Electrode Reaction Rate Research Articles

Graphdiyne-Induced CoN/CoS2 Heterojunction: Boosting Efficiency for Bifunctional Oxygen Electrochemistry in Zinc-Air Batteries.

The performance of zinc-air battery is constrained by the sluggish rate of oxygen electrode reaction, particularly under high current discharge conditions where the kinetic process of the oxygen reduction reaction (ORR) decelerates significantly. To address this challenge, we present a novel phase transition strategy that facilitates the creation of a heteroatom-doped heterointerface (CoN/CoS2). The meticulously engineered CoN/CoS2/NC electrocatalyst displays a superior ORR half-wave potential of 0.87 V and an OER overpotential of 320 mV at 10 mA cm-2. Experimental and computational analysis confirm that the CoN/CoS2 heterostructure optimizes local charge distribution, accelerates electron transfer, and tunes active sites for enhanced catalysis. Notably, this heterojunction improves stability by resisting corrosion and degradation under harsh alkaline conditions, thus demonstrating superior performance and longevity in a custom-made liquid zinc-air battery. This research provides valuable practical and theoretical foundations for designing efficient heterointerfaces in electrocatalysis applications.

Electrochemical H2O2 Production Modelling for an Electrochemical Bandage

Hydrogen peroxide (H2O2) is an environmentally friendly oxidizing agent used to treat wound infections. We have developed an electrochemical bandage (e-bandage), which generates H2O2 in situ and shown that it exhibites in vitro and in vivo efficacy. The electrochemical bandage comprises carbon fabric working and counter electrodes, as well as an Ag/AgCl quasi-reference electrode, separated by cotton fabric and the electrolyte is delivered by Xanthan gum with phosphate buffer saline. While the chemistry and electrochemistry of the e-bandage have been experimentally characterized, the system level description could aid in better designing these devices. Here, a model called electrochemical hydrogen peroxide production (EHPP) was used to evaluate factors influencing electrochemical generation of H2O2, including electrode potential, diffusion and reaction rates, temperature, and various geometries. EHPP model parameters estimated based on experimental results indicate that: (i) with diffusion limitations caused by changes in physical conditions (e.g., drying of hydrogel), the rate of H2O2 generation decreases, (ii) higher working electrode overpotentials increase H2O2 generation and higher counter electrode overpotentials do not affect H2O2 generation, (iii) increasing the distance between electrodes by adding more hydrogel reduces H2O2 generation, (iv) net H2O2 generation decreases ∼12% with temperature, and (v) H2O2 production is most effective in the initial 48 h of operation.

A Superior Catalytic Air Electrode with Temperature-Induced Exsolution toward Protonic Ceramic Cells.

Protonic ceramic cells merit extensive exploration, attributed to their innate capabilities for potent and environmentally benign energy conversion. In this work, a temperature-induced exsolution methodology to synthesize SrCo0.5Nb0.5O3-δ (SCN) nanoparticles (NPs) with notably elevated activity on the surface of PrSrCo1.8Nb0.2O6-δ (PSCN) is proposed, directly addressing the extant challenge of restrained catalytic activity prevalent in air electrode materials. In situ assessments reveal that SCN NPs commence exsolution from the matrix at temperatures surpassing 900 °C during straightforward calcination processes and maintain stability throughout annealing. Notably, the resultant SCN-PSCN interface facilitates vapor adsorption and protonation processes, which are poised to enhance surface reaction kinetics pertaining to the proton-involved oxygen reduction and evolution reaction (P-ORR and P-OER). A fuel-electrode-supported protonic ceramic cell leveraging SCN-PSCN as the air electrode manifests compelling performance, attaining a peak power density of 1.30 W·cm-2 in the fuel cell modality and a current density of 1.91 A·cm-2 at 1.3 V in the electrolysis mode, recorded at 650 °C. Furthermore, density functional theory calculations validate that the introduction of SCN NPs onto the PSCN surface conspicuously accelerates electrode reaction rates correlated with P-ORR and P-OER, by significantly mitigating energy barriers associated with surface oxygen and vapor dissociation.

