Electrochemical reforming of CH4−CO2 mixed gas using porous Gd-doped ceria electrolyte with Cu electrode

This paper reports on the composition and flow rate of outlet gas and current density during the reforming of CH₄ with CO₂ using three different electrochemical cells: cell A, with Ni−GDC (Gd-doped ceria: Ce_0.8Gd_0.2O_1.9) cathode/porous GDC electrolyte/Cu−GDC anode, cell B, with Cu−GDC cathode/ porous GDC electrolyte/Cu−GDC anode and cell C, with Ru−GDC cathode/ porous GDC electrolyte/ Cu−GDC anode. In the cathode, CO₂ reacts with supplied electrons to form CO fuel and O²⁻ ions (CO₂+2e⁻→CO+O²⁻). Too low affinity of Cu cathode to CO₂ in cell B reduced the reactivity of the CO₂ with electrons. The CO fuel, O²⁻ ions and CH₄ gas were transported to the anode through the porous GDC mixed conductor of O²⁻ ions and electrons. In the anode, CH₄ reacts with O²⁻ ions to produce CO and H₂ fuels (CH₄+O²⁻→2 H₂+CO+2e⁻). The reforming efficiency at 700−800 °C was lowest in cell B and highest in cell A. The Cu anode in cells A and C worked well to oxidize CH₄ with O²⁻ ions (2Cu+O²⁻→Cu₂O+2e⁻, Cu₂O+CH₄→2Cu+CO+2H₂). However, a blockage of the outlet gas occurred in all the cells at 700−800 °C. The gas flow is inhibited due to a reduction in pore size in the cermet cathode, as well as sintering and grain growth of Cu metal in the anode during the reforming.     

Improving CO2/CH4 adsorptive selectivity of carbon nanotubes by functionalization with nitrogen-containing groups

Multi-walled carbon nanotubes containing oxygenated groups (O-MWCNTs) have been functionalized with ammonia to improve the adsorption capacity and selectivity of CO₂/CH₄ in gas adsorption process. The effects of oxygen and nitrogen containing functional groups (e.g. hydroxyl and amine), on CO₂ and CH₄ adsorption were studied. The ideal adsorption capacities of MWCNTs were determined using volumetric method at ambient temperature and moderate pressures (from 0.1 to 3.0 MPa). The MWCNTs containing nitrogen groups (N-MWCNTs) showed much higher adsorption capacity of CO₂ and selectivity of CO₂/CH₄ against the O-MWCNTs at different pressures. The highest selectivity was observed at lower pressures at 298 K for the N-MWCNTs. The dynamic adsorption experiments were carried out with a feed containing one to fivefold of CO₂ to CH₄ in a packed bed of N-MWCNTs at 298 K and atmospheric pressure. The breakthrough curves and breakthrough times of CO₂ and CH₄ were determined for the mixed gases. The results indicated high efficiency of the prepared N-MWCNTs in dynamic separation of CO₂ and CH₄.     

Enhancement of H2 and CH4 adsorptivities of single wall carbon nanotubes produced by mixed acid treatment

Single wall carbon nanotubes (SWCNTs) were treated with a HNO₃/H₂SO₄ mixed solution to increase the number of narrow micropores. The mixed acid treatment increased the micropore volume from 0.13 to 0.35 mL g⁻¹ as measured by N₂ adsorption at 77 K. The micropore volume evaluated with CO₂ adsorption at 273 K increased from 0.06 to 0.27 mL g⁻¹. This remarkable micropore volume increase was ascribed to the formation of a highly packed and ordered SWCNT assembly with the acid treatment, which was confirmed by field emission scanning electron microscopy. The adsorption amount of supercritical H₂ at 77 K under 5 MPa pressure increased twofold as a result of the acid treatment, while the supercritical CH₄ adsorption amount at 303 K and 5 MPa pressure increased by 40%. These remarkable increases were caused by increased amount of narrow micropores as a result of the acid treatment.     

