Electrochemical Reaction Rate Research Articles

Corrosion inhibition study of marine Streptomyces against sulfate-reducing bacteria in oilfield produced water

A marine Streptomyces sp., which has an inhibitory effect on sulfate-reducing bacteria (SRB), was selected to study inhibitory effect and mechanism of X65 steel on SRB corrosion in oilfield produced water. Streptomyces and SRB had a competitive growth relationship. The Streptomyces metabolites affected the number and activity of SRB and had good corrosion inhibiting properties. The formation and development of SRB biofilm was inhibited. Mixed bacteria inhibited anodic dissolution of X65 steel and slowed down the electrochemical reaction rate. The film layer on the sample was denser, and the average and localized corrosion rates caused by SRB were significantly suppressed.

Quantum rate theory and electron-transfer dynamics: A theoretical and experimental approach for quantum electrochemistry

Quantum rate theory is based on a first-principle quantum mechanical rate concept that comprises with the Planck–Einstein relationship E=hν, where ν=e2/hCq is a frequency associated with the quantum capacitance Cq and E=e2/Cq is the energy associated with ν. For a single state mode of transmittance, e2/Cq corresponds to the chemical potential differences Δμ between donor and acceptor state levels comprising an electrochemical reaction. A statistical mechanic treatment of E is required to compute the contribution of the thermal dynamics at finite temperature. The Arrhenius equation for the temperature dependence of the reaction rate was obtained, as well as Marcus’s Arrhenius-type electron-transfer rate constant as a particular setting of the quantum rate ν. Consequently, this ν concept provides the quantum mechanical foundations for electrochemical reactions at room temperature. The present work also demonstrates that the electron-transfer rate of heterogeneous (diffusionless) reactions can be studied in detail within this theory by measuring Cq using time-dependent electrochemical methods. Since the electron transfer follows a statistical mechanics version of the Planck–Einstein E=hν relationship, the electrochemical reaction dynamics cannot be appropriately modeled using non-relativistic Schrödinger wave mechanics, which is the ongoing quantum approach to electrochemistry. Accordingly, a relativistic analysis that takes into account the spin dynamics of the electron is more appropriate. The latter assumption implies quantum electrodynamics within a particular quantum transport mode intrinsically coupled to the electron-transfer rate of electrochemical reactions that have not been considered thus far. Here it is demonstrated that the consideration of this inherent quantum transport is key to obtaining an in-depth understanding of the electron transfer phenomenon. Finally, the theory is validated through its description of electron transfer, quantum conductance, and capacitance in different electro-active molecular films.

Nanoarchitectonics of nest-like Co3O4 nanowires embedded nitrogen-doped graphene aerogel as electrochemical sensing platform for Pb2+ and Cd2+ trace detection

Nano Co3O4 embedded nitrogen-doped graphene aerogel (Co3O4@NGA) was directly prepared by one-pot hydrothermal synthesis method with ammonia water acting as both precipitant of Co3O4 and nitrogen source of nitrogen-doped graphene aerogel (NGA). This novel method leaved out the calcination process which was necessary for most methods to prepare Co3O4 nanomaterials. The effects of hydrothermal temperature on both morphologies and Pb2+/Cd2+ electrochemical detection performances of Co3O4@NGA were explored. As the hydrothermal temperature rising from 140 °C to 200 °C, the shapes of Co3O4 changed from nanoparticles to nanowires and then to nanoflowers, and nest-like Co3O4 nanowires were architected on NGA sheets at 180 °C. The electrochemical sensor based on the optimized Co3O4@NGA-180 exhibited low limit of detection (LOD) for Pb2+ (7.2 nM) and Cd2+ (10.06 nM) and high sensitivity for Pb2+ (10.51 μA·μM−1) and Cd2+ (8.053 μA·μM−1). The excellent performances were attributed to the synergistic effect of Co3O4 nanowires and porous NGA, which leaded to the fast electrochemical reaction rate in the detection process. Moreover, the Co3O4@NGA-180/GCE sensor had excellent selectivity, repeatability and stability, and could be used to detect traces of Pb2+ and Cd2+ in real water sample.

