Electrode Reaction Mechanism Research Articles

Hydrogen Electrode Reactions in Energy-Related Electrocatalysis Systems.

Hydrogen electrode reactions, including hydrogen evolution reactions and hydrogen oxidation reactions, are fundamental and crucial within aqueous electrochemistry. Particularly in energy-related electrocatalysis processes, there is a consistent involvement of hydrogen-related electrochemical processes, underscoring the need for in-depth study. This review encompasses significant reports, delving into elementary steps and reaction mechanisms of hydrogen electrode reactions, as well as catalyst design strategies. In addition, we focus on the application of hydrogen electrode reaction mechanism in different energy-related electrocatalytic reactions, and the significance of the promotion and suppression of reaction kinetics in different reaction systems. It thoroughly elucidated the significance of these reactions and the need for a deeper understanding, offering a novel perspective for the future development of this field.

Crown Ether Electrolyte Additive Enables High-Rate and Stable Polyviologen Cathode Material for Chloride Ion Batteries.

A variety of inorganic and inorganic cathode materials for chloride ion storage are reported. However, their application in chloride ion batteries (CIB) is hindered by poor rate capability and cycling stability. Herein, an organic poly(butyl viologen dichloride) (PBVCl2) cathode material with significantly enhanced rate and cycling performance in the CIB is achieved using a crown ether (18-Crown-6) additive in the tributylmethylammonium chloride-based electrolyte. The as-prepared PBVCl2 cathodes exhibit impressive capacity increases from 149.4 to 179.1 mAh g-1 at 0.1 C and from 57.8 to 111.9 mAh g-1 at 10 C, demonstrating the best rate performance with the highest energy density among those of various reported cathodes for CIBs. This impressive performance improvement is a result of the great boosts in charge transfer, ion transport, and interface stability of the battery by the use of 18-Crown-6, which also contributes to a more than twofold increase in capacity retention after 120 cycles. The electrode reaction mechanism of the CIB based on highly reversible chloride ion transfer is revealed by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy.

Composite LaNi0.6Fe0.4O3-δ - La0.9Sr0.1Sc0.9Co0.1O3-δ cathodes for proton conducting solid oxide fuel cells: Electrode kinetics study

Composite LaNi0.6Fe0.4O3-δ - La0.9Sr0.1Sc0.9Co0.1O3-δ (LNF-LSSCo) electrodes with the compositions 50/50, 60/40, and 80/20 wt% LNF/LSSCo are successfully applied for La0.9Sr0.1ScO3-δ proton conducting electrolyte. Electrochemical activity of the electrodes is studied by impedance spectroscopy, depending on temperature and oxygen partial pressure. The best performance is observed for 60/40 LNF/LSSCo electrodes. Detailed analysis of impedance data is performed using non-linear least squares and distribution of relaxation times methods taking into account the shunt effect of electronic conductivity of La0.9Sr0.1ScO3-δ electrolyte. Two main rate-determining stages of the electrode reaction are determined, which are assigned to oxygen ion diffusion in the bulk of the electrode and oxygen interphase exchange with the gas phase. The application of the LNF current collector layer improves the electrochemical activity of the electrodes without changes in the electrode reaction mechanism, while the modification of the electrodes with Pr6O11 leads to a sufficient decrease in the resistance of the stage, corresponding to oxygen interphase exchange, resulting in a twice-improved electrochemical activity of the electrodes.

A π-conjugated organic compound with multiple active sites as a cathode material for high-rate aqueous zinc-ion batteries

Aqueous zinc-ion batteries (AZIBs) have attracted much attention for owing to their environmental friendliness, low cost and high safety. Organic compounds have emerged as promising cathode materials for AZIBs due to their abundance of active sites, structural tunability and renewability. Here, a new π-conjugated compound with multiple active sites tris(3-amino-1,2,4-triazolyl) hexaazatriphenylenehexacarboxy triimide (TAT-HATTI) is prepared and evaluated firstly as a cathode material for AZIBs. The TAT-HATTI electrode displays a high discharge specific capacity (531 mAh g−1 at 0.05 A g−1), high-rate performance and better cycle stability (capacity retention of 78 % after 1000 cycles at 2 A g−1). The research results reveal that the electrode reaction mechanism involves insertion/extraction of Zn2+ and H+ ions. Impressively, the assembled flexible aqueous Zn//TAT-HATTI battery exhibits the higher volumetric energy density (4.4 mWh cm−3), high-rate capability, better cycle stability and superior flexibility, owning an application potential in wearable electronics.

