Exchange Current Density Values Research Articles

A new method for the preparation of MgAl layered double hydroxide-copper metal–organic frameworks structures: application to electrocatalytic oxidation of formaldehyde

In this research, we present a novel design protocol for the in-situ synthesis of MgAl layered double hydroxide-copper metal–organic frameworks (LDH-MOFs) nanocomposite based on the electrocoagulation process and chemical method. The overall goal in this project is the primary synthesis of para-phthalic acid (PTA) intercalated MgAl-LDH with Cu (II) ions to produce the paddle-wheel like Cu-(PTA) MOFs nanocrystals on/in the MgAl-LDH structure. The physicochemical properties of final product; Cu-(PTA) MOFs/MgAl-LDH, were characterized by the surface analysis and chemical identification methods (SEM, EDX, TEM, XRD, BET, FTIR, CHN, DLS, etc.). The Cu-(PTA) MOFs/MgAl-LDH nanocomposite was used to modification of the carbon paste electrode (CPE); Cu-(PTA) MOFs/MgAl-LDH/CPE. The electrochemical performance of Cu-(PTA) MOFs/MgAl-LDH/CPE was demonstrated through the utilization of electrochemical methods. The results show a stable redox behavior of the Cu (III)/Cu (II) at the surface of Cu-(PTA) MOFs/MgAl-LDH/CPE in alkaline medium (aqueous 0.1 M NaOH electrolyte). Then, the Cu-(PTA) MOFs/MgAl-LDH/CPE was used as a new electrocatalyst toward the oxidation of formaldehyde (FA). Electrochemical data show that the Cu-(PTA) MOFs/MgAl-LDH/CPE exhibits superior electrocatalytic performance on the oxidation of FA. Also the diffusion coefficient, exchange current density (J°) and mean value of catalytic rate constant (Kcat) were found to be 1.18 × 10–6 cm2 s−1, 23 mA cm-2 and 0.4537 × 104 cm3 mol−1 s−1, respectively. In general, it can be said the Cu-(PTA) MOFs/MgAl-LDHs is promising candidate for applications in direct formaldehyde fuel cells.

The impact of La/Y and Ni/Co substitutions on the gas-phase and electrochemical hydrogenation properties of the La3-xMgxNi9 alloys

This paper presents the results of investigations of the impact of elemental substitution on the hydrogenation properties of La3-xMgxNi9-based alloys, focusing on both gas-phase and electrochemical hydrogenation processes. Alloys derived from La3-xMgxNi9 with La → Y and Ni → Co substitutions were synthesized using powder metallurgy methods. All of them were crystallized with PuNi3 structure type. Gas-phase hydrogenation studies revealed that Y-free samples exhibited faster gas-phase hydrogenation rates compared to Y-substituted ones, whereas electrochemical performance measurements showed the opposite behaviour. Notably, the La1.5Y0.5MgNi6Co3 alloy demonstrated a discharge capacity of approximately 400 mAh/g, while the La1.5Y0.5MgNi7Co2 alloy exhibited good cyclic stability with a discharge capacity of 389.5 mAh/g and preserved approximately 84% of its capacity after 50 charge/discharge cycles at a current density of 50 mA/g. Y-containing samples demonstrated improved electrochemical characteristics, especially in terms of the HRD (high-rate dischargeability) parameter. The La1.5Y0.5MgNi9 alloy has shown ∼86% of its maximum discharge capacity at 1 A/g current density. This electrode with the highest HRD rate demonstrated highest diffusion coefficient (DH = 2.67·10−11 cm2/s), which also correlates with the highest value of exchange current density (I0 = 222 mA/g) and higher limit of the anodic current (IL=878 mA/g). This highlights the prospects of application of Y-containing alloys for areas where high-rate discharge capabilities are required for Ni-MH batteries.

