. We have found that oxygen reduction on PCO applied on CGO takes mainly place at the triple-phase boundary (TPB) since Adler–Lane–Steele (ALS) model is not valid. Therefore electrochemical characteristics of PCO electrode can be improved by further optimization of both microstructure of the electrode and electrode/electrolyte interface and PCO can be considered as a promising cathode material for intermediate temperature solid oxide fuel cells (IT-SOFC).     

Photovoltaic properties of SnCl2Pc films and SnCl2Pc/pentacene heterostructures

The optical and photovoltaic properties of dichlorotin phthalocyanine (SnCl₂Pc) films and SnCl₂Pc/pentacene (Pn) heterostructures (HS) have been studied. Weak bands at 1.35, 1.52 and 2.05 eV have been found in absorption and modulated photoreflectance spectra of SnCl₂Pc films. These bands can be caused by the formation of charge transfer states. The low concentration of recombination centers of charge carriers has been formed on a free surface of SnCl₂Pc films. This concentration essentially decreases at air evacuation before vacuum deposition of a Pn layer. Therefore, interface with an insignificant recombination rate of charge carriers is formed for SnCl₂Pc/Pn HS.     

In-situ constructing cobalt incorporated nitrogen-doped carbon/CdS heterojunction with efficient interfacial charge transfer for photocatalytic hydrogen evolution

Designing an efficient heterojunction interface is an effective way to promote the electrons' transfer and improve the photocatalytic H₂ evolution performance. In this work, a novel hollow hybrid system of Co@NC/CdS has been fabricated and constructed. CdS nanospheres are anchored on the hollow-structured cobalt incorporated nitrogen-doped carbon (Co@NC) through a one-pot in-situ chemical deposition approach, forming an intimate interface and establishing an excellent channel to improve the electrons transfer and charge carriers separation between CdS and Co@NC cocatalyst, which immensely promotes the photocatalytic activity. The rate of photocatalytic H₂ evolution over hollow structured Co@NC/CdS heterojunction can be achieved 8.2 mmol g^?1 h^?1, which is about 45 times of pristine CdS nanospheres. The photocatalytic H₂ evolution mechanism has been investigated by the techniques of photoluminescence (PL) spectra, photocurrent-time (i-t) curves, electrochemical impedance spectroscopy (EIS) etc. This work aims to provide a new way in developing of high-performance advanced 3D heterojunction for photocatalytic hydrogen evolution.     

Heavily neodymium doped ceria as an effective barrier layer in solid oxide electrochemical cells

10 mol% gadolinium doped ceria (GDC10) is widely used as a barrier layer between oxygen electrode and electrolyte to prevent interfacial reactions. A 50 mol% neodymium doped ceria (NDC50) barrier layer has been proposed and studied in this paper. Symmetrical cells with NDC50 and GDC10 barrier layers, Nd₂NiO_4+δ(NNO)–Ce_0.5Nd_0.5O_2-δ(NDC50) electrode, and YSZ electrolyte have been systematically studied using impedance spectroscopy (EIS) at various temperatures and oxygen partial pressure (pO₂). The NDC50 barrier layer has significantly decreased polarization resistance across a wide temperature and pO₂ range compared to the GDC10 barrier layer. The rare earth C-type structure of the NDC50 barrier layer causes barrier free migration of oxygen ions resulting in improved ionic conductivity compared to GDC10. Distribution of relaxation time (DRT) modeling has been used to obtain insights into the electrode processes.     

Impedance spectroscopy studies of Gd-CeO2-(LiNa)CO3 nano composite electrolytes for low temperature SOFC applications

Electrical properties of 20 mol % Gd doped CeO₂ with varying amounts of (LiNa)CO₃ have been investigated by employing AC-impedance spectroscopic technique. The impedance spectra show a high frequency depressed arc, represents the bulk composite and low frequency incomplete semicircle representing electrode contribution. The bulk resistance of the composites decreases with increasing carbonate content up to 30 wt% (LiNa)CO_3, thereafter the resistance increases, whereas all the compositions show a decrease in resistance with increasing temperature. The typical nature of the impedance spectra of the composite shows the possibility of coexistence of multi ionic transport or existence of space charge effect at the interface of Gd-CeO₂ and carbonate phase. The composite containing 25 wt% (LiNa)CO₃ shows the highest ionic conductivity of 0.1757 S cm⁻¹ at 550 °C and lowest activation energy of 0.127 eV in the temperature range 550-800 °C. A symmetric cell is fabricated with GDC-25 wt% (LiNa)CO₃ electrolyte, NiO-GDC(LiNa)CO₃ anode and lithiated NiO-GDC(LiNa)CO₃ cathode. Pure H₂ and air are used as fuel and oxidant. The cell delivers a maximum power density of 45 mW/cm², 58 mW/cm² and 92 mW/cm² at 450, 500 and 550 °C, respectively.     