Progress of organic, inorganic redox flow battery and mechanism of electrode reaction

Progress of organic, inorganic redox flow battery and mechanism of electrode reaction

BaCo0.4Fe0.4Zr0.1Y0.1O3−σ Cathode Performance for Proton Conducting Solid Oxide Fuel Cells with BaZr0.8−xCexY0.1Yb0.1O3−δ Electrolytes

BaCo0.4Fe0.4Zr0.1Y0.1O3−σ (BCFZY) is a proton, oxygen-ion, and electron-hole conducting cathode material for intermediate temperature solid oxide fuel cells. Its electrode reaction mechanism in air with moisture is not well understood. In this study, three types of symmetrical cells with the same BCFZY cathode were fabricated over three related proton conducting electrolytes: BaZr0.8−xCexY0.1Yb0.1O3−δ (x = 0.1, 0.4, and 0.7). The cathode shows similar performance over three different electrolytes in dry air but different responses to moisture introduction. The differences are hypothesized to relate to the mutual diffusion at the cathode/electrolyte interface. Such a hypothesis is supported by different techniques such as XRD Rietveld refinement of BCFZY cathode in mixtures with different electrolytes after firing, energy-dispersive X-ray spectroscopy (EDS) line scanning for element concentration distribution at the cathode/electrolyte interface, as well as electrochemical test for a related BaCoFeO-type cathode with Zr replaced by Ce.

BaCo0.4Fe0.4Zr0.1Y0.1O3-Σ Cathode Performance for Proton Conducting Solid Oxide Fuel Cells with BaZr0.8-XCexY0.1Yb0.1O3-Δ Electrolytes

BaCo0.4Fe0.4Zr0.1Y0.1O3-σ (BCFZY) is a proton, oxygen-ion, and electron-hole triple conducting cathode material for solid oxide fuel cells. Its electrode reaction mechanism including the rate-limiting step in air with moisture are not well understood. Therefore, we fabricated three types of symmetric cells with the same BCFZY cathode over three related proton conducting electrolytes: BaZr0.8-xCexY0.1Yb0.1O3-δ (x = 0.1, 0.4, and 0.7; Fig.1 are SEM images showing the surface of three different electrolytes). The cathode shows different electrochemical behaviors for the three electrochemical cells including the response to the introduction of moisture. The differences are hypothesized to relate to mutual diffusion at the cathode/electrolyte interface, which are tested by various techniques such as XRD Rietveld refinement of BCFZY cathode in mixtures with different electrolytes after firing, thermogravimetric analysis (TGA) for oxygen vacancy concentration and hydration behavior, electrical conductivity relaxation (ECR) for conductivity changes between dry and moist atmosphere, and energy-dispersive X-ray spectroscopy (EDS) line scanning for element concentration distribution at the cathode/electrolyte interface.Fig1. SEM images of electrolytes (a) BaZr0.1Ce0.7Y0.1Yb0.1O3-δ (Ce-rich), (b) BaZr0.4Ce0.4Y0.1Yb0.1O3-δ (ZrCe-bal) and (c) BaZr0.7Ce0.1Y0.1Yb0.1O3-δ (Zr-rich) Figure 1

Reaction characteristics of molten carbonate cell operated in fuel cell and electrolysis modes with reactant gas addition method

This work compares the electrode reaction mechanisms of 100 cm2 class molten carbonate cells (MCCs) operated in electrolysis cell (EC) and fuel cell (FC) modes using a reactant gas addition (RA) method. The RA method reveals essential information on an electrode reaction mechanism by measuring the overpotential of an electrode resulting from adding a reactant. The hydrogen electrode (HE) is revealed to be under a gas-phase mass transfer-controlled process in both modes. In addition, the HE overpotential at an inlet composition of H2: CO2: H2O = 0.3: 0.3: 0.4 atm is caused mainly by H2 species in FC mode, while CO2 contributes the majority in EC mode due to the production of H2 and consumption of CO2 by the water–gas shift reaction. On the other hand, most of the oxygen electrode (OE) overpotential is contributed by O2 species in both modes. The overpotential induced by O2 species was larger in FC mode than EC mode because EC mode generates O2 and provides less mass transfer resistance of O2 species in the liquid phase. The addition of CO2 to the OE raised overpotential in both modes. The overpotential was especially large in FC mode due to the reduced O2 partial pressure and relatively low in EC mode because of O2 generation. Therefore, the total overpotential in EC mode is less than in FC mode.

