Gas Diffusion Cell Research Articles

Porous Bi Nanosheets Derived from β-Bi2O3 for Efficient Electrocatalytic CO2 Reduction to Formate.

The electrochemical CO2 reduction reaction (ECO2RR) is a promising strategy for converting CO2 into high-value chemical products. However, the synthesis of effective and stable electrocatalysts capable of transforming CO2 into a specified product remains a huge challenge. Herein, we report a template-regulated strategy for the preparation of a Bi2O3-derived nanosheet catalyst with abundant porosity to achieve the expectantly efficient CO2-to-formate conversion. The resultant porous bismuth nanosheet (p-Bi) not only exhibited marked Faradaic efficiency of formate (FEformate), beyond 91% in a broad potential range from -0.75 to -1.1 V in the H-type cell, but also demonstrated an appreciable FEformate of 94% at a high current density of 262 mA cm-2 in the commercially important gas diffusion cell. State-of-the-art X-ray absorption near edge structure spectroscopy (XANES) and theoretical calculation unraveled the distinct formate production performance of the p-Bi catalyst, which was cocontributed by its smaller size, plentiful porous structure, and stronger Bi-O bond, thus accelerating the absorption of CO2 and promoting the subsequent formation of intermediates. This work provides an avenue to fabricate bismuth-based catalysts with high planar and porous morphologies for a broad portfolio of applications.

Aligned InS Nanorods for Efficient Electrocatalytic Carbon Dioxide Reduction.

Electrochemical CO2 reduction technology can combine renewable energy sources with carbon capture and storage to convert CO2 into industrial chemicals. However, the catalytic activity under high current density and long-term electrocatalysis process may deteriorate due to agglomeration, catalytic polymerization, element dissolution, and phase change of active substances. Here, we report a scalable and facile method to fabricate aligned InS nanorods by chemical dealloying. The resulting aligned InS nanorods exhibit a remarkable CO2RR activity for selective formate production at a wide potential window, achieving over 90% faradic efficiencies from -0.5 to -1.0 V vs reversible hydrogen electrode (RHE) under gas diffusion cell, as well as continuously long-term operation without deterioration. In situ electrochemical Raman spectroscopy measurements reveal that the *OCHO* species (Bidentate adsorption) are the intermediates that occurred in the reaction of CO2 reduction to formate. Meanwhile, the presence of sulfur can accelerate the activation of H2O to react with CO2, promoting the formation of *OCHO* intermediates on the catalyst surface. Significantly, through additional coupling anodic methanol oxidation reaction (MOR), the unusual two-electrode electrolytic system allows highly energy-efficient and value-added formate manufacturing, thereby reducing energy consumption.

Redox Replacement of Silver on MOF-Derived Cu/C Nanoparticles on Gas Diffusion Electrodes for Electrocatalytic CO2 Reduction.

Bimetallic tandem catalysts have emerged as a promising strategy to locally increase the CO flux during electrochemical CO2 reduction, so as to maximize the rate of conversion to C−C‐coupled products. Considering this, a novel Cu/C−Ag nanostructured catalyst has been prepared by a redox replacement process, in which the ratio of the two metals can be tuned by the replacement time. An optimum Cu/Ag composition with similarly sized particles showed the highest CO2 conversion to C2+ products compared to non‐Ag‐modified gas‐diffusion electrodes. Gas chromatography and in‐situ Raman measurements in a CO2 gas diffusion cell suggest the formation of top‐bound linear adsorbed *CO followed by consumption of CO in the successive cascade steps, as evidenced by the increasingνC−H bands. These findings suggest that two mechanisms operate simultaneously towards the production of HCO2H and C−C‐coupled products on the Cu/Ag bimetallic surface.