Improving EET kinetics and energy conversion efficiency of 3D hydrophilic composite hydrogel through 2D direction biofilm growth

The limited power output of microbial fuel cells (MFCs) has impeded their widespread adoption application. Thoughtful selection of a suitable anode material not only enhances extracellular electron transfer (EET) efficiency but also stimulates microbial adhesion and proliferation. Herein, a three-dimensional conductive polymer hydrogel MXene/(polypyrrole)-(polyacrylamide) (MPP) is proposed, which can enhance the power generation performance of the bioanode by promoting the enrichment of microorganisms in the two-dimensional direction. The integration of hydrogel molecular chains within the layers of MXene effectively inhibits the self-aggregation of MXene layers, thereby facilitating the formation of ion transport channels for expedited charge storage. As a result, the maximum power density increases from 3.12 W/m3 (CF) to 6.71 W/m3 (MPP-25), the protein content of MPP-25 bioanode (59.66 ± 2.39 mg/cm2) is 3.34 times higher than that of CF (17.85 ± 1.53 mg/cm2), and the exchange current density value increases from 0.06 mA/cm2 (CF) to 0.26 mA/cm2. Conductive hydrogels prepared by MXene as a modifier are a promising bioelectrocatalyst for high-performance MFCs.

Studying voltage losses during discharge for biphenyl-sodium polysulfide organic redox flow batteries

Voltage losses during discharge have been quantitatively investigated in a coulombically balanced biphenyl (Bp)|sodium-polysulfide (Na2Sx) organic redox flow battery. The individual half-cell electrochemical impedance spectroscopy (EIS) response was studied using a flow cell with an in-situ sodium/sodium-ion reference electrode. The anode, consisting of Bp/Bp− couple, contributed approximately 58% of the total cell overpotential during discharge. Further investigation revealed that kinetic overpotential dominating both anode and cathode voltage losses during discharge. The EIS response for the sodium-polysulfide half-cell exhibits two semicircles at high and low frequencies. Since there is limited literature relating the high-frequency semicircle to a physical process, this work extends the investigation of cathode high-frequency EIS features using in-situ and ex-situ electrochemical diagnostic tools. The Bp Nyquist plot consisted of a single semi-circle due to its simpler redox reaction relative to the more complicated Na2Sx. Tafel analysis was used to calculate exchange current density values, with Bp having a lower exchange current density than Na2Sx. This finding explains the relatively higher Bp kinetic voltage loss as compared to Na2Sx.

Hydrogen evolution reaction catalyzed by MoS2/CoS2 supported on nanocarbon hybrid in acidic medium

There is a high demand for evolving cost-operative and efficient non-noble electrocatalysts for hydrogen evolution reaction (HER). Free-standing MoS2 and their heterostructures are emerging as potential electrocatalysts due to their electrochemical stability in harsh acidic mediums. Herein, we report a one-pot hydrothermal synthesis of MoS2/CoS2 heterostructure with and without the support of carbon nanostructures. The electrical conductivity of the support material is enhanced by introducing f-MWCNT, which acts as pillars between the rGO layers, thus exposing a larger quantity of active sites that favors the hydrogen adsorption property and reduces the charge transfer resistance for facilitating the HER kinetics. The interfacial interaction between MoS2 and CoS2 with the synergistic effect of rGO/f-MWCNT (nanocarbon hybrid, NCHy) results in a potential catalyst yielding a current density of −10 mA/cm2 at −133 mV with an exchange current density value of 0.34 mA/cm2 and turnover frequency of 1.33/s. Catalyst stability is examined using a chronoamperometry test (CA) for 14 h, and the material shows high stability. Also, a study of change in electrochemical activity with change in transition metal in the heterostructure is systematically performed.