Functional LSM-ScSZ/NiO-ScSZ dual-layer hollow fibres for partial oxidation of methane

In this study, a functional La_0.80Sr_0.20MnO_3−δ (LSM)-Scandia-Stabilized-Zirconia (ScSZ)/NiO-ScSZ dual-layer hollow fibre has been developed using a single-step co-extrusion and co-sintering process, and has been employed as a dual-layer hollow fibre membrane reactor for partial oxidation of methane. Oxygen permeation rate between 0.49 and 1.82 ml/min and methane conversion between 53.55% and 98.78% have been achieved when operating temperature is elevated from 920 to 1060 °C, together with a significant reduction in coke-deposition. Oxygen permeation through the outer LSM-ScSZ permeation layer (approximately 109.2 μm in thickness) is found to be the controlling step to methane conversion at the operating temperature below 990 °C, above which the excessive oxygen permeation results in formation of CO₂ and H₂O as by-products. The experimental results further suggest that the amount of NiO in the inner NiO-ScSZ layer should be optimised based on the factors such as catalytic activity/stability, porosity and mechanical strength in addition to the sintering behaviour which has to be matched to the outer LSM-ScSZ layer.     

Gelled composite electrolyte comprising thermoplastic polyurethane and poly(ethylene oxide) for lithium batteries

Composite polymer electrolyte films consisting of poly(ethylene glycol) based thermoplastic polyurethane blended with poly(ethylene oxide) (denoted as TPU(PEG)/PEO) incorporating LiClO₄–PC have been prepared and their electrochemical properties were studied. The thermal analysis of the composite films were performed to demonstrate the miscibility of the polymer blend by using differential scanning calorimeter (DSC). TPU(PEG)/PEO based polymer electrolyte shows ionic conductivity of the order 6.4×10⁻⁴ S/cm at room temperature, irrespective of time evolution. Cyclic voltammogram shows that this composite electrolyte has good electrochemical stability in the working voltage ranging from 2 to 4.5 V. Cycling performances of Li/polymer electrolyte/LiCoO₂ cells are also followed. From AC impedance results, the recharging ability of the cells is proved to be dominated by the passive layer formation at Li electrode–polymer electrolyte interface.     

X-ray diffractometric study of in situ oxidation of Ni in Li/K and Li/Na carbonate eutectic

The formation of NiO, particularly the lithiation process, in molten carbonate at 923 K under oxidizing condition has been investigated by open circuit potential (OCP), AC impedance, and X-ray diffraction (XRD) measurements. Thin film electrodes of Ni were exposed to the Li/K and Li/Na carbonate eutectic and subjected to in situ oxidation. Quantification of lithium in the lithiated NiO with XRD revealed that the lithiation reaction continues even after the electrode potential reached the oxygen electrode potential. Lithium content, x in Li_xNi_1-xO, of the sample immersed in molten carbonate reached 0.041 and 0.033 in Li/K and Li/Na melt, respectively after 200 h of immersion. Difference observed in OCP decay and electrode impedance at 1 kHz for Ni oxidation in the Li/K and Li/Na carbonate has been also interpreted based on XRD data.     

Characterisation of CdCl2 treated electrodeposited CdS/CdTe thin film solar cell

An over 10% efficient electrodeposited CdS/CdTe solar cell has been prepared after CdCl₂ treatment. The open circuit voltage, V_oc, short-circuit current, J_sc and fill factor, FF were 758 mV, 21 mA cm⁻² and 0.65 respectively. The diode factor calculated from current-voltage-temperature measurements changed from 1.54 at 324 K to 2.64 at 146 K. The voltage factor, α ranged from 22.83 at 324 K to 29.46 at 146 K. Data from current-voltage-temperature measurements agrees with the model of Miller and Olsen and indicates that the current transport was a combination of tunneling and interface recombination. Capacitance-voltage-temperature measurements showed that capacitance decreased with increasing frequency and increased with temperature. Capacitance was insensitive to temperature indicating an intrinsic or low-doped depletion layer. The density of interface states was found to be 6.4 × 10¹⁰ cm⁻² eV⁻¹ at 293 K. The carrier concentration of CdTe calculated from Mott-Schottky plot was 1.5 × 10¹⁶ cm⁻³.     