Preparation of a highly microporous carbon from a carpet material and its application as CO2 sorbent

In order to increase the use of carpet wastes (pre- and/or post-consumer wastes), this work studies for the first time the preparation and characterisation of a microporous material from a commercial carpet (pile fiber content: 80% wool/20% nylon; primary and secondary backings: woven polypropylene; binder: polyethylene) and its application for CO₂ capture. The porous material was prepared from an entire carpet material using a standard chemical activation with KOH and then, characterised in terms of their porous structure and surface functional groups. Adsorption of CO₂ was studied using a thermogravimetric analyser at several temperatures (25-100 °C) and under different CO₂ partial pressures (i.e. pure CO₂ flow and a ternary mixture of 15% CO₂, 5% O₂ and 80% N₂). In order to examine the adsorbent regenerability, multiple CO₂ adsorption/desorption cycles were also carried out. The surface area and micropore volume of the porous adsorbent were found to be 1910.17 m² g^− 1 and 0.85 cm³ g^− 1, respectively. The CO₂ adsorption profiles illustrate that the maximum CO₂ capture on the sample was reached in less than 10 min. CO₂ adsorption capacities up to 8.41 wt.% and 3.37 wt.% were achieved at 25 and 70 °C, respectively. Thermal swing regeneration studies showed that the prepared adsorbent has good cyclic regeneration capacities.     

Synthesis of spinel LiMn2O4 with manganese carbonate prepared by micro-emulsion method

Micro-spherical particle of MnCO₃ has been successfully synthesized in CTAB-C₈H₁₈-C₄H₉OH-H₂O micro-emulsion system. Mn₂O₃ decomposed from the MnCO₃ is mixed with Li₂CO₃ and sintered at 800 °C for 12 h, and the pure spinel LiMn₂O₄ in sub-micrometer size is obtained. The LiMn₂O₄ has initial discharge specific capacity of 124 mAh g⁻¹ at discharge current of 120 mA g⁻¹ between 3 and 4.2 V, and retains 118 mAh g⁻¹ after 110 cycles. High-rate capability test shows that even at a current density of 16 C, capacity about 103 mAh g⁻¹ is delivered, whose power is 57 times of that at 0.2 C. The capacity loss rate at 55 °C is 0.27% per cycle.     

Calcium oxides for CO2 capture obtained from the thermal decomposition of CaCO3 particles coprecipitated with Al ions

Calcium-carbonate powders were coprecipitated with Al³⁺ and then decomposed in air and/or under a CO₂ flux between 590 °C and 1150 °C. The data were analysed using a consecutive-decomposition-dilatometer method and the kinetic results were discussed according to the microstructure analysis done by N₂ adsorption isotherms (78 K), SEM and FT-IR measurements. Below 1000 °C, CaCO₃ particle thermal-decomposition was pseudomorphic, resulting in the formation of a CaO grain porous network. When the CaO grains were formed, the Al³⁺ diffused among them, producing AlO₄ groups that promoted the CaO grain coarsening and reduced O²⁻ surface sites available to CO₂ adsorbed molecules to form CO₃²⁻. In pure CaO, CO₃²⁻ diffused through the grain boundary, enhancing Ca²⁺ and O²⁻ mobility; AlO₄ groups reduced CO₃²⁻ penetration and CaO sintering rate. Above 1000 °C, the sintering rate of the doped samples exceeded that of the undoped, likely because of Al³⁺ diffusion in CaO and viscous flow.     

Controllable synthesis of CaTi2O4(OH)2 nanoflakes by a facile template-free process and its properties

Serrated leaf-like CaTi₂O₄(OH)₂ nanoflake crystals were synthesized via a template-free and surfactant-free hydrothermal process. The samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). The growth process for CaTi₂O₄(OH)₂ nanoflakes was dominated by a crystallization–dissolution–recrystallization growth mechanism. BET analysis showed that CaTi₂O₄(OH)₂ nanoflakes had mesoporous structure with an average pore size of 8.7 nm, and a large surface area of 88.4 m² g⁻¹. Cyclic voltammetry and galvanostatic charge–discharge tests revealed that the electrode synthesized from CaTi₂O₄(OH)₂ nanoflakes reached specific capacitances of 162 F g⁻¹ at the discharge current of 2 mA cm⁻², and also exhibited excellent electrochemical stability.     

