Enhanced sinterability of BaZr0.1Ce0.7Y0.1Yb0.1O3−δ by addition of nickel oxide

The effect of nickel oxide addition on the sintering behavior and electrical properties of BaZr_0.1Ce_0.7Y_0.1Yb_0.1O_3−δ (BZCYYb) as an electrolyte for solid oxide fuel cells was systematically studied. Results suggest that the addition of a small amount (∼1 wt%) of NiO to BZCYYb greatly promoted densification, achieving ∼96% of the theoretical density after sintering at 1350 °C in air for 3 h (reducing the sintering temperature by ∼200 °C). Further, a sample sintered at 1450 °C for 3 h showed high open circuit voltages (OCVs) when used as the electrolyte membrane to separate the two electrodes under typical SOFC operating conditions, indicating that the electrical conductivity of the electrical conductivity of the BZCYYb was not adversely affected by the addition of ∼1 wt% NiO.     

Partial conductivities of mixed conducting BaCe0.65Zr0.2Y0.15O3–δ

The electrical properties of BaCe_0.65Zr_0.2Y_0.15O_3–δ (BCZY) were studied as a function of both oxygen partial pressure and water vapor partial pressure in the temperature range of 500–800 °C, and the partial conductivities of protons, holes, and oxygen vacancies were calculated from the defect model. P-type conduction was dominant in an oxidative atmosphere. In a wet atmosphere, BCZY was a mixed conductor of protons, holes, and oxygen ions. A conduction transition from protons to holes and/or oxygen ions was found with increasing temperature. The calculated activation energy of oxygen ion transport was 0.71 eV. The standard solution enthalpy for water dissolution was best fitted with a slope of −120.19 kJ/mol, which is somewhat smaller in absolute terms than that of BaCe_0.9Y_0.1O_3–δ and of BaCe_0.8Y_0.2O_3–δ. This result also agrees well with the literature reports that the Ba, rather than Sr, occupation of A-site and the Ce, rather than Zr, occupation of B-site in perovskite proton conductors induce more negative hydration enthalpies due to the increasing basicity of the corresponding oxides.     

Catalytic effect of MgFe2O4 on the hydrogen storage properties of Na3AlH6–LiBH4 composite system

The effect of MgFe₂O₄ on the hydrogen storage properties of the composite Na₃AlH₆4LiBH₄ was studied for the first time, where it was found that MgFe₂O₄ addition decreased the onset desorption temperature of Na₃AlH₆4LiBH₄. Hydrogen (～9.5 wt%) was released in three stages and the dehydrogenation temperatures were reduced to 80 °C, 350 °C, and 430 °C for the first, second, and third stage, respectively. The absorption kinetics of Na₃AlH₆4LiBH₄ was also significantly improved due to the catalytic effect of MgFe₂O₄. Using Kissinger analysis, the apparent activation energies of decomposition of the Li₃AlH₆ and NaBH₄ stages in Na₃AlH₆4LiBH₄-10 wt% MgFe₂O₄ were calculated to be 72 and 141 kJ/mol, respectively. These values were considerably lower than the corresponding values for the undoped composite. X-ray diffraction analysis revealed the formation of new products such as MgO and Fe during the heating process. Our results suggest that MgFe₂O₄ enhanced the hydrogen storage properties of Na₃AlH₆4LiBH₄ through the formation of active species, such as MgO and Fe.     

CO2 reforming of CH4 by combination of cold plasma jet and Ni/γ-Al2O3 catalyst

CO₂ reforming of CH₄ to synthesis gas was investigated by cold plasma jet (CPJ) only and combination of cold plasma jet with Ni/γ-Al₂O₃ catalyst at atmospheric pressure. The higher selectivity of H₂ and CO, and higher energy efficiency was obtained by this novel process. The optimum experimental conditions are: CH₄ = 3.33 Nl/min, CO₂ = 5.00 Nl/min, N₂ = 8.33 Nl/min, and the input power at 770 W. The results showed that, for the plasma only, the conversions of CH₄ and CO₂ were 46% and 34%, the selectivities of CO and H₂ were 85% and 78%, the energy efficiency was 2.9 mmol/kJ, respectively; for the combination of cold plasma jet with Ni/γ-Al₂O₃ catalyst, the conversions of CH₄ and CO₂ were increased by 14% and 6%, the yield of H₂ and CO increased by 18% and 11%, the energy efficiency reached at 3.7 mmol/kJ, respectively. And the catalyst hasn't accessorial heating. The CPJ method has the advantage of simple processing and is easy to be industrialized.     

