Discharge reaction mechanism of room-temperature sodium-sulfur battery with tetra ethylene glycol dimethyl ether liquid electrolyte

The first discharge curve of a sodium-sulfur cell using a tetra ethylene glycol dimethyl ether liquid electrolyte at room temperature shows two different regions: a sloping region and a plateau region of 1.66 V. The first discharge capacity is 538 mAh g⁻¹ sulfur and then decreases with repeated charge-discharge cycling to give 240 mAh g⁻¹ after ten cycles. Elemental sulfur of the cathode changes to sodium polysulfides Na₂S₂ and Na₂S₃, during full discharge. The sodium polysulfides, however, do not reduce completely to elemental sulfur after full charging. In summary, the mechanism of the battery with liquid electrolyte is 2Na + nS → Na₂S_n(4 > n ≥ 2) on discharge and Na₂S_n(4 > n ≥ 2) → x(2Na + nS) + (1 − x)Na₂S_n(5 > n > 2) on charge.     

Study of the H + O + M reaction forming OH: Kinetics of OH chemiluminescence in hydrogen combustion systems

The temporal variation of OH^∗ (A²Σ⁺) chemiluminescence in hydrogen oxidation chemistry has been studied in a shock tube behind reflected shock waves at temperatures of 1400-3300 K and at a pressure of 1 bar. The aim of the present work is to obtain a validated reaction scheme to describe OH^∗ formation in the H₂/O₂ system. Temporal OH^∗ emission profiles and ignition delay times for lean and stoichiometric H₂/O₂ mixtures diluted in 97-98% argon were obtained from the shock-tube experiments. Based on a literature review for the hydrogen combustion system, the key reaction considered was H + O + M = OH^∗ + M (R1). The temperature dependence of the measured peak OH^∗ emission from the shock tube and the peak OH^∗ concentration from a homogeneous closed reactor model are compared. Based on these results a reaction rate coefficient of k₁ = (1.5 ± 0.4) × 10¹³ exp(−25 kJ mol⁻¹/RT) cm⁶ mol⁻² s⁻¹ was found for the forward reaction (R1) which is slightly higher than the rate coefficient suggested by Hidaka et al. (1982). The comparison of measured and simulated absolute concentrations shows good agreement. Additionally, a one-dimensional laminar premixed low-pressure flame calculation was performed for where absolute OH^∗ concentration measurements have been reported by Smith et al. (2005). The absolute peak OH^∗ concentration is fairly well reproduced if the above mentioned rate coefficient is used in the simulation.     

Study of steam electrolysis using a microtubular ceramic reactor

Steam electrolysis was carried out using a microtubular ceramic reactor with the following cell configuration: La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ (LSCF)–Ce_0.8Gd_0.2O_1.9 (CGO) electrode/CGO buffer layer/(ZrO₂)_0.89(Sc₂O₃)_0.1(CeO₂)_0.01 (ScSZ) electrolyte/Ni-ScSZ electrode supporting tube. 10% H₂/Ar gas was used as steam carrier gas, and 18% steam was supplied to the ceramic reactors. The cell performance was as follows: 1.43 V at 0.1 A cm⁻² and 650 °C (Area specific resistance: 4.7 Ω cm²) or 1.37 V at 0.1 A cm⁻² and 700 °C (4.3 Ω cm²). During steam electrolysis, hydrogen production proportionally increased with current density according to Faraday's law, and heat generation at a low current density was observed by an electrochemical technique. Voids and Zr diffusion from the ScSZ electrolyte were confirmed in the CGO buffer layer. Such factors near the surface probably influenced the increase in ohmic loss and electrode polarization.     

Enhanced photocatalytic hydrogen evolution under visible light over Cd1−xZnxS solid solution with cubic zinc blend phase

A series of Cd_1−xZn_xS solid solutions were synthesized at 80 °C with the assistance of sodium dodecylsulfate. The structures, optical properties and morphologies of the solid solutions have been studied by X-ray diffraction, UV–vis diffuse reflectance spectroscopy, and transmission electron microscopy. The photocatalytic H₂ evolution over the solid solutions under visible-light irradiation was investigated and the highest rate reached 2640 μmol h⁻¹ g⁻¹ even without any co-catalysts. The solid solution with optimum performance exhibited cubic structure rather than previously-reported hexagonal one and the possible reasons were discussed. Moreover, the effects of sacrificial reagents on the photocatalytic H₂ evolution were explored by using Na₂S solution with different concentration.     