Synthesis and characterization of high-density non-spherical Li(Ni1/3Co1/3Mn1/3)O2 cathode material for lithium ion batteries by two-step drying method

Non-spherical Li(Ni_1/3Co_1/3Mn_1/3)O₂ powders have been synthesized using a two-step drying method with 5% excess LiOH at 800 °C for 20 h. The tap-density of the powder obtained is 2.95 g cm⁻³. This value is remarkably higher than that of the Li(Ni_1/3Co_1/3Mn_1/3)O₂ powders obtained by other methods, which range from 1.50 g cm⁻³ to 2.40 g cm⁻³. The precursor and Li(Ni_1/3Co_1/3Mn_1/3)O₂ are characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and scanning electron microscope (SEM). XPS studies show that the predominant oxidation states of Ni, Co and Mn in the precursor are 2⁺, 3⁺ and 4⁺, respectively. XRD results show that the Li(Ni_1/3Co_1/3Mn_1/3)O₂ material obtained by the two-step drying method has a well-layered structure with a small amount of cation mixing. SEM confirms that the Li(Ni_1/3Co_1/3Mn_1/3)O₂ particles obtained by this method are uniform. The initial discharge capacity of 167 mAh g⁻¹ is obtained between 3 V and 4.3 V at a current of 0.2 C rate. The capacity of 159 mAh g⁻¹ is retained at the end of 30 charge-discharge cycle with a capacity retention of 95%.     

Synthesis optimization of Li1 + x[Mn0.45Co0.40Ni0.15]O2 with different spherical sizes via co-precipitation

Li_1 + x[Mn_0.45Co_0.40Ni_0.15]O₂ spherical cathode materials with different sizes (about 2 and 5 μm) were fabricated by calcining uniform spherical metal carbonate, [Mn_0.45Co_0.40Ni_0.15]CO₃ with lithium hydroxide at high temperature. The precursor of spherical metal carbonate, [Mn_0.45Co_0.40Ni_0.15]CO₃, was obtained via co-precipitation method at room temperature, which was significantly dependent on synthetic conditions, such as the reaction temperature, the concentration of NH₄HCO₃, and stirring speed, etc. The optimized condition resulted in [Mn_0.45Co_0.40Ni_0.15]CO₃, of which the particle size distribution was uniform and the particle shape was spherical. The final products, Li_1 + x[Mn_0.45Co_0.40Ni_0.15]O₂, had a well-ordered layered structure and uniform homogeneity. Raman spectroscopy analysis showed the Raman-active species E_g and A_1g modes were observed at 488, 473 cm^− 1 and 597, 590 cm^− 1, respectively, for the obtained spherical cathode materials.     

High capacity three-dimensional ordered macroporous CoFe2O4 as anode material for lithium ion batteries

A three-dimensional ordered macroporous (3DOM) cobalt ferrite (CoFe₂O₄) was prepared using polystyrene (PS) colloidal crystal template. The scanning electron microscopy (SEM) and the transmission electron microscopy (TEM) micrographs showed that the as-prepared CoFe₂O₄ material had a typical 3DOM structure, which was constructed with about 130 nm-sized macropores and 10-20 nm-sized walls. The obtained CoFe₂O₄ material had a specific surface area of 66.67 m² g⁻¹, and could deliver a relatively high capacity of 702 mAh g⁻¹ (about double that of graphite) at a current density of 0.2 mA cm⁻² after 30 cycles. Owing to the 3DOM nanoarchitecture, the as-prepared CoFe₂O₄ electrode exhibited a good rate performance. The results suggest a promising application of the 3DOM CoFe₂O₄ as anode material for lithium ion batteries.     

Structural and electrochemical behaviors of metastable Li2/3[Ni1/3Mn2/3]O2 modified by metal element substitution

Layered metastable lithium manganese oxides, Li_2/3[Ni_1/3−xMn_2/3−yM_x+y]O₂ (x = y = 1/36 for M = Al, Co, and Fe and x = 2/36, y = 0 for M = Mg) were prepared by the ion exchange of Li for Na in P2-Na_2/3[Ni_1/3−xMn_2/3−yM_x+y]O₂ precursors. The Al and Co doping produced the T^#2 structure with the space group Cmca. On the other hand, the Fe and Mg doped samples had the O6 structure with space group R-3m. Electron diffraction revealed the 1:2 type ordering within the Ni_1/3−xMn_2/3−yM_x+yO₂ slab. It was found that the stacking sequence and electrochemical performance of the Li cells containing T^#2-Li_2/3[Ni_1/3Mn_2/3]O₂ were affected by the doping with small amounts of Al, Co, Fe, and Mg. The discharge capacity of the Al doped sample was around 200 mAh g⁻¹ in the voltage range between 2.0 and 4.7 V at the current density of 14.4 mA g⁻¹ along with a good capacity retention. Moreover, for the Al and Co doped and undoped oxides, the irreversible phase transition of the T^#2 into the O2 structure was observed during the initial lithium deintercalation.     