On the hydration of grain boundaries and bulk of proton conducting BaZr0.7Pr0.2Y0.1O3-δ

We report here for the first time bulk and grain boundary conductivities from impedance spectra of a ceramic proton conductor (BaZr_0.7Pr_0.2Y_0.1O_3-δ) taken during hydration and H/D isotope exchange transients (at 400 °C). The results suggest that water moves quickly along grain boundary cores, and then interact from there with the space charge layers and, in turn, grain interiors. Hydration and H/D isotope exchange have simple monotonic effects on the bulk conductivity in line with what is expected from it being dominated by protons. The transients for grain boundary conductivity exhibit however hysteresis: During hydration, the core charge and grain boundary resistance appear to go through transient minima related to non-equilibrium distributions of defects between the core and grain interior – notably because protons diffuse faster than oxygen vacancies between the grain boundary and grain interior. At equilibrium, hydration increases the core charge and the depletion of positive charge carriers in the space charge layers. During H/D isotope exchange relatively fast hysteretic transients indicate that the space charge layers experience changes in charge carrier (D⁺ vs. H⁺) mobility as well as in D₂O vs. H₂O hydration thermodynamics.     

Investigation of electrospun Ba0.5Sr0.5Co0.8Fe0.2O3−δ-Gd0.1Ce0.9O1.95 cathodes for enhanced interfacial adhesion

Fibrous Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3?δ-Gd_0.1Ce_0.9O_1.95 (BSCF-GDC) composite cathodes are fabricated by a facile electrospinning method. However, the electropun BSCF-GDC cathode shows poor adhesion to a GDC electrolyte because of the high shrinkage rate of the electrospun BSCF-GDC cathode during sintering. To solve this adhesion issue, mixed BSCF fiber-GDC powder cathode is investigated. As a result, mixed BSCF fiber-GDC powder cathode with an enhanced adhesion is successfully fabricated. This improvement can be attributed to the modified microstructure with the GDC powder that joins the BSCF fibers to the GDC electrolyte at the cathode and electrolyte interface. The polarization resistance of the mixed BSCF fiber-GDC powder cathode is 0.10 Ω cm², which is lower than 0.13 Ω cm² of conventional BSCF-GDC powder cathode at 700 °C. It is attributable to the improved oxygen gas and lattice oxygen diffusion, and the surface exchange of the mixed BSCF fiber-GDC powder cathode. The single cell with a mixed BSCF fiber-GDC powder cathode show 500 mW cm^?2 at 700 °C, which is 25% higher than conventional BSCF-GDC powder cathode.     

Effects of Y2O3-modification to Ni/γ-Al2O3 catalysts on autothermal reforming of methane with CO2 to syngas

The effects of Y₂O₃-modification to Ni/γ-Al₂O₃ catalysts on autothermal reforming of methane to syngas were investigated. It was found that the introduction of Y₂O₃ (5%, 8%, 10%) lead to significant improvement in catalytic activity and stability, and the H₂/CO ratio could be adjusted via controlling the O₂/CO₂ ratio of the feed gas. According to the characterization results of catalysts before and after reaction, it was found that the Y₂O₃·γ-Al₂O₃ supported Ni catalysts had higher NiO reducibility, smaller Ni particle size, higher Ni dispersion and stronger basicity than those of the Ni/γ-Al₂O₃ catalysts. The analysis of catalysts after reaction showed that the addition of Y₂O₃ inhibited the Ni sintering, changed the type of coke and decreased the amount of coke on the catalysts. All the experimental results indicated that the introduction of Y₂O₃ to Ni/γ-Al₂O₃ resulted in excellent catalytic performances in autothermal reforming of methane, and Y₂O₃ played important roles in preventing metal sintering and coke deposition via controlling NiO reducibility, Ni particle size and dispersion, and basicity of catalysts.     

