Transfer Of Hydrogen Ions Research Articles

The Dichotomy of Mn-H Bond Cleavage and Kinetic Hydricity of Tricarbonyl Manganese Hydride Complexes.

Acid-base characteristics (acidity, pKa, and hydricity, ΔG°H- or kH-) of metal hydride complexes could be a helpful value for forecasting their activity in various catalytic reactions. Polarity of the M-H bond may change radically at the stage of formation of a non-covalent adduct with an acidic/basic partner. This stage is responsible for subsequent hydrogen ion (hydride or proton) transfer. Here, the reaction of tricarbonyl manganese hydrides mer,trans-[L2Mn(CO)3H] (1; L = P(OPh)3, 2; L = PPh3) and fac-[(L-L')Mn(CO)3H] (3, L-L' = Ph2PCH2PPh2 (dppm); 4, L-L' = Ph2PCH2-NHC) with organic bases and Lewis acid (B(C6F5)3) was explored by spectroscopic (IR, NMR) methods to find the conditions for the Mn-H bond repolarization. Complex 1, bearing phosphite ligands, features acidic properties (pKa 21.3) but can serve also as a hydride donor (ΔG≠298K = 19.8 kcal/mol). Complex 3 with pronounced hydride character can be deprotonated with KHMDS at the CH2-bridge position in THF and at the Mn-H position in MeCN. The kinetic hydricity of manganese complexes 1-4 increases in the order mer,trans-[(P(OPh)3)2Mn(CO)3H] (1) < mer,trans-[(PPh3)2Mn(CO)3H] (2) ≈ fac-[(dppm)Mn(CO)3H] (3) < fac-[(Ph2PCH2NHC)Mn(CO)3H] (4), corresponding to the gain of the phosphorus ligand electron-donor properties.

Preparation and characterization of slow dissolving linezolid salts for direct pulmonary delivery

Linezolid is a second line antituberculosis which is currently available in the form of oral and parenteral dosage form. Compared to oral and parenteral dosage forms, the direct delivery of antituberculosis drugs to the lungs has proven to be better in maintaining the desire drug concentration. The present investigation was aimed to prepare the slow dissolving salts of linezolid using with long chained fatty acids – lauric acid(LA), palmitic acid (PA) and stearic acid (SA) as counterions for direct pulmonary delivery. The rotary vacuum evaporator and lyophilizer were used sequentially to evaporate the solvent in which the drug and counterions were dissolved. The results of DSC (differential scanning calorimetry) study, microscopic analysis and PXRD (powder X-ray diffraction) study proved the formation of novel crystalline material due to reaction between drug and counterions. The results of FTIR (Fourier transform infrared spectroscopy) and 1H NMR (Nuclear magnetic resonance) confirmed the transfer of hydrogen ion from the carboxylic acid group (–COOH–) of the counterions to the amide (–CONH–) group of the drug and thus the salt formation. The in-vitro dissolution study performed in the simulated lung fluid (SLG), the prepared salts exhibited significantly slower dissolution compared to pure drug and physical mixture. MMAD (Median mass aerodynamic diameter) for all the prepared salt was found to be less than 5 μm which proved ability of the prepared salt particles to reach deep affected area. MIC (Minimum inhibitory concetration) study indicated no significant difference in the MIC value of the pure drug and the prepared salts.

Environment-friendly surface acoustic wave humidity sensor with sodium alginate sensing layer

A low-cost and environment-friendly surface acoustic wave (SAW) humidity sensor was fabricated on a quartz substrate using sol-gel/spin-coated sodium alginate (SA) sensing layer. The sensing mechanism is based on the frequency shift of the SAW sensor caused by both mass loading and electrical loading, with the former being the dominant factor. The SA film prepared in this study is an environment-friendly material with a large number of hydroxyl and carboxylate groups, which easily adsorb and react with H2O molecules to form hydrogen bonds. These adsorbed H2O molecules lead to significantly enhanced mass loading and signal responses of the SAW sensor. Electrical loading effect is also generated due to the transfer of hydrogen ions in the H2O molecules, which alters the electrical resistance and results in changes of resonant frequencies of the SAW device. When the relative humidity (RH) is increased from 35% to 85%, the responses of the SAW sensor with 1 wt% SA are significantly decreased. Whereas in a low humidity environment (e.g., RH <35%), the responses of the sensor show a linear relationship with the change of humidity. The developed humidity sensor shows good short-term/long-term stabilities and a low temperature coefficient of frequency.

