Effect of MEA fabrication techniques on the cell performance of Pt–Pd/C electrocatalyst for oxygen reduction in PEM fuel cell

The effect of three different membrane electrode assembly (MEA) fabrication techniques, catalyst-coated substrate by direct spray (CCS) and catalyst-coated membrane by direct spray (CCM-DS) or decal transfer (CCM-DT), on the performance of oxygen reduction in a proton exchange membrane (PEM) fuel cell was carried out under identical conditions of Pt–Pd/C electrocatalyst loading. The results indicated that the fabrication technique had only a very slight effect on the ohmic resistance of the PEM fuel cell but it significantly affected the charge transfer resistance and open circuit voltage (OCV). The cells prepared by the CCM method, and particularly by decal transfer, exhibited a significantly higher OCV but a lower ohmic and charge transfer resistance compared with the other investigated fabrication techniques. By using cyclic voltammetry with H₂ adsorption, it was found that the electrochemical active area of the electrocatalyst prepared by CCM-DT was higher than those prepared by CCS and CCM-DS by around 1.76- and 1.05-fold, respectively. Under a H₂/O₂ system at 0.6 V, the cells with MEA made by CCM-DT provided the highest cell performance of around 350 mA/cm², significantly greater than those prepared by the CCS and CCM-DS (149 and 42 mA/cm², respectively).     

Zinc–air fuel cell,a potential candidate for alternative energy

A zinc–air fuel cell (ZAFC), which generates electricity by the reaction between oxygen and zinc pallets in a liquid alkaline electrolyte, is a potential candidate for an alternative energy generator. It is efficient, completely renewable, and cheap in fabrication because precious metal catalysts are not necessary. In addition, it is environmentally benign because of producing solely recyclable zinc oxide without gas emission. It is applicable to portable, mobile, stationary, and military purposes. In spite of its high potential as an alternative power source, it is yet in a preliminary stage of commercialization because of a few uncertainties remained. This paper reviews the present status of the ZAFC technology and the problems to be overcome for further advancement toward the potential next-generation alternative energy.     

Real time monitoring of bioreactor mAb IgG3 cell culture process dynamics via Fourier transform infrared spectroscopy: Implications for enabling cell culture process analytical technologyŽ 

Compared to small molecule process analytical technology (PAT) applications, biotechnology product PAT applications have certain unique challenges and opportunities. Understanding process dynamics of bioreactor cell culture process is essential to establish an appropriate process control strategy for biotechnology product PAT applications. Inline spectroscopic techniques for real time monitoring of bioreactor cell culture process have the distinct potential to develop PAT approaches in manufacturing biotechnology drug products. However, the use of inline Fourier transform infrared (FTIR) spectroscopic techniques for bioreactor cell culture process monitoring has not been reported. In this work, real time inline FTIR Spectroscopy was applied to a lab scale bioreactor mAb IgG3 cell culture fluid biomolecular dynamic model. The technical feasibility of using FTIR Spectroscopy for real time tracking and monitoring four key cell culture metabolites (including glucose, glutamine, lactate, and ammonia) and protein yield at increasing levels of complexity (simple binary system, fully formulated media, actual bioreactor cell culture process) was evaluated via a stepwise approach. The FTIR fingerprints of the key metabolites were identified. The multivariate partial least squares (PLS) calibration models were established to correlate the process FTIR spectra with the concentrations of key metabolites and protein yield of in-process samples, either individually for each metabolite and protein or globally for all four metabolites simultaneously. Applying the 2^nd derivative pre-processing algorithm to the FTIR spectra helps to reduce the number of PLS latent variables needed significantly and thus simplify the interpretation of the PLS models. The validated PLS models show promise in predicting the concentration profiles of glucose, glutamine, lactate, and ammonia and protein yield over the course of the bioreactor cell culture process. Therefore, this work demonstrated the technical feasibility of real time monitoring of the bioreactor cell culture process via FTIR spectroscopy. Its implications for enabling cell culture PAT were discussed.     

Extinction coefficient measurement of ambient aerosol particles using a ‘white cell’

It was possible to demonstrate in field experiments, that a ‘White Cell’ is a suitable instrument for ambient aerosol extinction measurements even under conditions of low mass concentration. Unsatisfactory agreement of measured and calculated extinction coefficients is due to insufficient information on particle bulk density. The margin within which the real and imaginary parts of the complex refractive index can be varied is sufficient to achieve agreement of measurement and calculation. Future measurements will include the explicit determination of the absorption and scattering coefficients. The additional absorption measurements will help to localize the limits of possible complex refractive index variations.     

