Channel Flow Cell Research Articles

An open source electrochemical channel flow cell setup for kinetics studies. Application to investigations on oxygen electrocatalysis

Herein, an electrochemical channel flow cell setup that allows for conducting electrochemical investigations up to 80°C and pressurized gases up to 3 bar is presented in details, including technical drawings and list of parts, in an attempt to facilitate the adoption of such setup by the community for electrochemical/electrocatalytic kinetic studies. The oxygen reduction reaction (ORR) on a commercial Pt/C catalyst, chosen as a model reaction, was investigated to demonstrate the reliability of the experimental setup, including the hydrodynamic properties, to provide hands on practical guidelines to carry out experiments, and, on the other hand, to illustrate the capabilities of this electrochemical setup for an assessment of basic quantities. Among the various quantities that have be determined experimentally for the ORR, a monotonic decay of the activation enthalpy and bell-shaped variation of the entropy of activation were resolved as the overpotential for the ORR increases. These fundamental thermodynamic/kinetic data are briefly discussed within the frame of the established reaction mechanism and can serve as a feed for the benchmarking of the outputs from theoretical/computational models. Furthermore, a remarkable agreement was obtained between the change in the activation free Gibbs energy determined for the ORR with the flow cell setup and the kinetic region of fuel cell polarization curve obtained with the same Pt/C catalyst embedded in the cathode of an a hydrogen proton exchange membrane fuel cell. This enables potentially a bridge of the environmental gap existing between model experiments conducted at active material level in contact with liquid electrolyte and experiments with porous gas diffusion electrode embedding the same active material that are employed in practical device.

New Electrochemical Channel Flow Cell Design for Electrochemical Studies at Elevated Temperatures and Pressures

Temperature exerts a considerable influence on the efficiency of chemical and electrochemical processes, and it is expected that studies under wide temperature and pressure (T and p) conditions can significantly impact fields of technological interest such as energy storage and conversion, water treatment, waste conversion, metal recovery, and electrosynthesis, among others.1 The electrochemical studies conducted by Bard’s group in near-critical and supercritical aqueous solutions,2 as well as the contributions made by MacDonald’s and Lvov’s3,4 groups on corrosion and pH determination in hydrothermal systems, offer valuable insights into the effects of temperature and pressure on electrochemical reactions under extreme conditions and construction materials and electrode designs. Other studies in the field, though they did not reach such harsh conditions, made valuable contributions by proposing innovative hydrodynamic electrode systems, from channel cells for studies up to 110 oC,5 a rotating disc electrode for temperatures up to 150 oC,6 and even an imping jet electrode able to reach 210 oC.7 Unfortunately, these studies were rarely expanded to more than one or two systems.In this work, various hydrodynamic electrode configurations have been examined to conclude that the channel flow cell design presents several advantages over other systems for high T and P applications. These cells can provide consistent and reproducible mass transport conditions across a broad range of flow rates and allow channel dimension adjustments to tackle diverse technological challenges. Furthermore, this configuration aligns well with spectroscopic techniques like Raman/SERS (surface-enhanced Raman spectroscopy). COMSOL Multiphysics was used when designing the cell prototype, and validation of the model was carried out using data from previous studies.8 The high T,p cell uses disposable thin-film electrodes (TFEs) patterned onto sapphire wafers through nanofabrication methods; a significant amount of time has been invested in testing the performance of the TFEs up to at least 150°C. These results will also be presented along with experiments conducted with the new channel cell under ambient conditions. References (1) Giovanelli, D.; Lawrence, N. S.; Compton, R. G., Electroanalysis (New York, N.Y.) 2004, 16 (10), 789-810.(2) Liu, C.-y.; Snyder, S. R.; Bard, A. J. J. Phys. Chem.B 1997, 101 (7), 1180-1185.(3) Macdonald, D. D. Corrosion 2013, 34 (3), 75-84.(4) Balashov, V. N.; Fedkin, M. V.; Lvov, S. N., J. Electrochem. Soc. 2009, 156 (7), C209.(5) Wang, H.; Jusys, Z.; Behm, R. J.; Abruña, H. D., J. Electroanal. Chem. 2021, 896, 115251.(6) Fleige, M. J.; Wiberg, G. K.; Arenz, M., Rev Sci Instrum 2015, 86 (6), 064101.(7) Trevani, L. N.; Calvo, E.; Corti, H. R., Electrochem. Commun 2000, 2 (5), 312-316.(8) Moorcroft, M. J.; Lawrence, N. S.; Coles, B. A.; Compton, R. G.; Trevani, L. J. Electroanal. Chem. 2001, 506 (1), 28-33.

