Stability of ionic-covalently cross-linked PBI-blended membranes for SO2 electrolysis at elevated temperatures

In this study, the effect of component composition on the chemical stability of the developed ionic-covalently cross-linked PBI-blended membrane concept from earlier studies for application in SO₂ electrolysis at elevated temperatures (>100 °C) is further investigated. Three different acid-base ratios were studied by blending a partially fluorinated sulfonated arylene main-chain polymer (SFS) with polybenzimidazole (F₆PBI) and a partially or non-fluorinated bromo-methylated polymer (BrPAE). In addition two different alkylated imidazoles (EMIm and TMIm) were included as quaternization agents. Accordingly, twelve different PBI-blended membranes were produced in this study. The suitability of these membranes for SO₂ electrolysis at elevated temperatures was determined in terms of i) the H₂SO₄ stability (80 wt% H₂SO₄ at 100 °C for 120 h), (ii) the oxidative stability (Fenton's test, FT) and (iii) the organic solvent stability (extraction in N,N-Dimethylacetamide). Membranes were characterized in terms of the percentage weight, the ion exchange capacity (IEC) and the thermal stability (TGA-FTIR) changes, before and after the various treatments. Although all blended membrane types were sufficiently stable during H₂SO₄ treatment, proton conductivity measurements indicated that the blends containing only partially fluorinated blend components displayed superior stability (better compatibility) as well as conductivity. Cell voltages showed an improvement of up to 190 mV for operations at 120 °C compared to earlier studies conducted at 80 °C for similar PBI-blended membranes. It was established that both chemically stable and conductive PBI-blended membranes, suitable for SO₂ electrolysis above 100 °C, could be obtained by varying the composition of selected polymer components.     

Thermal stability of propylene carbonate and ethylene carbonate–propylene carbonate-based electrolytes for use in Li cells

The thermal stability of mixed-solvent electrolytes used in lithium cells was investigated by differential scanning calorimetry (DSC) through the use of airtight containers. The electrolytes used were propylene carbonate (PC) and ethylene carbonate (EC)+PC, in which was dissolved 1 M LiPF₆, 1 M LiBF₄, 1 M LiClO₄, 1 M LiSO₃CF₃, 1 M LiN(SO₂CF₃)₂, or 1.23 M LiN(SO₂CF₃)(SO₂C₄F₉). The influence of lithium metal or the Li_0.5CoO₂ addition on the thermal behavior of these electrolytes was also investigated. The peak temperature of PC-based electrolytes increased following the order of LiPF₆<LiClO₄<LiBF₄<LiN(SO₂CF₃)₂<LiSO₃CF₃<LiN(SO₂CF₃)(SO₂C₄F₉). The order of peak temperature of EC–PC-based electrolytes shows a similar tendency to that of EC–PC-based electrolytes, with the exception of the LiN(SO₂CF₃)₂ electrolyte. The EC–PC-based electrolytes with Li metal show a more stable profile compared with the DSC curves of the PC-based electrolytes with the Li metal. The solid electrolyte interphase (SEI) covers the surface of the Li metal and prevents further reduction of the electrolytes. EC may form a better SEI compared with PC. The PC-based electrolytes of LiSO₃CF₃, LiN(SO₂CF₃)₂ and LiN(SO₂CF₃)(SO₂C₄F₉) with the coexistence of Li_0.49CoO₂ show a broad peak at around 200 °C, which may be caused by the reaction of the Li_0.49CoO₂ surface and electrolytes. The PC-based electrolytes of LiPF₆, LiClO₄ and LiBF₄ with Li_0.49CoO₂ show exothermic peaks at higher temperatures than 230 °C. The peak temperatures of the EC–PC-based electrolytes with the coexistence of Li_0.49CoO₂ are nearly the same temperature as the EC–PC-based electrolytes.     