Porous membrane based on chitosan–SiO2 for coin cell proton battery

Porous chitosan–SiO₂ membranes were prepared by ultrasonic mixing solution-cast and porogen removal method at different SiO₂ weight ratios. To remove SiO₂ from chitosan membranes, NaOH solution was used to dissolve SiO₂. Porous chitosan:SiO₂ membrane with the weight ratio 1:2 produced optimum average pore size (8.5 μm) with an amorphous structure and the highest water uptake (257.1%). Further soaking of this membrane in NH₄CH₃COO electrolyte solution for two days produced the highest conductivity (3.6×10⁻³ S cm⁻¹) and optimum breakdown voltage (1.8 V). Fabrication of coin cell proton battery displayed an open circuit potential of 1.5 V for 7 days, maximum power density (6.7 mW cm⁻²) and small current resistance (0.03 Ω). The specific discharge capacities obtained from discharge profile of 39.7 mA h g⁻¹ (0.5 mA) and 43.8 mA h g⁻¹ (1.0 mA) increased as the discharge currents were increased. These results showed that a porous chitosan–SiO₂ membrane is suitable membrane for the proton batteries.     

A simplified model to predict the current–voltage relationship of an electro-chlorination cell

A simplified model is described to predict the Current–Voltage (I–V) relationship of a parallel plate electro-chlorination cell containing aqueous NaCl solution as electrolyte. The simplifications allowed obtaining an analytical solution without recourse to computationally intensive numerical solutions like finite element method. The anodic and cathodic exchange current densities and symmetry factors for the model were obtained using linear sweep voltammetry experiments for two different electrodes, viz. graphite and mixed metal oxide coated titanium. Using them, anodic and cathodic overpotential values (for a particular device current I) were predicted using the Butler–Volmer equation. The solution potential drop for the same device current was determined using a modified Nernst–Plank equation. The predicted device voltage (for the device current I), which is the sum of equilibrium electrode potentials, electrode overpotentials and solution potential drop, was compared with experimental (I–V) data for the two electrochemical cells as mentioned above. Results showed that the simplified model could predict the I–V data well, when the electrode surface area was assumed to be twice the superficial area.     

TUM–WelChem cell model for the prediction of liquid distribution in random packed columns

Liquid maldistribution is one of the main deficiencies in random packed column design. Therefore, the knowledge of liquid distribution and its model-based prediction is of great interest. This work aims to further develop and validate the TUM–WelChem Cell Model for random packed columns. First, cell dimension calculations and the determination of random packing element orientations are standardized. The original WelChem Cell Model applies a liquid distribution mechanism based on liquid spread factors derived by virtual 3D irrigation experiments. An extension of the model involves the implementation of liquid and gas load related distribution mechanisms, considering dispersion effects caused by liquid loading and the countercurrent gas flow. The wall flow is refined by an increase of packing porosity at the column wall. Liquid distribution profiles provided by the TUM–WelChem Cell Model are validated against experimental data and show good agreement for both uniform and point source initial liquid distribution.     

Sol–gel hydrothermal synthesis of bismuth–TiO2 nanocubes for dye-sensitized solar cell

Bismuth–TiO₂ nanocubes were synthesized via a facile sol–gel hydrothermal method with titanium tetraisopropoxide as the precursor. The influence of the bismuth on the size, morphology, crystallinity and optical behavior of TiO₂ nanocubes were investigated. The samples were characterized by X-ray diffraction analysis (XRD), transmission electron microscopy (TEM), energy dispersive X-ray (EDX), field emission scanning electron microscopy (FESEM) and UV–visible spectroscopy (UV–vis). Photovoltaic behavior of dye-sensitized solar cells (DSSCs) fabricated using Bi–TiO₂ nanocubes was studied. The DSSCs had an open-circuit voltage (V_oc) of 590 mV, a short-circuit current density (J_sc) of 7.71 mA/cm², and the conversion efficiency (η) of 2.11% under AM 1.5 illumination, a 77% increment as compared to pure TiO₂ nanocubes.     