A finite volume model for maintaining stationarity and reducing spurious oscillations in simulations of sewer system filling and emptying

This paper introduces a model for simulating the unsteady dynamics of sewer systems filling and emptying, offering greater accuracy and stability. This article presents two novel contributions: first, the HLLS scheme (Harten–Lax–van Leer + Source term) is adapted to ensure the preservation of stationary conditions not only in free surface flows, as originally conceived, but also in pressurized flows and mixed flow scenarios. Second, a new method is proposed for the treatment of open channel flow cells near pressurization or adjacent to pressurized cells to minimize spurious oscillations when utilizing the two-component pressure approach (TPA) model. To verify the new model's effectiveness, it was tested for various conditions against the outcomes of the Open Source Field Operation and Manipulation (OpenFOAM) computational fluid dynamics (CFD) model. Furthermore, to demonstrate the model's potential for simulating real systems, the model was applied to three sewer systems that closely resemble real-world conditions, each of which had been intentionally modified for confidentiality purposes. The results show that the improved model successfully maintains stationary conditions within a sloped pipe across various flow conditions, while also preventing spurious oscillations at mixed flow interfaces even when using a pressure wave speed of 1000 m s − 1 .

Ionic Diffusion in Slurry Electrolytes for Redox Flow Batteries

Slurry electrodes have been proposed as a method to decouple the storage and power capacities of hybrid redox flow batteries by allowing the reduced metal to adhere to a flowing dispersion of electrically conductive particles rather than accumulate in the flow cell. In this work, the ionic mass transport through these slurry electrolytes is investigated via voltammetry at a rotating disc electrode and in a parallel channel flow cell. A modified Levich equation, il=0.62nFCω1/2ν−1/6(D+r2Φωm)2/3, is developed to describe limiting currents to a rotating disc electrode when using a particle filled electrolyte. Mass transfer is demonstrated to be enhanced by greater particle loading so long as there are sufficient particles such that their respective flow velocity boundary layers interact. In the flow cell, faradaic current in a carbon black slurry electrolyte was observed to decrease over time. This suggests that the carbon particles adhere and accumulate on the stationary electrode, impeding mass transport by imposing diffusion path tortuosity. This accumulation is undesirable in hybrid redox flow batteries as it encourages metal deposition in the cell, limiting the scalability of the technology.

High-Throughput Activity Screening of Oxygen Reduction and Oxygen Evolution Catalysts

High-throughput techniques are being actively studied to expedite the evaluation of the electrocatalytic activity of newly developed materials. These techniques include the use of optical sensing or electrochemical array cells in stagnant or hydrodynamic aqueous electrolytes [1-2]. A new high-throughput electrochemical cell has been developed utilizing multiple glassy carbon working electrodes with dimensions comparable to those of a conventional ring-disk electrode (RDE) that are inserted into a channel flow cell (Figure 1) comprised of two PEEK blocks separated by a gasket that defines the electrolyte channel depth. This cell enables evaluation of the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) activity as a function of the potential of multiple catalyst samples simultaneously that are deposited on the glassy carbon electrodes using standard methods used for RDE electrodes (e.g., using a hand-held micropipette). As shown in Figure 1, a common reference electrode is located in the lower cell block across an electrolyte channel from the working electrodes and a common counter electrode is located in the electrolyte outlet. Electrolyte flow has been simulated to ensure that the electrolyte is evenly distributed throughout the shallow flow channel with uniform laminar electrolyte flow and identical flow rate for all working electrodes. The new cell is coupled with a Bio-logic multichannel Potentiostat (VSP) that allows the use of multiple working electrodes simultaneously with a common counter electrode and common reference electrode. The catalyst activity and stability results obtained with the new cell have been verified by comparison with RDE measurements for the same catalysts. Acknowledgments This work was supported by the U.S. Department of Energy, Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office under the auspices of the Electrocatalysis Consortium (ElectroCat). Argonne National Laboratory is managed for the U.S Department of Energy by the University of Chicago Argonne, LLC, also under contract DE-AC-02-06CH11357.