Electrochemical Extraction of Fission Element Samarium from Molten NaCl-2CsCl Eutectic Salt Using the Liquid Gallium Cathode

The effective extraction of neutron poison samarium from nuclear waste to prevent reactions with metallic uranium is crucial for the sustainable development of nuclear energy. The electrochemical recovery of samarium on the liquid gallium cathode from the NaCl-2CsCl molten salts has been investigated by a variety of electrochemical techniques, and its electrochemical reduction properties and kinetic parameters have been provided. It was revealed that the reduction reaction on the Mo cathode of Ga(III) to Ga(0) and Sm(III) to Sm(II) is a two-step and one-step reaction process, respectively, and both reactions are reversible. The diffusion coefficients of Ga(III)/Ga(II) and Sm(III)/Sm(II) were identified, and the activation energies were 20.07 and 42.96 kJ mol–1, respectively. Simultaneously, the codeposition mechanism of Ga(III) and Sm(III) on the Mo cathode was systematically investigated, and the potential and types of formation of binary intermetallic compounds were explored. Subsequently, it was determined that there are two main reaction processes for Sm(III) on the liquid Ga cathode, and the deposition potential of Sm becomes more positive due to the formation of the alloy. The exchange current density values of Sm(III)/Sm(Ga) obtained by both linear polarity (LP) and Tafel techniques increased with temperature, meanwhile the charge transfer resistance decreased, as well as the transfer coefficient. In addition, the apparent electrode potential of Sm(III)/Sm(Ga) was also calculated. Based on the electrochemical analysis, the fission element Sm was deposited on the liquid Ga cathode by potentiostatic electrolysis at a suitable potential, and the alloy products were verified by X-ray diffraction, scanning electron microscopy, and energy-dispersive spectroscopy. Ultimately, the highest separation efficiency of Sm on the liquid Ga cathode reached 92.43% according to the analysis of inductively coupled plasma atomic emission spectrometry (ICP-AES) results.

Slow O–H Dissociation in the First-Order Oxygen Evolution Reaction Kinetics on Polycrystalline γ-FeO(OH)

To unravel the reaction mechanism of the electrochemical oxygen evolution reaction (OER), analysis of the intrinsic activity parameters obtained via electrokinetic investigation remains effective. In this study, polycrystalline γ-FeO(OH), synthesized at room temperature, was used as a stable, albeit reactive, anode for OER, and electrokinetic studies were performed to unravel the oxygen evolution reaction pathway. The cell temperature, hydroxyl ion concentration, and the cation of the supporting electrolyte were varied, and the influence of external bias on the OER activity was recorded. Changes in the cell temperature from 30 to 65 °C lead to an enhanced OER activity due to small overpotential, Tafel slope, and charge-transfer resistance (Rct) values at high temperatures, which unambiguously highlights the influence of the thermodynamic barrier and electron-transfer kinetics. The calculated anodic charge-transfer coefficient (αa) and specific exchange current density (j0,s) values are 0.65 and 2.24 × 10–5 mA cm–2, respectively. The faster OER kinetics on polycrystalline γ-FeO(OH) can also be attributed to an appreciably low activation energy of 8.26 ± 2 kJ mol–1, where variation of the electrolyte concentration indicated a first-order dependence on [OH]−. Experimentally obtained intrinsic kinetic parameters such as the Tafel slope, anodic charge-transfer coefficient, exchange current density, activation energy (Ea), reaction order (m), and deuterium isotope effect implicate the dissociation of hydroxyl ions on the polycrystalline γ-FeO(OH) as the rate-determining step. The direct effect of cations such as Li+, Na+, and K+ of the electrolyte on OER highlights a weak interaction of the cations with the surface-active [FeIII-OH] species. A change in the electrode substance from three-dimensional highly conductive nickel foam (NF) to two-dimensional less conductive carbon cloth (CC) resulted in a change in the slow step, leading to the formation of a high-valency iron oxo intermediate from the iron hydroxy species.