Exogenous electric field as a biochemical driving factor for extracellular electron transfer: Increasing power output of microbial fuel cell

Although microbial fuel cells (MFCs) offer a promising avenue for clean power production, they are hindered by inefficient extracellular electron transfer (EET), thereby resulting in a low power output. This study focused on augmenting MFC power by boosting the EET rate using an exogenous electric field (EEF). By leveraging the dual benefits of microbial electrolysis cells (MECs) in organic waste treatment and energy recovery, we developed an MFC–MEC system that utilizes the EEF from MEC as a connecting link. Two configurations, EEF in the same direction (SD-MFC–MEC) and EEF in the reverse direction (RD-MFC–MEC), were used to examine the EET kinetic rate at the MFC anode in the EEF environment using various electrochemical methods for quantitative evaluation. Our findings revealed that EEF significantly enhanced MFC anode biofilm formation and electrochemical activity, leading to a prominent improvement in electrode reaction rates. The EET rate constants in the SD-MFC–MEC and RD-MFC–MEC were more than double those in the control R-MFC, with power density increases of 117.8% and 108.4%, respectively. The formation of electrochemically active sites within the biofilm induced by EEF has emerged as a crucial factor in amplifying the EET rate, and consequently, the MFC power output. Additionally, the variation in EET rate constants between the SD-MFC–MEC and RD-MFC–MEC was minimal, thereby indicating the negligible impact of the EEF orientation on the EET efficiency. This study provides a novel method for quantitatively examining EET rates, opens up new avenues for further facilitating microbe-to-electrode electron transfer, and promotes the application of MFC–MEC systems in energy recovery, CO2 emission reduction, and waste treatment.

Conversion-intercalation competing behaviour of halogen storage on graphite electrode from fluid ZnCl2/ZnBr2 hydrates.

Zinc-based aqueous dual-ion batteries (ADIBs) with halogen-graphite intercalation compound positive electrodes are among the most competitive candidates for next-generation electrochemical energy storage systems. However, most of the electrolytes employed have been gel-like electrolytes; hence, a fundamental understanding of the halogen storage process using fluid hydrates will be essential for constructing efficient Zn-based ADIBs. Herein, the halogen storage mechanism on a graphite electrode from fluid ZnCl2/ZnBr2 hydrates is studied by experimental and computational methods. The results indicate that the halogen storage mechanism is a competition between conversion and intercalation. Moreover, the macroscopic electrode reaction is determined by both the ion-pair solvation state at the graphite-electrolyte interface and the subsequent reactant supply is influenced by the electrode reaction rate.

Recent advances in noble-metal-free bifunctional oxygen electrode catalysts

The oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are crucial reactions in a range of energy storage. However, the sluggish rate of these oxidation electrode reactions and the...

Mechanistic and kinetic investigation of electro-activated (Bi)sulfite system for pollutants reduction and oxidation: Role of oxysulfur radicals

Electro-activated sulfite or bisulfite [E-S (IV)] system is a green technology in environmental remediation. This study developed a comprehensive kinetic model to simulate S (IV) oxidation and contaminants degradation. The results revealed that the mechanism and kinetics of S (IV) oxidation varied across different regions, leading to the dominance of different radicals. In kinetics-controlled and mix-controlled regions at low current density, the rate-determining step (RDS) for S (IV) electro-oxidation was the first electron transfer with the generation of SO3•-/HSO3• contributing to BrO3- reduction. In diffusion-controlled region at high current density, oxygen evolution accelerated the rate of quenching SO3•-/HSO3•, being the RDS for S (IV) oxidation. Consequently, SO4•- dominated benzoic acid (BA) oxidation. However, due to the SO3•-/HSO3• oxidation by oxygen and SO4•- reduction by S (IV), the utilization of specific radicals was limited. To maximize the reduction and oxidation efficiency, the influence of current density and S (IV) concentration on the electrode reaction rates (i.e., electro-generation rates of SO3•-/HSO3• (r1) and oxygen (rO2)) and radical conversion efficiencies were simulated. Enhancing r1 but inhibiting rO2 in mix-controlled region improved the reduction rate. Meanwhile, balancing r1 and rO2 in diffusion-controlled region maximized the oxidation rate. Specifically, the E-HSO3- system was more effective for reduction due to the lower electro-oxidation rate and oxygen oxidation rate of HSO3• compared to SO3•-. Conversely, the E-SO32- system was more suitable for oxidation with higher rates of oxysulfur radical conversions. Based on the kinetic model, the most cost-effective current density and S (IV) concentration for reduction, oxidation and simultaneous reduction and oxidation were determined. This study significantly guided the utilization of the E-S (IV) system for various contaminants degradation.

