Effect of culture time on the growth curve and power performance in a microbial fuel cell at a fixed amount of liquid culture

The microbial fuel cell uses the microorganism biochemistry to carry on the energy conversion. Concerning the experimental precision, the colony culture would be replaced by a fixed amount of liquid culture for Microbial fuel cell of Escherichia coli. The anode and cathode chambers whose each volume is 100 mL were utilized, the effective surface area of proton exchange membrane Nafion-117 is about 9 cm². In addition, the electrode area of carbon cloth is 20 cm². Three kinds of Escherichia coli, named as BCRC No. 10322, 10675 and 51534, respectively, would be selected. Results show that the electricity performance of Escherichia coli of BCRC No.51534 is better than the other microorganism studied because of having a larger open circuit voltage of 1.01 V and limiting current 22 mA, the maximum power density of 1342 mW/m^2, and average working power density of 295 mW/m² would be produced. These results would be useful to improve the performance of microbial fuel cell.     

Impact of nonuniform reactant flow rate on the performance of proton exchange membrane fuel cell stacks

ABSTRACT

In this study, a proton exchange membrane (PEM) fuel cell stack composed of five cells in series is numerically investigated to study the impact of the nonuniform reactant flow rate on the performance of the stack. A comparison of the water concentration, temperature, reaction heat source, and current density of change rule of two groups of fuel cell stacks with uniform and nonuniform reactant flow rate reveals the performance degradation mechanism caused by nonuniform reactant flow. The results indicate that while operating under low-voltage conditions, the nonuniform reactant flow rate will cause the accumulation of excess liquid water near the PEM that is near the cathode exhaust outlet, and the local area reacts strongly on the catalyst, whereas the local area reacts slowly. When the average voltage of the stack is 0.55 V, the current density under the nonuniform reactant flow rate condition is 12.9% lower than that of the uniform reactant flow rate condition. In the case of uniform and nonuniform reactant flow rate at low current densities, the performance difference is not evident, but it is expected to be pronounced with the increase in current density. The simulation results are compared with the experimental data reported in the literature through a polarization curve, and they turn out to be well correlated with the experimental results.     

A nanocomposite of CoFe2O4-carbon microspheres for electrochemical energy storage applications

A carbon/CoFe₂O₄ composite was synthesized by precipitation method. The morphology of the composite was analyzed using scanning electron microscopy, X-ray diffraction, transmission electron microscopy, Fourier Transform Infrared Spectra, and vibrating sample magnetometry. The electrocapacitive behaviors of the composite has been studies by cycle voltammogram and galvanic charge/discharge. The size of the nanoparticles carbon composite of CoFe₂O₄ was uniform and 209 nm. Due to a high percent of carbon, electrochemical measurements showed electrical double layer mechanism. Specifically, the carbon/cobalt ferrite electrode exhibited high specific capacitance of 102.5 F g^?1 at a current density of 0.16 A g^?1, and high rate capability with 30% retention of capacitance even up to 20 A g^?1, and excellent cycling stability with 81.5% retention of the initial capacitance after 6000 charge/discharge cycles, supporting that the carbon cobalt ferrite composite electrode could be a potential candidate for supercapacitor application.     

Preparation and characterization of activated carbon from a new raw lignocellulosic material: Flamboyant (Delonix regia) pods

Activated carbons were prepared from flamboyant pods by NaOH activation at three different NaOH:char ratios: 1:1 (AC-1), 2:1 (AC-2), and 3:1 (AC-3). The properties of these carbons, including BET surface area, pore volume, pore size distribution, and pore diameter, were characterized from N₂ adsorption isotherms. The activated carbons obtained were essentially microporous and had BET surface area ranging from 303 to 2463 m² g⁻¹.¹³C (CP/MAS and MAS) solid-state NMR shows that the lignocellulosic structures were completely transformed into a polycyclic material after activation process, thermogravimetry shows a high thermal resistance, Boehm titration and Fourier-transform infrared spectroscopy allowed characterizing the presence of functional groups on the surface of activated carbons. Scanning electron microscopy images showed a high pore development. The experimental results indicated the potential use of flamboyant pods as a precursor material in the preparation of activated carbon.     