Autonomous electrochemical system for ammonia oxidation reaction measurements at the International Space Station

An autonomous electrochemical system prototype for ammonia oxidation reaction (AOR) measurements was efficiently done inside a 4'' x 4'' x 8'' 2U Nanoracks module at the International Space Station (ISS). This device, the Ammonia Electrooxidation Lab at the ISS (AELISS), included an autonomous electrochemical system that complied with NASA ISS nondisclosure agreements, power, safety, security, size constrain, and material compatibility established for space missions. The integrated autonomous electrochemical system was tested on-ground and deployed to the International Space Station as a “proof-of-concept” ammonia oxidation reaction testing space device. Here are discussed the results of cyclic voltammetry and chronoamperometry measurements done at the ISS with a commercially available channel flow-cell with eight screen-printed electrodes, including Ag quasi-reference (Ag QRE) and carbon counter electrodes. Pt nanocubes in Carbon Vulcan XC-72R were used as the catalyst for the AOR and 2 μL drop of Pt nanocubes/ Carbon Vulcan XC-72R, 20 wt%, ink was placed on the carbon working electrodes and allowed to dry in air. After the AELISS was prepared for launch to the ISS, a 4 days delayed (2 days in the space vehicle Antares and 2 days space transit to the ISS) cause a slight shift on the Ag QRE potential. Nevertheless, the AOR cyclic voltametric peak was observed in the ISS and showed ca. 70% current density decrease due to the buoyancy effect in agreement with previous microgravity experiments done at the zero-g aircraft.

The effect of the gypsum formation on the water quality of reservoirs: A case study of Kosar dam basin, Iran

The principal objectives of this study are the identification of the dissolution rate of gypsum formations and their effect on reservoir water quality. In this regard, total dissolved solids (TDS), calcium, and sulfate concentration were simulated using both the completely mixed model and a two-dimensional model, CE-QUAL-W2, in Kosar dam, Iran. The proposed method attempts to reduce the defects of the past laboratory methods such as the rotary disk and the channel flow cell, using real data and conditions. Moreover, long-term quality data were used. Finally, the average dissolution rate for calcium and sulfate, and TDS flux were calculated in two scenarios.

Study on the Effect of Magnetic Field on Seawater Electrolysis using a Channel Flow Cell to Simulate a Linear-type Seawater Magnetohydrodynamic Power Generator

A seawater magnetohydrodynamic (MHD) power generator is a unique system that not only transforms the kinetic energy of ocean and tidal currents directly into electric energy but also generates hydrogen gas by seawater electrolysis. In this study, we constructed experimental equipment and an electrochemical flow cell, which simulated a linear-type seawater MHD power generator, and investigated the effect of magnetic field on seawater electrolysis. Under magnetic field under solution flow conditions, we clarified that the strength of the magnetic field affected the current value of seawater electrolysis, which indicates that the MHD power generation was successfully simulated by the developed experimental equipment and electrochemical flow cell. Our electrochemical measurement results suggested that magnetic field was correctly applied to the cell and that the Lorentz force acted on the ions in the electrolyte solution, showing improvement in hydrogen evolution reaction (HER) efficiency under the MHD power generation conditions.

A channel flow cell with double disk electrodes for oxygen electroreduction study at elevated temperatures and pressures: Theory

• A new double-disk-electrode channel flow cell (DDECFC) was designed, constructed, and tested. • The DDECFC can be used for studying electrocatalysis such as ORR at elevated temperatures and pressures. • The hydrodynamic behaviors were numerically simulated, and experimentally characterized. • The hydrodynamic equation of the DDECFC was derived. • ORR on a carbon supported Pt catalyst was studied with the DDECFC. A new double-disk-electrode channel flow cell has been designed, constructed and tested. A theoretical treatment and implicit finite difference numerical simulations are presented, which permit the computation of the hydrodynamic behavior of this cell under steady state conditions, i.e., the diffusion limited current at the working electrode and the collection efficiency of the detector. The simulated results are consistent with those measured experimentally, indicating that our simulations appropriately describe the hydrodynamic behavior of this cell. The oxygen reduction reaction (ORR) on a carbon-supported nanoparticle Pt catalyst at both room temperature and 110 °C were preliminarily studied with this cell.