Influence of the GDL and assembly mode of a PEM cell on the ethanol revalorization into chemicals

This work reports the influence of the gas diffusion layer (GDL) and cell assembly mode on the ethanol revalorization through the electro-reforming process, focusing on hydrogen and value-added organics (acetaldehyde, ethyl acetate and acetic acid) products distribution. All essays were conducted in a Proton Exchange Membrane (PEM) Electrolysis Cell of 5 cm2 at mild conditions (80 °C and 1 atm) on commercial Pt/C (cathode) and PtRu/C (anode) catalysts. In this scenario the selection of a proper GDL and way of assembly proves to be a critical step influencing the electrochemical performance. Carbon paper-based configurations exhibited the best profiles in terms of electro-catalytic activity, reaching high current density values (600–720 mA·cm−2 at 1.4 V of cell potential), which are close to those obtained in alkaline media. Conversely, that based on porous titanium showed a lower efficiency (less than a half) due to the mass transfer limitations of reactants and products through the GDL, as confirmed by the electrochemical impedance spectroscopy essays. Regarding organic product distribution, non-assembled carbon paper-based configuration displayed the best results, increasing the production of value-added organics and shifting the acetic acid generation to lower cell potential values (close to 0.7 V). This was attributed to the direct deposition of the catalytic layers over the membrane instead of over the carbon GDL, which enhances the reactants and ions transport, improving the electrochemical activity. In addition, this configuration showed quite lower energy requirements for H2 production (<20 kWh·kgH2−1 at 0.8 V) in comparison with a PEM water electrolyzer stack.

Verification of the Competitive Effect between Heterogeneous and Gas Diffusion-Induced Cell Nucleation in Determining the Cell Structure in Polystyrene/Poly(methyl methacrylate) Blends via Structural Evolution Driven by Phase Separation

The objective of the present work is to verify the competitive effect between the heterogeneous and gas-diffusion cell nucleation in foaming of polystyrene/poly(methyl methacrylate) (PS/PMMA) blends with PS or PMMA as the dispersed phase after structural evolution driven by phase separation. Four PS/PMMA blends were thermally annealed for various times. Scanning electron microscopy (SEM) was employed to study the phase morphology. The domain size and domain density were thus obtained, and the interface area was then calculated. The samples were foamed via a batch foaming process, and SEM was used to study the cell structure. It was found that with thermal annealing, the phase domain size was increased, the domain density was decreased, and the interface area was decreased. For PS20/PMMA80 and PS30/PMMA70, the cell size was increased and cell density was decreased, while for PS80/PMMA20 and PS70/PMMA30, the cell size was decreased and cell density was increased. The expansion ratio was decreased for all of...

Three-dimensional simulation of a PEM fuel cell with experimentally measured through-plane gas effective diffusivity considering Knudsen diffusion and the liquid water effect in porous electrodes

A fundamental understanding of the gas diffusion properties in porous electrodes, such as catalyst layers (CLs), micro porous layers (MPLs) and gas diffusion layers (GDLs) is necessary for the optimal design of polymer electrolyte membrane (PEM) fuel cell. The conventional Bruggeman correlation has been proven to overestimate through-plane gas effective diffusivity (TP-GED) in GDLs; however, few studies have shed light on the influence of gas diffusion in MPLs and CLs in simulations of PEM fuel cells. In this study, to accurately predict the gas diffusion process and cell performance, a three-dimensional, two-phase and non-isothermal PEM fuel cell model was developed with experimentally measured TP-GED considering Knudsen diffusion and the liquid water effect in porous electrodes. The numerical results indicate that the conventional Bruggeman correlation greatly overpredicts TP-GED in porous electrodes and the oxygen reduction reaction (ORR) within the cathode CL and thus cannot accurately reflect the mass transport loss at high current density. The gas diffusion properties in the cathode porous electrode play a dominant role in determining cell performance. Furthermore, MPLs and CLs exhibit lower TP-GED than GDLs due to Knudsen diffusion; therefore, the distinction among the gas diffusion properties of GDLs, MPLs and CLs must be considered in quantitative modeling and optimization of PEM fuel cells.

Thiocyanate Determination using Technique of Flow Injection-Gas Diffusion Spectrophotometry with Cerium (IV)-Ninhydrin Reagent.