Free-standing and binder-free nickel polymeric nanofiber membrane for electrocatalytic oxidation of ethanol in alkaline solution

In-situ chemical reduction technique was exploited to fabricate free-standing and binder-free active nanocatalyst materials for direct ethanol fuel cells using nickel nanoparticles onto polyvinylidenefluoride-co-hexafluoropropylene membrane [Ni/PVdF-HFP]. Homogeneously distributed nickel nanoparticles with face-centered cubic structure were observed onto smooth membrane surfaces. Cyclic voltammetric measurements indicated the enhanced activity of Ni/PVdF-HFP membrane for oxidizing the alcohol molecules in NaOH solution. The measured oxidation current density increased with increasing the added ethanol concentration into the supporting electrolyte up to 0.64 M. Some kinetic parameters were calculated such as the charge transfer coefficient (α), Tafel slope and exchange current density values to record 0.468, 369 mV dec−1 and 1.28 μA cm−2, respectively. The three dimensional nanostructure of these fabricated metallic membranes and the increased number of their active voids could provide largely exposed surface areas for adsorbed alcohol molecules. The good stability of nickel nanoparticles onto PVdF-HFP membrane surface with minimum leaching level during prolonged ethanol oxidation in alkaline solution can offer unique possibilities for utilizing these polymeric electrocatalyst structures for energy production applications.

Electrochemical determination of ornidazole at silver electrode: analytical application in human blood

This paper reports on the electrocatalytic and electroanalytical activity of metallic silver electrode (MSE) for ornidazole (ONZ) reduction using cyclic voltammetry (CV), square wave voltammetry (SWV), chronoamperometry, Tafel plots, and electrochemical impedance spectroscopy (EIS). Voltammetry results show an irreversible response with a significant shift to positive potentials. Based on the polarization curves, the Tafel slope is higher than 120 mV per decade indicating the Volmer step as rate determining step. The MSE presents the highest exchange current density (i0) value (6.452 µA/cm2), which further confirms their higher electrocatalytic activity towards ONZ reduction. Under the optimized conditions, MSE showed a good linearity in the concentration range from 8.0 × 10–7 mol L–1 to 6.0 × 10–5 mol L–1, with a detection limit (LOD) of 4.38 × 10–7 mol L–1. The MSE was successfully applied for the determination of ONZ in human blood.

Boosting oxygen electrode kinetics by addition of cost-effective transition metals (Ni, Fe, Cu) to platinum on graphene nanoplatelets

Pt and Pt-M (M = Ni, Fe, Cu) nanoparticles supported on graphene nanoplatelets (GNPs) were synthesized by simultaneous supercritical carbon dioxide deposition method. Morphology analysis by TEM revealed the formation of metal nanoparticles of 2–3 nm size uniformly distributed over GNPs, while XPS was used to determine their oxidation states. Four materials were tested as electrocatalysts for ORR and OER in unitized regenerative fuel cells and rechargeable metal-air batteries. PtFe/GNPs exhibited favorable ORR kinetics in terms of the highest diffusion-limited current density, the lowest Tafel slope, and a high number of exchanged electrons (n = 3.66), which might be attributed to its high double-layer capacitance and, thus, high electrochemically active surface area. Furthermore, this material performance was comparable to that of commercial Pt/C electrocatalyst containing double the amount of Pt. The same material showed the best performance toward OER as evidenced by the highest current density, the lowest value of exchange current density, and overpotential to reach a current density of 10 mA cm-2, as well as the lowest Tafel slope.

Electrochemical measurement and analysis of YCl3, ScCl3, GdCl3 and MgCl2 in molten eutectic LiCl-KCl

Electrochemical measurements of YCl3, ScCl3, GdCl3 and MgCl2 were obtained in molten LiCl-KCl eutectic at 773 K using a three-electrode configuration. Tungsten rods were used as the working and counter electrodes. Two quasi- and one reference electrode(s) (glassy carbon, nickel wire, and Ni/NiO) were used to collect electrochemical measurements of the analyte salts. Cyclic voltammetry data were analyzed to calculate values of diffusion coefficient, exchange current density, and charge transfer resistance and were determined to be on the order of 10−5 cm2 s−1, 10−2 A cm−2, and 100 Ω; respectively. In general, the values of diffusion coefficients were found to be consistent with those reported of high-temperature molten salts. Relatively large values of exchange current density corresponded with smaller values of charge transfer resistance. These values were found to be reasonable in comparison to results available in the literature. The measured cyclic voltammograms were normalized with respect to both lithium reduction and chloride ion oxidation potentials. Such a normalization technique is effective for comparing experimentally obtained cyclic voltammetry data to those that have been published. An analysis of experimentally obtained results indicates the relation of electrode reactions (e.g., differences of reduction potentials) are independent of the choice of reference electrode. Additionally, the choice of reference electrode did not affect the electrochemical window, exchange current density, or diffusion coefficient values.