Development of in situ A-SAXS and XAS Measurements of Pt Catalyst under Controlled Electrochemical Condition Using Channel Flow Electrode Cell

Understanding of the structural and the chemical properties of Pt catalysts in polymer electrolyte fuel cells (PEFCs) is necessary to improve the activity for the durability of the catalysts. The small-angle X-ray scattering (SAXS) and the X-ray absorption spectroscopy (XAS) measurements are widely used to investigate these properties. Recently, we developed a measurement system of SAXS and fluorescence-yield (FY)XAS in the same observed area to investigate the structural and the chemical properties of low-concentrated catalysts. [1] As the results, the diameter size, distributions, and chemical state of catalysis were successfully characterized. Our measurement system also found to be easy to combine the electrochemical cell. In this study, we newly developed a channel flow cell to control the electrochemical conditions during SAXS and FYXAS measurement in the same observed area.All experiments were carried out at SPring-8 BL19B2. Electrochemical measurements were conducted using a newly developed channel flow cell. Using the flow system, the electrolyte solution with a controlled temperature was continuously supplied to the cell during the in-situ measurements. A commercial Pt/carbon black catalyst(TEC10E50E, Tanaka Kikinzoku Kogyo) was used as the sample in this experiment. In situ SAXS and FYXAS measurement was conducted while holding the potential at 0.4 V, 1.0 V, and 1.5 V vs. the reversible hydrogen electrode (RHE). For the XAS measurements, the Pt LⅢ edge was used. The ionization chamber and a single-element Ge solid state detector were used to obtain the FYXAS spectra. For the SAXS measurements, the X-ray energy was set to 11.5 keV and 11.55 keV, which are below and near to the Pt LIII absorption edge, respectively. The scattered X-ray was detected using an area detector (PILATUS 2M).As the result, we could estimate the diameter size, distributions, and chemical state of Pt catalysis under controlling the electrochemical conditions. We will discuss the degradation mechanism of the Pt nanoparticle catalyst from both SAXS and FYXAS data.Takeshi Watanabe, et al., ECS 236th I01D-1593, (2019) Atlanta, USA.

A Realistic View of Proteins : Solution Scattering at the Life Sciences X‐ray Scattering Beamline (LIX)

Small angle X‐ray scattering is an important tool that reveals the behavior of proteins in their native environment. The scattering pattern produced from a SAXS experiment represents an average of all conformations present in the solution. Since most proteins in our body function in a solution environment, SAXS data can reveal additional biologically relevant states of a molecule or molecular complex. Furthermore, SAXS provides data about the shape and size of the molecule of interest and is a complementary technique to other structural methods. Combining SAXS data with X‐ray crystallography, NMR or Cryo‐EM can lead to a more robust understanding of the species being studied. High quality SAXS data can be used to build ab initio low resolution bead models, which provide a 3D envelope of your molecule. Here at the life sciences X‐ray scattering beamline (LiX), we collect data by flowing sample through the X‐ray path in a 3 channel flow cell. As the sample enters the X‐ray path, the simultaneous collection of SAXS and wide angle X‐ray scattering (WAXS) is obtained via a 3 detector setup. The detector setup has a q‐range of 0.006Å−1 to 3.2 Å−1, primarily to obtain scattering data from the water peak to normalize buffer subtraction. Automated sample handling at LiX allows for collection of up to 360 samples, packaging of data and processing. One challenge in obtaining high quality SAXS data is preparation of pure, monodisperse samples. For these complicated samples that have multiple species, our in‐line HPLC system seamlessly integrates with our beamline for SEC‐SAXS (size‐exclusion chromatography‐SAXS), and increases the chances of obtaining a more pure, monodisperse sample immediately before data collection.Support or Funding InformationLiX beamline is part of the Life Science Biomedical Technology Research resource, co‐funded by the National Institute of General Medical Sciences (NIGMS) under grant P41 GM111244 and by the DOE Office of Biological and Environmental Research under grant KP1605010, with additional support from NIH under grant S10 OD012331. The operation of NSLS2 is supported by US Department of Energy, Office of Basic Energy Sciences, under contract No. DE‐SC0012704.