Electrochemical characterization of La0.6Ca0.4Fe0.8Ni0.2O3 cathode on Ce0.8Gd0.2O1.9 electrolyte for IT-SOFC

For Solid Oxide Fuel Cells (SOFCs) to become an economically attractive energy conversion technology, suitable materials and structures which enable operation at lower temperatures, while retaining high cell performance, must be developed. Recently, the perovskite-type La_0.6Ca_0.4Fe_0.8Ni_0.2O₃ oxide has shown potential as an intermediate temperature SOFC cathode. An equivalent circuit describing the cathode polarization resistances was constructed from analyzing impedance spectra recorded at different temperatures in oxygen. A competitive electrode polarization resistance is reported for this oxygen electrode using a Ce_0.8Gd_0.2O_1.9 electrolyte, determined by impedance spectroscopy studies of symmetrical cells sintered at 800 °C and 1000 °C. Scanning electron microscopy (SEM) studies of the symmetrical cells revealed the absence of any reaction layer between cathode and electrolyte, and a porous electrode microstructure even when sintered at a temperature of only 800 °C. The performance of this cathode shows favorable oxygen reduction reaction (ORR) properties potentially making it an excellent choice for IT-SOFC application.     

Electrochemical characterization of electrodes in the electrochemical Bunsen reaction of the sulfur–iodine cycle

In the electrochemical Bunsen reaction, SO₂ is oxidized to H₂SO₄ at the anode while I₂ is reduced to HI at the cathode. Both electrodes were electrochemically characterized using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The effects of H₂SO₄ concentration in the anolyte, as well as HI concentration and I₂/HI molar ratio in the catholyte, were explored. The cyclic voltammograms of platinum electrode shift with rising scan rate, indicating the irreversibility of two electrode reactions. The equivalent circuit for the cathode reaction impedance consists of an ohmic resistance of the solution, in series with a parallel combination of a charge transfer resistor and a constant phase element, yet the impedance spectra for the anode reaction can be modeled using a parallel combination of a charge transfer resistor and a constant phase element. The electrode reaction kinetics was also analyzed using the exchange current density (j₀) and the standard reaction rate constant (k⁰). The results indicate that a high electrode reaction rate in the cell can be obtained for a HI concentration of 8 mol/kg_H2O and an I₂/HI molar ratio of 0.5 in the catholyte and a H₂SO₄ concentration of 13 mol/kg_H2O in the anolyte.     

Effects of a YSZ porous layer between electrolyte and oxygen electrode in solid oxide electrolysis cells on the electrochemical performance and stability

The delamination of (La,Sr)MnO₃ (LSM) oxygen electrode is considered as a key reason for the degradation of solid oxide electrolysis cells (SOEC). In this study, a YSZ porous layer prepared by spinning coating has been introduced to inhibit significant degradation of LSM oxygen electrode during anodic polarization for 100 h under constant 500 mA cm⁻². Impedance spectra of LSM oxygen electrode are recorded before and after anodic polarization. By performing distribution of relaxation time (DRT) processing on the impedance spectra, it is indicated that the introduction of YSZ porous layer provides more active sites or three phase boundary (TPB) for oxygen oxidation reaction. The potential relaxation process of LSM oxygen electrode is measured by three-sequence chronopotentiometry. The result proves that the sample with a YSZ porous layer has lower the oxygen activity and faster the oxygen ion diffusion at the solid-solid two-phase (oxygen electrode and electrolyte) interface (SSTPI) due to more TPB and shorter oxygen ion diffusion paths.     

Study of the multipeak deuterium thermodesorption in YFe2Dx (1.3 ≤ x ≤ 4.2) by DSC,TD and in situ neutron diffraction

The deuterium thermal desorption of various YFe₂D_x (x = 1.3, 2.5, 3.5, 4.2) compounds has been studied using differential scanning calorimetry (DSC) and thermal desorption (TD) experiments. These studies show that the number of desorption peaks increases with the deuterium content. In order to understand the origin of this multipeak behaviour, in situ neutron diffraction experiments during thermal desorption have been performed from 290 K to 680 K on YFe₂D_4.2. Upon heating, a multipeak TD spectrum is observed. It relates to the existence of several YFe₂D_x phases with different stabilities. The rate limiting step of this thermal desorption has been therefore attributed to several successive phase transformations rather than to different types of interstitial sites as proposed in previous TD models reported for C15-Laves phase compounds.     