Gas Chromatography-Mass Spectrometry-based Phytochemical Analysis and In-Vitro Anti-Lipid Peroxidation, Cyclooxygenase Inhibition Activities of Saudi Eruca sativa Leaves

Eruca sativa is a wholesome yearly shrubbery herb in Saudi Arabia. Eruca sativa leaves are a conventional food and are consumed raw in salads. The present research reports the phytochemical analysis, in-vitro anti-lipid peroxidation, total anti-oxidant capability, cyclooxygenase-1, and -2 (COX1 and COX2) inhibition activities of Saudi Eruca sativa leaves water decoction (EWD). Gas chromatography-mass spectrometry (GC-MS) of EWD revealed seventeen constituents of six different chemical groups: phenolics (23.60%), aromatic and aliphatic esters (16.97%), terpenoids (31.91%), heterocyclics (14.83%), sulfur containing organics (11.25%), and silyl compounds (1.44%). The presence of Astaxanthin (1.96%), Clionasterol (12.81%), Ingol-12-acetate (4.77%), and Phytol (12.37%) in EWD indicated that the decoction technique was effective in extracting thermostable terpenoids. This research is the first report on Eruca sativa unraveling the thermostable phytochemicals. The EWD exhibited a straight-line relationship between liver lipid peroxidation inhibition and 150 to 400 μg/ml concentrations. The % anti-lipid peroxidation effect produced by EWD and Quercetin was statistically significant. At the highest 400 μg/ml dose, EWD exhibits 68.46 and#177; 0.01% anti-lipid peroxidation activity. The demonstrated IC50 of EWD and Ascorbic acid concerning the total anti-oxidant capability is 217.90 μg/ml and 74.91 μg/ml. The in-vitro assay protocols delineated the modes of inhibition of the biological oxidation processes by Eruca sativa, indicating transfer of hydrogen ion and metal ions reduction. The COX inhibitory potential was screened using Ellmannand#39;s reagent. The IC50 values for COX1 and COX2 inhibitions were 152.31μg/ml and 146.4 μg/ml, respectively, indicating that EWD has a potent COX inhibitory potential compared to Indomethacin. The COX2/COX1 ratio of inhibition, less than one, suggested that EWD phytochemicals would be preferential inhibitors of COX2. The current investigation justifies Eruca sativa leaves as a beneficial health food by establishing the chemical composition of water decoction that contributed to the anti-oxidant and COX inhibition activity.

VISCOMETRIC STUDY ON BINARY LIQUID MIXTURES OF PROPIOPHENONE WITH ANILINE AND N-ALKYL SUBSTITUTED ANILINES, AT 303.15 TO 318.15 K

Densities and viscosities of binary mixtures of Propiophenone with Aniline, N-methylaniline, N, N- dimethylaniline, N, N- diethylaniline were measured over the entire composition range at T = (303.15 to 318.15) K (with 5K interval) and atmospheric pressure. Experimental data were used to calculate the deviation of viscosity Δη, excess Gibb’s free energy G*E activation of viscous flow for each binary system, and these excess thermodynamic properties were fitted to the Redlich-Kister polynomial equation to obtain the fitting coefficients and standard deviations. McAllister’s three-body /four-body interaction models were used for the correlation of viscosity data. The studied systems exhibit good intermolecular interactions due to hydrogen ion transfer and charge dispersion in the carbonyl group and NH2 groups of Aniline and Alkyl Substituted Anilines. Experimental results are useful in various pharmaceutical industries.