EIS and relaxation times analysis of the electric double layer construction on Pt cathode surface in MgCl2 molten salt hydrate

The electric double layer on Pt cathode surface in the process of cathodic polarization was analyzed with cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), Raman spectroscopy, and Scanning electron microscope (SEM) in magnesium chloride (MgCl2) solution and MgCl2 molten salt hydrate (MSH). The effects of KCl on the structure of MgCl2 molten salt hydrate and electrode reaction were discussed. EIS data were fitted to propose the equivalent electric circuits to simulate the structure of electric double layers on Pt electrodes. Distribution of relaxation times (DRT) analysis was estimated to identify each process for MgCl2 solution and MgCl2 molten salt hydrate on the Pt cathode. The results show that the solution transforms into MSHs as the water content in the solution decreases. The solution and molten salt exhibit different double-layer properties. The movement of hydrated ions has greater resistance in MSHs which leads to the reduction of electrode reaction rate. The DRT and EIS results demonstrate that H+ and hydrated Mg2+ are simultaneously adsorbed on the Pt surface to form a double electric layer in MgCl2 solution or MSHs. In the MgCl2 MSHs, H+, H2O, and compact hydrated Mg2+ on the Pt electrode surface form a double layer. KCl plays an important role in changing the structure of MgCl2 molten salt hydrate, increasing the active H2O, and offering H+ adsorbed on the Pt surface.

Asymmetric batteries based on customized positive and negative electrodes-an effective strategy to further improve the performance of vanadium redox flow batteries

There are significant differences in the cathodic and anodic kinetics of vanadium redox flow batteries (VRFBs), thus the use of a single composition and structure of electrode materials is unbefitting according to the barrel principle. Herein, W and Sb based electrocatalysts are evenly embedded into the electrospun carbon nanofibers (ECNFs), and the active functional groups and surface defects of the W-ECNFs and Sb-ECNFs electrodes are increased effectively, which resulted in a significant improvement in their hydrophilicity, specific surface area and electrocatalytic activity towards the VO2+/VO2+ and V3+/V2+redox reactions. The electrode reaction rate constant k and diffusion coefficient D of the positive and negative reactions on W-ECNFs and Sb-ECNFs are more similar and closely matched, which is more conducive to the effective improvement of battery performance. As a results, the asymmetric battery with W-ECNFs and Sb-ECNFs as positive and negative electrode shows the highest energy efficiency of 81.33% at 200 mA/cm2, higher than that of the VRFBs with pristine ECNFs as both two electrodes (75.66%) or that only optimizing one electrode (79.76% and 78.15%). The excellent battery performance further verifies the feasibility of constructing asymmetric batteries according to the difference of the positive and negative reaction kinetics in VRFBs.

Effect of Zr4+ doping on the electrochemical properties of Na3MnTi(PO4)3/C cathode materials

NASICON structural materials have the advantages of structural stability, high ion conductivity, and high working potential, which have attracted widespread attention as cathode for sodium-ion batteries. Although the three-electron reaction in the NASICON structure Na3MnTi(PO4)3 increases the specific capacity of the material, poor electronic conductivity remains a key factor restricting its practical application. Herein, Na3Mn1-xZrxTi(PO4)3/C (x = 0, 0.01, 0.03, 0.05, 0.07 and 0.1), a typical three-dimensional NASICON structure cathode material for sodium-ion batteries, was synthesized by the sol-gel method. Through powder X-ray diffraction, the Zr4+ doping in the Na3MnTi(PO4)3 (NMTP) structure was verified. It was found that doping trace amounts of Zr at the Mn site can not only reduce the Jahn-Teller effect caused by Mn3+, but also strengthen the Zr-O bond compared to the Mn-O bond, making the crystal structure more stable by reducing the proportion of Mn. According to the findings of the EIS test, a suitable amount of Zr doping can enhance the electronic conductivity and Na ion diffusion coefficient of NMTP/C electrode materials, weaken polarization phenomena, increase electrode reaction rate, and significantly improve the rate performance and cycling performance of Na3Mn1-xZrxTi(PO4)3 material. The Na3Mn1-xZrxTi(PO4)3/C sample prepared has high initial capacity of 124mAh/g, a capacity retention rate of 86 % after 200 cycles at 0.2C, and a capacity retention rate of 84 % after 500 cycles at 1C. This proves that the material still exhibits excellent cycling stability and structural stability after high current cycling. More importantly, the Na3Mn0.95Zr0.05Ti(PO4)3 (Zr5-NMTP)//Hard carbon full battery also exhibits ideal electrochemical performance.