UV/Vis-based process analytical technology to improve monoclonal antibody and host cell protein separation

Process analytical technology(PAT) is gaining more interest in the biomanufacturing industry because of its potential to improve operational control and compliance through real-time quality assurance.Currently, biopharmaceutical producers mainly monitor chromatographic processes with ultraviolet/visible(UV/Vis) absorbance. However, this measurement has a very limited correlation with purity and quantity. The current study aims to determine the concentration of monoclonal antibody(mAb) and host c...     

Nafion® reinforced with polyacrylonitrile/ZrO2 nanofibers for direct methanol fuel cell application

Nafion® membrane blended with polyacrylonitrile nanofibers decorated with ZrO₂ was successfully fabricated. The composite membrane showed improved proton conductivity, swelling ratio, thermal and mechanical stability, reduced methanol crossover, and enhanced fuel cell efficiency. The nanocomposite membranes achieved a reduced methanol crossover of 5.465 × 10⁻⁸ cm² S⁻¹ compared to 9.118 × 10⁻⁷ cm² S⁻¹ of recast Nafion® membrane using a 5 M methanol solution at 80°C. The composite membrane also showed an ion conductivity of 1.84 compared to 0.25 S cm⁻¹ recast Nafion® at 25°C. The composite membranes showed a peak power density of 68.7 mW·cm⁻² at 25°C, these results show a promising composite membrane for fuel cell application.     

Screen printing of sol–gel-derived electrolytes for solid oxide fuel cell (SOFC) application

The idea of using the sol–gel technique for producing low-cost components for solid oxide fuel cell (SOFC) application has attracted great interest. Besides its economic advantages, the sol–gel technique additionally offers the chance to reduce either the thickness of the electrolyte and therefore to reduce ohmic resistances or to lower the sintering temperature of single components like the electrolyte layer, due to the clearly reduced particle sizes of colloidal distributed particles in the sol.The work presented here deals with the development of sols and their application in combination with yttria fully stabilized zirconia mixed-oxide powders for the preparation of screen-printing pastes. Besides physical, chemical and thermal characterization of the sols, variations of the composition of the sol as well as of the pastes composed of sol and mixed-oxide powder were evaluated for preparing dense, gas-tight layers sintered at various temperatures, resulting in sufficient gas-tightness to ensure high power density SOFCs. Additionally, technological screen-printing parameters were studied.Single cell tests (50 mm × 50 mm) revealed current densities of approx. 1 A/cm². These values are comparable to current densities obtained by cells based on normal electrolyte layers, which were prepared in parallel.     

Condensational particle growth device for reliable cell exposure at the air–liquid interface to nanoparticles

Abstract

A first-of-its-kind aerosol exposure device for toxicity testing, referred to as the Dosimetric Aerosol in Vitro Inhalation Device (DAVID), was evaluated for its ability to deliver airborne nanoparticles to lung cells grown as air–liquid interface (ALI) cultures. For inhalation studies, ALI lung cell cultures exposed to airborne nanoparticles have more relevancy than the same cells exposed in submerged culture because ALI culture better represents the respiratory physiology and consequently more closely reflect cellular response to aerosol exposure. In DAVID, water condensation grows particles as small as 5?nm to droplets sized >5 µm for inertial deposition at low flow rates. The application of DAVID for nanotoxicity analysis was evaluated by measuring the amount and variability in the deposition of uranine nanoparticles and then assessing the viability of ALI cell cultures exposed to clean-air under the same operational conditions. The results showed a low coefficient of variation, <0.25, at most conditions, and low variability in deposition between the exposure wells, trials, and operational flow rates. At an operational flow rate of 4 LPM (liter per minute), no significant changes in cell viability were observed, and minimal effects observed at 6 LPM. The reliable and gentle deposition mechanism of DAVID makes it advantageous for nanoparticle exposure.