Exchange Current Density of Solid Oxide Electrolysis Cell Electrodes

Introduction Numerical simulation is a powerful technique in evaluating solid oxide fuel cell (SOFC) performance. Such method enables to visualize SOFC performance e.g. in using new materials. It is also desirable to develop such method that visualizes internal phenomena in solid oxide electrolysis cell (SOEC). While various parameters are important in simulating phenomena in SOEC stacks, we focus on exchange current density (1,2). Here, exchange current density is experimentally measured and evaluated using single SOEC / SOFC reversible cells. Furthermore, the exchange current density for different electrode materials in both SOEC and SOFC operation modes is examined. Exchange current density is defined as the current exchanged at the electrode/electrolyte interfaces in both directions in equilibrium and thus , so that an identical value for a given electrode has to be obtained in both SOFC and SOEC modes. However, as such values are practically measured by applying certain current in opposite directions, apparent exchange current density measured could be somehow different due to various irreversible processes at the electrode/electrolyte interfaces. In this study, such apparent exchange current density values are obtained and discussed. Experimental In this study, we evaluated the exchange current densities of solid oxide cells with three types of fuel electrodes (A-1, 2, 3) and two types of air electrodes (B-1, 2). The exchange current densities were measured in the SOFC and SOEC modes using following materials: (A-1) Ni-ScSZ (NiO-ScSZ (ScSZ: 10mol%Sc2O3-1mol%CeO2-89mol%ZrO2)), (A-2) Rh-GDC (La0.1Sr0.9TiO3, Gd0.1Ce0.9O2, volume ratio 50:50 (LST-GDC), Rh 0.178 mg/cm2 supported on LST-GDC) co-impregnated material, and (A-3) Ni-GDC (Ni 0.167 mg/cm2 supported on LST-GDC) co-impregnated material for the fuel electrode; (B-1) LSCF/GDC ((La0.6 Sr0.4)(Co0.2 Fe0.8)O3/GDC), and (B-2) LSM ((La0.8Sr0.2)0.98MnO3) for the air electrode. The exchange current density was derived using the Butler-Volmer-type equation. The exchange current density obtained was fitted by the commonly used phenomenological formula of the exchange current density. We compared the obtained parameters and the dependencies on gas partial pressure. Results and Discussion Here, the differences in exchange current density at the fuel electrode are examined. Figure 1 shows the exchange current density as a function of humidity in the fuel, and fitted curves. The fitted curves of exchange current densities are almost similar in the SOFC and SOEC modes. However, the maximum value measured in the SOFC mode shown in Fig. 1 (b) was somehow higher than that measured in the SOEC mode shown in Fig. 1 (a). The difference in using the Ni-ScSZ fuel electrode was more remarkable than that using the Rh-GDC co-impregnated fuel electrode shown in Figs. 1 (c) and (d). It may be possible that the apparent exchange current density at the fuel electrode could include influences of irreversible processes, associated with steam electrolysis. The dependence of exchange current density on gas partial pressure (3) will be examined to discuss electrode processes in steam electrolysis. The exchange current density obtained in this study enables various simulations for SOECs, besides SOFCs. References T. Yonekura, Y. Tachikawa, T. Yoshizumi, Y. Shiratori, K. Ito, and K. Sasaki, ECS Trans., 35 (1), 1007-1014 (2011).K. Takino, Y. Tachikawa, K. Mori, S. M. Lyth, Y. Shiratori, S. Taniguchi, and K. Sasaki, Int. J. Hydrogen Energy, 45 (11), 6912-6925 (2020).T. Hosoi, T. Yonekura, K. Sunada, and K. Sasaki, J Electrochem Soc., 162 (1), F136-F152 (2015). Figure 1