In-Situ Monitoring of Both Pt and Cu Dissolved from Pt-Cu Alloys Using Channel Flow Multi Electrode

Introduction Polymer electrolyte fuel cell (PEFC) is considered to be clean energy conversion device due to its low operating temperature and portability. Previously, Pt is used as cathode catalyst in PEFC, because Pt exhibits high catalytic activity for oxygen reduction reaction (ORR). Since Pt is limited resources and high cost, Pt alloy catalysts should be developed instead of Pt catalysts. Pt-Cu alloys exhibit greater catalytic activity for ORR than Pt, 1 however, Pt-Cu alloys would degrade under PEFC operating conditions. Therefore, we need to clarify dissolution mechanism of Pt-Cu alloys. In our previous work, we established channel flow double electrode (CFDE) for in-situ detection of Pt, and we proposed dissolution mechanism of Pt under simulating PEFC operating condition using CFDE. 2 In this study, we firstly improved CFDE to in-situ detect both Pt and Cu dissolved from Pr-Cu alloys, and then dissolution behavior of Pt-Cu alloys has been investigated by using this technique. Experimental In order to determine detection potential (E CE) of Cu2+ dissolved from Pt-Cu alloys, we prepared various concentration (0, 0.1, 0.5, 1.0 mM) of CuSO4, whose pH was adjusted to around 0.5 by adding H2SO4. Under laminar flow condition of the electrolyte (10 cm s-1), Au electrode was subjected to cathodic polarization at 298 K in Ar-purged these solutions. Potential range of the experiment from open circuit potential (OCP) to −0.2 V vs. SHE at 1 mV s-1. In order to confirm quantitativity of E CE determined by the cathodic polarization experiments, dissolved Cu2+ was detected on downstream Au collector electrode during anodic polarization of upstream Cu working electrode using channel flow cell. Au collector electrode potentiostatically polarized at (E CE=) 0, −0.1, and −0.2 V in Ar-purged 0.5 M H2SO4, when the working electrode anodically polarized from OCP to 1.0 V at 2 mV s-1. Results and Discussion Diffusion limiting current of residual oxygen was observed between 0.2 − −0.1 V in the cathodic polarization curve in 0 mM CuSO4 (Cu2+ free). And then, cathodic current increased by hydrogen evolution reaction (HER) below −0.1 V. On the other hand, cathodic current observed in the solution containing more than 0.1 mM CuSO4 was higher than that in 0 mM CuSO4. This is caused by the following reaction on the Au electrode: Cu2+ + 2e- → Cu. In addition, Cu2+ reduction current almost increased proportionally to Cu2+ concentration below −0.15 V. However, this concentration-dependent current overlapped with HER current. Therefore, quantitative determination of E CE for Cu2+ detection needs further experiments. Cu working current (i WE) exponentially increased with increasing potential from the OCP, and reached almost constant value (0.1 A cm-2). During this anodic polarization, Au collector current (i CE) at E CE = 0, −0.1, and −0.2 V shows similar trend in the i WE. After subtracting residual current from the i CE, we calculated dissolution current (i Diss.) using collection number (N = 0.38). When E CE was 0 V, i WE was not completely match i Diss. during the polarization, which means that E CE = 0 V is not quantitative potential for Cu2+ detection. On the contrary, i WE almost equals to i Diss. at E CE = −0.1, and −0.2 V. Hence, Cu2+ dissolved from Cu is quantitatively detected on Au electrode at E CE < −0.1 V. Reference 1. P. Strasser, S. Koh, and J. Greeley, Phys. Chem. Chem. Phys., 10, 3670 (2008). 2. Z. Wang, E. Tada, and A. Nishikata, J. Electrochem. Soc., 161 (4), F380 (2014).