Ag/Reduced Graphene Oxide/Carbon Fiber Composites as Electrodes for Highly Stable and Responsive Marine Electric Field Sensors

The increasing demand for maintenance-free, cost-effective, and high-stability flexible electrodes is highly anticipated for the research of marine electric-field sensors, and various carbon fibers (CFs) are considered the most suitable carbon-based electrode for the purpose. Nevertheless, the conventional fabrication of acidified or nitrogenized CF electrodes did not attract great attention for commercial application, which has limitations in the case of simultaneous cost-effectiveness and long-term stability. In this study, with homemade reduced graphene oxide (rGO) load, the prepared double carbon substrate Ag-rGO-CF composite electrodes have a honeycomb rGO conductive skeleton and the dispersed Ag nanoparticles via a facile hermetic oxidation process and hydrothermal method. The prepared Ag-rGO-CF composite electrode demonstrated an outstanding electrode performance, including low resistance, high electrochemical reaction rate, and stable potential with long-term stability and low cost. The electric double-layer (EDL) structure theory from the Gouy–Chapman–Stern model and double carbon substrate mechanism between CFs and rGO with the help of Ag were clarified, whose principle is to strengthen the adsorption force and electrostatic attraction of the electrode and to offset the residual charge while reducing the thickness of the electric double layer to achieve the purpose of potential balance. The Ag-rGO-CF composite electrode has presented long-term stability and high sensitivity, especially a wide application bandwidth. The Ag-rGO-CF composite electrode made in this study is a competitive candidate material as a flexible marine electrode field sensor.

3D Numerical Simulation of Metal Bipolar Plate Proton Exchange Membrane Fuel Cell Considering Wavy Interlaced Flow Field

A metal bipolar plate fuel cell (FC) composed of gas distribution zones (GDZ) with ordered distribution of “dot matrix” structures, a complex waveform staggered fluid region, and the effect of cooling flow field (FF) is proposed in this investigation. The 3D multiphase model is applied to simulate the two‐phase flow in the FC. First, the cathode catalyst layer (CCL) has a higher electrochemical reaction rate (ERR) when gas diffusion layer (GDL) is anisotropic, and the ERR under channels is much higher than ribs. Increasing the thickness of GDL is not conducive to gas mass transfer, and the maximum current density reduction rate is 2.94%. Increasing the porosity of GDL is beneficial to improve the mass transport efficiency, and the liquid discharge is promoted. Second, the increase of GDL contact angle affects the cathode microporous layer and liquid saturation in CCL, and the current density is the highest when the contact angle is 120°. Finally, the volume‐of‐fluid model is utilized to analyze the drainage process in the GDZ and cathode small‐size FF. It is indicated in the results that water tends to concentrate at the outlet corner of GDZ in liquid form.

Analysis of the Effect of Applied Load on Crevice Corrosion Behavior

A two-dimensional numerical model incorporating solid mechanics, electrochemistry, mass diffusion, and ion migration processes is developed to investigate the load effect on the crevice corrosion. The model is a transient model of crevice corrosion occurring in cracks of 304 stainless steel in a dilute NaCl solution, and the interaction between stress and electrochemical corrosion was considered. By solving the multiphysical coupling model in COMSOL, the effect of applied load on electrochemical corrosion in the crack tip region was calculated, and the local corrosion current density in the crack tip region with stress concentration within the crack was also calculated by using the Tafel relationship. The distribution of Fe2+ ion, Na+ ion, CL− ion, and H and O2 substance concentrations within the crack cavity is predicted by the equation analysis of substance transport. The results show that metal oxidation is more clearly affected by plastic deformation, the rate of hydrogen evolution reaction increases with stress enhancement, and the oxygen absorption reaction is not affected by stress strain. The distribution of iron ions, hydrogen, and oxygen within the crack is affected by the electrochemical reaction rate, and the distribution of iron ions, sodium ions, and chloride ions is affected by the electrolyte potential.