Chemical Influence of Carbon Interface Layers in Metal/Oxide Resistive Switches.

Thin layers introduced between a metal electrode and a solid electrolyte can significantly alter the transport of mass and charge at the interfaces and influence the rate of electrode reactions. C films embedded in functional materials can change the chemical properties of the host, thereby altering the functionality of the whole device. Using X-ray spectroscopies, here we demonstrate that the chemical and electronic structures in a representative redox-based resistive switching (RS) system, Ta2O5/Ta, can be tuned by inserting a graphene or ultrathin amorphous C layer. The results of the orbitalwise analyses of synchrotron Ta L3-edge, C K-edge, and O K-edge X-ray absorption spectroscopy showed that the C layers between Ta2O5 and Ta are significantly oxidized to form COx and, at the same time, oxidize the Ta layers with different degrees of oxidation depending on the distance: full oxidation at the nearest 5 nm Ta and partial oxidation in the next 15 nm Ta. The depth-resolved information on the electronic structure for each layer further revealed a significant modification of the band alignments due to C insertion. Full oxidation of the Ta metal near the C interlayer suggests that the oxygen-vacancy-related valence change memory mechanism for the RS can be suppressed, thereby changing the RS functionalities fundamentally. The knowledge on the origin of C-enhanced surfaces can be applied to other metal/oxide interfaces and used for the advanced design of memristive devices.

Effect of dichloromethane and toluene on the structure, property, and Al electrodeposition in 1-butyl-3-methylimidazolium chloroaluminate ionic liquid

The electrodeposition of aluminum in ionic liquid has broad application prospects, and additives are an effective way to improve the performance of the aluminum coating. However, the relevant mechanism behind this remains to be clarified. In the present work, the effects of dichloromethane (DCM) and toluene (C7H8) on the microstructure, physicochemical properties, and aluminum electrodeposition with 1-butyl-3-methylimidazolium chloride/aluminum chloride ([BMIM]Cl/AlCl3) were studied using quantum chemistry and molecular dynamics simulation. It is found that DCM easily forms hydrogen bonds with anions and cations of ionic liquids. Since DCM is distributed between anion and cation, the distance between the anion and cation increases, and the interaction energy decreases. As a result, the diffusion ability of anions and cations is enhanced, and the aluminum complex anions tend to exist in the form of \begin{document}${\rm{A}}{{\rm{l}}_2}{\rm{Cl}}_7^ - $\end{document} . The viscosity of the system decreases, and the conductivity increases, so the electrochemical properties of the system are significantly improved, which are in good agreement with the experimental values. C7H8 is adsorbed on the protruding part of the electrode surface in a flat way, which plays a leveling role and results in a flat white coating. Alternatively, DCM easily interacts with the electroactive ion \begin{document}${\rm{A}}{{\rm{l}}_2}{\rm{Cl}}_7^ - $\end{document} , which makes it difficult to reduce this electroactive ion. At the same time, the concentration of the electroactive ion decreases as the concentration of the additive is increased, which leads to a large overpotential in the electrochemical process, resulting in a decrease in the electrode reaction rate that plays a role in grain refinement. Moreover, the interaction between DCM and cations is also strong, and they can be adsorbed on the protruding part of the electrode surface during the electrochemical process, playing a certain leveling role. Therefore, the addition of DCM can obtain specular gloss deposits. The effect of C7H8 on the interaction between anions and cations is not as good as DCM, which consequently results in inferior electrochemical properties compared to DCM. Therefore, DCM is more favorable for the electrodeposition of aluminum than the aromatic hydrocarbon C7H8.

Expanding the frontiers of hydrogen evolution electrocatalysis–searching for the origins of electrocatalytic activity in the anomalies of the conventional model

After decades of research, understanding the origins of electrocatalytic activity remains a fundamental scientific challenge. While most of the efforts were directed towards comprehending what dictates bonding of intermediates, attempts to go beyond the paradigm of optimal adsorption energies are rare. In this work, by analysis of the conventional hydrogen electrocatalysis model, and by comparative analysis of Pt and Pd, we propose what can be an important contributor to electrocatalytic activity, besides adsorption energies of intermediates. Discussion is initiated about the possible link between bulk electronic structure of a metal and charge transfer coefficient (including symmetry factor of activation barrier) as a key contributor to electrode reaction rate.