Cascade amplification strategy based on ultra-thin graphdiyne and CRISPR/Cas for real-time detection of tumor biomarker

As an important cancer markers, the sensitive, portable and highly specific detection of miRNA-141 is impendency. Currently, self-powered electrochemical sensors based on enzyme biofuel cells still difficult to be applied for rapid and sensitive detection for miRNAs. In this work, a sensitivity self-powered biosensor constructed by ultra-thin graphdiyne nanomaterials with good thermal stability and high electron mobility, combination of 3D DNA Walker mediated CRISPR/Cas12a cascade signal amplification strategy. In the linear range of 0.5–10000 fM, the detection limit is as low as 0.14 fM. Most importantly, the sensor platform can achieve real-time detection of miRNA-141 through smartphone. Finally, the relevant electrode reaction and signal amplification mechanism of sensing platform is explored, and the accurate determination of low content miRNA in complex biological samples is realized, which is expected to provide an effective method for the early diagnosis and prognosis of cancer patients.

Cerium oxide as cathode material for aqueous zinc-ion battery

Zinc-ion battery is regarded as one of the potential alternatives for advanced energy storage system, due to its high discharge capacity, low cost, and environmental benignity. The research and development of new electrode materials and reaction mechanism for zinc-ion battery have attracted most attention. Herein, cerium oxide is systematically investigated as a novel cathode material for aqueous zinc-ion battery. The battery charge and discharge test results show that cerium oxide has a discharge specific capacity comparable to that of manganese oxide cathode material, the discharge specific capacity is stable at 143.8 mAh g−1 after 500 cycles. The cyclic voltammetry curves and charge-discharge curves of cerium oxide are very similar to manganese oxide cathode materials. The results of X-ray diffraction and X-ray photoelectron spectroscopy demonstrate that the performance of cerium oxide as a cathode material for aqueous zinc-ion battery is related to the reaction product of zinc sulfate hydroxide hydrate and manganese ion in the electrolyte. And it is found that the discharge cut-off voltage also plays a crucial role in the discharge capacity of the aqueous zinc-ion battery with manganese ion.

Energy-efficient electrochemical degradation of ciprofloxacin by a Ti-foam/PbO2-GN composite electrode: Electrode characteristics, parameter optimization, and reaction mechanism

Reducing energy comsuption is crucial to commercialize electrochemical oxidation technologies. In this study, a novel PbO2 composite electrode (Ti-foam/PbO2-GN) was successfully fabricated based on a porous titanium (Ti) foam substrate and a β-PbO2 active layer embedded with multiple graphene (GN) interlayers, and applied as an anode for energy-efficient pulse electrochemical oxidation of ciprofloxacin (CIP). In contrast to PbO2 and Ti-foam/PbO2 electrodes, the Ti-foam/PbO2-GN electrode surface exhibited a more compact structure, smaller crystal grain size, and greater electrochemical active surface area. CIP removal of 89.7% was obtained with a low energy consumption (EE/O) of 6.17 kWh m−3 under pulse electrolysis conditions with a current density of 25.00 mA cm−2, pulse frequency of 5000 Hz, and pulse duty cycle of 50.0%. Up to 70.7% of the energy was saved in the pulse current mode compared to the direct current mode. Narrowing the electrode spacing to 2 cm facilitated the mass transfer process and enhanced oxidation efficiency. According to the intermediates identified, the pulse electrolysis of CIP primarily involved hydroxylation of the quinolone ring, breaking of the piperazine ring, defluorination, and decarboxylation processes, and a possible degradation mechanism of CIP was proposed. The continuous oxidation performance of CIP and the relatively low leaching of Pb2+ suggested that the Ti-foam/PbO2-GN electrode exhibited excellent stability, repeatability, and safety. The degradation results of CIP in real water also exhibits the great potential of environmental application. As a result, pulse electrochemical oxidation using a Ti-foam/PbO2-GN electrode has proven to be an energy-efficient and promising alternative for antibiotic wastewater treatment.