Synergistic effect of ultrasonic and magnetic fields on the performance of non-aqueous iron-vanadium redox flow battery with deep eutectic solvent electrolyte

In this paper, the synergistic effect of magnetic and ultrasonic fields on FeV redox flow battery with deep eutectic solvent (DES) electrolyte is studied. The results show that the synergistic effect of the two physical fields can reduce the high viscosity and increase diffusion coefficient of the DES electrolyte, and has a positive effect on the oxidation and reduction peaks of DES electrolyte of the FeV redox flow battery. Due to ultrasonic cavitation, the bursting of cavitation bubbles transfers energy to the DES electrolyte. The magnetic field changes the motion rate of charged particles through Lorentz force driving the charged particles in the electrolyte, and influences the electrochemical reaction rate. When the two physical fields are synergistically applied, ultrasonic plays a leading role, and the effect of the two physical fields acting together is better than that of either single physical field: The performance increment for the one with two fields affecting together is 37.1 %, which is larger than the sum of increments for applying a single field (for magnetic field, the increment is 8.6 %; for ultrasonic, 20.8 %). Besides, the application of magnetic field could reduce the cost of ultrasonic application, which is conducive to the application of ultrasonic technology in non-aqeous flow battery with DES electrolyte. In brief, this study shows that an effective and simple method improving the physical and electrochemical properties of DES electrolytes together with enhancing electrochemical reaction rate, which has the potential to be widely used in non-aqueous flow batteries.

Influence of different parameters on PEM fuel cell output power: A three-dimensional simulation using agglomerate model

Gas diffusion layer and catalyst layer are the main components in a proton exchange membrane fuel cell. Gas diffusion layer porosity, platinum, carbon and ionomer inside catalyst layer are also the kay parameters in these two porous layer, the values have a great effect on cell output performance. Considering the correlation between mass transfer and electrochemical reaction rate, there is a strong interaction among these four parameters. Thus, a 3D agglomerate model is established to analyze the effect mechanism of these four parameters on cell performance from mass transfer. Then, these parameters are optimized simultaneously. The results show that more oxygen on the surface of platinum improves electrochemical reaction rate. Cell performance can be improved with platinum or carbon loading increasing, while higher porosity or less ionomer can improve cell performance at high current density. More platinum or carbon, or lower ionomer content all reduces oxygen transfer resistance. Activation and concentration loss reduce obviously under higher porosity or more carbon. Higher performance corresponds to stronger bidirectional mass transfer at the interface between gas diffusion layer and catalyst layer of cathode side. The current density of the cell with optimized parameters can be improved at least 9.1%.

Effect of anode conditions on the performance of direct borohydride–hydrogen peroxide fuel cell system

Direct borohydride–hydrogen peroxide fuel cells (DBHPFCs) are attractive power sources for space applications. Although the cathode conditions are known to affect the system performance, the effect of the anode conditions is rarely investigated. Thus, in this study, a DBHPFC system was tested under various anode conditions, such as electrocatalyst, fuel concentration, and stabilizer concentration, to investigate their effects on the system performance. A virtual DBHPFC system was analyzed based on the experimental data obtained from fuel cell tests. The anode electrocatalyst had a considerable effect on the mass and electrochemical reaction rate of the fuel cell system, but had minimal effect on the decomposition reaction rate. The NaBH4 concentration greatly influenced the mass and decomposition reaction rate of the fuel cell system; however, it had minimal impact on the electrochemical reaction rate. The NaOH concentration affected the electrochemical reaction rate, decomposition reaction rate, and mass of the fuel cell system. Therefore, the significant effects of the anode conditions on the electrochemical reaction rate, decomposition reaction rate, and mass of the fuel cell system prompt the need for their careful selection through fuel cell tests and system analysis.

Understanding Electron Transfer Reactions Using Constrained Density Functional Theory: Complications Due to Surface Interactions.