High performance intermediate temperature micro-tubular SOFCs with Ba0.9Co0.7Fe0.2Nb0.1O3−δ as cathode

In this study, anode supported intermediate temperature micro-tubular solid oxide fuel cells (MT-SOFCs) have been fabricated by combination of phase-inversion, dip-coating, co-sintering and printing method. The MT-SOFC consists of a ∼300 μm wall-thickness Ni–Sc₂O₃ stabilized ZrO₂ (ScSZ) anode tube, ∼10 μm ScSZ dense electrolyte layer, ∼10 μm Ce_0.9Gd_0.1O_2−δ (GDC) membrane buffer layer and ∼50 μm Ba_0.9Co_0.7Fe_0.2Nb_0.1O_3−δ (BCFN) cathode layer. SEM and electrochemical impedance spectroscopy (EIS) analysis suggested that the novel structured anode can remarkably diminish the porous anode geometrical tortuosity and improve the fuel gas diffusivity. High peak power densities of 0.34, 0.51 and 0.72 W cm⁻² have been achieved with humidified hydrogen as the fuel and ambient air as oxidant at 550, 600 and 650 °C, respectively. Further, the cell has demonstrated a very stable performance with no significant cell voltage degradation under a constant current of 0.6 A cm⁻² for over 213 h test at 650 °C.     

Hydrogen absorption and desorption kinetics of MgH2 catalyzed by MoS2 and MoO2

The catalytic effect of MoS₂ and MoO₂ on the hydrogen absorption/desorption kinetics of MgH₂ has been investigated. It is shown that MoS₂ has a superior catalytic effect over MoO₂ on improving the hydrogen kinetic properties of MgH₂. DTA results indicated that the desorption temperature decreased from 662.10 K of the pure MgH₂ to 650.07 K of the MgH₂ with MoO₂ and 640.34 K of that with MoS₂. Based on the Kissinger plot, the activation energy of the hydrogen desorption process is estimated to be 101.34 ± 4.32 kJ mol⁻¹ of the MgH₂ with MoO₂ and 87.19 ± 4.48 kJ mol⁻¹ of that with MoS₂, indicating that the dehydriding process energy barrier of MgH₂ can be reduced. The enhancement of the hydriding/dehydriding kinetics of MgH₂ is attributed to the presence of MgS and Mo or MgO and Mo which catalyze the hydrogen absorption/desorption behavior of MgH₂. The detailed comparisons between MoS₂ and MoO₂ suggest that S anion has superior properties than O anion on catalyzing the hydriding/dehydriding kinetics of MgH₂.     

Facile preparation of BiVO4/FeVO4 heterostructure for efficient water-splitting applications

In this paper, a BiVO₄/FeVO₄ heterostructure photoanode was synthesized by electrospray technique, and its photoelectrochemical water oxidation performance was investigated. The maximum photocurrent density of 0.4 mA cm⁻² at 1.23 V_RHE was 6 times higher than that of pristine BiVO₄ films (0.06 mA cm⁻²). Through the analysis of the electrochemical impedance spectroscopy (EIS) results, the improvement of photoelectrochemical performance could be attributed to the formation of heterostructure at the two-phase interface, which led to the effective separation of electron-hole pairs. This work offers a new effective strategy to construct semiconductor nanocomposites for efficient photoelectrochemical water oxidation.     

Evaluation of nafion based double layer capacitors by electrochemical impedance spectroscopy

In this work some electrochemical characteristics of all solid double layer capacitors prepared by high surface carbon and Nafion polymer electrolyte are reported. Carbon composite electrodes with a Nafion loading of 30 wt.% were prepared and evaluated. Nafion 115 membrane, recast Nafion membrane and 1 M H₂SO₄ solution in a matrix of glass fiber have been used as electrolyte, in the double layer capacitors. The different double layer capacitors (DLCs) have been evaluated by electrochemical impedance spectroscopy. The capacitor with a recast Nafion electrolyte exhibits a proton conductivity of about 3×10⁻² S cm⁻¹ at ambient temperature, that is higher of that reported for solid electrolytes (10⁻³ to 10⁻⁴ S cm⁻¹) in the current literature on capacitors. A maximum of specific capacitance of 13 F/g of active materials (carbon+Nafion) corresponding to 52 F/g for a single electrode measured in a three-electrode arrangement has been achieved with the capacitor with recast Nafion. The capacitance of the capacitor with recast Nafion electrolyte, evaluated in low-frequency region below 10 mHz, was practically equivalent at that with sulphuric acid electrolyte. The interpretation of the characteristics of the microporous structure of carbon material of the electrodes by impedance analysis is also discussed.