Some aspects of hydrogen oxidation in solid oxide fuel cell: A brief historical overview

Environmentally friendly and resource-efficient ways to generate, convert, store and transport electricity are important areas of scientific and technological development. Fuel cells are direct converters of chemical energy into electricity with low emissions of harmful components. One of the most promising types of fuel cells is the solid oxide fuel cell (SOFC). The electrical power generated by the SOFC is mainly limited by the ohmic resistance of the electrolyte and the polarization of the electrodes. The ohmic resistance can be reduced by reducing the thickness of the electrolyte. To reduce the polarization resistance, other approaches are needed, namely a detailed study of the mechanisms of electrode reactions and the determination of the nature of rate-determining stages. Until now, fuel oxidation at the anode of the SOFC, as opposed to oxygen reduction at the cathode, has not been well understood. Even for conventional nickel-ceramic anodes, there is no clear understanding of the nature of the rate-determining steps of hydrogen oxidation. This review provides a brief historical background on the development of SOFCs, some insights into the oxygen reduction mechanisms, and a more detailed review of the kinetics of hydrogen oxidation at SOFC anodes.

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

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

New electroanalytical method for the determination of trans-anethole in spices and sweets

A completely new method for the determination of trans–anethole (TAN) based on the anodic oxidation of this flavouring substance in pure acetonitrile using differential–pulse voltammetry has been developed. A nonaqueous carbon paste electrode bulk-modified with solid sodium dodecyl sulphate of 40 % (w/w) content was chosen as optimum. To propose TAN electrode reaction mechanism, its electrochemical behaviour was investigated at glassy carbon electrode in nonaqueous media. At optimum working conditions, the current response could be calibrated within a linear range 2–200 µmolL−1 TAN, a coefficient of determination of 0.9971, a sensitivity of 0.1122µALµmol−1, and a detection limit of 0.7 µmolL−1. A satisfactory precision (relative standard deviation of 4 %) has been achieved. The validation performed by analysis of spices and sweets provided comparable results with reference reverse–phase HPLC with spectrophotometric detection, thus confirming the practical use of the developed voltammetric method in food analysis.

Voltammetric Determination of Marbofloxacin at Carbon Paste Sensor Integrated with Copper Oxide Nanoparticles

AbstractThe present work introduced copper oxide nanoparticles as an efficient electrode modifier for sensitive adsorptive differential pulse voltammetric assaying of marbofloxacin (MRB) in pharmaceutical formulations and surface water samples. In the presence of sodium dodecyl sulphate (SDS) at pH 4.0, the marbofloxacin molecule was irreversibly oxidized at the electrode surface showing an anodic oxidation peak at 0.954 V. The electrode reaction mechanism was assumed as adsorption‐reaction controlled accompanied by the transferring of two electrons and proton exchange in agreement with the molecular orbital calculations performed on MRB molecule suggesting the oxidation of the amino group in the piperazinyl ring. At the optimized measuring conditions, the recorded peak heights were linearly correlated with the MRB concentration within the range from 6.67 to 360 ng mL−1, and the estimated LOD value was 2.2 ng mL−1. The integrated sensor showed a prolonged operational lifetime with good reproducibility of measurements. Based on the selectivity and sensitivity of the proposed method, MRB was successfully assayed in pharmaceutical formulations and surface water samples with mean average recoveries agreeable with the official method.

Glucose Incorporated Graphite Matrix for Electroanalysis of Trimethoprim.