The kinetic rates of electrochemical reactions depend on electrodes and molecules in question. In a flow battery, where the electrolyte molecules are charged and discharged on the electrodes, the efficiency of the electron transfer is of crucial importance for the performance of the device. The purpose of this work is to present a systematic atomic-level computational protocol for studying electron transfer between electrolyte and electrode. The computations are done by using constrained density functional theory (CDFT) to ensure that the electron is either on the electrode or in the electrolyte. The ab initio molecular dynamics (AIMD) is used to simulate the movement of the atoms. We use the Marcus theory to predict electron transfer rates and the combined CDFT-AIMD approach to compute the parameters for the Marcus theory where it is needed. We model the electrode with a single layer of graphene and methylviologen, 4,4'-dimethyldiquat, desalted basic red 5, 2-hydroxy-1,4-naphthaquinone, and 1,1-di(2-ethanol)-4,4-bipyridinium were selected for the electrolyte molecules. All of these molecules undergo consecutive electrochemical reactions with one electron being transferred at each stage. Because of significant electrode-molecule interactions, it is not possible to evaluate outer-sphere ET. This theoretical study contributes toward the development of a realistic-level prediction of electron transfer kinetics suitable for energy storage applications.

MoWS2 Nanosheet Composite with MXene as Lithium-Sulfur Battery Cathode Material

Due to their superior theoretical specific capacity and energy density, lithium-sulfur (L‒S) batteries are gaining popularity in order to achieve the growing terms for more power generation. However, drawbacks such as low electrical conductivity of the active ingredient sulfur, severe volume expansion and shuttle effect of polysulfides, rapidly decaying battery capacity, and short battery life have hampered their development. A MoWS2@MXene@CNT composite material is used as the main cathode material for L-S batteries in this study. MoWS2 can improve the electrochemical reaction rate by accelerating polysulfide conversion, whereas MXene can suppress electrode volume expansion. Furthermore, the addition of carbon nanotubes (CNT) with high electrical conductivity improves the rate of the electrochemical reaction. Therefore, the MoWS2@MXene@CNT composites have good capacity and versatility as cathode materials and enhance the behavior of L-S batteries.

EFFECT OF NON-UNIFORMLY DISTRIBUTED POROSITY OF GAS DIFFUSION LAYERS ON MASS TRANSFER IN PROTON EXCHANGE MEMBRANE FUEL CELLS

Gas diffusion layer porosity can affect mass and charge transfer inside proton exchange membrane fuel cells and influence cell performance. Moreover, the electrochemical reaction rate distribution in various regions inside the cell is not uniform. Proper porosity distribution is very important to improve cell performance. In this paper, a three-dimensional fuel cell model with three steps porosity along the gas flow direction is established. Four cases of non-uniformly distributed porosity, both in anode and cathode gas diffusion layers are simulated, which are compared with uniform porosity distribution to study the effect of these structures on mass transfer inside the cell. Then, an optimization calculation is carried out to obtain the optimal porosity distribution along gas flow direction at 0.2 V and 0.6 V. The numerical results indicate that non-uniformly distributed porosity can change cell performance, and porosity increasing along the gas flow direction makes cell performance be better. Porosity increasing along the gas flow direction can improve the uniformity of current density distribution at low voltage. Diffusive mass flux plays a dominant role in reactant mass transfer. Higher porosity near the outlet region increases total mass flux at the interface, and the proportion of diffusion mass flux in total mass flux also increases.

Electrocatalytic CO 2 Reduction over Bimetallic Bi-Based Catalysts: A Review

Electrocatalytic CO ₂ Reduction over Bimetallic Bi-Based Catalysts: A Review

Effects of membrane swelling on structural deformation and performance of proton exchange membrane fuel cell

ABSTRACT The change of relative humidity (RH) leads to the expansion and shrinkage of the membrane, resulting in hygrothermal stress, performance degradation and mechanical damage of proton exchange membrane (PEM) fuel cell. In this study, a two-dimensional PEM fuel cell deformation model and a three-dimensional computational fluid dynamics (CFD) model are coupled to study the performance of fuel cell. Emphasis is placed on the influence of membrane swelling and clamping force on the performance of fuel cell. It is found that membrane swelling leads to the structural change of membrane electrode assembly (MEA) and stress in the MEA. The simulated fuel cell performance considering membrane swelling is lower than that of the undeformed membrane, due to smaller electrochemical reaction rate under the rib and higher ionic resistance. The membrane deformation and PEM fuel cell performance under different RHs are also investigated, and medium RH values are found to achieve good fuel cell performance if considering the membrane swelling effect.