Copyright © 2019 American Association for Aerosol Research     

Mechanical behavior of Ce0.9Gd0.1O1.95-La0.6Sr0.4Co0.2Fe0.8O3−δ oxygen electrode with a coral microstructure for solid oxide fuel cell and solid oxide electrolyzer cell

The objective of this work is to investigate the mechanical behavior of CGO-LSCF composite developed by electrostatic spray deposition as an oxygen electrode for Solid Oxide Fuel Cell and Solid Oxide Electrolysis Cell. The coating is characterized by a highly porous morphology designated coral microstructure. Its mechanical behavior was studied by scratch and ultramicroindentation tests and a model of material degradation under progressive compressive loading has been proposed. The coral's damage mechanism involves three regimes: at very low loads stresses are concentrated at the tips of individual corals that fracture and fill the spaces between corals (regime I); as load increases, generalized fracture of the corals occurs and the material starts compacting into an increasingly dense layer (regime II); finally, at the highest loads, the material behaves like an almost fully dense (regime III). As load increases during testing porosity decreases from about 60 to about 5 vol% in the compacted material. The transitions between regimes are associated to increases in the contact stress and the same damage mechanism is found during scratching and indentation. Hardness increases from about 2–100 MPa, while the Young's modulus varies in the range 1–18 GPa, as the porosity decreases. Calculations of the real contact pressure during loading allowed estimating a yield stress of 83 MPa that can be considered as a low limit for the materials fracture strength.     

Experimental measurements of effective diffusion coefficient of oxygen–nitrogen mixture in PEM fuel cell diffusion media

PEM fuel cells are increasingly designed to operate at high current densities. At these densities, mass transport limitations become very significant, but they are not well understood, with many modeling studies but few experimental observations. The use of accurate transport coefficients to simulate the mass transport at high current densities is crucial. In this study, experimental measurements have been carried out to determine the effective diffusion coefficient in the carbon paper gas diffusion layer that is commonly used in PEM fuel cells. It was found that almost all the existing theoretical models significantly overpredict the effective diffusion coefficient by as much as 4–5 times; thus, underestimating the transport limitations considerably. Further, the effects of temperature, Teflon treatment for hydrophobicity and porosity on the effective diffusion coefficient were investigated. It was found that temperature does not affect the overall diffusibility of the gas. The diffusibility is decreased with the increase of Teflon treatment and decrease in porosity. Further work on better understanding the diffusion process in the gas diffusion layer is under way.     

Mesoporous carbons supported non-noble metal Fe–N X electrocatalysts for PEM fuel cell oxygen reduction reaction

Three types of iron–nitrogen-containing non-noble metal catalysts, supported on an ultrasonic spray pyrolysis mesoporous carbon (USPMC), a hollow core mesoporous shell carbon (HCMSC), and a standard carbon (Ketjen Black CJ600, KB), respectively, are synthesized using a wet-impregnation method. The morphologies and structure as well as composition of the synthesized carbon supports and their corresponding supported Fe–N _X catalysts (namely Fe–N _X /USPMC, Fe–N _X /HCMSC, and Fe–N _X /KB, respectively) are physically characterized using EDX, SEM, FESEM, and BET analysis, respectively. The catalytic activities of these three electrocatalysts toward oxygen reduction reaction (ORR) are measured using rotating disk electrode technique in O₂-saturated 0.5 M H₂SO₄ solution. The catalyzed ORR exchange current densities are also obtained using the Tafel method based on the measured data. Among these three electrocatalysts, Fe–N _X /HCMSC can give the best ORR performance, which is correlated to its higher nitrogen, mesopore, and micropore contents, compared to the other electrocatalysts. It is rationalized that the performance improvement of these electrocatalysts may be achieved as long as an optimal relationship among mesopores, micropores, and even macropores for increasing both ORR kinetics and reactant gases accessibility to the active sites can be found.     

Synthesis and evaluation of acyl-chain- and galactose-6'-modified analogues of α-GalCer for NKT cell activation

α-GalCer is an immunostimulating glycolipid that binds to CD1d molecules and activates invariant natural killer T (iNKT) cells. Here we report a scaled-up synthesis of α-GalCer analogues with modifications in the acyl side chain and/or at the galactose 6'-position, together with their evaluation in vitro and in vivo. Analogues containing 11-phenylundecanoyl acyl side chains with aromatic substitutions (14, 16-21) and Gal-6'-phenylacetamide-substituted α-GalCer analogues bearing p-nitro- (32), p-tert-butyl (34), or o-, m-, or p-methyl groups (40-42) displayed higher IFN-γ/IL-4 secretion ratios than α-GalCer in vitro. In mice, compound 16, with an 11-(3,4-difluorophenyl)undecanoyl acyl chain, induced significant proliferation of NK and DC cells, which should be beneficial in killing tumors and priming the immune response. These new glycolipids might prove useful as adjuvants or anticancer agents.     