Effect of design parameters on enhancement of hydrogen charging in metal hydride reactors

The effects of heat transfer mechanisms on the charging process in metal hydride reactors are studied under various charging pressures. Three different cylindrical reactors with the same base dimensions are designed and manufactured. The first one is a closed cylinder cooled with natural convection, the fins are manufactured around the second reactor and the third reactor is cooled with water circulating around the reactor. The temperatures of the reactor at several locations are measured during charging with a range of pressure of 1–10 bar. The third reactor shows the lowest temperature increase with the fastest charging time under all charging pressures investigated. The effective heat transfer coefficients of the reactors are also calculated according to the experimental results and they are found to be 5.5 ± 1 W m⁻² K⁻¹, 35 ± 2 W m⁻² K⁻¹ and 113 ± 1 W m⁻² K⁻¹, respectively. The experimental results showed that the charging of hydride reactors is mainly heat transfer dependent and the reactor with better cooling exhibits the fastest charging characteristics.     

Photocatalytic hydrogen production from aqueous methanol solutions under visible light over Na(BixTa1−x)O3 solid-solution

A series of equivalent substitution solid-solution Na(Bi_xTa_1−x)O₃ (x = 0–0.10) was prepared by a simple hydrothermal method using Ta₂O₅ and NaBiO₃ as precursors. The Na(Bi_0.08Ta_0.92)O₃ photocatalyst exhibited the highest performance of H₂ evolution (59.48 μmol h⁻¹ g⁻¹) under visible-light irradiation (λ > 400 nm) without co-catalyst, whereas no H₂ evolution is observed for NaTaO₃ under the same conditions. The UV-Vis spectra indicate that the Na(Bi_0.08Ta_0.92)O₃ powders can absorb not only ultraviolet light like pure NaTaO₃ powder but also the visible-light spectrum. The absorption edge corresponds to a band gap of 2.88 eV. The results of density functional theory calculation illuminate that the visible-light absorption bands in the Na(Bi_xTa_1−x)O₃ catalysts are attributed to the band transition from the O2p to the Bi2s + 2p + Ta5d hybrid orbital.     

Photocatalytic degradation of oil industry hydrocarbons models at laboratory and at pilot-plant scale

Photodegradation/mineralization (TiO₂/UV Light) of the hydrocarbons: p-nitrophenol (PNP), naphthalene (NP) and dibenzothiophene (DBT) at three different reactors: batch bench reactor (BBR), tubular bench reactor (TBR) and tubular pilot-plant (TPP) were kinetically monitored at pH = 3, 6 and 10, and the results compared using normalized UV light exposition times. The results fit the Langmuir-Hinshelwood (LH) model; therefore, LH adsorption equilibrium constants (K) and apparent rate constants (k) are reported as well as the apparent pseudo-first-order rate constants,  = kK/(1 + Kc_r). The batch bench reactor is the most selective reactor toward compound and pH changes in which the reactivity order is: NP > DBT > PNP, however, the catalyst adsorption (K) order is: DBT > NP > PNP at the three pH used but NP has the highest k values. The tubular pilot-plant (TPP) is the most efficient of the three reactors tested. Compound and pH photodegradation/mineralization selectivity is partially lost at the pilot plant where DBT and NP reaches ca. 90% mineralization at the pH used, meanwhile, PNP reaches only 40%. The real time, in which these mineralization occur are: 180 min for PNP and 60 min for NP and DBT. The mineralization results at the TPP indicate that for the three compounds, the rate limiting step is the same as the degradation one. So that, there is not any stable intermediate that may accumulate during the photocatalytic treatment.     