Thermal stability and decomposition mechanism of HFO‐1336mzz(Z) as an environmental friendly working fluid: Experimental and theoretical study

HFO‐1336mzz(Z) is a promising working fluid used in high‐temperature heat pump and organic Rankine cycle (ORC) system because of its environmental friendly features and good thermal performance. In this work, a test system is designed to assess the thermal stability of HFO‐1336mzz(Z). The fluoride ion concentration is used as an indicator of HFO‐1336mzz(Z) dissociation. The experimental results show that the pressure has a great effect on the dissociation of HFO‐1336mzz(Z) and the dissociation temperatures of HFO‐1336mzz(Z) at 2.1, 3.1, and 4.0 MPa for 24 hours are 310°C to 330°C, 290°C to 310°C, and 270°C to 290°C, respectively. The decomposition products of HFO‐1336mzz(Z) are measured by a Fourier transform infrared spectrometer (FTIR); the main decomposition products are HF, CF₄, CHF₃, C2F₄, C₂F₆, C₂HF₅, and C₃F₈. Finally, density functional theory (DFT) method is used to study the decomposition mechanism of HFO‐1336mzz(Z). The main initial decomposition reaction is the fracture of C?C bond into C–C bond, and then the CF₃ group is separated from HFO‐1336mzz(Z) molecule to produce CF₃ radical. H, F‐abstraction, and combination reactions are important in the consequent reactions to generate the main decomposition products.     

Sulfur poisoning of La(Ni0.6Fe0.4)O3 cathode material for solid oxide fuel cells

Sulfur poisoning of cathode materials is one of the important factors to cause cathode performance degradation resulting in shortening lifetime of SOFC. The sulfur attacks alkali earth components of the rare earth-transition metal perovskite oxides, such as Ba, Ca, Sr, which reacts with SO₂ to form sulfates. In this work, the La(Ni_0.6Fe_0.4)O₃ (LNF) cathode material without alkali earth elements was employed to investigate the sulfur poisoning behavior by flowing 30 ppm SO₂ at different temperatures of 500 °C–800 °C. It was found that SO₂ readily reacts with the La₂O₃ component in LNF to form La₂O₂SO₄ at 700 °C and 800 °C. The extent of the chemical reaction is temperature dependent. These results confirm that sulfur poisoning also occurs in cathode materials free of alkali earth components. The study prompts the exploration of new materials and new strategies for the developing new cathode materials with high sulfur tolerance.     

CF4 plasma treatment for preparing gas diffusion layers in membrane electrode assemblies

The hydrophobic properties of carbon fibers improved by a CF₄ plasma treatment were used to fabricate gas diffusion layers (GDLs) for use in proton exchange membrane fuel cells. The water contact angle of the CF₄ plasma treated GDL was measured as 132.8 ± 0.2° at 45 °C and very few surface gas diffusion pores were either sealed or blocked by the excessive hydrophobic material residuals. Polarization measurements verified that the CF₄ plasma treated modules can indeed enhance fuel cell performance, compared to the membrane electrode assemblies (MEAs) with a non-wet-proofed GDL, 10 wt% PTFE dip-coated GDL, and commercially available GDL (10 wt% PTFE).     

Interface properties between a lithium metal electrode and a poly(ethylene oxide) based composite polymer electrolyte

The interface resistance between a lithium metal electrode and a polymer electrolyte has been measured for composite polymer electrolytes using various ceramic fillers with poly(ethylene oxide) (PEO) and lithium salts (LiX). The interface resistance depended on the properties of added fillers and lithium salts. The PEO with LiClO₄ electrolyte contacted with lithium metal showed the high interfacial resistance of 1000 Ω cm² at 70°C for 25 days. In contrast, the interface resistance between lithium metal and PEO with Li(CF₃SO₂)₂N was as low as 67 Ω cm² after contacting at 80°C for 30 days. The interface stability and the lithium ion conductivity were improved by addition of a small amount of ferroelectric BaTiO₃ as the filler into the PEO–LiX electrolyte.     