Numerous food plants contain thiocyanate, which can inhibit iodine uptake of thyroid gland and induce to the risk of iodine deficiency disorders (IDD). This research is focused on the development of new method for thiocyanate determination based on the formation of red hydrindantin using spectrophotometric flow injection (FI)–gas diffusion technique. In this technique, thiocyanate is oxidized by cerium (IV) in the acid donor stream to form hydrogen cyanide which diffuses through the membrane in the gas diffusion cell and reacts selectively with alkaline ninhydrin in the acceptor stream to form a red hydrindantin detected by spectrophotometer at 485 nm. The common operational conditions including sample volume, the length of mixing coil, and the flow rate as well as chemical parameters (concentration of cerium (IV) and ninhydrin, and pH reaction) were optimized with respect to sensitivity, analysis time, and linearity. The optimum condition notified by highest absorbance with sharp single peak and fast analysis was obtained under flow rate of 2 mL min−1, 300 µL sample volume, 75 cm mixing coil, 0.01 M cerium (IV), 1 % ninhydrin, and pH of 11. The interfering ions frequently exist with thiocyanate were also studied. Under the optimized conditions, the method showed linear for thiocyanate concentration from 5-30 mgL−1 and sampling rate of 120 s/h with a satisfactory reproducibility (RSD < 2% at n=3). This method has been successfully applied to determine thiocyanate in saliva from smoker and non-smoker and the results showed good agreement with those obtained from standard spectrophotometry method.

Automatic determination of arsenate in drinking water by flow analysis with dual membrane-based separation

The sequential application of a polymer inclusion membrane (PIM), composed of poly(vinylidenefluoride-co-hexafluoropropylene) and the anionic extractant Aliquat 336, and a microporous polytetrafluoroethylene (PTFE) gas-permeable membrane was utilized for the first time to develop a flow analysis (FA) system, for the automatic determination of trace levels of arsenate (As(V)) in drinking water as arsine. The system incorporated a flow-through extraction cell for separation and preconcentration of arsenate and a gas-diffusion cell for the separation of arsine prior to its spectrophotometric determination based on the discoloration of a potassium permanganate solution. Under optimal conditions the FA system is characterized by a limit of detection of 3.0 μg L−1 As(V) and repeatability of 1.8% (n = 5, 25 μg L−1 As(V)) and 2.8% (n = 5, 50 μg L−1 As(V)). The newly developed FA method was successfully applied to the determination of arsenate in drinking water samples in the μg L−1 concentration range.

Conductometric Determination of Sulfur Dioxide in Wine Using a Multipumping System Coupled to a Gas-Diffusion cell

A conductometric system with a multipumping module and a gas-diffusion cell has been developed to determine free and total sulfur dioxide (SO2) in wine. The developed method has two protocols to determine both types of SO2 using the same system. For free SO2, sulfite is converted to H2SO4 by acidification and diffusion with H2O2 in an acceptor channel. The sample was previously hydrolyzed by mixing the sample with NaOH and heated at 70 °C prior making the determination of total SO2 in order to break the bonds of the combined SO2. Free and total SO2 were determined in the ranges of 2.5–25.4 and 10.2–76.2 mg L−1 with a sample throughput of 13 and 12 h−1, respectively. The calibration curves of free and total SO2 were in the range of ΔG (mS cm−1) = (–1.0242 ± 0.2871) + (0.6613 ± 0.0201) [SO2, mg L−1], r2 of 0.997 and ΔG (mS cm−1) = (–0.5850 ± 0.1678) + (0.1236 ± 0.0033) [SO2, mg L−1], r2 of 0.997. The proposed automated method is simple and easy to apply for the determination of SO2 in wine using simple reagents.

Gas Diffusion Cell Geometry for a Microfluidic Dissolved Inorganic Carbon Analyzer

Variable gas diffusion cell geometries were tested for the extraction of dissolved inorganic carbon (DIC) from a microfluidic (tens to hundreds of microliters) seawater sample. With a focus on optimization of diffusion cell geometry, we compare five unique diffusion cell designs. Using 3-D printing technology to streamline the prototyping and testing process, we were able to conceive, design, fabricate, and thoroughly evaluate each design over the course of about one month. In total, 1043 DIC measurements were carried out in 109 experiments for the five working manifolds. We find that a small diameter, cylindrical diffusion cell design offers several advantages over its planar counterparts and a larger diameter cylindrical cell, most notably the ability to increase the ratio of the exchange membrane’s contact surface area to solution volume (the “aspect ratio”) without sacrificing channel integrity. Multiple designs approached short-term repeatability of $\mu \text{L}$ of sample.