Performance stability of impregnated La0.6Sr0.4Co0.2Fe0.8O3−δ–Y2O3 stabilized ZrO2 cathodes of intermediate temperature solid oxide fuel cells

The stability of La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ impregnated Y₂O₃ stabilized ZrO₂ (LSCF–YSZ) cathodes was investigated under the condition of open circuit or current polarization at 750 °C in air. The electrochemical measurement and the microstructure characteristic show that the flattening of LSCF particles has great contribution to the increase of resistance of LSCF–YSZ cathodes after 500 h heat treatment at 750 °C. Microstructure coarsening and the damage of well-connected porous structure are main reasons of the performance degradation for LSCF–YSZ cathodes testing at 200 mA cm⁻² and 750 °C in air. Higher current density of 500 mA cm⁻² applying on cathodes accelerates degradation processes. X-ray photoelectron spectroscopy (XPS) shows that Sr concentration on the cathode surface decreases after current polarization, which plays a main role in performance activation processes observed at the beginning stage. The enhancement of cobalt activity in LSCF lattice by current polarization increases the conductivity and decreases the stability of LSCF–YSZ cathodes.     

Improved hydrogen storage performance of MgH2–NaAlH4 composite by addition of TiF3

In a previous paper, it was demonstrated that a MgH₂–NaAlH₄ composite system had improved dehydrogenation performance compared with as-milled pure NaAlH₄ and pure MgH₂ alone. The purpose of the present study was to investigate the hydrogen storage properties of the MgH₂–NaAlH₄ composite in the presence of TiF₃. 10 wt.% TiF₃ was added to the MgH₂–NaAlH₄ mixture, and its catalytic effects were investigated. The reaction mechanism and the hydrogen storage properties were studied by X-ray diffraction, thermogravimetric analysis, differential scanning calorimetry (DSC), temperature-programmed-desorption and isothermal sorption measurements. The DSC results show that MgH₂–NaAlH₄ composite milled with 10 wt.% TiF₃ had lower dehydrogenation temperatures, by 100, 73, 30, and 25 °C, respectively, for each step in the four-step dehydrogenation process compared to the neat MgH₂–NaAlH₄ composite. Kinetic desorption results show that the MgH₂–NaAlH₄–TiF₃ composite released about 2.4 wt.% hydrogen within 10 min at 300 °C, while the neat MgH₂–NaAlH₄ sample only released less than 1.0 wt.% hydrogen under the same conditions. From the Kissinger plot, the apparent activation energy, E_A, for the decomposition of MgH₂, NaMgH₃, and NaH in the MgH₂–NaAlH₄–TiF₃ composite was reduced to 71, 104, and 124 kJ/mol, respectively, compared with 148, 142, and 138 kJ/mol in the neat MgH₂–NaAlH₄ composite. The high catalytic activity of TiF₃ is associated with in situ formation of a microcrystalline intermetallic Ti–Al phase from TiF₃ and NaAlH₄ during ball milling or the dehydrogenation process. Once formed, the Ti–Al phase acts as a real catalyst in the MgH₂–NaAlH₄–TiF₃ composite system.     

Structure and electrochemical characteristics of Ti0.10Zr0.15V0.35Cr0.10Ni0.30–LaNi4Al0.4Mn0.3Co0.3 composite hydrogen storage alloy

Structure and electrochemical characteristics of Ti_0.10Zr_0.15V_0.35Cr_0.10Ni_0.30 (matrix alloy) — 1 mass% LaNi₄Al_0.4Mn_0.3Co_0.3 composite hydrogen storage alloy have been investigated systematically. The main phase of composite alloy is composed of V-based solid solution phase with a BCC structure and C14 Laves phase with hexagonal structure, while secondary phase which has a composition close to Zr (Ti, V, Ni, Cr, Al, Co, La)_1.8 also exists in the composite alloy. The real maximum discharge capacity of the composite alloy electrode is 354.9 mAh g⁻¹, and distinct synergetic effect appears during composite process. Comparing with the matrix alloy, the thermodynamic performances, electrochemical characteristics, dynamic performances for the composite alloy electrode have been improved. The secondary phase is probably responsible for the improvement of electrochemical characteristics of the matrix alloy.     