Solvothermal synthesis of iron phosphides and their application for efficient electrocatalytic hydrogen evolution

In this paper, we present a solvothermal synthesis of iron phosphide electrocatalysts using a triphenylphosphine (TPP) precursor. The synthetic protocol generates Fe₂P phase at 300 °C and FeP phase at 350 °C. To enhance the catalytic activities of obtained iron phosphide particles heat-treatments were carried out at elevated temperatures. Annealing at 500 °C under reductive atmosphere induced structural changes in the samples: (i) Fe₂P provided a pure Fe₃P phase (Fe₃P−500 °C) and (ii) FeP transformed into a mixture of iron phosphide phases (Fe₂P/FeP−500 °C). Pure Fe₂P films was prepared under argon atmosphere at 450 °C (Fe₂P−450 °C). The electrocatalytic activities of heat-treated Fe₂P−450 °C, Fe₃P−500 °C, and Fe₂P/FeP−500 °C catalysts were studied for hydrogen evolution reaction (HER) in 0.5 M H₂SO₄. The HER activities of the iron phosphide catalyst were found to be phase dependent. The lowest electrode potential of 110 mV vs. a reversible hydrogen electrode (RHE) at 10 mA cm⁻² was achieved with Fe₂P/FeP−500 °C catalyst.     

Biohydrogen production from thermochemically pretreated corncob using a mixed culture bioaugmented with Clostridium acetobutylicum

Bovine ruminal fluid (BRF) bioaugmented with Clostridium acetobutylicum (Clac) was assessed for hydrolyzing cellulose and produce biohydrogen (BioH₂) simultaneously from pretreated corncob in a single step, without the use of external hydrolytic biocatalysts. The corncob was pretreated using three thermochemical methods: H₂SO₄ 2%, 160 °C; NaOH 2%, 140 °C; NaOCl 2%, 140 °C; autohydrolysis: H₂O, 190 °C. Subsequently, BioH₂ production was carried out using the pretreated material with the highest digestibility applying a Taguchi experimental array to identify the optimal operating conditions. The results showed a higher glucose released from pretreated corncob with H₂SO₄ (134.7 g/L) compared to pretreated materials by autohydrolysis, NaOH and NaOCl (123 g/L, 89.8 g/L and 52.9 g/L, respectively). The mixed culture was able to hydrolyze the pretreated corncob and produce 575 mL of H₂ (at 35 °C, pH 5.5, 1:2 ratio of BRF:Clac and 5% of solids loading) equivalent to 132 L H₂/Kg of biomass.     

Four volts class solid lithium polymer batteries with a composite polymer electrolyte

Polyethylene oxide (PEO)-based polymer electrolytes with BaTiO₃ as a filler have been examined as electrolytes in 4 V class lithium polymer secondary batteries. A mixture of 90 wt.% LiN(CF₃SO₂)₂–10 wt.% LiPF₆ was found to be the best candidate as the salt in PEO, and showed high electrical conductivity, good corrosion resistance to the aluminum current collector and low interfacial resistance between the lithium metal anode and the polymer electrolyte. The cyclic performance of the cell, Li/[PEO₁₀–(LiN(CF₃SO₂)₂–10 wt.% LiPF₆)]–10 wt.% BaTiO₃/LiNi_0.8Co_0.2O₂/Al, showed good charge–discharge cycling performance. The observed capacity fading on charging up to 4.2 V at 80 °C in the cell was about 0.28% per cycle in the first 30 cycles, compared to that of 0.5% for the polymer electrolyte without LiPF₆ in the lithium salt.     