Multilayer crystal-amorphous Pd-based nanosheets on Si/SiO2 with interface-controlled ion transport for efficient hydrogen storage

This contribution shows an unusually high hydrogen storage of multilayer amorphous (A)-crystalline (C) Pd–Si based nanosheets when stacked in the right order. Samples with A/C/A/C/A stacking sequence exhibit 40 and 12 times larger hydrogen sorption than monolithic crystalline and amorphous samples, respectively. The maximum capacitance calculated from the fitting of electrochemical impedance measurements of the same sample is twice larger than that of the conventional polycrystalline Pd films of similar thickness. Five times higher diffusion coefficient calculated from modified Cottrell equation is obtained compared to specimens with C/A/C/A/C stacking. For the A/C/A/C/A multilayers, nanobubbles with diameters of 1–2 nm are homogeneously distributed at Si/SiO2 interface, and PdHx crystal formation in these regions confirms hydrogen-metal interactions. Furthermore, corrosion-resistant amorphous top layer permits larger amounts of hydrogen ion transfer to inner layers. Thus, hydrogen storage and production can be enhanced by smart design of multilayers targeted for proton exchange membrane electrolysis or fuel cells.

Acid retardation for deeper stimulation—Revisiting the chemistry and evaluation methods

AbstractAcid fracturing treatment in upstream oil and gas production is done to extend the connectivity of the wellbore deep into the reservoir. This is achieved through a dissolution process using acid in conjunction with hydraulic fracturing. A key to success is to impart favourable reaction kinetics between the acid and rock matrix. If the reaction proceeds too rapidly, it results in large voids in the near‐wellbore area but insufficient dissolution in the reservoir. Hydrochloric acid (HCl) is ubiquitous in the petroleum industry for acidizing applications due to its high dissolving capacity towards carbonate minerals, soluble reaction products, and low cost. Its corrosive nature coupled with rapid reaction kinetics have forced the industry to search for mechanisms to address these limitations. The concepts for slowing down reaction rate centre around (1) reducing mass transfer of hydrogen ions, H+; (2) limiting H+ ion dissociation; and (3) altering the wetting property of the rock surface. Reaction kinetics data is critical to guiding the selection of the suitable acid formulations for acid fracturing process. They are commonly measured in the lab using instruments such as a rotating disk reactor, flow cells, and diffusion cell. Though routinely applied, these experimental methods, including their setups and procedures, are rarely questioned. The experimental artefacts can lead to wrong conclusions. Deeper understanding of the fundamental assumptions behind the apparatus design and test procedures is critical. This paper discusses the chemistries employed in acid retardation, and more importantly the attention needed when extending the experimental data to field treatment.

Antibacterial activity and main action pathway of benzyl isothiocyanate extracted from papaya seeds.

The development of natural antimicrobial agents has attracted long-term attention due to the increasing demand for food preservation. Papaya, a widely cultivated nutritious tropical fruit, has benzyl isothiocyanate (BITC) as one of the most important secondary metabolites in its seeds. And the antibacterial activity of BITC toward different strains and the main antibacterial pathway remain unclear. The current study focused on characterizing the antibacterial effect and exploring the major bacteriostatic pathway of BITC. BITC was shown to have a broad-spectrum antibacterial effect, with a minimum inhibitory concentration of 1µL/mL for Escherichia coli, Bacillus subtilis, and Aspergillus niger, and 0.5µL/mL for Salmonella enterica, Staphylococcus aureus, and Penicillium citrinum. Additionally, BITC was identified to affect the integrity of the biological oxidation system rather than the permeability or morphology of cell membranes. Furthermore, BITC was found not only to affect ATP production but also to hinder a series of important chemical reactions of the coenzymes involved in the transfer of hydrogen ions in the respiratory chain. The bacteriostatic pathway of BITC was shown to be implicated in an incomplete respiratory chain and the deregulation of the metabolism system. These results indicate the potential of BITC as a natural preservative in the food industry. PRACTICAL APPLICATION: BITC is present in papaya seeds and can be extracted and purified. Exploring its antibacterial activity and main action pathway may facilitate its application as a new bacteriostatic agent in food industry.