Systematic Investigation of the Physical and Electrochemical Characteristics of the Vanadium (III) Acidic Electrolyte With Different Concentrations and Related Diffusion Kinetics.

Owing to the lack of systematic kinetic theory about the redox reaction of V(III)/V(II), the poor electrochemical performance of the negative process in vanadium flow batteries limits the overall battery performance to a great extent. As the key factors that influence electrode/electrolyte interfacial reactivity, the physicochemical properties of the V(III) acidic electrolyte play an important role in the redox reaction of V(III)/V(II), hence a systematic investigation of the physical and electrochemical characteristics of V(III) acidic electrolytes with different concentrations and related diffusion kinetics was conducted in this work. It was found that the surface tension and viscosity of the electrolyte increase with increasing V(III) concentration, while the corresponding conductivity shows an opposite trend. Both the surface tension and viscosity change slightly with increasing concentration of H2SO4, but the conductivity increases significantly, indicating that a lower V(III) concentration and a higher H2SO4 concentration are conducive to the ion transfer process. The electrochemical measurements further show that a higher V(III) concentration will facilitate the redox reaction of V(III)/V(II), while the increase in H2SO4 concentration only improves the ion transmission and has little effect on the electron transfer process. Furthermore, the diffusion kinetics of V(III) have been further studied with cyclic voltammetry and chronopotentiometry. The results show that an elevated temperature facilitates the V(III)/V(II) redox reaction and gives rise to an increased electrode reaction rate constant (ks) and diffusion coefficient [DV(III)]. On this basis, the diffusion activation energy (13.7 kJ·mol−1) and the diffusion equation of V(III) are provided to integrate kinetic theory in the redox reaction of V(III)/V(II).

NO Detection By Cyclic Voltammetry with Platinum Electrodes on YSZ

Introduction Solid electrolyte sensors (SES) based on yttria stabilized zirconia (YSZ) can be used to detect traces of other components in inert gases such as Ar or N2. The O2--conducting solid electrolyte YSZ is thermodynamically highly stable and can be operated at high temperatures with stationary (potentiometry, amperometry) or dynamic methods (pulse polarization [1], cyclovoltammetry (CV) [2]). In the stationary mode, the selectivity of such sensors is limited to an extend that it is usually not possible to distinguish between individual gas components. In contrast to that, dynamic methods allow a significantly increased selectivity by using different rates of electrode reactions of the individual components in order to detect them independently in a gas mixture [2]. Dynamic electrochemical methods have been successfully used in liquids for many decades, and preliminary investigations on solid electrolyte gas sensors also show that such methods can be used to measure the concentrations of several redox-active gases, for example, oxygen and carbon monoxide [3]. The commercial solid electrolyte sensor used in this work was previously successfully tested to measure selectively different gases such as hydrogen, oxygen and water vapor [4] in nitrogen by using CV. In this work, these studies will be continued to investigate the ability of CV for selective detection of nitrogen oxides (NOx) and to elucidate the mechanisms of signal formation. Experimental setup The experimental setup shown in Fig. 1 and described in detail in [2] was used to adjust the O2 concentration (SES 1) and the measurement of the concentrations of O2 and NO in nitrogen (SES 2). Both SES of the type "Test gas, Pt|YSZ|Pt, air" contain a YSZ-tube equipped with two cylindrical platinum mesh electrodes at the inner and outer surface. The area of the inner measuring electrode was estimated by SEM to be about 3.5 cm2. A porous YSZ sintered layer was applied to join electrolyte and electrodes. Covering large parts of the reference and measuring electrode this porous layer offers an extended three-phase boundary for the oxygen transfer.SES 1 was continuously polarized during each experiment providing a constant O2 concentration in the purified carrier gas N2. At SES 2, the CVs were obtained at polarization voltages between -0.1 and -0.9 V against the Pt air reference electrode and scan rates in the range 100 ... 5000 mV/s. In each experiment, the second cycle was evaluated to obtain reproducible results. Between two consecutive cyclovoltammograms (CVM), the open circuit potential (OCP) was measured to monitor depolarization of the measuring electrode. Results and discussion The CVMs shown in Fig. 2 exhibit NO-related peaks developing in the cathodic scan direction between -0.2 and -0.7 V at scan rates between 100 and 2000 mV/s. The peak maximum shifts in the cathodic direction with increasing scan rate. The highest sensitivity was achieved at 2000 mV/s for 650 °C. At higher scan rates it decreases again. This is apparently caused by the shift of the oxygen reduction peaks from range -0.1 ... -0.3 V at lower scan rates to the cathodic direction at higher scan rates and leads to their superposition with the NO peaks. The curve shifts to higher electrolysis currents with increasing NO-concentration in the cathodic region, visible for every scan rate at U < -0.7 V correspond to the Faraday currents calculable for the NO reduction. The different peak potentials for O2 and NO enable a highly selective determination NO in O2 containing gases at scan rates between 200 – 2000 mV/s at concentrations c(NO) ≥ 10 vol.-ppm.The height of the NO peak as a suitable NO-related signal was calculated and plotted in Fig. 3 for different scan rates. This peak height rises almost linearly with the NO concentration and the curve slopes increase with the scan rate up to 2000 mV/s. Further investigations revealed that this scan rate-induced slope increase depends also on flow rate.OCP measurements at different NO concentrations and sensor temperatures (Fig. 4) indicate the known tendency of NO to decompose at hot and catalytically active platinum electrodes into N2 and O2. Therefore, in the investigated temperature range, the absolute value of the OCP decreases with increasing NO concentration, coming with rising oxygen partial pressure according to NO decomposition. Another process guiding the OCP in the NO-free carrier gas is the electronic conductivity of the solid electrolyte that increases exponentially with temperature [5].