A polyblend electrolyte (PVP/PEG+KI+I2) for dye-sensitized nanocrystalline TiO2 solar cells

A novel polyblend electrolyte consisting of KI and I₂ dissolved in a blending polymer of polyvinyl pyrrolidone (PVP) and polyethylene glycol (PEG) was prepared. The formation of ⁻I₃ in the polymer electrolyte was confirmed by X-ray photoelectron spectroscopy (XPS) characterization. Due to the coordinating and plasticizing effect by PVP, the ionic conductivity of the polyblend electrolyte is enhanced. The highest ionic conductivity of 1.85 mS cm⁻¹ for the polyblend electrolyte was achieved by optimizing the compositions as 40 wt.% PVP + 60 wt.% PEG + 0.05 mmol g⁻¹ I₂ + 0.10 mmol g⁻¹ KI. Based on the polyblend electrolyte, a DSSC with fill factor of 0.59, short-circuit density of 9.77 mA cm⁻², open-circuit voltage of 698 mV and light-to-electricity conversion efficiency of 4.01% was obtained under AM 1.5 irradiation (100 mW cm⁻²).     

LiNi0.8Co0.15Al0.05O2 cathode materials prepared by TiO2 nanoparticle coatings on Ni0.8Co0.15Al0.05(OH)2 precursors

Synthesis, electrochemical, and structural properties of LiNi_0.8Co_0.15Al_0.05O₂ cathodes prepared by TiO₂ nanoparticles coating on a Ni_0.8Co_0.15Al_0.05(OH)₂ precursor have been investigated by the variation of coating concentration and annealing temperature. TiO₂-coated cathodes showed that Ti elements were distributed throughout the particles. Among the coated cathodes, the 0.6 wt% TiO₂-coated cathode prepared by annealing at 750 °C for 20 h exhibited the highest reversible capacity of 176 mAh g⁻¹ and capacity retention of 92% after 40 cycles at a rate of 1C (=190 mA g⁻¹). On the other hand, an uncoated cathode showed a reversible first discharge capacity of 186 mAh g⁻¹ and the same capacity retention value to the TiO₂-coated sample at a 1C rate. However, under a 1C rate cycling at 60 °C for 30 cycles, the uncoated sample showed a reversible capacity of 40 mAh g⁻¹, while a TiO₂-coated one showed 71 mAh g⁻¹. This significant improvement of the coated sample was due to the formation of a possible solid solution between TiO₂ and LiNi_0.8Co_0.15Al_0.05O₂. This effect was more evident upon annealing the charged sample while increasing the annealing temperature, and at 400 °C, the coated one showed a more suppressed formation of the NiO phase from the spinel LiNi₂O₄ phase than the uncoated sample.     

Synthesis, microstructure, and photocatalysis of In2O3 hollow particles

Indium oxide (In₂O₃) microspheres with hollow interiors have been prepared by a facile implantation route which enables indium ions released from indium-chloride precursors to implant into nonporous polymeric templates in C₂Cl₄ solvent. The templates are then removed upon calcination at 500 °C in air atmosphere, forming hollow In₂O₃ particles. Specific surface area (0.5-260 m² g⁻¹) and differential pore volume (7 × 10⁻⁹ to 3.8 × 10⁻⁴ m³ g⁻¹ Å⁻¹) of the hollow particles can be tailored by adjusting the precursor concentration. For the hollow In₂O₃ particles with high surface area (260 m² g⁻¹), an enhanced photocatalytic efficiency (up to ∼one-fold increase) against methylene blue (MB) dye is obtained under UV exposure for the aqueous In₂O₃ colloids with a dilute solids concentration of 0.02 wt.%.     