Low operational temperature Li–CFx batteries using cathodes containing sub-fluorinated graphitic materials

Commercial lithium/polycarbon monofluoride batteries [Li–(CF)_n] are typically current-limited and are therefore not implemented in high-rate or low-temperature applications. Recent results suggest, however, that CF-based cathodes that use sub-fluorinated CF_x (SFCF_x) active materials in a thin electrode form factor are able to support very high currents (up to 5 C) while still providing a significant fraction of their specific capacity. In this work, the low temperature efficacy of these materials is examined in a −40 °C environment. CF_0.54 and CF_0.65 powders were characterized using X-ray diffraction, scanning electron microscopy, and X-ray energy dispersive spectroscopy. These materials were then implemented in a spray-deposited electrode using a 1-mil (∼25 μm) aluminum foil current collector and PVDF as a binder. Electrochemical tests showed that these materials were able to deliver specific capacity values up to five times greater than commercial CF_1.08 powder inserted into identically fabricated test cells tested at −40 °C. Testing also indicated that a room-temperature pre-discharge step was necessary to condition the electrode materials before exposure to the low-temperature test environment.     

Conductivity and oxygen diffusion in bixbyites and fluorites Ln6−xMoO12−δ (Ln = Er,Tm; x = 0, 0.5)

In the present work erbium and thulium molybdates Ln_5.5MoO_11.25?δ (Ln = Er and Tm) with fluorite and Ln₆MoO_12?δ (Ln = Er and Tm) with bixbyite structure have been studied. The materials have been obtained by mechanical activation method followed by sintering at 1600°С for 3 h. New compounds have been characterized by X-ray diffraction. The total conductivity was investigated using impedance spectroscopy method in dry and wet air. Oxygen diffusivity data was acquired by oxygen isotope exchange with C¹⁸O₂. The combination of different techniques allowed us to determine ionic conductivity components in these compounds. Er and Tm fluorites and bixbyites showed oxygen-ion conductivity in dry air and oxygen-ion and proton conductivity in wet air up to 550–600°С. In wet atmosphere Er and Tm fluorites and bixbyites have total conductivity of about 2?10^?6 S/cm at 500 °C. At higher temperatures they are mixed oxygen-electronic conductors in dry and wet atmosphere. At lower (T < 400 °C) temperatures bixbyites are slightly better ionic conductors compared to fluorites. A high oxygen-ion mobility in all compounds above 200°С has been confirmed by isotope exchange method with С¹⁸O₂: tracer diffusion coefficient values were ~10^?11 – 10^?10 cm²/s at 700 °C. Fluorites were demonstrated to have a higher oxygen mobility compared to bixbyites; the effect is more pronounced for Tm molybdates.     

Production,performance and cost analysis of anode-supported NiO-YSZ micro-tubular SOFCs

In the present study, the anode-supported micro-tubular solid oxide fuel cells (MT-SOFCs) with an electrolyte thin interlayer were manufactured. The anode support tubes consisting of 56 wt% nickel oxide and 44 wt% YSZ (8 mol% yttria (Y₂O₃) stabilized zirconia (ZrO₂)) were produced by using the thermo-extrusion method, whereas the electrolyte and cathode layers were manufactured using the dip-coating method. The half-cells consisting of anode and electrolyte were manufactured by using two different methods. In the first method, the anode-support tubes were pre-sintered at 1200 °C, then covered with the electrolyte layer by using the dip-coating method and then exposed to second sintering at 1400 °C. In the second method, the anode and electrolyte layers were sintered together at 1400 °C (co-sintering) in order to produce the half-cells. The half-cells that were produced and then coated with cathode solutions by using the dip-coating method and the final cells were successfully produced at the end of the sintering at 1150 °C. The porosity and shrinkage percentage values of these MT-SOFCs differed from each other. The power densities of these cells were tested at 700 °C, 750 °C, and 800 °C by using H₂ gas as fuel and the results of the microstructural and cost analyses were compared.     