ОСОБЕННОСТИ КАТОДНЫХ И АНОДНЫХ РЕАКЦИЙ НА УГЛЕРОДИСТОЙ СТАЛИ В ЗАВИСИМОСТИ ОТ ГЛУБИНЫ ПОГРУЖЕНИЯ В НЕЙТРАЛЬНЫЙ РАСТВОР

The investigation of the depth immersion of the specimens on corrosion rate of steel St3 in 3 % NaCl solution. Simulation of atmospheric corrosion (humid and wet) was performed by immersing of a steel sample by the size of (50×10×2) mm in a neutral solution of 3% NaCl at different depths. By leading the lower boundary of the working surface of the sample to the level of the solution (about 0 mm), humid corrosion was simulated, submerged to a depth of 2 mm (up to the upper boundary), wet corrosion, and 10 mm from the upper boundary - the electrolyte volume. The developed method allowed to carry out electrochemical researches by the method of polarization curves. The polarization curves were measured in the potentiodynamic mode with the potential scanning rate of 5∙10-4 V/s .The working electrode was a sample of steel St3 by the size (10×50×2) mm. A work surface (10×2) mm was separated on the sample, the rest of the surface was isolated with a non-conductive varnish. The results of the investigation of the effect of depth immersion of samples into electrolyte solution on corrosion rate of St3 steel are presented. The conditions of “humid” and “wet” atmospheric corrosion of the metal were simulated by the immersion of samples on a depth from 0 to 10 mm into 3% sodium chloride solution. It was found, that on the base on determination of the rate of particular electrode reactions occurring on the electrode at various depths of its immersion into the solution, the corrosion rate of steel St3 was determined by the value of the limiting diffusion current.It was shown that the value of limiting current increases from 0.51 to 2 A/m2 with decreasing of the film thickness. It has been established that the cathodic process rate depends both on the concentration of oxygen in the layers of the solution, which are at different distances from the solution/air boundary, and on the speed of its diffusion to the metal surface. Because the method of polarization resistance allows to measure the currents smaller than the currents of oxygen reduction in thin films of the solution, it can be used to estimate the rate of atmospheric corrosion of steel. Based on simulation of humid and wet atmospheric corrosion the effect of immersion depth of the specimens on the cathodic reaction rate of steel St3 in 3 % NaCl solution was established. The cathodic current density (limit diffusion current) is raised from 0,51 to 2 A/m2 under decreasing of immersion depth. The suggested method of simulation of atmospheric corrosion may be used for electrochemical investigations in thin films of moisture of different thickness which are form on the metals and sensors surfaces. The possibility of application of polarization resistance method for atmospheric conditions was presented.