Analysis of Sensitivity of PEMFC Parameters to Non-Uniform Platinum Deposition

Recently, we have proposed a robust and computationally efficient numerical algorithm for the optimization of 2-D and 3 -D catalysts distributions in Proton Exchange Membrane Fuel Cells (PEMFCs) using a gradient-based technique [1-3]. The algorithm is based on the computation of the catalyst sensitivity functions of the cell current and cell voltage by using the adjoint method. This method was initially developed by the applied mathematics community to solve optimization problems in fluid dynamics, climate, and heat transfer problems and, later, by other research groups to solve optimization problems in magnetics, model parameter determination, and semiconductor devices [4-6]. It was only recently that COMSOL, a popular finite element solver, has introduced the adjoint method, which has started to be used by the electrochemical community for calculation of sensitivities of platinum distribution in PEMFCs [7,8]. In this presentation we analyze the cell current, cell voltage, and spectral electrochemical impendence properties of PEMFCs by using the catalyst sensitivity functions of cell voltage, γPt(r). These functions show how much the cell voltage is increasing by adding 1 unit amount of platinum at a given location inside the catalyst layer (and assuming the cell is operating at the same current density). For instance, the figure below shows the 2-D catalysis sensitivity functions of the cell voltage for two cells with membrane thicknesses of 60 mm and 25 mm, in which the catalyst is distributed uniformly inside the cell. It is apparent from these figures that in order to increase the cell voltage and consequently the power of the cell, one needs to increase the concentration of Pt particles in the regions under the oxygen openings. As it will be shown at the conference the optimum catalyst distribution also depends on the operating temperature, catalyst and gas diffusion layers porosities, Nafion content, and cell current. In addition to the above analysis, we will also introduce a technique for the analysis of variability of polarization curves induced by the randomness of pore sizes and pore shapes in the catalyst and gas diffusion layers in PEMFCs. The technique is based on the evaluation of sensitivity functions of the cell voltage and can also be extended to the analysis of variability induced by the random platinum distribution in the catalyst layers (which is assumed to have a uniform random distribution). More details about the method for the analysis of variability effects, as well as about the numerical implementation of the adjoint method in the case of finite element simulations and its computational efficiency will be presented at the conference. [1] J. Lamb, G. Mixon, and P. Andrei, “Optimization of polymer electrolyte membrane fuel cells with a large number of degrees of freedom”, ECS 231Meeting, New Orleans, LA, 2017. [2] J. Lamb, G. Mixon, and P. Andrei, “Mathematical optimization of the spatial distribution of platinum particles in the catalyst layer of PEMFCs”, PRIME 2016 Meeting, Honolulu, HI, 2016. [3] P. Andrei, G. Mixon, M. Mehta, and V. Bevara, “Design of the catalyst layers in PEMFCs using an adjoint sensitivity analysis approach”, ECS Transactions 66(8), 91-128, 2015. [4] D. Cacuci, M. Ionescu-Bujor and M. N. Ionel, Sensitivity and Uncertainty Analysis, Volume 2: Applications to Large-Scale Systems, Chapman & Hall/CRC (2005) [5] W. K. Anderson and V. Venkatakrishnan, “Aerodynamic design optimization on unstructured grids with a continuous adjoint formulation”, Computers & Fluids, 28, 443 (1999). [6] P. Andrei, I. Mayergoyz, “Quantum mechanical effects on random oxide thickness and random doping induced fluctuations in ultrasmall semiconductor devices”, Journal of Applied Physics, 94, 7163-7172 (2003). [7] COMSOL Multiphysics Software, https://www.comsol.com. [8] F. C. Cetinbas, S. G. Advani and A. K. Prasad, “Three dimensional proton exchange membrane fuel cell cathode model using a modified agglomerate approach based on discrete catalyst particles”, Electrochimica Acta, 174, 787 (2015). Figure 1

A novel flow injection chemiluminescence method for automated and miniaturized determination of phenols in smoked food samples