Electrical conductivity of cobalt doped La0.8Sr0.2Ga0.8Mg0.2O3−δ

La_0.8Sr_0.2Ga_0.8Mg_0.2O_3−δ (LSGM8282), La_0.8Sr_0.2Ga_0.8Mg_0.15Co_0.05O_3−δ (LSGMC5) and La_0.8Sr_0.2Ga_0.8Mg_0.115Co_0.085O_3−δ (LSGMC8.5) were prepared using a conventional solid-state reaction. Electrical conductivities and electronic conductivities of the samples were measured using four-probe impedance spectrometry, four-probe dc polarization and Hebb–Wagner polarization within the temperature range of 973–1173 K. The electrical conductivities in LSGMC5 and LSGMC8.5 increased with decreasing oxygen partial pressures especially in the high (>10⁻⁵ atm) and low oxygen partial pressure regions (<10⁻¹⁵ atm). However, the electrical conductivity in LSGM8282 had no dependency on the oxygen partial pressure. At temperatures higher than 1073 K, PO₂$P_{{\text{O}}_2}$ dependencies of the free electron conductivities in LSGM8282, LSGMC5 and LSGMC8.5 were about −1/4, and PO₂$P_{{\text{O}}_2}$ dependencies of the electron hole conductivities were about 0.25, 0.12 and 0.07, respectively. Oxygen ion conductivities in LSGMC5 and LSGMC8.5 increased with decreasing oxygen partial pressures especially in the high and low oxygen partial pressure regions, which was due to the increase in the concentration of oxygen vacancies. The change in the concentration of oxygen vacancies and the valence of cobalt with oxygen partial pressure were determined using a thermo-gravimetric technique. Both the electronic conductivity and oxygen ion conductivity in cobalt doped lanthanum gallate samples increased with increasing concentration of cobalt, suggesting that the concentration of cobalt should be optimized carefully to maintain a high electrical conductivity and close to 1 oxygen ion transference number.     

Microstructural characterization and electrochemical properties of Ba0.5Sr0.5Co0.8Fe0.2O3−δ and its application for anode of SOEC

Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCF) was synthesized successfully by a novel citric acid–nitrate combustion method and employed as the anode of solid oxide electrolysis cells (SOEC) for hydrogen production for the first time in this paper. The crystal structure, chemical composition and electrochemical properties of BSCF were investigated in detail. The results showed that BSCF is in good stoichiometry of Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−σ formation. ASR of BSCF/YSZ is only 0.077 Ω cm² at 850 °C, remarkably lower than the commonly used oxygen materials LSM as well as the current focus materials LSC and LSCF. Also, BSCF electrode exhibited much better performance than LSM under both SOEC and SOFC operating modes. The hydrogen production rate of BSCF/YSZ/Ni-YSZ can be up to 147.2 mL cm⁻² h⁻¹, about three times higher than that of LSM/YSZ/Ni-YSZ, which indicates that BSCF could be a very promising candidate for the practical application of SOEC technology.     

Effects of bi-layer La0.6Sr0.4Co0.2Fe0.8O3−δ-based cathodes on characteristics of intermediate temperature solid oxide fuel cells

In this study, anode-supported planar IT-SOFCs, with a thin Sm_0.2Ce_0.8O_2−δ (SDC) electrolyte film and a bi-layer cathode, are fabricated using tape-casting and screen-printing processes. The bi-layer cathode consists of a current collector La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ (LSCF) layer and a functional LSCF-SDC composite layer in various thicknesses. Microstructure studies reveal that the interfaces among various layers show good adhesion, except for Cell A equipped with a cathode of pure LSCF. Cell A reports the lowest ohmic (R₀) and polarization (R_P) resistances. R_P, which increases with the thickness of the LSCF-SDC composite layer in the cathode, rises rapidly as the temperature drops, particularly at temperatures ≤550 °C. This indicates the high electrical conductivity of the cathode as a major contribution to the decrease of R_P at 500 °C. The best cell performances are observed at 650 °C for all cases, in which Cell A shows a maximum power density of 1.51 W cm⁻² and an open circuit voltage of 0.80 V. Considering both of the electrical and the mechanical integrity of the single cell, insertion of the composite layer is required to guarantee a good adhesion of cathode layer to electrolyte layer. However, the thickness of the composite layer should be retained as thin as possible to minimize the R₀ and R_P and maximize the cell performance.     