Investigation of three system shut-down strategies alongside optimization suggestion for proton exchange membrane fuel cells via in-situ measurements

ABSTRACT

Carbon corrosion caused by H₂/O₂ interface during the shut-down process is one of the factors that exacerbate the overall degradation of proton exchange membrane fuel cells (PEMFC) in automotive applications. Numerous studies have shown that system strategies are beneficial for reducing the duration of H₂/O₂ interface and alleviating performance degradation. In this paper, three different shut-down strategies are investigated and compared based on the internal behaviors acquired by in-situ measurements. For the three shut-down strategies, reverse current and high potential are mainly observed in a lower constant current and constant power strategy. Comparatively speaking, the internal uniformity of the cell under constant current and power load is better than that with constant voltage strategy when the shut-down time is about the same. The results suggest that adopting a higher constant power load followed by a larger voltage load during the shut-down process can effectively shorten the shut-down time and relieve carbon corrosion. These results add significant new insights into the shut-down process and will be of practical importance in directing design of combined shut-down strategy that can withstand carbon corrosion.     

Generation Performance of Gas-Feed Direct Methanol Fuel Cell

Abstract

The modification effect of Nafion on the generation performance at different temperatures and methanol concentrations was investigated. The direct methanol fuel cell performances and electrochemical properties of the DMFC system using as-received Nafion117, a modified Nafion membrane, and using the Nafion117 MEA preparation by spray treatment on the surface of each catalyst layer for conductivity improvement. The open circuit voltage using the modified Nafion membrane was higher than that using Nafion117 at the cell temperature of 343–383 K and methanol concentration of 1.5–10 kmol/m³. The spray treatment of MEA was effective and improved the short circuit current up to 461 mA/cm² at a 5 kmol/m³ methanol concentration in comparison with no treatment of MEA because of the low interfacial resistance. The power density of 75 mW/cm² (no treatment Nafion117 MEA:40 mW/cm²) was obtained. The method of the spray treatment was found to be very effective for the DMFC system. The cell performance of Nafion117 MEA increased with the methanol concentration because of the reduction of the concentration overvoltage.     

CO2 removal using membrane gas absorption

The objective of this study is to investigate the potential process for the removal of carbon dioxide (CO₂) from flue gas using fundamental membrane contactor, which is a membrane gas absorption (MGA) system. The experiments consisted of microporous polyvinylidenefluoride (PVDF) flat sheet membrane with 0.1 μm (as module I) and 0.45 μm (as module II) pore size. 2-Amino-2-methyl-1-propanol (AMP) solution was employed as the liquid absorbent. The effect of AMP concentration was studied with variation in the range 1–5 M. In addition, the experiments were carried out with 10%, 20%, 30% and 40% gas ratio of CO₂ to N₂ and pure CO₂ as well. Through contact angle measurement, membranes for module I and module II were obtained with CA values of around 130.25° and 127.77°, respectively. The mass transfer coefficients for module II are lower than those of module I for 1–5 M of AMP. Furthermore, the increase in CO₂ concentration in the feed gas stream enhanced the CO₂ flux as the driving force of the system was increased in sequence from 1 M to 5 M of AMP. However, after the particular percentage (40%) of CO₂ inlet concentration, the CO₂ fluxes seem saturated. The combination of AMP as liquid absorbent and PVDF microporous membrane in MGA system has shown the potential to remove the CO₂ from flue gas. In addition, the higher AMP concentration gave higher mass transfer coefficient at low liquid flow rates.     