Polysulfide-Permanganate Flow Battery Using Abundant Active Materials

A new flow battery is presented using the abundant and inexpensive active material pairs permanganate/manganate and disulfide/tetrasulfide. A wetted material set is identified for compatibility with the strongly oxidizing manganese couple at ambient and elevated temperatures. Both solutions allow high active material solubility, with cells tested at theoretical energy densities up to 43 Wh l−1 for the ∼1.2 V cell. Full cells built with nickel foam electrodes and sodium-exchanged Nafion 115 membranes deliver a baseline area-specific resistance of 2.7 Ω-cm2. Incorporation of high-surface-area cobalt-coated carbon paper and high-surface-area stainless steel mesh electrodes, and an expanded Nafion 115 membrane delivers cells with 44% lower resistance at 1.6 Ω-cm2. All cells show performance decay over the course of cycling. The Co-decorated carbon paper electrodes provide significant kinetic improvements, shifting electrode performance from non-linear with Ni-foam to linear with a volume-normalized exchange current density value of 3.2 A cm−3. The expanded membrane provides increased conductivity over the 13 mS cm−1 conductivity observed in as-received, sodium-exchanged Nafion 115. Although boiled membranes provide improved conductivity, it is at the cost of decreased Coulombic efficiency and poorer manufacturability. Full cell models suggest that similar cell resistances (1.7 Ω-cm2) should be feasible with as-received Nafion 115 and advanced electrodes.

Electrodeposition Mechanism of La3+ on Al, Ga and Al-Ga Alloy Cathodes in LiCl-KCl Eutectic Salt

Studying the electrodeposition mechanism of La3+ in LiCl-KCl salt is extremely important for understanding the main characteristics of the deposition of An/Ln in the pyrochemical reprocessing of spent nuclear fuels. In this work, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and Tafel methods were employed to investigate the electrodeposition mechanism and kinetic processes of La3+ on Al, Ga and Al-Ga alloy cathodes in LiCl-KCl eutectic salt at the temperature range of 723−873 K. The EIS spectra were measured by applying a minimum overpotential near the equilibrium potential, and the suitable equivalent circuits were fitted. The values of exchange current density (i 0) calculated by EIS ranged from 0.078 to 0.42 A cm−2. Finally, Al2Ga2La ternary and Al3La, Ga6La binary alloys were obtained by the potentiostatic electrolysis, which were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS).

Correlation of Morphology and Crystal Structure of Metal Powders Produced by Electrolysis Processes

In this review paper, morphologies of metal powders produced by the constant (potentiostatic and galvanostatic) regimes of electrolysis from aqueous electrolytes are correlated with their crystal structure at the semiquantitative level. The main parameters affecting the shape of powder particles are the exchange current density (rate of electrochemical process) and overpotential for hydrogen evolution reaction. Depending on them, various shapes of dendrites (the needles, the two-dimensional (2D) fern-like, and the three-dimensional (3D) pine-like dendrites), and the particles formed under vigorous hydrogen evolution (cauliflower-like and spongy-like particles) are produced by these regimes of electrolysis. By decreasing the exchange current density value, the crystal structure of the powder particles is changed from the strong (111) preferred orientation obtained for the needle-like (silver) and the 2D (lead) dendrites to the randomly orientated crystallites in particles with the spherical morphology (the 3D dendrites and the cauliflower-like and the spongy-like particles). The formation of metal powders by molten salt electrolysis and by electrolysis in deep eutectic solvents (DESs) and the crystallographic aspects of dendritic growth are also mentioned in this review.