Effect of La–Mg-based alloy addition on structure and electrochemical characteristics of Ti0.10 Zr0.15V0.35Cr0.10Ni0.30 hydrogen storage alloy

Effect of La–Mg-based alloy (AB₅) addition on Structure and electrochemical characteristics of Ti_0.10Zr_0.15V_0.35Cr_0.10Ni_0.30 hydrogen storage alloy has been investigated systematically. XRD shows that the matrix phase structure is not changed after adding AB₅ alloy, however, the amount of the secondary phase increases with increasing AB₅ alloy content. The electrochemical measurements show that the plateau pressure Ti_0.10Zr_0.15V_0.35Cr_0.10Ni_0.30 + x% La_0.85Mg_0.25Ni_4.5Co_0.35Al_0.15 (x = 0, 1, 5, 10, 20) hydrogen storage alloys increase with increasing x, and the width of the pressure plateau first increases when x increases from 0 to 5 and then decreases as x increases further, and the maximum discharge capacity changes in the same trend. The activation performance, the low temperature dischargeabilities, high-rate dischargeability and cyclic stability of composite alloy electrodes increase greatly with increasing x. The improvement of the electrochemical characteristics caused by adding AB₅ alloy seems to be related to formation of the secondary phase.     

Effect of RuO2–CoS2 anode nanostructured on performance of H2S electrolytic splitting system

An innovative, nanostructured composite, anode electrocatalyst, material has been developed for the electrolytic splitting of (100%) H₂S feed content gas operating at 135 kPa and 150 °C. A new class of anode electrocatalyst with general composition, RuO₂–CoS₂ has shown great stability and desired properties at typical operating conditions. This configuration showed stable electrochemical operation over the period of 24 h and also exhibited a maximum current density of (0.019 A/cm²). The kinetic behaviors of various anode-based electrocatalysts demonstrated that, exchange current density, which is a direct measure of the electrochemical reaction, increased with RuO₂–CoS₂-based anodes. Moreover, high levels of feed utilization were possible using these materials. Electrochemical performance, current density, and sulfur tolerance were enhanced compared to the other tested anode configurations. The structural, microstructural and surface behavior of RuO₂–CoS₂ anode electrocatalyst was investigated in detail.     

Effects of B addition on the hydrogen absorption–desorption property of Ti0.32Cr0.43V0.25 alloy

The effects of boron addition on the hydrogen absorption–desorption properties of the _{Ti0.32Cr0.43V0.25}${\mathrm{Ti}}_{0.32}{\mathrm{Cr}}_{0.43}{\mathrm{V}}_{0.25}$ alloy were studied. Boron was added either directly or indirectly through a mother alloy _Ti0.75B0.25${\mathrm{Ti}}_{0.75}{\mathrm{B}}_{0.25}$. Direct boron addition caused the decrease in the titanium content of the BCC matrix through formation of Ti–B phases, resulting in the decrease in the lattice constant. Conversely, mother alloy addition increased the titanium content and the lattice constant of the matrix, for it contained enough titanium to contribute to the matrix even after forming the second phase TiB. Such lattice constant changes caused by boron addition resulted in drastic changes in hydrogen plateau pressure and great decrease in effective hydrogen storage capacity.     

Steam reforming of ethanol over Co3O4–Fe2O3 mixed oxides

Co₃O₄, Fe₂O₃ and a mixture of the two oxides Co–Fe (molar ratio of Co₃O₄/Fe₂O₃ = 0.67 and atomic ratio of Co/Fe = 1) were prepared by the calcination of cobalt oxalate and/or iron oxalate salts at 500 °C for 2 h in static air using water as a solvent/dispersing agent. The catalysts were studied in the steam reforming of ethanol to investigate the effect of the partial substitution of Co₃O₄ with Fe₂O₃ on the catalytic behaviour. The reforming activity over Fe₂O₃, while initially high, underwent fast deactivation. In comparison, over the Co–Fe catalyst both the H₂ yield and stability were higher than that found over the pure Co₃O₄ or Fe₂O₃ catalysts. DRIFTS-MS studies under the reaction feed highlighted that the Co–Fe catalyst had increased amounts of adsorbed OH/water; similar to Fe₂O₃. Increasing the amount of reactive species (water/OH species) adsorbed on the Co–Fe catalyst surface is proposed to facilitate the steam reforming reaction rather than decomposition reactions reducing by-product formation and providing a higher H₂ yield.     