Pressure drop through platinized titanium porous electrodes for cerium‐based redox flow batteries

The pressure drop, , across a redox flow battery is linked to pumping costs and energy efficiency, making fluid properties of the electrolyte important in scale‐up operations. The at diverse platinized titanium electrodes in Ce‐based redox flow batteries is reported as a function of mean linear electrolyte velocity measured in a rectangular channel flow cell. Darcy's friction factor and permeability vs. Reynolds number are calculated. Average permeability values are: 7.10 × 10−4 cm2 for Pt/Ti mesh, 4.45 × 10−4 cm2 for Pt/Ti plate + turbulence promoters, 1.67 × 10−5 cm2 for Pt/Ti micromesh, and 1.31 × 10−6 cm2 for Pt/Ti felt. The electrochemical volumetric mass transport coefficient, , is provided as a function of . In the flow‐by configuration, Pt/Ti felt combines high values with a relatively high , followed by Pt/Ti micromesh. Pt/Ti mesh and Pt/Ti plate gave a lower but poorer electrochemical performance. Implications for cell design are discussed. © 2017 American Institute of Chemical Engineers AIChE J, 64: 1135–1146, 2018

Inhibition of CO2 corrosion of mild steel − Study of mechanical effects of highly turbulent disturbed flow

The failure mechanisms of corrosion inhibitors in highly turbulent flow remain a disputed topic. In the present study, corrosion experiments of X65 pipeline steel were performed with an imidazoline-based corrosion inhibitor using a high-shear turbulent channel flow cell, which included a flow disturbance in the form of a small protrusion. Localized corrosion was observed at the protrusion that could be mitigated with an excess inhibitor concentration. It was found that wall shear stress (up to 5000Pa) was not the cause of inhibitor failure. The flow acceleration at the leading edge of the protrusion caused a drop in pressure and led to cavitation, with bubble collapse further downstream. This was the main cause of inhibitor failure and localized corrosion. The observed behavior was interpreted in terms of corrosion inhibitor adsorption/desorption kinetics and the associated activation energy analysis.

A Miniaturized High-Throughput Flow Injection Analysis System for Electrochemiluminescence Detection

In this work a miniaturized flow injection analysis (FIA) system coupled with optical detection for carrying out electrochemiluminescence (ECL) based assays is presented. Screen-printed electrodes integrated in one channel flow-cell (TLFCL, Thin layer flow-cell) were used as the electrodic surface. In these electrodes a transparent slide, that usefully allows the detection of air bubbles inside the cell, is attached over the screen-printed electrodes platform delimiting a flow channel (height 400 μm; volume 100μL). The injection is done through an “in-line luer injection port” where sample volume can be easily controlled by operator through a precise syringe. This configuration brings important advantages since it simplifies operability and effectiveness of working in FIA systems. TLFCL working electrodes were modified with different nanomaterials in order to carry-out innovative ECL based proofs-of-concept. By combining the bipotentiostat/galvanostat and the UV-VIS spectrometer of SPELEC device, the ECL signal was simultaneously (electrochemically) generated and captured (with the aid of a reflection probe connected to the spectrometer). The ECL behaviour of the developed electro-generated luminescent assays was carefully evaluated assessing aspects as sensitivity, limits of detection and reproducibility and the analytical figures of merit were obtained. Moreover, 3D dynamic ECL plots were registered for the acquisition of real-time luminescent spectrum, relating wavelength emission, potential, and ECL signal in a 3D perspective. Acknowledgements MB González-García work was supported by Torres Quevedo grant (PTQ-13-05994) of the National Program for the Promotion of Talent and Its Employability of the Spanish Ministry of Economy and Competitiveness.

3D-printed porous electrodes for advanced electrochemical flow reactors: A Ni/stainless steel electrode and its mass transport characteristics

Porous electrodes have shown high performance in industrial electrochemical processes and redox flow batteries for energy storage. These materials offer great advantages over planar electrodes in terms of larger surface area, superior space time yield and enhanced mass transport. In this work, a highly ordered porous stainless steel structure was manufactured by 3D-printing and coated with nickel from an acidic bath by electrodeposition in a divided rectangular channel flow cell. Following the electrodeposition, the volumetric mass transport coefficient of this electrode was determined by the electrochemical reduction of 1.0×10−3moldm−3 of ferricyanide ions by linear sweep voltammetry and chronoamperometry. The convection diffusion characteristics are compared with other geometries to demonstrate the novelty and the advantages of 3D-printed porous electrodes in electrochemical flow reactors. Robust porous electrodes with tailored surface area, composition, volumetric porosity and flow properties are possible.