Low temperature synthesis of Cu1−xAl2.5 spinel solid solution as sustained release catalyst for methanol to hydrogen

In order to find a method to synthesize spinel solid solution at low temperature, in this paper, pseudo-boehmite and copper nitrate were used as raw materials, and citric acid was used as accelerator for the first time, the Cu_1?xAl_2.5 spinel solid solutions were synthesized by ball milling treatment of the solid mixture and then calcined at elevated temperatures. The obtained materials were characterized by X-ray diffraction (XRD), Brunner?Emmett?Teller (BET) measurements, H₂-temperature programmed reduction (H₂-TPR), infrared (IR) and thermogravimetric methods (TG), and the mechanism of citric acid promoting the synthesis of the spinel solid solution was suggested. The results show that an optimal amount of citric acid can significantly promote the formation of the spinel structure, thus substantially decreasing the synthetic temperature from the above 900 °C–700 °C. At 700 °C, the preparation without the accelerator resulted in small amount of the spinel solid solution, while the use of accelerator gave rise to 82.96% spinel solid solution. Importantly, the Cu_1?xAl_2.5 spinel solid solution prepared at 700 °C demonstrates the best sustained release catalytic performance, and the catalytic activity reached more than 90% and remained stable within 50 h. The findings of this report might be provide guidance for the solid phase preparation of catalysts at relatively lower temperatures, thus facilitating the commercialization of the sustained release catalyst system.     

Heat and mass transfer analysis in single cell of PEFC using different PEM and GDL at higher temperature

According to the H₂ and fuel cell road map in Japan, the target operating temperature of polymer electrolyte fuel cell (PEFC) should be 90 °C from 2020 to 2025. In this study, the impact of polymer electrolyte membrane (PEM) and gas diffusion layer (GDL)'s thickness on heat and mass transfer characteristics as well as power generation performance of PEFC is investigated at operating temperature of 90 °C. The in-plane temperature distributions on anode and cathode separator are also measured using thermograph. As a result, it is observed that the increase in power from 1 W to 5 W at the current density of 0.80 A/cm² as well as even temperature distribution within 1 °C can be obtained at operating temperature of 90 °C by decrease in GDL's thickness from 190 μm to 110 μm. In addition, the power is increased from 3 W to 4 W at the current density of 0.80 A/cm² operated at 90 °C by decrease in the PEM's thickness from 127 μm to 25 μm.     

The lithium—sulfur dioxide primary battery — its characteristics,performance and applications

The lithium—sulfur dioxide battery is a new primary battery system with many advantages over conventional batteries. It has an energy density up to 330 W h/kg (150 W h/lb.), two to four times greater than zinc batteries, and can perform to temperatures as low as ?54 °C (?65 °F). The battery can withstand high temperature storage 71 °C (160 °F) for long periods of time and its shelf life is projected to be 5 – 10 years at 21 °C (70 °F). The chemistry, construction and detailed performance characteristics of the battery are presented. The Li/SO₂ system provides an all-purpose, all-climate primary battery that is capable of filling a wide variety of military, industrial and consumer applications. A number of these applications are discussed. With increasing production and cost reduction, the Li/SO₂ battery will be cost-competitive and will receive wide acceptability and use.     

Hydrothermal synthesis of CuV2O6 supported on mesoporous SiO2 as SO3 decomposition catalysts for solar thermochemical hydrogen production

Hydrothermal synthesis of CuV₂O₆ supported on 3-D ordered mesoporous SiO₂ (CuV/SiO₂) was studied to evaluate the catalytic activity for SO₃ decomposition, which is a key step in solar thermochemical hydrogen production. A composite oxide hydrate, Cu₃O(V₂O₇)·H₂O, and an oxide hydroxide hydrate, Cu₃(OH)₂V₂O₇·(H₂O)₂, were formed at lower hydrothermal temperatures (≤200 °C). The oxide hydrate phase mainly yielded Cu₂V₂O₇ after calcination at 600 °C in air. By contrast, the hydrothermal synthesis at 250 °C (CuV/SiO₂@250) directly crystallized CuV₂O₆ from the oxide hydroxide hydrate, although its very large particle size (∼5 μm) is not suitable for the catalytic application. The SO₃ decomposition activity measured at 600 °C was associated with the yield as well as the dispersion of CuV₂O₆, giving rise to the maximum for the hydrothermal synthesis at 200 °C. CuV/SiO₂@250 achieved the highest catalytic activity at the reaction temperature of 650 °C, because the melting phase of CuV₂O₆ penetrated mesoporous SiO₂ and thus improved the dispersion of the active phase.     