Investigation of the combined effects of acetate and photobioreactor illuminated fraction in the induction of anoxia for hydrogen production by Chlamydomonas reinhardtii

In the context of hydrogen production by microalgae, the growth of Chlamydomonas reinhardtii was characterized under autotrophic and mixotrophic conditions in a fully controlled photobioreactor (PBR). The combined effect of light transfer conditions, as represented by the illuminated fraction γ, with acetate consumption was observed upon establishment of anoxia. Anoxia was reached in batch cultures when γ was close to 1 (almost fully illuminated culture) in mixotrophic conditions while a value of γ ≈ 0.46 in autotrophic conditions was not sufficient. Based on these results, continuous hydrogen production was established in a cylindrical PBR operated in luminostat with constant illumination and in mixotrophic conditions. Maximum hydrogen gas production was equal to 1.4 ± 0.1 ml_H2 l⁻¹ h⁻¹ for photon flux density of 110 μmol m⁻² s⁻¹ and reactor illuminated fraction of γ = 0.5. Carbon mass balance was realized, emphasizing the necessity to work in strictly autotrophic conditions for hydrogen production with no concomitant CO₂ release.     

Photocatalytic property of partially substituted Pt-intercalated layered perovskite, ASr2TaxNb3−xO10 (A=K, H; x=0, 1, 1.5, 2 and 3)

A series of layered perovskite photocatalysts, ASr₂Ta_xNb_3−xO₁₀ (A=K, H; x=0, 1, 1.5, 2 and 3), were synthesized by conventional solid-state reaction followed by an ion-exchange reaction. Pt was incorporated in the interlayer of HSr₂Ta_xNb_3−xO₁₀ by the stepwise intercalation reaction. The HSr₂Ta_xNb_3−xO₁₀ showed hydrogen production activity and the activities were greatly enhanced by Pt co-incorporating. The x value in HSr₂Ta_xNb_3−xO₁₀ had an important effect on the photocatalytic activity of the catalyst. When the x=1, the HSr₂TaNb₂O₁₀/Pt photocatalyst showed a photocatalytic activity of 208 cm³ g⁻¹ h⁻¹ hydrogen evolution rate in 10 vol% methanol solution under irradiation with wavelength more than 290 nm from a 100-W mercury lamp at 333 K. The HSr₂TaNb₂O₁₀/Pt photocatalyst exhibited much higher photocatalytic activity than the well-known TiO₂/Pt photocatalyst under the same conditions.     

Detailed investigation of ion exchange in ball-milled LiH + MgB2 system using ultra-high field nuclear magnetic resonance spectroscopy

The present study with the detailed ¹H-⁶Li cross polarization NMR analysis confirms the formation of a ternary compound, (Mg_1−xLi_2x)B₂, during ball milling of LiH + (1/2)MgB₂ at room temperature. The ⁶Li sites in (Mg_1−xLi_2x)B₂ exhibit spinning sidebands (SSBs), whereas the ⁶Li sites in LiH do not. The SSBs and the very short spin-lattice relaxation time manifested by the ⁶Li sites in (Mg_1−xLi_2x)B₂ indicate that the Li ions in (Mg_1−xLi_2x)B₂ are located between the layered boron structures and close to Mg ions. The formation of (Mg_1−xLi_2x)B₂ explains the previous observation that the LiH + (1/2)MgB₂ mixture ball-milled effectively has a greatly enhanced hydriding kinetics at temperatures below the melting point of LiBH₄.     

Significant improvement of photocatalytic hydrogen generation rate over TiO2 with deposited CuO

TiO₂ photocatalyst with deposited CuO (CuO-TiO₂) was synthesized by the impregnation method using P25 (Degussa) as support, and exhibited high photocatalytic hydrogen generation activity from methanol/water solution. A substantial hydrogen evolution rate of 10.2 ml min⁻¹ (18,500 μmol h⁻¹ g⁻¹_catalyst) was observed over this efficient CuO-TiO₂ with optimal Cu content of 9.1 mol% from an aqueous solution containing 10 vol% methanol; this improved hydrogen generation rate is significantly higher than the reported Cu-containing TiO₂, including some Pt and Pd loaded TiO₂. Optimal Cu content of 9.1 mol% provided maximum active sites and allowed good light penetration in TiO₂. Over this efficient CuO-TiO₂, the hydrogen generation rate was accelerated by increasing the methanol concentration according to Freundlich adsorption isotherm. However, the photocatalytic hydrogen generation rate was suppressed under long time irradiation mainly due to accumulation of by-products, reduction of CuO and copper leaching, which requires further investigation.     