The antibiotic drug trimethoprim (TMP) is used to treat bacterial infections in humans and animals, and frequently TMP is used along with sulfonamides. However, a large portion of TMP is excreted in its active state, which poses a severe problem to humans and the environment. A sensitive, rapid, cost-effective analytical tool is required to monitor the TMP concentration in biological and environmental samples. Hence, this study proposed an analytical methodology to analyze TMP in clinical, biological and environmental samples. The investigations were carried out using a glucose-modified carbon paste electrode (G-CPE) employing voltammetric techniques. Electrochemical behavior was examined with 0.5 mM TMP solution at optimum pH 3.4 (Phosphate Buffer Solution, I = 0.2 M). The influence of scan rate on the electro-oxidation of TMP was studied within the range of 0.05 to 0.55 V/s. The effect of pH and scan rate variations revealed proton transfer during oxidation. Moreover, diffusion phenomena governed the irreversibility of the electrode reaction. A probable and suitable electrode interaction and reaction mechanism was proposed for the electrochemical oxidation of TMP. Further, the TMP was quantitatively estimated with the differential pulse voltammetry (DPV) technique in the concentration range from 9.0 × 10−7 to 1.0 × 10−4 M. The tablet, spiked water and urine analysis demonstrated that the selected method and developed electrode were rapid, simple, sensitive, and cost-effective.

(Invited) Novel Air Electrode and Catalyst Materials for High-Performance and Durable Regenerative Proton-Conducting Solid Oxide Cells

Regenerative solid oxide cells can operate in either a fuel cell mode or an electrolysis mode as needed. Recently, regenerative proton-conducting solid oxide cells (R-PSOCs) have attracted considerable attention due to their potential for efficient and low-cost power and fuel co-generation.1, 2 However, the performance and durability of R-PSOCs are still limited by the lack of highly active and robust air electrode/catalyst materials for dual-mode operation. In this presentation, we will highlight the critical scientific challenges facing the development of efficient and durable air electrode/catalyst materials for R-PSOCs as well as the strategies for dramatically enhancing electrode activity and durability. We will then present our recent progress in the development of new air electrodes 3, 4 as well as the mechanism of electrode reactions and degradation, as revealed by a combination of modeling, simulation, and in situ/operando characterization of electrode processes 5, 6. Catalytic activity, evolution of the surface chemistry, and contaminant (e.g., water and chromium) tolerance of both the conventional La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) electrode and the newly developed PrBa0.8Ca0.2Co2O5+δ–BaCoO3−δ (PBCC–BCO) electrode will be discussed. Performance, long-term stability, and degradation mechanism of R-PSOCs using LSCF and PBCC–BCO air electrodes will be reported. We will further introduce our recent progress in the development of highly active and durable catalyst coatings for the air electrodes with significantly enhanced performance and durability under typical operating conditions with the presence of contaminants. Reference: L. Yang, S. Wang, K. Blinn, M. Liu, Z. Liu, Z. Cheng and M. Liu, Science, 2009, 326, 126-129.C. Duan, J. Huang, N. Sullivan and R. O'Hayre, Appl. Phys. Rev., 2020, 7, 011314.Y. Zhou, E. Liu, Y. Chen, Y. Liu, L. Zhang, W. Zhang, Z. Luo, N. Kane, B. Zhao and L. Soule, ACS Energy Lett., 2021, 6, 1511-1520.Y. Zhou, W. Zhang, N. Kane, Z. Luo, K. Pei, K. Sasaki, Y. Choi, Y. Chen, D. Ding and M. Liu, Adv. Funct. Mater., 2021, 2105386.J. H. Kim, S. Yoo, R. Murphy, Y. Chen, Y. Ding, K. Pei, B. Zhao, G. Kim, Y. Choi and M. Liu, Energy Environ. Sci., 2021, 14, 1506-1516.Y. Niu, Y. Zhou, W. Zhang, Y. Zhang, C. Evans, Z. Luo, N. Kane, Y. Ding, Y. Chen and X. Guo, Adv. Energy Mater., 2022, 2103783.