Copper ferrite supported reduced graphene oxide as cathode materials to enhance microbial electrosynthesis of volatile fatty acids from CO2

Copper ferrite/reduced graphene oxide (CF/rGO) nanocomposites (NCs) was synthesized using the bio-combustion method and applied as a cathode catalyst in the microbial reduction of CO2 to volatile fatty acids (VFAs) in a single chamber microbial electrosynthesis system (MES). The synthesized NCs exhibited a porous network-like structure with a high surface area of CF/rGO (158.22 m2/g), which was 2.24 folds higher than that of CF. The Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS) analysis for CF/rGO/Carbon cloth (Cc) revealed a high reduction current density of −7.3 A/m2 and a low charge transfer resistance of 2.8 Ω. The isobutyrate and acetate in MES-2 (Cu/rGO/Cc) were produced at 35.37 g/m2/d, which was 1.53 folds higher than that of MES-1 (bare Cc: 23.10 g/m2/d). The columbic efficiency (77.78%) and total VFA concentration (1941.13 ± 83 mg COD/L) were noted to be 1.97 and 1.6 folds higher for MES-2 than MES-1, respectively. The Tafel plot drawn from the CV curves exhibited an exchange current density value of MES-2 that was 3.46 A/m2, and this value was 1.19 and 33.92 folds higher than that of MES-1 and abiotic CF/rGO/Cc, respectively. Field emission scanning electron microscopy (FESEM) observations revealed enhanced rod-shaped bacteria had grown on the cathode suggesting excellent biocompatible and multi-length scale porosity of CF/rGO catalysts for enhanced colonization of microbes. The phyla Proteobacteria (Betaproteobacteria), Bacteroidetes, and Firmicutes were highly abundant as the dominant microbial communities on the cathode, which might played a major role in bioelectrochemical CO2 reduction to VFAs. The results from this study clearly demonstrate that the CF/rGO/Cc electrode could serve as a conductive element between microbes and bactericidal electrodes with excellent electrochemical properties to enable performance of the MES.

Electrochemical oxidation of sulphite in neutral media on graphite

In this paper, electrochemical behavior of sulphite ions on graphite electrode in neutral solution (1 molL−1 Na2SO4) has been studied in order to identify the relationship between the sulphite concentration in the electrolyte solution (10−3, 10−2, 10−1, 5·10−1 and 1 mol L−1) and kinetic parameters of the anodic process. Electrochemical behavior of sulphite in the test solutions has been studied by square wave voltammetry (SWV) and differential pulse voltammetry (DPV), as well as by linear (LV) and cyclic voltammetry (CV). Tafel slopes between 167 and 191 mV dec−1 have been obtained, corresponding to an anionic transfer coefficient in the range of 0.31–0.34. Exchange current density values up to 0.80 A m−2 reveals that the rate of the electrochemical oxidation of sulphite in the neutral media is at the same order of magnitude as in the alkaline solution. The general aim of these studies is to obtain new anodes with electrocatalytic properties for sulphite oxidation in SO32−/O2 alkaline fuel cells.

Revisiting trends in the exchange current for hydrogen evolution

Nørskov and collaborators proposed a simple kinetic model to explain the volcano relation for hydrogen evolution reaction. Our new model decreases the discrepancy between calculated and experimental exchange current density values.

Preparation of cobalt–manganese-modified lead dioxide anodes and the study of their electrochemical performance in electrowinning copper

The anode materials PbO2–MnO2, PbO2-CoOx, and PbO2–MnO2-CoOx, were prepared by anodic oxidation in the nitrate system. The microstructure and chemical composition of the anode materials were characterized by scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The electrochemical performance of the anode materials were studied by linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS) and Tafel polarization curves (Tafel). The results indicate that the coating of PbO2–MnO2-CoOx anode materials with a spherical structure, and the PbO2–MnO2 and PbO2-CoOx anode materials with a stacked pellet structure. Compared with PbO2, PbO2–MnO2, and PbO2-CoOx anodes, PbO2–MnO2-CoOx anodes have the maximum exchange current density (j0) values, the minimum charge transfer resistance (Rct) values, and minimum the self-corrosion current density (icorr) in electrowinning Copper solution. The cell voltage of Cobalt-containing Manganese anode material is lower than that of traditional Pb–Sn–Sb anode material, Indicating that the Cobalt-containing Manganese anode material is of practical value to reduce energy consumption.