Comparison of AlPO4- and Co3(PO4)2-coated LiNi0.8Co0.2O2 cathode materials for Li-ion battery

Electrochemical and thermal properties of Co₃(PO₄)₂- and AlPO₄-coated LiNi_0.8Co_0.2O₂ cathode materials were compared. AlPO₄-coated LiNi_0.8Co_0.2O₂ cathodes exhibited an original specific capacity of 170.8 mAh g⁻¹ and had a capacity retention (89.1% of its initial capacity) between 4.35 and 3.0 V after 60 cycles at 150 mA g⁻¹. Co₃(PO₄)₂-coated LiNi_0.8Co_0.2O₂ cathodes exhibited an original specific capacity of 177.6 mAh g⁻¹ and excellent capacity retention (91.8% of its initial capacity), which was attributed to a lithium-reactive Co₃(PO₄)₂ coating. The Co₃(PO₄)₂ coating material could react with LiOH and Li₂CO₃ impurities during annealing to form an olivine Li_xCoPO₄ phase on the bulk surface, which minimized any side reactions with electrolytes and the dissolution of Ni⁴⁺ ions compared to the AlPO₄-coated cathode. Differential scanning calorimetry results showed Co₃(PO₄)₂-coated LiNi_0.8Co_0.2O₂ cathode material had a much improved onset temperature of the oxygen evolution of about 218 °C, and a much lower amount of exothermic-heat release compared to the AlPO₄-coated sample.     

Cobalt(II) porphyrin complex immobilized on the binary oxide SiO2/Sb2O3: electrochemical properties and dissolved oxygen reduction study

In this work, SiO₂/Sb₂O₃ prepared by the sol-gel processing method, having a specific surface area, S_BET, of 790 m² g⁻¹, an average pore diameter of 1.9 nm and 4.7 wt.% of Sb, was used as substrate base for immobilization of the 5,10,15,20-tetrakis(1-methyl-4-pyridyl)-21H,23H-porphine ion. Cobalt(II) ion was inserted into the porphyrin ring with a yield of complex bonded to the substrate surface of 59.4 μ mol g⁻¹. A carbon paste electrode of this material was used to study, by linear sweeping voltammetric and chronoamperometric techniques, the electrocatalytic reduction of dissolved oxygen. The reduction, at the electrode solid-solution interface, occurred at −0.25 V versus SCE in 1.0 mol l⁻¹ KCl solution, pH 5.5, by a four electron mechanism. The electrode response was invariant under various oxidation-reduction cycles showing that the system is chemically very stable. Such characteristics allowed the study of the electrode response towards various dissolved oxygen concentrations using the chronoamperometry technique. The cathodic peak current intensities plotted against O₂ concentrations, between 1.0 and 12.8 mg l⁻¹, showed a linear correlation. The electrode response time was very fast, i.e. about 1 s. This study was extended using the electrode to determine the concentration of dissolved oxygen in sea water samples.     

Pure and mixed gas CH4 and n-C4H10 sorption and dilation in poly(1-trimethylsilyl-1-propyne)

Pure and mixed gas n-C₄H₁₀ and CH₄ sorption and dilation in poly(1-trimethylsilyl-1-propyne) (PTMSP) are reported at temperatures ranging from −20 to 35 °C. The presence of n-C₄H₁₀ in the mixture considerably reduces CH₄ solubility. For example, CH₄ solubility (in the limit of zero CH₄ fugacity) at 25°C decreases from 4.0 (pure gas) to 0.78 cm³(STP)/(cm³ polymer atm) in the presence of n-C₄H₁₀ at an activity of 0.60. At −20 °C, CH₄ solubility decreases by almost an order of magnitude, from 10.2 (pure gas) to 1.22 cm³(STP)/(cm³ polymer atm) in the presence of n-C₄H₁₀ at an activity of 0.61. In contrast, n-C₄H₁₀ mixture sorption properties are not measurably affected by the presence of CH₄. The dual mode sorption model parameters for CH₄ and n-C₄H₁₀ in PTMSP were determined from pure and mixed gas sorption measurements, and this model can adequately describe the sorption data. The n-C₄H₁₀/CH₄ mixed gas solubility selectivity in PTMSP decreases as temperature increases and as n-C₄H₁₀ activity increases. For example, at 25 °C, the n-C₄H₁₀/CH₄ solubility selectivity decreases from 250 to 120 as n-C₄H₁₀ activity increases from 0.02 to 0.25. At −20 °C and an n-C₄H₁₀ activity of 0.24, the n-C₄H₁₀/CH₄ solubility selectivity is 590. Penetrant-induced volume dilation of PTMSP can be adequately modeled by assuming that all swelling is caused by penetrant molecules sorbed in the polymer's dense equilibrium region (i.e., the Henry's law region) during sorption. However, the best fit partial molar volumes in the Henry's law region for the dilation data are considerably lower than the penetrant partial molar volumes in liquids, suggesting that further theoretical efforts are needed to develop predictive models of volume dilation in high free volume glassy polymers.     