Synthesis and electrochemical properties of Na-doped Li3V2(PO4)3 cathode materials for Li-ion batteries

Na-doped Li_3−xNa_xV₂(PO₄)₃/C (x = 0.00, 0.01, 0.03, and 0.05) compounds have been prepared by using sol-gel method. The Rietveld refinement results indicate that single-phase Li_3−xNa_xV₂(PO₄)₃/C with monoclinic structure can be obtained. Among three Na-doped samples and the undoped one, Li_2.97Na_0.03V₂(PO₄)₃/C sample has the highest electronic conductivity of 6.74 × 10⁻³ S cm⁻¹. Although the initial specific capacities for all Na-doped samples have no much enhancement at the current rate of 0.2 C, both cycle performance and rate capability have been improved. At the 2.0 C rate, Li_2.97Na_0.03V₂(PO₄)₃/C presents the highest initial capacity of 118.9 mAh g⁻¹ and 12% capacity loss after 80 cycles. The partial substitution of Li with Na (x = 0.03) is favorable for electrochemical rate and cyclic ability due to the enlargement of Li₃V₂(PO₄)₃ unit cells, optimizing the particle size and morphology, as well as resulting in a higher electronic conductivity.     

Developing a statistical model to predict hydrogen production by a mixed anaerobic mesophilic culture

Optimizing the hydrogen (H₂) yield at several initial pH conditions in a mixed batch anaerobic mesophilic culture fed with glucose and linoleic acid (LA) was performed using a three factor three level Box–Benkhen design (BBD). Based on the BBD approach, a statistical model was developed to predict the H₂ yield. The variables considered for the experimental design were the LA concentration, the initial pH and the number of times glucose was added to the culture. The D-optimality method predicted a maximum H₂ yield of 3.49 mol H₂ mol glucose⁻¹ for cultures fed 1.9 g l⁻¹ LA, maintained at an initial pH of 5.15 and received 1.79 glucose additions. The response outcome (H₂ yield of 3.38 ± 0.22 mol mol glucose⁻¹) at the nearest setting of the experimental factors (2.0 g l⁻¹ LA, an initial pH of 5.0 and two glucose additions) was 3.3% less than the predicted maximum value. The model provides a useful approach for predicting H₂ production when H₂ consumers are inhibited in mixed batch anaerobic cultures.     

Sodium inhibition of fermentative hydrogen production

A continuous-stirred-tank reactor (CSTR) was fed with low-sodium influent containing 0.27 g of Na⁺/L for 70 days (Phase I), and then subjected to higher concentrations of Na⁺/L, i.e. 2.41 (Phase II), 5.36 (Phase III), and 10.14 g (Phase IV-1). At the quasi-steady state of each phase, biomass was sampled for an acute sodium toxicity assay. Unlike the control biomass, which exhibited a monotonic decrease of specific H₂ production activity (SHPA) with increasing sodium concentration from 0.27 to 21.00 g Na⁺/L, the acclimated biomass maintained their activity up to 6.00 g Na⁺/L. Soluble microbial product analysis revealed that a sudden increase of the exterior sodium concentration changed the metabolic pathway such that it became favorable to lactate production while depressing butyrate production. Meanwhile, when the biomass was allowed for sufficient time to adapt to the chronic toxicity condition, the volumetric H₂ production rate (VHPR) was maintained above 4.05 L H₂/L/d at up to Phase III. However, an irrecoverable H₂ production drop was observed at Phase IV-1 with a significant increase of lactate and propionate production. Although the sodium concentration decreased to 8.12 (Phase IV-2), 6.61 (Phase IV-3), and 5.36 g Na⁺/L (Phase V) at further operation, the performance was never recovered. A PCR-DGGE analysis revealed that lactic acid bacteria (LAB) and propionic acid bacteria (PAB) were only detected at Phases IV and V, which are not capable of producing H₂.     