Recovery and pre-treatment of fats,oil and grease from grease interceptors for biodiesel production

Fats, oil and grease (FOG) can be recovered efficiently from grease interceptors for biodiesel production. FOG is susceptible to hydrolysis because of its inherent high moisture content and the presence of lipases associated with food residuals in the grease interceptors. This study reveals that the FFA content of FOG derived from grease interceptors did not exceed 8% (w/w) due to constant influx of fresh FOG from wastewater. However, if the FOG is allowed to hydrolyze without dilution, the FFA content can reach 15% (w/w) in more than 20 days. Experiments were conducted to optimize reaction parameters for the esterification of FOG prior to the conventional alkali-catalyzed biodiesel production process. Sulphuric acid (H₂SO₄) was a more efficient catalyst than Fe₂(SO₄)₃ in reducing the acid value to ?1 mg KOH/g under identical reaction conditions. At reaction temperatures of ?50 °C, only H₂SO₄ was capable of reaching the recommended acid value within 24 h. The optimum methanol to FFA ratio for an H₂SO₄-catalyzed reaction was 20:1, whereas for Fe₂(SO₄)₃ it was above 26:1. Esterification occurred under static, non-mixed conditions, although conversion rates were low. The rate of conversion increased with mixing speed, with a 200 rpm orbital shaking speed as optimum.     

Room temperature molten salt as electrolyte for carbon nanotube-based electric double layer capacitors

Electric double layer capacitors (EDLCs) have been assembled with carbon nanotubes (CNTs) as the electrodes and a novel binary room temperature molten salt (RTMS) composed of lithium bis(trifluoromethane sulfone)imide (LiN(SO₂CF₃)₂, LiTFSI) and acetamide as the electrolyte. The electrochemical performances of the RTMS and the EDLC are evaluated with cyclic voltammetry (CV), ac impedance spectroscopy and galvanostatic charge/discharge, etc. The EDLC with these components show excellent electrochemical properties in specific capacitance, rate and cycling performances at ambient and elevated (60 °C) temperatures, indicating that RTMS is a promising electrolyte for advanced EDLCs.     

Effect of the acid type on clinoptilolite-rich tuff for hydrogen storage

Clinoptilolite from Gördes (Turkey) was treated with HCl, HNO₃ and H₂SO₄ solutions of varying concentrations (from 2.0 M to 6.0 M) at 90 °C for 4 h to evaluate its potential for possible applications in hydrogen storage. X-ray diffraction, X-ray fluorescence and nitrogen adsorption techniques were applied for characterization of the zeolites. Hydrogen adsorption capacities of clinoptilolite samples were found in the range between 1.609 and 2.391 mmol/g. The effects of the acid modification process on the structure and hence hydrogen adsorption was evaluated according to the obtained results.     

Production of crude bio-oil via direct liquefaction of spent K-Cups

Spent K-Cups were liquefied into crude bio-oil in a water-ethanol co-solvent mixture and reaction conditions were optimized using response surface methodology (RSM) with a central composite design (CCD). The effects of three independent variables on the yield of crude bio-oil were examined, including the reaction temperature (varied from 255 °C to 350 °C), reaction time (varied from 0 min to 25 min) and solvent/feedstock mass ratio (varied from 2:1 to 12:1). The optimum reaction conditions identified were 276 °C, 3 min, and solvent/feedstock mass ratio of 11:1, giving a mass fraction yield of crude bio-oil of 60.0%. The overall carbon recovery at the optimum conditions was 93% in mass fraction. The effects of catalyst addition (NaOH and H₂SO₄) on the yield of crude bio-oil were also investigated under the optimized reaction conditions. The results revealed that the presence of NaOH promoted the decomposition of feedstock and significantly enhanced the bio-oil production and liquefaction efficiency, whereas the addition of H₂SO₄ resulted in a negative impact on the liquefaction process, decreasing the yield of crude bio-oil.