Nickel–Ceramic Electrodes with High Nickel Content for Solid Electrolyte Electrochemical Devices

Composite powders (66 wt % NiO + 34 wt % Zr0.84Y0.16O1.92 were obtained according to the solution combustion synthesis technique by crystallization of nickel oxide particles on the surface of Zr0.84Y0.16O1.92particles. The samples pressed from powders after sintering and reduction in moist hydrogen had high electrical conductivity, more than 16 × 103 S cm–1 at room temperature. Impedance spectroscopic studies have shown that in a humid atmosphere of Ni – Zr0.84Y0.16O1.92, electrodes formed on the surface of a dense Zr0.84Y0.16O1.92 electrolyte have low electrochemical activity. The impregnation of the electrodes with a solution of cerium nitrate followed by thermolysis made it possible to increase the electrochemical activity of the electrode by two to three orders of magnitude. An analysis of the electrochemical impedance spectra through the calculation of the distribution function of the relaxation time showed that the rate of hydrogen oxidation at the electrodes is limited by surface–adsorption processes. After impregnation, the gas diffusion resistance significantly limits the electrode reaction rate.

A novel pH sensor with application to milk based on electrochemical oxidative quinone-functionalization of tryptophan residues

The electrochemical oxidative quinone-functionalization of tryptophan (Trp) residues, and the proton-coupled electron transfer properties between quinonized Trp (Trp=O) and its re-reduced species (Trp-OH) are investigated for potentiometric pH sensors. The Trp=O/Trp-OH couples are assembled on a graphite electrode using multiple cyclic voltammetry, and exhibit a pair of well-defined redox peaks at redox potential of 0.090 V (vs. SCE) at pH 7.0 and 298 K. The proton-coupled electron transfer properties of Trp=O/Trp-OH couples are dependent on electrode substrate material, incubation temperature and pH values, and Trp residue sources including amino acid, peptide and protein. The Trp=O/Trp-OH-based surface-confined exothermic electrode reaction rates show a decrease with increasing incubation temperature from 283 to 323 K at pH 5.0. Both of redox peak potential and open-circuit potential under optimum conditions have a good linear pH dependence between 1.0 and 12.0 with sensitivity of more than 52 mV pH −1 and relative standard derivation of 1.5%. The proposed potentiometric pH sensor has significant advantages of low cost, good stability and reproducibility, and strong anti-interference ability. The present study shows a new approach to endow Trp, Trp-containing peptides and non-conjugated proteins with analogous proton-coupled electron transfer performance to prosthetic groups of quinoproteins for monitoring pH changes in milk samples.

Complementary effect of ceria on the hydrogen oxidation kinetics on Ni - Ce0.8Sm0.2O2-δ anode

The paper illustrates the electrode kinetics studies results on Ni - Ce0.8Sm0.2O2-δ (Ni-SDC) anodes in a wet hydrogen atmosphere in the temperature range of 600–850°С by the electrochemical impedance spectroscopy before and after ceria addition to the anode. The addition of ceria to the anode by the solution impregnation technique is shown to result in the anode electrochemical activity growth by 10–24 times. An approach to the analysis of the impedance spectra based on the combination of the distribution of relaxation times method (DRT) and non-linear least squares method was verified. Based on data obtained from DRT functions, we found that the Ni-SDC anode reaction rate was limited by three processes, whereas the ceria-impregnated Ni-SDC anode electrode reaction rate was limited by two processes. The correlation of the DRT functions of both anodes demonstrated unambiguously that ceria addition to the Ni-SDC anode caused a significant decrease in the middle-frequency step of the electrode reaction, while the resistances of the other electrode reaction steps decreased less. Highly disperse ceria addition to the Ni-SDC anode was assumed to increase significantly the rate of reactions on the anode surface between the adsorbed species.

Electrochemical characterization of polymer electrolyte membrane fuel cells and polarization curve analysis

This paper presents the diagnostic results of single polymer electrolyte membrane fuel cell assemblies characterized by polarization curves. Single PEM fuel cell assemblies were investigated through accelerated voltage cycling test at different values of relative humidity. The fuel cells are tested at different humidity level. The cells are discussed in this paper with analysis results at different relative humidity at atmospheric pressure. This represents a nearly fully humidified, a moderately humidified, and a low humidified condition, respectively. This technique is useful for diagnosing the main sources of loss in MEA development work, especially for high temperature/low relative humidity operation where several sources of loss are present simultaneously. All the fuel cells showed better performance in terms of limiting current density value through polarization curves when oxygen was fed to the cathode side of each cell instead of air. The results indicate that the performance of the fuel cell could be depressed significantly by decreasing RH from 100 to 33%. Decrease in RH can result in slower electrode kinetics, including electrode reaction and mass diffusion rates, and higher membrane resistance.