Designing graded fuel cell electrodes for proton exchange membrane (PEM) fuel cells with recurrent neural network (RNN) approaches

The graded distribution of Pt loading in the catalyst layer (CL) and the porosity of the gas diffusion layer (GDL) significantly affect the spatial distributions of electrochemical reaction and mass transport rates, thus influencing the cell performance and durability. A sophisticated physics-based model is established to study the influence of graded Pt loading and GDL porosity at the cathode, with their distribution function obeying the elliptic equation along the in-plane and through-plane directions, on the current density and its uniformity at a given cell voltage. To reduce the computational time and resources, an RNN algorithm-based data-driven surrogate model is developed to assist in the identification of the relationship between the design parameters and the objective functions. Latin hypercube sampling (LHS) method is implemented for sampling and then the initial data acquisition is conducted for training and testing the surrogate model. Results show that the machine learning (ML) algorithm could effectively assist the optimal design of the functionally graded electrode, and the surrogate model achieves > 97.9 % prediction accuracy for current density and less than 0.13 root mean square error (RMSE) for current homogeneity. Both the individual variation of Pt loading and GDL porosity and their interaction are respectively analysed. Results also indicate that the inhomogeneous Pt distribution improves the current density. On the contrary, GDL porosity has a greater impact on the cell performance since current density monotonically increases with the homogeneous GDL porosity. When both the inhomogeneous distributions of Pt loading and GDL porosity are simultaneously considered, the homogeneity of current density is improved. However, the improvement of the homogeneity of current density (increases by 54 %) sacrifices the maximum current density (reduces by 22 %).

Nucleation and propagation of stress corrosion cracks: Modeling by cellular automata and finite element analysis

The stress corrosion cracking process of pipeline steel was modeled using cellular automata and finite element analysis, the initiation and propagation of the cracks were simulated. Before the initiation of cracks, the extent of pitting corrosion was revealed to be controlled by anodic reactions and mechanical factors, in which electrochemical corrosion played a leading role. The deposition of corrosion products created a diffusion barrier between the reactants participating in the corrosion process, limiting the rate of electrochemical reactions. During the crack propagation process, the mechanochemical effects caused by plastic deformation promoted anodic dissolution at the crack tip, driving crack propagation.

Projection Diagram for Determining Polarization Curves under Variation of Activation Criterion Using Similarity Theory.

Revealing the correlation between polarization curve and input parameters is a highly concerned topic in proton exchange membrane fuel cell (PEMFC) research. Till now, three-dimensional (3D) numerical models have been the most comprehensive methods to predict the polarization curve under variational conditions. However, due to the diversity and complexity of the parameters involved, an immense numerical or experimental burden is required to obtain the above-referred correlation based on 3D numerical model. Application of the similarity theory is considered as a promising breakthrough in PEMFC research to obtain generalized and compact laws. Activation criterion, a relative magnitude of the effect of temperature on electrochemical reaction rate versus the effect of activation overpotential, is the most important criterion on the PEMFC performance. Revealing its impact on the dimensionless polarization curve in the aspects of slope, intercept, and curvature is one of the major challenges for further investigation. Herein, a projection diagram is proposed to determine polarization curves under variation of activation criterion using similarity theory based on a series of results with other criteria variation. As a validation of the concept, two scenarios are exhibited by numerical approach. Results suggest that the maximum relative deviation of polarization curves predicted by the projection diagram is 0.14%, which reaches a high accuracy. The projection diagram reveals the reason why the activation criterion has a comprehensive and complex impact on the dimensionless polarization curve.