Simulation and Visualization of Internal Heat and Mass Flow Distribution of SOFCs

Introduction In recent years, electrochemical energy conversion technologies receive much attention, as a very high power-generation efficiency beyond 70 to 80% using SOFCs may be possible (1). Although it is important to understand the phenomena in SOFC stacks for highly efficient power generation, it is rather difficult to measure the distribution of internal power generation characteristics experimentally. Here, the performance visualization and prediction by simulation techniques are useful. Exchange current density is an important phenomenological parameter in simulating electrochemical performance (2-3). The exchange current density, expressing the electrode performance quantitatively, is a physical value which depends on gas composition, operating temperature, cell electrode materials, and cell structure. Whilst it is therefore essential to take into account these effects in the numerical calculation, there are not many consistent studies fairly comparing experimental and numerical results.Here in this study, the cell performance is experimentally measured using planar cells composed of typical materials under humidified hydrogen fuel supply. In parallel, the cell performance is also numerically simulated using the exchange current density values. Both results are then compared each other. The aim of this study is to develop three-dimensional simulation technique for visualizing the internal distribution in solid oxide fuel cells, by comparing experimental results with numerical results. Experimental and calculation conditions Electrolyte-supported 50 mm × 50 mm size planar cells with ScSZ electrolyte (ScSZ: 10 mol% Sc2O3–1 mol% CeO2–89 mol% ZrO2) were used to measure the actual cell performance. NiO-ScSZ cermet and (La0.8Sr0.2)0.98MnO3-ScSZ (LSM-ScSZ) composite were used as the anode and the cathode, respectively. Electrode layers with the electrode area of 40 mm×40 mm (16 cm2) were prepared via screen printing technique. In this study, I-V characteristics were measured as a function of fuel utilization (Uf) at the outlet by varying the inlet flow rate of humidified hydrogen fuel supplied to the anode under a given current value. In the simulation, a three-dimensional actual-shape CAD model with cross-flow channels was constructed, using numerical simulation software COMSOL Multiphysics (Ver. 5.2). Cell performance simulation was performed at the operating temperature of 1073 K for 3%-humidified hydrogen fuels. The phenomenological equation describing exchange current density was applied which has been determined for the cells using the same materials and the same preparation conditions. Results and discussion The comparison between experimental and calculated results for various flow rates is shown in Figure 1. The current density value in the simulation is the average current density for the geometric electrode area. The experimental results showed that the OCV decreased as the inlet flow rate decreased. While the experimental value and the simulation result are slightly different due to a difference in the OCV, the slopes of these I-V characteristics are identical in all these cases. These results indicate that this numerical model can simulate I-V characteristics experimentally obtained for the SOFC planar cells under any local conditions.The current density distribution at the electrode/electrolyte interface, at the inlet flow rate for Uf =10% and at the in-plane average current density of 0.2 A cm-2, is shown in Figure 2. The current density distribution exhibited a maximum value near the fuel inlet. The current density gradually decreased towards the fuel outlet. These results indicate that the concentration distribution of hydrogen affects the current density distribution. These results suggest that the electrochemical reaction tends to occur mainly near the anode inlet for humidified hydrogen fuels. Hydrogen is consumed along with the gas flow from the inlet to the outlet, leading to a decrease in current density. Various simulation and visualization results will be reported and discussed. References Y. Matsuzaki, Y. Tachikawa, T. Somekawa, T. Hatae, H. Matsumoto, S. Taniguchi, and K. Sasaki, Sci. Rep., 5, 12640 (2015).T. Hosoi, T. Yonekura, K. Sunada, and K. Sasaki, J. Electrochem. Soc., 162 (1), F136-F152 (2015).T. Yonekura, Y. Tachikawa, T. Yoshizumi, Y. Shiratori, K. Ito, and K. Sasaki, ECS Trans., 35 (1), 1007-1014 (2011). Acknowledgment This study is partially supported by the Center of Innovation (COI) program (JPMJCE1318) of the Japan Science and Technology Agency. Figure 1