Effect of synthesis condition on the structural and electrochemical properties of Li[Ni1/3Mn1/3Co1/3]O2 prepared by the metal acetates decomposition method

In order to get homogeneous layered oxide Li[Ni_1/3Mn_1/3Co_1/3]O₂ as a lithium insertion positive electrode material, we applied the metal acetates decomposition method. The oxide compounds were calcined at various temperatures, which results in greater difference in morphological (shape, particle size and specific surface area) and the electrochemical (first charge profile, reversible capacity and rate capability) differences. The Li[Ni_1/3Mn_1/3Co_1/3]O₂ powders were characterized by means of X-ray diffraction (XRD), charge/discharge cycling, cyclic voltammetry and SEM. XRD experiment revealed that the layered Li[Ni_1/3Mn_1/3Co_1/3]O₂ material can be best synthesized at temperature of 800 °C. In that synthesized temperature, the sample showed high discharge capacity of 190 mAh g⁻¹ as well as stable cycling performance at a current density of 0.2 mA cm⁻² in the voltage range 2.3-4.6 V. The reversible capacity after 100 cycles is more than 190 mAh g⁻¹ at room temperature.     

Adsorption of CO2 from dry gases on MCM-41 silica at ambient temperature and high pressure. 2: Adsorption of CO2/N2, CO2/CH4 and CO2/H2 binary mixtures

Adsorption equilibrium capacity of CO₂, CH₄, N₂, H₂ and O₂ on periodic mesoporous MCM-41 silica was measured gravimetrically at room temperature and pressure up to 25 bar. The ideal adsorption solution theory (IAST) was validated and used for the prediction of CO₂/N₂, CO₂/CH₄, CO₂/H₂ binary mixture adsorption equilibria on MCM-41 using single components adsorption data. In all cases, MCM-41 showed preferential CO₂ adsorption in comparison to the other gases, in agreement with CO₂/N₂, CO₂/CH₄, CO₂/H₂ selectivity determined using IAST. In comparison to well known benchmark CO₂ adsorbents like activated carbons, zeolites and metal-organic frameworks (MOFs), MCM-41 showed good CO₂ separation performances from CO₂/N₂, CO₂/CH₄ and CO₂/H₂ binary mixtures at high pressure, via pressure swing adsorption by utilizing a medium pressure desorption process (PSA-H/M). The working CO₂ capacity of MCM-41 in the aforementioned binary mixtures using PSA-H/M is generally higher than 13X zeolite and comparable to different activated carbons.     

The performances of higher alcohol synthesis over nickel modified K2CO3/MoS2 catalyst

Ni modified K₂CO₃/MoS₂ catalyst was prepared and the performance of higher alcohol synthesis catalyst was investigated under the conditions: T = 280–340 °C, H₂/CO (molar radio) = 2.0, GHSV = 3000 h^− 1, and P = 10.0 MPa. Compared with conventional K₂CO₃/MoS₂ catalyst, Ni/K₂CO₃/MoS₂ catalyst showed higher activity and higher selectivity to C₂⁺OH. The optimum temperature range was 320–340 °C and the maximum space-time yield (STY) of alcohol 0.30 g/ml h was obtained at 320 °C. The selectivity to hydrocarbons over Ni/K₂CO₃/MoS₂ was higher, however, it was close to that of K₂CO₃/MoS₂ catalyst as the temperature increased. The results indicated that nickel was an efficient promoter to improve the activity and selectivity of K₂CO₃/MoS₂ catalyst.