Development of La0.6Sr0.4Co0.2Fe0.8O3−δ cathode with an improved stability via La0.8Sr0.2MnO3-film impregnation

Uniform, dense and continuous coatings of La_0.8Sr_0.2MnO_3−δ (LSM) have been successfully deposited on dense/porous La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ (LSCF) substrates via a one-step drop-coating process using a water-based solution in order to improve the operating stability of solid oxide fuel cell cathode. The processing conditions were optimized by precise control of the composition of infiltrating solution, including chelating agents (glycine, citric acid and ethylene glycol), surfactants (polyvinyl alcohol (PVA), polyethylene glycol (PEG) and polyvinyl pyrrolidone (PVP)) and pH values (5.25, 4.29, 3.01 and 2.09). Ethanol was found to improve the wetting ability of the water-based solution significantly, but unfortunately causing precipitation. The symmetrical and full cells tests demonstrated that both performance and stability of LSCF cathode can be enhanced by surface modification with an optimized LSM film coating, leading to ∼31% reduction in cathodic polarization resistance and ∼45% improvement in power density (without observable degradation) for almost 350 h operation at 750 °C under a constant voltage of 0.7 V.     

Electrochemical performance of La0.9Sr0.1Co0.8Ni0.2O3−δ-Ce0.8Sm0.2O1.9 composite cathode for solid oxide fuel cells

The mixed ionic and electronic conductors (MIEC) of La_0.9Sr_0.1Co_0.8Ni_0.2O_3−δ (LSCN)-Ce_0.8Sm_0.2O_1.9 (SDC) were investigated for potential application as a cathode material for solid oxide fuel cells (SOFCs) based on a SDC electrolyte. Electrochemical impedance spectroscopy (EIS) technique was performed over the temperature range of 600-850 °C to determine the cathode polarization resistance, which is represented by area specific resistance (ASR). This study systematically investigated the exchange current densities (i₀) for oxygen reduction reaction (ORR), determined from the EIS data and high-field cyclic voltammetry. The 70LSCN-30SDC composite cathode revealed a high exchange current density (i₀) value of 297.6 mA/cm² at 800 °C determined by high-field technique. This suggested that the triple phase boundary (TPB) may spread over more surface of this composite cathode and revealing a high catalytically active surface area. The activation energies (E_a) of ORR determined from the slope of Arrhenius plots for EIS and high-field techniques are 96.9 kJ mol⁻¹ and 90.4 kJ mol⁻¹, respectively.     

Characterization of nanosized Ce0.8Sm0.2O1.9-infiltrated Sm0.5Sr0.5Co0.8Cu0.2O3−δ cathodes for solid oxide fuel cells

This study investigates the microstructure and electrochemical properties of Sm_0.5Sr_0.5Co_0.8Cu_0.2O_3−δ (SSC-Cu) cathode infiltrated with Ce_0.8Sm_0.2O_1.9 (SDC). The newly formed nanosized electrolyte material on the cathode surface, leading the increase in electrochemical performances is mainly attributed to the creation of electrolyte/cathode phase boundaries, which considerably increases the electrochemical sites for oxygen reduction reaction. Based on the experiment results, the 0.4 M SDC infiltration reveals the lowest cathode polarization resistance (R_P), the cathode polarization resistances (R_p) are 0.117, 0.033, and 0.011 Ω cm² at 650, 750, and 850 °C, and the highest peak power density, are 439, 659, and 532 mW cm⁻² at 600, 700, and 800 °C, respectively. The cathode performance in SOFCs can be significantly improved by infiltrating nanoparticles of SDC into an SSC-Cu porous backbone. This study reveals that the infiltration approach may apply in SOFCs to improve their electrochemical properties.