Benchmark Computations of the Binding Energy of Amino Acids to Benzene: The Role of Water

The binding energies of single amino acids to benzene have been computed quantum mechanically using DFT, ccCA-CC(2,3) and ccCA-S4. The goal is to produce binding energies of chemical accuracy that can be used as a comparison with MM force-fields. Even in these small systems we found that water plays a major role in determining the binding energy of the amino acids. A small number of explicit water molecules must be present on the amino acids to accurately model the binding. These water molecules cannot be modeled with a continuum approximation. DFT calculations indicate that approximately two water molecules are needed to saturate the carboxylic acid group and lead to a stable binding energy. In addition it was found that while the zwitterion form of the amino acid is unstable in a vacuum with respect to hydrogen ion transfer, the addition of a single water molecule allows the zwitterion to form a shallow local minimum. We were unable to determine how many water molecules were required to fully solvate the zwitterion.

Emergent electric field control of phase transformation in oxide superlattices

Electric fields can transform materials with respect to their structure and properties, enabling various applications ranging from batteries to spintronics. Recently electrolytic gating, which can generate large electric fields and voltage-driven ion transfer, has been identified as a powerful means to achieve electric-field-controlled phase transformations. The class of transition metal oxides provide many potential candidates that present a strong response under electrolytic gating. However, very few show a reversible structural transformation at room-temperature. Here, we report the realization of a digitally synthesized transition metal oxide that shows a reversible, electric-field-controlled transformation between distinct crystalline phases at room-temperature. In superlattices comprised of alternating one-unit-cell of SrIrO3 and La0.2Sr0.8MnO3, we find a reversible phase transformation with a 7% lattice change and dramatic modulation in chemical, electronic, magnetic and optical properties, mediated by the reversible transfer of oxygen and hydrogen ions. Strikingly, this phase transformation is absent in the constituent oxides, solid solutions and larger period superlattices. Our findings open up this class of materials for voltage-controlled functionality.

(Invited) Design of Catalyst Layer Structure for High Fuel Cell Performance

The low Pt electrode is an important research topic for the commercialization of polymer electrolyte fuel cell (PEFC). Platinum nanoparticles act as a catalyst for the fuel cell electrode and promote the oxygen reduction reaction (ORR). In this process, the surface properties and structure of adjacent carbon supports and ionomer binders greatly affect the Pt catalyst. Therefore, the performance of the Pt/C catalyst in the fuel cell electrode is determined not only by the intrinsic activity of the catalyst itself, but also by the interface structure between the ionomer binder and the Pt/C catalyst. It has been reported that the ORR activity of the Pt/C catalyst in the fuel cell electrode is affected by the Pt poisoning of the sulfonic acid group tethered to the Nafion backbone as well as the oxygen permeability of the ionomer binder [1]. The difference in pore characteristics of the carbon support affects the optimum ionomer content [2] and Pt utilizaton [3] in the electrode. The surface properties of the carbon support also affect ionomer distribution and ionomer thickness on the catalyst surface, thereby altering the activity of the catalyst [4]. In spite of recent studies, understanding of complicated physicochemical phenomena in the microstructure of electrode is still very limited. In this talk, we will discuss the fuel cell performance characteristics based on several electrochemical analyses according to the microstructure control of the catalyst layer. Various functional groups were introduced on the surface of Pt/C catalyst by post treatment and the catalyst layer was prepared to observe the ionomer distribution and ion transport characteristics according to functional groups. In addition, a multilayer catalyst layer having different ionomer contents in the thickness direction of the catalyst layer was prepared using an ultrasonic spraying process, and changes in hydrogen ion transfer and oxygen diffusion transfer characteristics in these catalyst layers were observed in a fuel cell. Finally, the electrochemical properties of the catalyst layer made of the ionomer dispersed in the high-boiling organic solvent will be introduced. 1. V. Yarlagadda, M. K. Carpenter, T. E. Moylan, R. S. Kukreja, R. Koestner, W. Gu, L. Thompson, A. Kongkanand, ACS Energy Lett. 3 (2018) 618. 2. Y. Liu, C. Ji, W. Gu, J. Jorne, H. A. Gasteiger, J. Electrochem. Soc. 158(6) (2011) B614. 3. Y.-C. Park, H. Tokiwa, K. Kakinuma, M. Watanabe, M. Uchida, J. Power Sources 315 (2016) 179. 4. A. Orfanidi, P. Madkikar, H. A. El-Sayed, G. S. Harzer, T. Kratky, H. A. Gasteiger, J. Electrochem. Soc. 164 (2017) F418.