Robust reliability and electrical performances by the bulk-contact modulation in 60-V p-channel LDMOS power components

To increase reliability and electrical performance, shallow-trench isolation (STI) (or called field-oxide (FOX)) structures were inserted in the bulk-contact region of 60-V high-voltage p-channel lateral-diffused MOSFET (pLDMOS) devices in this study. As the FOX ratio increased with the addition of FOX segments, the value of the secondary breakdown current (I_t2) was enhanced. Therefore, the anti-electrostatic discharge ability of a pLDMOS device can be efficiently improved using this novel method. In addition, when the weighting ratio of FOX structures increased, variation values in the trigger voltage (V_t1) and holding voltage (V_h) of the corresponding samples remained within the range of approximately 1–4 V. The R_on value decreased because of more uniform conduction. The experimental data for the FOX structures added to the bulk revealed that the I_t2 value was improved by approximately 13.98%, V_h values were greater than 60 V (which is favorable for latch-up immunity), and the R_on value was decreased by approximately 12.62% compared with a reference device under test (without FOX segments in the bulk-contact region).     

Validation of a dynamic model of hydrogen permeation through Pd-based membranes

Pd-based membranes have been studied for pure hydrogen separation from syngas: in particular, a mathematical model of a Pd membrane for hydrogen separation has been developed.This model can be used in process and assessment studies of the parameters which characterize the mass transfer phenomena (such as: hydrogen permeability, surface coverage and limiting step). By coupling the permeation and water gas shift reaction kinetics, it can also be used to evaluate the performances of the membrane reactor. Further, it can be helpful to evaluate the best assembly and sizing of a H₂/CO₂ separation system.The model takes into account the kinetics of H₂ adsorption/desorption on Pd surface, the H₂ permeation into the palladium bulk and in the porous layer, and the kinetics of CO, CO₂, H₂O, O₂, H₂S competitive adsorption/desorption on Pd surface. It is also comprehensive of flux equations and bulk mass, momentum and energy balance.The results released by the model were compared to the experimental data during both the transient phase and the steady state conditions. A satisfactory agreement between model and experimental data was found.     

Effects of alkali promoters on the textural and catalytic properties of mesoporous Fe–Al–Cu catalysts for water gas shift reaction

Mesoporous Fe₂O₃–Al₂O₃–CuO catalysts promoted with alkali oxides were synthesized and used in water gas shift reaction (WGSR) at high temperatures for hydrogen purification. These chromium-free catalysts were characterized using nitrogen adsorption/desorption, hydrogen temperature programmed reduction, X-ray diffraction (XRD), and transmission electron microscopy techniques. The synthesized catalysts with narrow single-modal pore size distribution in mesopore region possessed high specific surface area. The catalytic results revealed that except Cs, the addition of other alkali promoters declined the catalytic activity. However, all catalysts showed higher catalytic performance than the conventional commercial catalyst. The results showed an optimum content of Cs promoter (3 wt.%) for the promoted Fe–Al–Cu catalyst (3 wt.% Cs-FAC), which exhibited the highest activity in WGSR at high temperature.     

Capture of carbon dioxide from flue or fuel gas mixtures by clathrate crystallization in a silica gel column

A column of silica gel was employed to contact water with flue gas (CO₂/N₂) mixture to assess if CO₂ can be separated by hydrate crystallization. Three different silica gels were used. One with a pore size of 30 nm (particle size 40–75 μm) and two with a pore size of 100 nm and particle sizes of 40–75 and 75–200 μm respectively. The observed trends indicate that larger pores and particle size increase the gas consumption, CO₂ recovery, separation factor and water conversion to hydrate. Thus, the gel (gel #3) with the larger particle size and larger pore size was chosen to carry out experiments with concentrated CO₂ mixtures and for experiments in the presence of tetrahydrofuran (THF), which itself is a hydrate forming substance. Addition of THF reduces the operating pressure in the crystallizer but it also reduces the gas uptake. Gel #3 was also used in experiments with a fuel gas (CO₂/H₂) mixture in order to recover CO₂ and H₂. It was found that the gel column performs as well as a stirred reactor in separating the gas components from both flue gas and fuel gas mixtures. However, the crystallization rate and hydrate yield are considerably enhanced in the former. Finally the need for stirring is eliminated with the gel column which is enormously beneficial economically.     