Ion transport and ion-filler-polymer interaction in poly(methyl methacrylate)-based, sodium ion conducting, gel polymer electrolytes dispersed with silica nanoparticles

Experimental studies are carried out on novel sodium ion conducting, gel polymer electrolyte nanocomposites based on poly(methyl methacrylate) (PMMA) and dispersed with silica nanoparticles. The nanocomposites are obtained in the form of free-standing transparent films.A gel electrolyte with ∼4 wt.% SiO₂ offers the maximum electrical conductivity of ∼3.4 × 10⁻³ S cm⁻¹ at ∼20 °C with good mechanical, thermal and electrochemical stability. Physical characterization by X-ray diffraction, Fourier transformed infra-red and scanning electron microscopy is performed to examine ion/filler-polymer interaction and the possible changes in the texture of the host polymer due to liquid electrolyte entrapment and the dispersion of SiO₂ nanoparticles. The temperature dependence of the electrical conductivity is consistent with an Arrhenius-type relationship in the temperature range from 25 to 75 °C. Sodium ion conduction in the gel electrolyte film is confirmed from cyclic voltammetry and transport number measurements. The value of the sodium ion transport number (tNa⁺) of the undispersed gel electrolyte is ∼0.23 and it is almost unaffected due to the dispersion of SiO₂ nanoparticles. The effect of SiO₂ dispersion on ionic conduction is described in terms of anion-filler surface interaction.     

Innovative microbial fuel cell for electricity production from anaerobic reactors

A submersible microbial fuel cell (SMFC) was developed by immersing an anode electrode and a cathode chamber in an anaerobic reactor. Domestic wastewater was used as the medium and the inoculum in the experiments. The SMFC could successfully generate a stable voltage of 0.428 ± 0.003 V with a fixed 470 Ω resistor from acetate. From the polarization test, the maximum power density of 204 mW m⁻² was obtained at current density of 595 mA m⁻² (external resistance = 180 Ω). The power generation showed a saturation-type relationship as a function of wastewater strength, with a maximum power density (P_max) of 218 mW m⁻² and a saturation constant (K_s) of 244 mg L⁻¹. The main limitations for achieving higher electricity production in the SMFC were identified as the high internal resistance at the electrolyte and the inefficient electron transfer at the cathode electrode. As the current increased, a large portion of voltage drop was caused by the ohmic (electrolyte) resistance of the medium present between two electrodes, although the two electrodes were closely positioned (about 3 cm distance; internal resistance = 35 ± 2 Ω). The open circuit potential (0.393 V vs. a standard hydrogen electrode) of the cathode was much smaller than the theoretical value (0.804 V). Besides, the short circuit potential of the cathode electrode decreased during the power generation in the SMFC. These results demonstrate that the SMFC could successfully generate electricity from wastewater, and has a great potential for electricity production from existing anaerobic reactors or other anaerobic environments such as sediments. The advantage of the SMFC is that no special anaerobic chamber (anode chamber) is needed, as existing anaerobic reactors can be used, where the cathode chamber and anode electrode are immersed.     

Noble metal-free cobalt oxide (CoOx) nanoparticles loaded on titanium dioxide/cadmium sulfide composite for enhanced photocatalytic hydrogen production from water

In this present paper, cobalt oxide (CoO_x) is studied as an effective cocatalyst in a photocatalytic hydrogen production system. CoO_x-loaded titanium dioxide/cadmium sulfide (TiO₂/CdS) semiconductor composites were prepared by a simple solvothermal method and characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), ultraviolet–visible diffuse reflectance spectroscopy (UV–Vis DRS), and X-ray photoelectron spectroscopy (XPS). Photocatalytic hydrogen production was studied using the as-synthesized photocatalysts in aqueous solution containing sodium sulfide (Na₂S)/sodium sulfite (Na₂SO₃) as hole scavengers under visible light irradiation (λ > 400 nm). The optimal cobalt content in CoO_x-loaded TiO₂/CdS composite is determined to be 2.1 wt% and the corresponding rate of hydrogen evolution is 660 μmol g⁻¹ h⁻¹, which is about 7 times higher than TiO₂/CdS and CdS photocatalysts under the same condition. Visible light-driven photocurrents of the semiconductor composites were further measured on a photoelectrochemical electrode, revealing that the photocorrosion of CdS can be prevented due to the presence of TiO₂–CoO_x.     