An easily performed fully automated and miniaturized flow injection chemiluminescence (CL) method for determination of phenols in smoked food samples has been proposed. This method includes the ultrasound assisted solid-liquid extraction coupled with gas-diffusion separation of phenols from smoked food sample and analytes absorption into a NaOH solution in a specially designed gas-diffusion cell. The flow system was designed to focus on automation and miniaturization with minimal sample and reagent consumption by inexpensive instrumentation. The luminol – N-bromosuccinimide system in an alkaline medium was used for the CL determination of phenols. The limit of detection of the proposed procedure was 3·10−8·molL−1 (0.01mgkg−1) in terms of phenol. The presented method demonstrated to be a good tool for easy, rapid and cost-effective point-of-need screening phenols in smoked food samples.

Determination of Ammonium in Seawater by Purge-and-Trap and Flow Injection with Fluorescence Detection

ABSTRACTAn improved method for the determination of ammonium in seawater was established using purge-and-trap pretreatment coupled with flow injection fluorescence. An appropriate volume of sodium hydroxide was added to seawater to convert ammonium to gaseous ammonia that was purged from the solution to the vapor phase by argon at 350 mL/min for 15 min at 80°C and trapped in hydrochloric acid. The solution was analyzed based on the fluorescence detection of the reaction product of o-phthaldialdehyde, sulfite, and ammonium. Parameters affecting the purge-and-trap efficiency and determination were optimized, and the matrix effects of seawater were investigated. The influence of primary amines and amino acids was tested and negligible effects were found. The detection limit was 7.4 nmol/L. The relative standard deviation was 4.4% for a seawater fortified with 200 nmol/L ammonium. Compared to the use of gas diffusion cell, this approach offers higher sensitivity, higher collection efficiency, and negligible effects from salinity. In addition, deionized water was used for standard preparation instead of matrix-matched standards.

A review of the gas diffusion layer in proton exchange membrane fuel cells: Durability and degradation

Abstract For successful commercialization of a proton exchange membrane fuel cell, the durability requirement must be satisfied. The degradation of a proton exchange membrane fuel cell has been extensively studied, and a number of review papers investigating the durability issue have already been published. However, the gas diffusion layer has rarely been examined, even though it might be a key factor for managing mass transport and two-phase flow while mechanically supporting a membrane-electrode assembly and a bipolar plate. This paper reviews the published works on the durability of the gas diffusion layer of the proton exchange membrane fuel cell. The degradation of the gas diffusion layer can be divided into mechanical degradation, including the compression force effect, freeze/thaw cycle effect, dissolution effect, and erosion effect, and chemical degradation, which consists of the carbon corrosion effect. Following these categories, the methods of accelerated stress tests, the degradation mechanisms, and the influential factors are investigated along with various measurements of gas diffusion layer properties and cell performances.