Parametric investigation of the calcium looping process for CO2 capture in a 10 kWth dual fluidized bed

Calcium looping (CaL) is a promising post-combustion CO₂ capture technology which is carried out in a dual fluidized bed (DFB) system with continuous looping of CaO, the CO₂ carrier, between two beds. The system consists of a carbonator, where flue gas CO₂ is adsorbed by CaO and a regenerator, where captured CO₂ is released. The CO₂-rich regenerator flue gas can be sequestered after gas processing and compression. A parametric study was conducted on the 10 kW_th DFB facility at the University of Stuttgart, which consists of a bubbling fluidized bed carbonator and a riser regenerator. The effect of the following parameters on CO₂ capture efficiency was investigated: carbonator space time, carbonator temperature and calcium looping ratio. The active space time in the carbonator, which is a function of the space time and the calcium looping ratio, was found to strongly correlate with the CO₂ capture efficiency. BET and BJH techniques provided surface area and pore volume distribution data, respectively, for collected sorbent samples. The rate of sorbent attrition was found to be 2 wt.%/h which is below the expected sorbent make-up rate required to maintain sufficient sorbent activity. Steady-state CO₂ capture efficiencies greater than 90% were achieved for different combinations of operational parameters. Moreover, the experimental results obtained were briefly compared with results derived from reactor modeling studies. Finally, the implications of the experimental results with respect to commercialization of the CaL process have been assessed.     

Preparation of activated carbons from unburnt coal in bottom ash with KOH activation for liquid-phase adsorption

In this work, unburnt coal (UC) in bottom ash from coal-fired power plants was soaked in KOH solution and activated for 1 h at 780 °C. The yield of activated carbons varied from 47.8 to 54.8% when the KOH/UC weight ratio changed from 2 to 4. Pore properties of these activated carbons including the BET surface area, pore volume, pore size distribution, and pore diameter were characterized based on N₂ adsorption isotherms. It was shown that the isotherms for the adsorption of methylene blue, acid blue 74, and 4-chlorophenol from aqueous solutions on these activated carbons at 30 °C were well fitted by the Langmuir equation (correlation coefficient r² > 0.9968). The adsorption capacities of methylene blue, acid blue 74, and 4-chlorophenol were obtained to be 2.40–2.88, 0.57–1.29, and 2.34–5.62 mmol/g, respectively. Moreover, the adsorption kinetics could be suitably described by the Elovich equation.     

Ferric-manganese doped sulphated zirconia nanoparticles catalyst for single-step biodiesel production from waste cooking oil: Characterization and optimization

Biodiesel of waste cooking oil origin is gaining attention as a replacement for current fossil fuels, as its low-priced, recycled feedstock shall prevent food source competition, which is estimated to happen with current biodiesel production processes. As a result, waste cooking oil has been claimed to be a highly potential feedstock for biodiesel production. In the present research work, Fe-Mn doped sulphated zirconia catalyst was synthesized and used in simultaneous esterification and transesterification of waste cooking oil to biodiesel synthesis. The catalyst was prepared through the impregnation method and characterized by using XRD, TPD-NH_3, FT-IR, BET, and TEM. Response surface methodology (RSM) in conjunction with the central composite design (CCD) was applied to statistically evaluate and optimize the biodiesel preparation process. It was found that the synthesis of biodiesel achieved an optimum level of 97.2% waste cooking oil methyl ester’s (WCOME’s) yield at the following reaction conditions: methanol/oil molar ratio: 10:1, catalyst concentration: 3.0 wt %, and reaction temperature: 160 °C. The extremely high WCOME’s yield of 97.2% was proved to be due to high acidity, surface area, and large pore diameter; reactants can easily diffuse into the interior pore of the catalyst and allow them to be in contact with active sites that enhance catalytic activity.     