Editors' Choice—Electrodeposition of Platinum on Titanium Felt in a Rectangular Channel Flow Cell

Highly porous platinized titanium substrates are attractive electrode materials for industrial electrochemical processing and electrochemical energy storage. The electrodeposition of platinum on titanium felt was carried out in a divided, rectangular channel flow cell from an alkaline bath without additives. The morphology and spatial distribution of the platinum deposits in the porous material were analyzed using SEM and EDS microscopy in addition to X-ray computed tomography (CT). The electroplated surface area was estimated from the charge transfer current ratio for Ce(IV) reduction and related to a theoretical electrosorbed hydrogen monolayer surface area. The platinized titanium felt showed a significant enhancement of active surface area in comparison to conventional electrode materials. Although platinum was present throughout the porous electrode, CT revealed heterogeneous deposits accumulating in regions near the membrane (during electrodeposition), as a result of the potential distribution in the felt material and flowing electrolyte. Uniform platinum coatings are possible on thin titanium felt under 200 μm thick, by either potentiostatic or galvanostatic electrodeposition.

Mass transport and active area of porous Pt/Ti electrodes for the Zn-Ce redox flow battery determined from limiting current measurements

The conversion of soluble cerium redox species in the zinc-cerium redox flow battery and other electrochemical processes can be carried out at planar and porous platinised titanium electrodes. The active area, current density, mass transfer coefficient and linear electrolyte flow velocity through these structures have a direct influence on the reaction yield and the relationship between cell potential and operational current density during charge and discharge of a flow battery. A quantitative and practical characterization of the reaction environment at these electrodes is required. The volumetric mass transfer coefficient, kmAe has been calculated for diverse electrode structures from limiting current measurements for Ce(IV) ion reduction in a laboratory, rectangular channel flow cell. This factor can be used to predict fractional conversion and required electrode dimensions. Platinised titanium felt shows superior kmAe values compared to other materials and is a practical, high performance electrode for the Ce(III)/Ce(IV) ion redox reaction.

Novel thin layer flow-cell screen-printed graphene electrode for enzymatic sensors

A new Screen-printed electrodes (SPE) integrated in one channel flow-cell was developed. The one channel flow-cell is attached and directly changeable with electrode. In the new flow-cell the injection is done through an “in-line luer injection port” which can be less aggressive than wall-jet flow cell for a biological recognition element immobilized on the surface of the electrode. The sample volume can be easily controlled by the operator through a syringe. In this novel thin layer flow-cell screen-printed electrodes, the working electrode was modified with graphene materials, and an enhancement of electroactive area to 388% over a standard electrode was found. This new configuration was applied to study the entrapped cellobiose dehydrogenase from the ascomycete Corynascus thermophilus (CtCDH) in a photocrosslinkable PVA-based polymer. The calibration curve of lactose using optimized parameters shows a wide linear measurement ranges between 0.25 and 5mM. A good operational stability of the CtCDH-PVA-modified graphene electrode is obtained, which keeps the same initial activity during 8h and exhibits a good storage stability with a decrease of only 9% in analytical response after 3 months storage at 4◦C.

Effect of humidity content and direction of the flow of reactant gases on water management in the 4-serpentine and 1-serpentine flow channel in a PEM (proton exchange membrane) fuel cell

The performance of a PEM (proton exchange membrane) fuel cell depends on design and operating parameters such as relative humidity, operation pressure, and number of channels and direction of the flow of reactant gases. In this study, a three-dimensional, two-phase model has been established to investigate the water management and performance of PEM fuel cell with rectangular geometry and 1-serpentine and 4-serpentine with parallel flow, counter flow and cross flow for hydrogen and oxygen. The numerical simulation was realized with a PEM fuel cell model based on the FLUENT. The active area of each cell is 24.8 cm2 that its weight is 1300 gr. The material of the gas diffusion layer is carbon clothes, the membrane is nafion117 and the catalyst layer is a plane with 0.004 g cm−2 platinum. Pure hydrogen is used on the anode side and oxygen on the cathode side. Simulation results are obtained for voltage as a function of current density at different humidity. The simulation results are compared with the experimental data, and the agreement is found to be good. The results show that the cell performance at lower voltages increases with increasing humidity in cell with 4-Serpentine flow channel and also in cell with 1-Serpentine flow channel, cell performance at all voltages increases with increasing humidity. In cell with 4-Serpentine and parallel flow channel cell performance is better than counter and cross flow in low voltage and in cell with 1-Serpentine and parallel flow, performance is better than counter and cross flow in high voltage.