Electroreduction of CO2 at Cu and Sn Foams

Previous studies on the electrochemical reduction of CO2 at metallic electrodes suggest that the adsorption of hydrogen species is structure-sensitive.[1] Surface roughening is likely to introduce defects favorable for the reaction of adsorbed hydrogen atoms, an important intermediate step in the electro-reduction of CO2 in protic media.[1, 2] Furthermore, roughened surfaces have been shown to be more selective toward hydrocarbon products, which was attributed to a higher number of uncoordinated metal sites.[2] These finding were confirmed by DFT calculations, which suggest that CO2 activation and reduction occurs at these sites. [3] To further gauge the effect of morphology on the faradaic efficiency and distribution of products obtained during the electroreduction of CO2, Cu and Sn foams were electrosynthesized on Cu substrates using a recently reported process.[4] The metal foams were found to be mechanically stable during their preparation, handling, and use in the electrocatalytic reduction of CO2. Both Cu and Sn foams are attractive metals for the electrocatalytic reduction of CO2because of their low cost and non-toxic nature.Electroreduction of CO2 was performed in a typical H-cell under potentiostatic conditions. The faradaic efficiency of producing formate from CO2 at the metal foams and the equivalent planar metal electrode are compared in Figure 1a and 1b. The faradaic efficiencies obtained with the Cu foam electrode were found to be higher at all potentials with a maximum efficiency of 37% at -1.5V for HCOOH. Previously reported data is included for comparison.[5] Likewise, the faradaic efficiencies for HCOOH generation at the Sn foam electrode were found to be higher at all potentials with a maximum efficiency of 89.5% at -1.7V. Previously reported data with slightly different conditions (Sn gas diffusion cell in 0.5 M NaHCO3) is included for comparison.[6] XRD analysis of the Cu and Sn foams did not reveal major differences in the relative ratio of dominant crystal facets when compared to the equivalent planar samples of high purity metal. The hierarchical nature of the pore architecture along with high surface area of the metal foams could affect the reaction kinetics and contribute to the observed increase in faradaic efficiency. For example, the porous nature of the metal foams may promote interactions between incoming CO2, adsorbed surface species, electrolyte, and reducing equivalents that are novel relative to the same reaction at a planar electrode. The effect of varying the electrodeposition time and resulting foam architecture on the electroreduction of CO2will be the focus of this presentation. References Hori, Y., A. Murata, and R. Takahashi, Formation of hydrocarbons in the electrochemical reduction of carbon dioxide at a copper electrode in aqueous solution. Journal of the Chemical Society, Faraday Transactions 1: Physical Chemistry in Condensed Phases, 1989. 85(8): p. 2309-2326.Tang, W., A.A. Peterson, A.S. Varela, Z.P. Jovanov, L. Bech, W.J. Durand, S. Dahl, J.K. Norskov, and I. Chorkendorff, The importance of surface morphology in controlling the selectivity of polycrystalline copper for CO2 electroreduction. Physical Chemistry Chemical Physics, 2012. 14(1): p. 76-81.Durand, W.J., A.A. Peterson, F. Studt, F. Abild-Pedersen, and J.K. Nørskov, Structure effects on the energetics of the electrochemical reduction of CO2 by copper surfaces. Surface Science, 2011. 605(15–16): p. 1354-1359.Shin, H.C., J. Dong, and M. Liu, Nanoporous Structures Prepared by an Electrochemical Deposition Process. Advanced Materials, 2003. 15(19): p. 1610-1614.Kuhl, K.P., E.R. Cave, D.N. Abram, and T.F. Jaramillo, New insights into the electrochemical reduction of carbon dioxide on metallic copper surfaces. Energy & Environmental Science, 2012. 5(5): p. 7050-7059.G.K.S. Prakash, F.A. Viva, G.A. Olah, Electrochemical reduction of CO2 over Sn-Nafion® coated electrode for a fuel-cell-like device, Journal of Power Sources, 223 (2013) 68-73.

Conductometric determination of ammonium by a multisyringe flow injection system applying gas diffusion

A multisyringe flow injection system (MSFIA) coupled to a gas-diffusion cell has been developed for the conductometric determination of ammonium in different water samples. Operation strategies, membrane, reagent concentrations, and flow rates have been studied to optimize the sensitivity of detection and to fit the required working range. The proposed MSFIA system has been compared with former FIA and SIA systems using gas diffusion. The system was applied to the determination of ammonium in water samples of different matrices in order to evaluate its performance. These samples were coastal waters, pond waters, and compost aqueous extracts. Good recoveries of 102 ± 13% were obtained and no significant differences with the reference methods were found. The system can be used for a wide concentration range of ammonia, from 0.075 to 360 mg L−1, without sample dilution and with a precision better than 2% of RSD. The throughput of the method was 32 injections per hour.