Dopant passivation by adsorbed water monomers causes high humidity sensitivity in PEDOT: PSS thin films at ppm-level humidity

Thin layers of hole conducting polymer poly(3,4-ethylenedioxythiophene)–poly(styrenesulfonate) (PEDOT:PSS) are widely utilized in the fabrication of organic light emitting devices. More recently, the material has been considered as a platform for humidity sensor fabrication. This is interesting as the conductive component of this composite, PEDOT, is hydrophobic. Moreover, charge transport mechanism in PEDOT:PSS is not yet fully established and understanding the cause of sensitivity to humidity may shed further light on the obscure charge conduction in this conductive polymer composite. Here, we investigate the humidity sensitivity in PEDOT:PSS thin films in a wide relative humidity (RH) range and report the existence of a distinctly higher humidity sensitivity in the RH < 1% range. The observed sensitivity is electronic in nature, and is described by considering the hydrogen bonding of the airborne water monomers to the surface-exposed sulfonate groups on the hydrophilic PSS chain, which, in turn, passivates the doping process involving hydrogen ion transfer to the PEDOT chain from those sulfonate groups. This dopant passivation mechanism reduces the charge carrier population in the layer and increases its impedance. The results are anticipated to pave the way for the fabrication of a printable organic humidity sensor with an unprecedented wide dynamic range spanning to sub-ppm humidity levels.

Hydronium ions diffusion behavior in nafion membrane by mesoscopic simulation

To study the mesoscopic transfer characteristics of water and hydronium ions in Nafion membrane of all vanadium flow battery, a mesoscopic model was developed in this paper. In this model, Nafion membrane, water, and hydronium ions were coarse-grained according to the Dissipative Particle Dynamics (DPD) method by Materials Studio software, and the three-dimensional topology of water channel is developed by the DPD theory as well. The impact of temperature, water content and hydronium ions content on diffusion coefficient was analyzed by the diffusion coefficient, and the radial distribution function and its influencing factor were also studied. The results show that, the adsorbed water on sulfonic acid group in the Nafion membrane forms the water channel for hydrated hydrogen ion transfer; more water and higher temperature respectively increase the transfer coefficient of hydrated hydrogen ion in the Nafion membrane by increasing water channel and speeding up movement of the hydrated hydrogen ion. This work is helpful to understand working principle of Nafion membrane and will promote the application of all vanadium flow battery.

Electrochemical Characterization and Voltammetric Determination of β-N-oxalyl-L-α,β-diaminopropionic Acid in Grass Pea Seeds

ABSTRACTThe oxidation of the neurotoxic amino acid, β-N-oxalyl-L-α, β-diaminopropionic acid was characterized by cyclic and square-wave voltammetries on a glassy carbon electrode. An electrochemical protocol was developed and validated for the determination of β-N-oxalyl-L-α,β-diaminopropionic acid in grass pea seeds. Solid-phase extraction was used to separate homoarginine while simultaneously eluting and presenting similar electrochemical behavior amino acid. The analyte, β-N-oxalyl-L-α,β-diaminopropionic acid, exhibited a prewave and a quasireversible anodic peak at 147 mV (prewave) and 200 mV (oxidation peak) versus Ag/AgCl in 0.10 M phosphoric acid buffer at pH 3.0. The oxidation of β-N-oxalyl-L-α,β-diaminopropionic acid was proceeded by adsorption on a glassy carbon electrode by two steps involving two electrons and one hydrogen ion transfer via a quasireversible electrode mechanism. The rate constant was calculated using the quasireversible maximum. The β-N-oxalyl-L-α,β-diaminopropionic acid was electropolymerized on the carbon electrode surface to form poly-β-N-oxalyl-L-α,β-diaminopropionic acid by cyclic voltammetry, analogous to glutamic acid. A linear dependence of the peak current with concentration was observed from 1.20 to 44.6 µM with a detection limit of 1.28 µM using square-wave adsorptive stripping voltammetry and accumulation at −0.4 V versus Ag/AgCl for 60 s. The glassy carbon electrode was cleaned by photocatalytic pretreatment, and the results were compared with alumina polishing. The method was used to analyze grass pea seeds with good specificity and accuracy.