In‐Depth Analysis of Electrochemical Reaction Rate Distribution in Microfluidic Fuel Cell with Flow‐Through Electrodes

Nonuniform reaction rate distributions are commonly observed in the microfluidic fuel cell (MFC) systems, which bring a significant limit to the cell output. Herein, systematic analyses are performed to explore the electrochemical reaction rate distributions in the flow‐through electrodes of MFCs, and in‐depth understanding of the distribution mechanisms under various operating conditions is presented via a MFC performance simulation model. The results demonstrate that the high‐reaction‐rate regions locate at the inner parts of the flow‐through electrodes in the high flow rate and high‐reactant concentration cases which are ohmic‐resistance dominated, while moving toward the outer parts of the electrodes with the decreasing of flow rate and/or reactant concentration due to the increased concentration‐related activation resistance. A series of performance enhancement strategies are also proposed and examined. It is found that smaller electrode aspect ratio, reduced electrode distance, excess supporting electrolyte, and larger specific surface area are desirable in the high flow rate and high‐reactant concentration cases, which can boost the cell performances significantly. This work can contribute to the optimal designs of microfluidic fuel cells under various application scenarios in the future.

YSZ-based mixed potential type acetone gas sensor attached with CuSb2O6 sensing electrode for ketosis diagnosis

Acetone in exhaled breath can be employed as a diabetic-specific biomarker for noninvasive, painless, quick and in-house screening of diabetes. Herein, a mixed potential type acetone gas sensor using yttria-stabilized zirconia (YSZ) and CuSb 2 O 6 sensing electrode (SE) was manufactured. The sensitivities of the sensor to 0.2–5 ppm acetone and 5–200 ppm acetone were − 24.9 mV/decade and − 76.2 mV/decade at 680 °C. The response time for 10 ppm acetone of the sensor was only 3 s and the recovery time was 17 s. The sensor also displayed good repeatability, long-term stability, reliability and selectivity. It was worth noting that the response value of the sensor increased with the increase of relative humidity (RH) value, which could be account for the increase of acetone gas concentration and electrochemical reaction rate at TPB. Moreover, the sensor could realize the distinction between the diabetic ketosis patients and non-ketotic volunteers by the response values of the sensor in the clinical breath detection, proving its potential in the field of ketosis diagnosis. • CuSb 2 O 6 material is used as sensing electrode to fabricate a mixed potential type YSZ-based acetone sensor. • The sensor with CuSb 2 O 6 -SE exhibits high sensitivity, response and recovery speed and selectivity to acetone at 680 °C. • The acetone gas concentration and electrochemical reaction rate at TPB increased with the increase of RH. • The sensor could also realize the distinction between the diabetic ketosis patients and non-ketotic volunteers.

Electrochemical Catalysis Generated By an External Electric Field in Conjunction with a Low Density-of-States Conductor

In electrochemistry the reaction rate depends strongly on the voltage difference applied between the two electrodes. A voltage increase at the electrodes will generate a larger electric field in the electric double layer (EDL), which increases the reaction rate, but this will also cause additional power to be dissipated. We show both theoretically and experimentally that one can increase the electrochemical reaction rate, at no additional cost in power, by utilizing an external electric field in the proximity of a material catalyst. This is not surprising since, although the exact mechanism for catalysis due to a material compound can be quite intricate, the basic underlying physical processes for catalysis can often be shown to be due to the molecular electric field at a specific catalyst surface site. Here we generalize this observation and show how the application of a ‘simple external’ electrostatic field in conjunction with a low density-of-states conductor such as graphene can be used to intensify the already large electric field in the EDL layer - thus accelerating the reaction rate without additional power dissipation. We focus on water electrolysis (more specifically, the hydrogen evolution reaction - HER) in our electrochemical reaction study. Based on our observed experimental results as well as our theoretical analysis we show how an electrode incorporating trapped charge at the interface between two dielectrics will generate a large electrostatic field which, in conjunction with the quantum capacitance of a low density-of-states conductor, allows penetration of this field into the electric double layer (EDL), thereby adding to the original EDL field and thus, functioning as a reaction rate accelerant or a catalyst. Our experiment shows a 100% increase in the hydrogen generation rate for the HER reaction when employing our external electrostatic ‘catalyst’ technique. Since this method depends primarily on the enhancement of the EDL electric field for the reaction rate increase, it can be universally applied to all electrochemical reactions without requiring a detailed molecular level understanding of the reaction of interest.