Laboratory calibration of the seismo-acoustic response of CO2 saturated sandstones

Ultrasonic experiments were undertaken on CO₂ flooded sandstone core samples, both synthetic sandstones and core plugs from the CRC1 CO₂ injection well in the Otway Basin, Victoria, South Eastern. Australia. The aim of these laboratory tests was to investigate the effects of CO₂ as a pore fluid on the seismo-acoustic response of the sandstone and ultimately to provide an indication of the sensitivity of time-lapse seismic imaging of the eventual CO₂/CH₄ plume in the Otway, Waarre C formation.The synthetic sandstones were manufactured using both a proprietary calcium in situ precipitation (CIPS) process and a silica cementing technique. Samples were tested in a computer controlled triaxial pressure cell where pore pressures can be controlled independently of the confining pressures. The pressure cell is equipped with ultrasonic transducers housed in the loading platens. Consequently, effective pressures equivalent to those expected in the reservoir can be applied while ultrasonic testing is undertaken. Both compressional, P and shear waves, S were recorded via a digital oscilloscope at a range of effective pressure steps. Pore pressures were varied from 4 MPa to 17 MPa to represent both the gaseous and liquid phase regions of the CO₂ phase diagram. Similar experiments were conducted on core plugs from the Waarre C reservoir horizon obtained from the CRC1 injection well, but with an intervening brine-saturated step and in some cases with a CO₂/CH₄ mix of 80%/20% molar fraction which is representative of the field situation. However, the pore pressure in these experiments was held at 4 MPa. Finally, acoustic impedances and reflection coefficients were calculated for the reservoir using Gassmann theory and the implications for imaging the CO₂ plume is discussed.     

High-affinity ouabain receptors: primary membrane sensors for ionizing radiation

Although the high sensitivity of the Na/K pump in cell membrane to ionizing radiation is well known in literature, the individual role of different isoforms of pump in determination of its radio-sensitivity is not clear yet. This is the subject of the present investigation. Using isotope, electro-physiological and enzymological methods, the effect of γ-ionizing radiation on cell membrane voltage-current characteristics, acetylcholine-induced membrane current, ²²Na⁺ and ⁴⁵Ca²⁺ exchange between cells and bathing solution, Na+K⁺-ATPase activity, dose-dependent ouabain binding with cell membrane, intracellular cAMP and membrane phosphorylation in snail neurons were studied. The changes in neurons as a result of 30-min γ-radiation exposure of snails to 5.16 Ci/kg at the end of the first 30 min of post-radiation period were as follows: the increase in membrane ionic conductance reversed the ouabain sensitivity of acetylcholine-induced currents, stimulation of ²²Na⁺ and ⁴⁵Ca²⁺ uptakes, inhibition of Na/K pump, activation Na/Ca exchange in reversed mode, increase in ouabain binding with high-affinity α₃ and decrease with α₂ middle-affinity receptors, decrease in intracellular cAMP content and membrane dephosphorylation. On the basis of the obtained data, it is suggested that both α₃ and α₂ catalytic subunits of Na⁺+K⁺-ATPase serve primary membrane sensors through the activation of which the biological effect of γ-radiation on neurons is realized. The IR has activation effects on α₃-dependent Na⁺/Ca²⁺ exchange in forward and its inactivation on α₂-dependent reverse modes.     