Effects of pH value and substrate concentration on hydrogen production from the anaerobic fermentation of glucose

A series of batch experiments were conducted to investigate the effects of pH and glucose concentrations on biological hydrogen production by using the natural sludge obtained from the bed of a local river as inoculant. Batch experiments numbered series I and II were designed at an initial and constant pH of 5.0–7.0 with 1.0 increment and four different glucose concentrations (5.0, 7.5, 10 and 20 g glucose/L). The results showed that the optimal condition for anaerobic fermentative hydrogen production is 7.5 g glucose/L and constant pH 6.0 with a maximum H₂ production rate of 0.22 mol H₂ mol⁻¹ glucose h⁻¹, a cumulative H₂ yield of 1.83 mol H₂ mol⁻¹ glucose and a H₂ percentage of 63 in biogas.     

Aluminum chloride for accelerating hydrogen generation from sodium borohydride

The present research paper reports preliminary results about the utilization of anhydrous aluminum chloride (AlCl₃) for accelerating hydrogen generation through hydrolysis of aqueous solution of sodium borohydride (NaBH₄) at 80 °C. To the best of our knowledge, AlCl₃ has never been considered for that reaction although many transition metal salts had already been assessed. AlCl₃ reactivity was compared to those of AlCl₃·6H₂O, AlF₃, CoCl₂, RuCl₃ and NiCl₂. With AlCl₃ and a NaBH₄ solution having a gravimetric hydrogen storage capacity (GHSC) of 2.9 wt.%, almost 100% hydrogen was generated in few seconds, i.e., with a hydrogen generation rate (HGR) of 354 L min⁻¹ g⁻¹(Al). This HGR is one of the highest rates ever reported. Higher HGRs were obtained by mixing AlCl₃ with CoCl2, RuCl₃ or NiCl₂. For example, the system RuCl₃:AlCl₃ (50:50 mass proportion) showed a HGR > 1000 L min⁻¹ g⁻¹(Ru:Al). The hydrolysis by-products (once dried) were identified (by XRD, IR and elemental analysis) as being Al(OH)₃, NaCl and Na₂B(OH)₄Cl and it was observed that even in situ formed Al(OH)₃ has catalytic abilities with HGRs of 5 L min⁻¹ g⁻¹(Al). All of these preliminary results are discussed, which concludes that AlCl₃ has a potential as accelerator for single-use NaBH₄-based storage system.     

Synthesis of (CuIn)xCd2(1−x)S2 photocatalysts for H2 evolution under visible light by using a low-temperature hydrothermal method

A new series visible-light driven photocatalysts (CuIn)_xCd_2(1−x)S₂ was successfully synthesized by a simple and facile, low-temperature hydrothermal method. The synthesized materials were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) surface area measurement, X-ray photoelectron spectroscopy (XPS) and ultraviolet-visible spectroscopy (UV–Vis DRS). The results show that the morphology of the photocatalysts changes with the increase of x from 0.01 to 0.3 and their band gap can be correspondingly tuned from 2.37 eV to 2.30 eV. The (CuIn)_xCd_2(1−x)S₂ nanocomposite show highly photocatalytic activities for H₂ evolution from aqueous solutions containing sacrificial reagents, SO₃²⁻ and S²⁻ under visible light. Substantially, (CuIn)_0.05Cd_1.9S₂ with the band gap of 2.36 eV exhibits the highest photocatalytic activity even without a Pt cocatalyst (649.9 μmol/(g h)). Theoretical calculations about electronic property of the (CuIn)_xCd_2(1−x)S₂ indicate that Cu 3d and In 5s5p states should be responsible for the photocatalytic activity. Moreover, the deposition of Pt on the doping sample results in a substantial improvement in H₂ evolution than the Pt-loaded pure CdS and the amount of H₂ produced (2456 μmol/(g h)) in the Pt-loaded doping system is much higher than that of the latter (40.2 μmol/(g h)). The (CuIn)_0.05Cd_1.9S₂ nanocomposite can keep the activity for a long time due to its stability in the photocatalytic process. Therefore, the doping of CuInS₂ not only facilitates the photocatalytic activity of CdS for H₂ evolution, but also improves its stability in photocatalytic process.