Effects of electrode distance and mixing velocity on current density and methane production in an anaerobic digester equipped with a microbial methanogenesis cell

The microbial methanogenesis cell (MMC) has been studied to enhance organic removal efficiency and methane production in an anaerobic digester (AD). However, its applicability remains limited without practical approaches to scale-up the design for commercialization. Internal resistance within MMC is closely related to the transfer of hydrogen ions between electrodes. We analyzed the effects of various electrode distances and mixing velocities on the current density and methane production in a single AD equipped with an MMC. As the distance between electrodes increased from 1 cm to 5 cm, methane production and current density decreased to 51% and 92%, respectively. Although an increase in mixing velocity decreased the internal resistance, this effect was not significant below a certain distance. For larger distances, an increase in mixing velocity not only increased current density by a factor of approximately 2.5, but also enhanced methane production by a factor of approximately 1.4.

Electrocatalytic Oxidation of Oxalic Acid Using a Multielectrolytic Modified Glassy Carbon Electrodes

Electrocatalytic oxidation activity of oxalic acid can be observed by using a multielectrolytic modified glassy carbon electrode (MMGCE). The MMGCE was fabricated by using the following electrolytic-oxidation/reduction processes. First, the functional groups containing nitrogen atoms such as amino group are introduced by the electrode oxidation of a bare glassy carbon electrode in an ammonium carbamate aqueous solution, and next, this electrode was electroreduced in sulfuric acid, and it was found that the reduction current gradually increased as the electrolysis time increased. This suggests that functional groups containing nitrogen atoms contributing the catalytic electron transfer of hydrogen ion are introduced. To observe the electrode oxidation wave of oxalic acid, the voltammmetric measurements of oxalic acid was carried out by using MMGCE in an acidic medium. The oxidation wave of oxalic acid at low potential range was appeared in the linear sweep voltammograms. The MMGCE exhibited well-defined peak of oxalic acid oxidation in acidic medium.

The Mechanism of the Hydrogen Ion Conduction in Liquid Light and Heavy Water Derived from the Temperature Dependence of Their Limiting Conductivities

The anomalous behavior of liquid water is apparent from the temperature dependence of many experimental properties. Among these are the abnormal high limiting ionic conductivities λ(0) of protons and hydroxyl ions, which in a previous paper we found to depend linearly on the square root of the absolute temperature T(1/2). Here we describe a further study of these conductivities in both light and heavy water, together with the remarkable transition temperature T(0) [242.7 K in H(2)O and 250.5 K in D(2)O], where the supercooled liquid becomes inert and, for example, restricted water molecule rotation is arrested. From T(0) the rotation barrier heights for the two solvents are determined. The conductivity data enable to obtain experimentally the zero point energies of H(+) and D(+) in liquid water, with results in the right order of magnitude as compared to values estimated along quantum mechanical routes. Contrary to general opinion, the isotope effect λ(0)(H(+))/λ(0)(D(+)) is temperature dependent, its value being close to 2(1/2) only near 20 °C. The isotope effect λ(0)(OH(-))/λ(0)(OD(-)) also takes temperature dependent values, substantially higher than 2(1/2). Still, the linear relationships with T(1/2) sustain a model based on water rotation control for the conductivity mechanism. For a quantitative analysis, the rotation frequency ω is expressed by a simple linear function of T(1/2) in terms of the moment of inertia I and the quantity T(0)(1/2). This "ab initio" calculation is found to be in perfect agreement with theoretical and experimental data in the literature, when ω is identified with the reciprocal of the so-called single molecule relaxation time τ(s). The data analysis eventually leads to the conclusion that the hydrogen ion transfer between water molecules proceeds via two parallel pathways. Next to the rotation controlled hopping mechanism there exists a temperature independent transfer controlled by tunnelling, occurring at all relative orientations of the participating water molecules. The applicability of the excess conductivity concept for hydrogen and hydroxyl ions is critically discussed.