Tailor-made FAU zeolite composite membrane for wastewater treatment

In this work, a novel multipurpose Faujasite (FAU) zeolite composite membrane was fabricated by in-situ hydrothermal method to separate different solute molecules such as vanillic acid, phenol, and brilliant green from the aqueous solution. The coal fly ash based ceramic substrate was synthesized and used as substrate for preparing the zeolite composite membrane. The X-ray diffraction (XRD) pattern confirmed the crystalline nature of membranes and the presence of Quartz and hematite in the composite membrane. The presence of Si-O and Al-O in zeolite coated composite membrane was confirmed by Fourier Transform infrared spectroscopy (FTIR) analysis. Scanning electron microscope (SEM) analysis showed the porous structure and 8.34 μm thickness of zeolite coating on membrane. The isoelectric point of composite membrane was observed at pH 2.07 through zeta potential analysis. Brunauer-Emmett-Teller (BET) surface area, average pore volume and pore diameter of zeolite composite membrane were estimated as 6.406 m²/gm, 0.0070 cm³/gm, and 4.371 nm, respectively. The hydraulic pore radius and porosity of composite membranes were 27.7 nm and 20.1%. The maximum separation efficiency of FAU zeolite composite membrane towards vanillic acid, phenol and brilliant green was estimated as 78.67%, 89.13%, and 94.28%, respectively, for 200 mg/L feed concentration at 276 kPa applied pressure. The results obtained in this study reveals that the multipurpose FAU zeolite composite membrane fabricated in this study can be effectively used for separation of various solutes molecules present in the wastewater.     

Nano-textured polysilicon solar absorption films

Nano-textured polysilicon (poly-Si) solar absorption films are to be applied to the solar receiver of solar thermal electricity Stirling engine. These films were fabricated by deposition of hydrogenated amorphous silicon films (a-Si:H) into poly-Si films, using the pulse-wave modulation plasma and furnace annealing of the a-Si:H films. This is followed by wet etching of poly-Si films into nano-textured structures. The films are then coated with a-SiN_x:H films as the antireflection and protection layers. It was observed that increasing the pulsed plasma turn-on (t_on) time leads to deposition of less dense a-Si:H film with high hydrogen content and void density. This results in films having low dielectric constant and refractive index, and high optical bandgap. Less-dense a-Si:H film can be transferred into large grain size poly-Si film, using annealing. Also, highly rough nano-textured surface structure can be produced, by etching. The denser a-Si:H film, large grain size poly-Si film, and nano-textured surface poly-Si film can enhance the absorbance of sunlight and reduce the emissivity of far infrared light. The nano-textured poly-Si film coated with an a-SiN_x:H layer can effectively increase the absorbance of sunlight to approximately 85% and reduce the emissivity of far infrared light to 49%. The nano-textured poly-Si/a-SiN_x:H films can be used as efficient solar absorption films for solar thermal electricity Stirling engine.     

Hollow fiber membrane separation process in the presence of gaseous and particle impurities for post-combustion CO2 capture

The membrane separation process for CO₂ capture can be interfered by the gaseous components and the fine particles in flue gas, especially in desulfurized flue gas. In this work, the pint-sized Polyimide(PI) hollow fiber membrane contactors were self-packed to investigate the membrane CO₂ separation from flue gas containing fine particles and gaseous contaminants (SO₂,SO₃,H₂O). First, the effects of SO₂, SO₃, water vapor, and gypsum particles on the CO₂ capture were studied independently and synergistically. The results showed that the effect of SO₂ on the membrane separation properties is indistinctive; however, the membrane performance was damaged seriously with the addition of SO₃. The high humidity promoted the CO₂ separation initially before inhibiting the PI membrane performance. Moreover, the decrease of the CO₂/N₂ selectivity and the permeation rate were accelerated with the coexistence of SO₂. The membrane performance showed an obvious deterioration in the presence of gypsum particles, with a 21% decrease in the CO₂/N₂ selectivity and 51% decrease in the permeation rate. Furthermore, the gypsum particles exerted dramatic damage. Under the WFGD conditions, the combined effects of SO₂, water vapor, and the gypsum particles influenced the stability of the membrane significantly. This tendency is mainly attributed to the deposition of fine particles and aerosol on the membrane surface, which occupied the effective area and enhanced the mass transfer resistance. This study of impurities’ influence could play an important role in further industrial application of membrane CO₂ capture.