Determination of acetaldehyde in saliva by gas-diffusion flow injection analysis

The consumption of ethanol is known to increase the likelihood of oral cancer. In addition, there has been a growing concern about possible association between long term use of ethanol-containing mouthwashes and oral cancer. Acetaldehyde, known to be a carcinogen, is the first metabolite of ethanol and it can be produced in the oral cavity after consumption or exposure to ethanol. This paper reports on the development of a gas-diffusion flow injection method for the online determination of salivary acetaldehyde by its colour reaction with 3-methyl-2-benzothiazolinone hydrazone (MBTH) and ferric chloride. Acetaldehyde samples and standards (80μL) were injected into the donor stream containing NaCl from which acetaldehyde diffused through the hydrophobic Teflon membrane of the gas-diffusion cell into the acceptor stream containing the two reagents mentioned above. The resultant intense green coloured dye was monitored spectrophotometrically at 600nm. Under the optimum working conditions the method is characterized by a sampling rate of 9h−1, a linear calibration range of 0.5–15mgL−1 (absorbance=5.40×10−2 [acetaldehyde, mgL−1], R2=0.998), a relative standard deviation (RSD) of 1.90% (n=10, acetaldehyde concentration of 2.5mgL−1), and a limit of detection (LOD) of 12.3μgL−1. The LOD and sampling rate of the proposed method are superior to those of the conventional gas chromatographic (GC) method (LOD=93.0μgL−1 and sampling rate=4h−1). The reliability of the proposed method was illustrated by the fact that spiked with acetaldehyde saliva samples yielded excellent recoveries (96.6–101.9%), comparable to those obtained by GC (96.4–102.3%) and there was no statistically significant difference at the 95% confidence level between the two methods when non-spiked saliva samples were analysed.

Rate determination of the catalytic oxidation of methane and propane in an electrochemical solid-electrolyte reactor

The possibility of using a solid-electrolyte reactor in kinetic studies of the catalytic oxidations of hydrocarbon with molecular oxygen was investigated. A theoretical analysis of processes in a catalytically asymmetric gas-diffusion cell in N2 + O2 + CH4 and N2 + O2 + C3H8 gas mixtures was performed. Analytical expressions are presented for calculating the oxygen, methane, and propane concentrations and the methane and propane oxidation rates in the inner space of the cell from the emf of the latter. The potentiometric response was studied experimentally after the addition of methane and propane in the gas mixture in a reactor with silver electrodes and samples with applied catalytic materials. The concentrations of the components in the inner space of the reactor and the oxidation rates of hydrocarbons were calculated from the experimental data.

Flow injection analysis of ethyl xanthate by gas diffusion and UV detection as CS 2 for process monitoring of sulfide ore flotation

A sensitive and robust analytical method for spectrophotometric determination of ethyl xanthate, CH 3CH 2OCS 2 − at trace concentrations in pulp solutions from froth flotation process is proposed. The analytical method is based on the decomposition of ethyl xanthate, EtX −, with 2.0 mol L −1 HCl generating ethanol and carbon disulfide, CS 2. A gas diffusion cell assures that only the volatile compounds diffuse through a PTFE membrane towards an acceptor stream of deionized water, thus avoiding the interferences of non-volatile compounds and suspended particles. The CS 2 is selectively detected by UV absorbance at 206 nm ( ɛ = 65,000 L mol −1 cm −1). The measured absorbance is directly proportional to EtX − concentration present in the sample solutions. The Beer's law is obeyed in a 1 × 10 −6 to 2 × 10 −4 mol L −1 concentration range of ethyl xanthate in the pulp with an excellent correlation coefficient ( r = 0.999) and a detection limit of 3.1 × 10 −7 mol L −1, corresponding to 38 μg L −1. At flow rates of 200 μL min −1 of the donor stream and 100 μL min −1 of the acceptor channel a sampling rate of 15 injections per hour could be achieved with RSD < 2.3% ( n = 10, 300 μL injections of 1 × 10 −5 mol L −1 EtX −). Two practical applications demonstrate the versatility of the FIA method: (i) evaluation the free EtX − concentration during a laboratory study of the EtX − adsorption capacity on pulverized sulfide ore (pyrite) and (ii) monitoring of EtX − at different stages (from starting load to washing effluents) of a flotation pilot plant processing a Cu–Zn sulfide ore.

The role of catalytic reactions in the generating of electrode potentials in chemically irreversible gas mixtures

The formation of steady-state potential at an electrode of solid-electrolyte electrochemical cell placed in chemically irreversible gas mixture is discussed; the potential emerges due to the change in the gas activities at the electrode, caused by the passing of catalytic reaction. This mechanism of potential change is analyzed theoretically for a catalytically asymmetrical gas-diffusion cell located in a CH4 + CO + CO2 gas mixture. Experimental studies demonstrated an agreement between the experimental results and theoretical considerations. Dependence of the potential changing rate on the kinetics of the methane catalytic oxidation is revealed experimentally.