Two types of ammonium uncoupling in pea chloroplasts.

The effect of ammonium on ATP synthesis, electron transfer, and light-induced uptake of hydrogen ions in pea chloroplasts was studied. It is shown that the dependence of these reactions on ammonium concentration could be due to effects of two different uncoupling processes. The first process is induced by low ammonium concentrations (<0.2 mM); the second one is observed in the NH(4)Cl concentration interval of 0.5-5.0 mM. The first type of uncoupling is stimulated by palmitic acid or by N,N'-dicyclohexylcarbodiimide, while the second is stimulated by chloroplast thylakoid swelling caused by energy-dependent osmotic gradients. In the presence of the fluorescent dye sulforhodamine B, which does not penetrate through the cell membrane, this swelling causes the dye to enter the lumens. It is supposed that ammonium activates two different routes of cation leakage from the lumen. The first route involves channel proteins, while the second is a mechanosensitive pore that opens in response to osmotic gradients.

Rate determining step of direct hydrogen and electricity production in SrZr 0.9Yb 0.1O 3−a fuel cell supplied with CH 4 + H 2O

Direct hydrogen production and its subsequent electricity generation in a ceramic fuel cell system of a SrZr 0.9Yb 0.1O 3− a tube with one end closed is investigated experimentally under the condition where moist CH 4 (or H 2) is supplied to its anode compartment and moist O 2 is supplied to its cathode compartment. Experiments are performed based on an alternating current impedance method. The following three mass transfer resistances are determined separately: (i) the steam generation reaction on its Ni anode (CH 4 + H 2O = CO + 3H 2); (ii) the transfer of hydrogen ions through the proton conducting ceramic; and (iii) the cathode reaction between H 2 and O 2. It is found that the rate determining step of the overall hydrogen transfer in the cell system of CH 4 + H 2O|Ni|SrZr 0.9Yb 0.1O 3− a |NiO|O 2 + H 2O is the steam reformation reaction on the anode. The electrochemical polarization of the anode due to the CH 4-steam reformation has the activation energy of 89.5 kJ/mol. On the other hand, the rate determining step of the system described as H 2(+H 2O)|Ni|SrZr 0.9Yb 0.1O 3− a |NiO|O 2 + H 2O is H + migration through the ceramic electrolyte when T > 700 °C. The activation energy of H + migration through the ceramic is 31.5 kJ/mol. The values of the Warburg impedance constants and capacitances of an electric double layer are determined as a function of temperature from 600 °C to 800 °C, when either a CH 4 + H 2O or H 2 + H 2O mixture is supplied to the anode.

Overall Conductivity and Electromotive Force of SrZr0:9Yb0:1O3–a Cell System Supplied with Moist CH4

A proton-conducting ceramic cell for recovering tritium from process streams was investigated for its application to a fusion reactor system. The ceramic cell tested here was composed of a SrZr0:9Yb0.1O3–a tube, one end of which was closed, and Ni/SiO2 and NiO/SiO2 porous electrodes. Its anode was supplied with moist CH4 or H2 and its cathode with moist O2. All of the j-V curves obtained by a direct-current method were correlated to the relation V = E 0 − jd/σ at 600–700°C regardless of the two different conditions of the CH4 + H2O and H2 + H2O supply. The rate-controlling step of charged hydrogen ion transfer was determined from the dependences of the overall conductivity σ and the electromotive force E 0 on the anode H2O partial pressure and temperature. The E 0 value under the condition of the CH4 + H2O supply was affected by the diffusion of reaction products of CH4 + H2O = CO + 3H2 through the porous anode. On the other hand, the σ value was limited by the oxygen reduction rate at the cathode interface between the ceramic and the Ni electrode regardless of the different conditions between CH4 + H2O and H2 + H2O. These results were consistent with our results obtained by an alternating-current method. The activation energy of the overall conductivity was 60 kJ/mol.