Advances in novel SDC@Al2O3 core−shell electrolyte for low-temperature solid oxide fuel cell

The preparation of electrolyte with excellent ionic conduction is an important development direction in the practical application of solid oxide fuel cell (SOFC). Traditional methods to improve ion conduction was structure doping to develop electrolyte materials. In this work, the ionic conductor Ce_0.8Sm_0.2O_2-δ (SDC) was modified by insulator Al₂O₃ to enhance ion conduction and apply as electrolytes for the SOFC. The transmission electron microscopy (TEM) characterization clearly clarified that a thin Al₂O₃ layer in the amorphous state coated on SDC to form the SDC@Al₂O₃ core−shell structure. The SDC@Al₂O₃ electrolyte with the core−shell structure possesses a super ionic conductivity of 0.096 S cm⁻¹ and results in advanced cell performance of 1190 mW cm⁻² at 550°C. The X-ray photoelectron spectroscopy (XPS) analysis revealed that the concentration of oxygen vacancies in the SDC@Al₂O₃ core–shell structure significantly improved in comparison with pure SDC, the newly produced oxygen vacancies can promote the oxygen ion transport. Moreover, the interface between SDC and Al₂O₃ provides a fast channel for the proton transport. In addition, the SDC-based SOFC was usually suffered from the reduction of the SDC electrolyte and the accompanying generated electron conduction should deteriorate the cell performance, this is the main challenge for the SDC electrolyte application. In our case, the Al₂O₃ shell on the SDC surface not only can avoid the contact between SDC and hydrogen to eliminate the reduction of SDC but also can restrain electron conduction due to the electron insulation characteristic of the Al₂O₃ shell. This work demonstrates an efficient approach to develop the advanced low-temperature SOFC technology from material fundamentals.     

A novel heteropolyacid-doped carbon nanotubes/Nafion nanocomposite membrane for high performance proton-exchange methanol fuel cell applications

A novel proton-exchange polymer composite membrane was synthesized using Nafion^®, tetraethoxysilane-modified carbon nanotubes (CNTs) and phosphotungstic acid-modified carbon nanotubes with the aim of using direct methanol fuel cells (DMFCs). Physicochemical properties of the modified CNTs and fabricated composite membranes were investigated by Fourier transform infrared spectroscopy, field emission scanning electron microscopy, water uptake, thermogravimetric analysis, ion exchange capacity, proton conductivity and methanol permeability tests. It was demonstrated that chemical surface modification of CNTs and introduction of the phosphotungstic acid (PWA) groups effectively improved the performance of DMFC. It was found that the presence of PWA groups on the surface of CNTs led to the formation of strong electrostatic interactions between the PWA groups and clusters of sulfonic acid in Nafion^® macromolecules. Hence, the incorporation of inorganic phosphotungstic super-acid-doped silicon oxide-covered carbon nanotubes (CNT@SiO₂-PWA) into Nafion^® matrices enhanced the proton conductivity of the prepared membranes. Moreover, the methanol permeability was reduced to 2.63 × 10^?7 cm² s^?1 in comparison with the recast Nafion^® membrane (2.25 × 10^?6 cm² s^?1). Enhancing the proton conductivity and reducing the methanol permeability, the selectivity of the prepared nanocomposite membranes was enhanced to a greater value of 330,700 S s cm^?3 as compared to the value of 38,222 S s cm^?3 for recast Nafion^®.     

Plasma for cancer treatment: How can RONS penetrate through the cell membrane? Answers from computer modeling

Plasma is gaining increasing interest for cancer treatment, but the underlying mechanisms are not yet fully understood. Using computer simulations at the molecular level, we try to gain better insight in how plasma-generated reactive oxygen and nitrogen species (RONS) can penetrate through the cell membrane. Specifically, we compare the permeability of various (hydrophilic and hydrophobic) RONS across both oxidized and nonoxidized cell membranes. We also study pore formation, and how it is hampered by higher concentrations of cholesterol in the cell membrane, and we illustrate the much higher permeability of H2O2 through aquaporin channels. Both mechanisms may explain the selective cytotoxic effect of plasma towards cancer cells. Finally, we also discuss the synergistic effect of plasma-induced oxidation and electric fields towards pore formation.