Carbonaceous nanomaterials integrated carbon paste sensors for adsorptive anodic voltammetric determination of butenafine in the presence of its degradation product

Butenafine (BUT) is a new synthetic benzylamine antifungal with an effective inhibitory effect on squalene epoxidase. The present work introduced for the first time a novel sensitive adsorptive differential pulse voltammetric method for sensitive and selective determination of butenafine in pharmaceutical preparations in the presence of its degradation products. Integration of the working carbon paste electrodes with various carbonaceous nanostructures with their enhanced electrocatalytic effect towards the oxidation of butenafine improved the performance of the method. Comprehensive and in-depth studies were performed including the effect of the nature of the nanomaterial, modification mode, and pH under the optimized electroanalytical parameters. Functionalized carbon paste electrodes with multiwall carbon nanotubes (MWCNTs) showed a sharp well-defined oxidation peak for butenafine at 1.119 V following an adsorption electrode reaction mechanism through the participation of one proton/electron, as assumed by the pH, scan rate studies and molecular orbital calculations. Improved sensitivity was recorded within the linear BUT concentration range from 2.0 to 18.0 µg mL−1 with limit of detection 0.477 µg mL−1. A prolonged operational lifetime of more than 4 months and high measurement reproducibility was the promising futures of the fabricated sensors. The selectivity of the proposed method was established in the presence of the BUT degradation product and other interfering species present in pharmaceutical formulations. The achieved selectivity and sensitivity suggested the application of the proposed approach for BUT assay in medicinal creams in the presence of butenafine degradation products.

Optical Study of the Surface Film Formed during Li-Metal Deposition and Dissolution Investigated by Surface Plasmon Resonance Spectroscopy.

The features of the electrode surface film during Li-metal deposition and dissolution cycles are essential for understanding the mechanism of the negative electrode reaction in Li-metal battery cells. The physical and chemical property changes of the interface during the initial stages of the reaction should be investigated under operando conditions. In this study, we focused on the changes in the optical properties of the electrode surface film of the negative electrode of a Li-metal battery. Cu-based electrochemical surface plasmon resonance spectroscopy (EC-SPR) was applied because of its high sensitivity to optical phenomena on the electrode surface and its stability against Li-metal deposition. The feature of SPR reflectance dip depends on the optical properties of the electrode surface; namely, the wavelength and depth of the reflectance dip directly connected the refractive index and extinction coefficient (color of electrode surface film), which was confirmed by reflectance simulation. In the operando EC-SPR experiment, various changes in optical properties were clearly observed during the cycles. In particular, the change in the extinction coefficient was more remarkable at the second process than the first process of Li-metal deposition. By electrochemical quartz-crystal microbalance (EQCM) measurements, surface film formation was confirmed during the first Li-metal deposition process. The remarkable change in the extinction coefficient is based on the color change of the surface film, which is caused by the chemical condition change during Li-metal deposition cycles.

Rapid direct cathodic voltammetric determination of insecticide flonicamid by renewable silver-amalgam film electrode

ABSTRACT The voltammetric characterisation and determination of insecticide flonicamid (N-cyanomethyl-4-(trifluoromethyl)nicotinamide) were performed for the first time using a simple electrochemical sensor, renewable silver-amalgam film electrode (Hg(Ag)FE). During the development of the direct cathodic square wave voltammetric method (SWV) for the determination of flonicamid, a voltammetric behaviour of a target analyte in aqueous Britton-Robinson buffer solution from pH 2.0 to pH 11.98 was examined. In the investigated pH range, the peak which appeared in the potential span between −0.86 V and −1.56 V vs. saturated calomel electrode depending on the applied pH value was chosen for analytical purposes. As optimal pH for the determination of flonicamid, pH 2.5 was selected. Cyclic voltammetric measurements at pH 2.5 confirmed that the electrode reaction mechanism is an irreversible reduction controlled by the diffusion of flonicamid at Hg(Ag)FE. The optimised Hg(Ag)FE-SWV method resulted in good linearity in the concentration range of 1.96–41.2 µg mL−1 while the relative standard deviation of the method was 0.30%. Flonicamid was successfully determined in commercial formulation Teppeki 500 WG® and spiked river water sample by the developed method using the standard addition procedure. The average value of flonicamid amount found in a commercial formulation based on three repetitions was 497.8 ± 0.9 g kg−1, which is in good agreement with the manufacturer’s declaration (500 ± 25 g kg−1) and with comparative high-performance liquid chromatographic measurements with diode array detection where a found average value of flonicamid content was 497.5 ± 11.5 g kg−1. The obtained results also indicate that the developed SWV procedure using Hg(Ag)FE was appropriate for the determination of flonicamid in a spiked river water sample with the recovery of 92.86% and RSD of 6.19%.