Journal of Electroanalytical Chemistry最新文献

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.

A facile route was proposed in preparing phosphorus and nitrogen dual carbon quantum dots (N,P-CQD) from banana flower bract extract by hydrothermal synthesis for selective and reliable detection of catecholamines such as dopamine (DA). By morphologically characterizing the synthesized CQD using Transmission Electron Microscopy (TEM), it is discovered that its average particle size is 3.8 nm. While the doping of the heteroatoms upsurges the electrical conductivity of the CQD, the presence of the functional sites like acid (–COOH), (–NH₂) and phosphate (-PO₄^3-) groups selectively attract the cations via., an ion-exchange mechanism leaving behind the anions, due to the electrostatic repulsion. The synthesized N,P-CQD/PIGE electrode-based electrochemical sensors demonstrated high selectivity and sensitivity for DA with a relatively low limit of detection (LOD) (∼500 pM) and a wide linear range, extending from 6.0 μM to 0.1 mM. The N,P-CQD's detection selectivity is further validated by utilizing a combination with a somewhat larger concentration of uric (UA) and ascorbic (AA) acids and only a modest amount of DA. Additionally, the N,P-CQD/PIGE electrode successfully detects DA with a LOD as low as 630 pM and a larger linear range of 2.5 M to 0.16 mM in real-time samples of dopamine injection.

The carbon dioxide reduction reaction (CO₂RR) is a key reaction that efficiently uses CO₂ to produce value-added chemicals. However, the main limitation of this reaction is its low selectivity which results in the formation of a variety of by-products. As a result, the current challenge for CO₂RR is the efficient formation of product with high Faradaic efficiency (FE). Our main goal is to replace precious metal electrocatalysts with more abundant transition metal/conducting support hybrid catalysts. Herein, we’ve synthesized a cuprite-polyaniline (Cu₂O@PANI) composites. The superior catalytic activity in terms of activity and selectivity for methanol (MeOH) synthesis could be attributed to the synergism between Cu₂O and PANI that enables it to scale back multiple species, higher electrical conductivity, and lowest resistance during the charge/mass transfer processes. These properties were confirmed using Electrochemical impedance spectroscopy (EIS), Electron transfer rate constant (Ks), Mott-Schottky (MS), Double-layer capacitance (DLC), and Density-functional theory (DFT) analysis. Based on these findings Cu₂O@PANI matrix easily forms many intermediate (CO) species and maintains a higher CO₂ concentration around the electrode surface throughout the experiment. The results of the given electrocatalytic system show that the Cu₂O@PANI matrix significantly suppressed the by-product throughout the experiment, resulting in MeOH (45.21%) FE within 90 min. Given these benefits, the catalytic system is appropriate for CO₂RR.

The paper analyzes how the structure of porphyrin affects its electrochemical characteristics, film formation process and physicochemical properties of the obtained materials. A comparison of the redox processes of 21H,23H-5,15-bis-(4-aminophenyl)-10,20-di-phenyl porphyrin (Porph I) and 21H,23H-5,10,15-tris-(4-aminophenyl)-20-phenyl porphyrin (Porph II) shows that Porph I is more stable in oxidation and less stable in reduction processes than Porph II. The presence of electrochemically active amino groups in the composition of the porphyrin molecules allows the superoxide-assisted electrochemical deposition method to be applied to successfully form poly-Porph I and poly-Porph II films from dimethyl sulfoxide solutions. Spectral methods confirm that the obtained materials preserve their porphyrin structure. The structure of the initial monomer molecules is demonstrated to affect the film formation and surface morphology of the prepared materials. Oxygen electroreduction in an alkaline medium is shown to have smaller kinetic limitations on poly-Porph II films than that on poly-Porph I ones.

As histamine is one of the important mediators for allergic reactions, its efficient detection methods and real-time monitoring systems are required for food analyses and drug discoveries to suppress allergic reactions. Although histamine dehydrogenase (HmDH) is a promising candidate for developing enzyme-based electrochemical biosensors, some electron mediators are frequently employed to observe electrocatalytic currents for histamine oxidation. Here, direct electrochemistry of HmDH was studied at the surface of graphite nanofibers (GNFs), which provide active reaction sites for redox species. Air plasma-treated GNFs were used for constructing a three-dimensional network that works both as an electrical nanowire and an enzyme support. Even though the amount of oxygen-containing functional groups didn’t significantly increase at the GNF surface with increase in the air plasma treatment time, direct electron transfer from reduced HmDH by histamine to the GNFs was improved probably due to capped and curvature of the graphite edge sites with oxygen-containing functional groups, which were generated by the air plasma treatment. The air plasma-treated GNFs also allowed enhancement of the complex-formation reaction rate of HmDH with histamine, as the air plasma treatment time increased.

In this work, β-PbO₂/Ti and RuO₂-IrO₂/Ti anodes and Ti cathodes were employed to conduct electrocatalytic phenol degradation experiments at various current densities. The difference in degradation rates between the two anodes indicated that the oxygen evolution reaction (OER) is related to the organic matter concentration. Consequently, a coupling mechanism “active-site competition mechanism (ACM) + adsorbate evolution mechanism (AEM)” for anodic oxygen evolution was described. Based on this mechanism and experimental results, it can be concluded that the ACM influences the initial degradation rate, and the AEM affects final organic matter concentrations. DFT calculations showed that RuO₂-IrO₂ exhibits excellent AEM activity attributed to the lower OER overpotential (0.7 V) and stronger adsorption energies of *O oxygenated intermediate (-1.52 eV). At the same time, RuO₂-IrO₂ possesses slight thermodynamic reaction energy of ACM, which are 103.3, 31.6 and 89.5 kJ/mol. Therefore, the slower degradation rates and lower removal efficiency on RuO₂-IrO₂/Ti are owing to the better ACM and AEM activity. Then, electrocatalytic experiments at various pH were conducted to verify the conclusion that AEM affects final organic matter concentrations. Finally, this work has implications for a better understanding of the OER mechanism and provides theoretical guidance for improving the removal efficiency of organic pollutants.

Ternary Sn-Ag-Cu solderable alloy coatings were electrodeposited using deep eutectic solvent-based electrolytes, at different deposition potentials. The obtained deposits have been characterized from surface morphology, composition, crystalline grain and phase via Scanning Electron Microscopy (SEM) associated with Energy Dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD). To get information on the alloy melting point, Differential Scanning Calorimetry (DSC) has been involved.

The results showed that the crystalline grain became finer and the coating became denser as the deposition potential increased. In addition, the presence of Cu₆Sn₅ phase is facilitated by more cathodic deposition potentials while the Ag₃Sn phase was evidenced at lower potential values. The value of the melting point of Sn-Ag-Cu alloy (Sn90.9-Ag7.6-Cu1.5) deposited at potentials of −1.2 V was of 215.02 ℃. Based on the results obtained during the analysis of the current–time curves using the Scharifker-Hills' model, it has been found that both single metal and alloy deposition processes correspond to a nucleation and tridimensional growth controlled by diffusion. The deposition processes of Sn and Ag are conducted by an instantaneous mechanism, while in the case of Cu, a progressive one has been determined. The deposition process of Sn-Ag-Cu alloy showed a deviation from the instantaneous nucleation.

The volume expansion of Si electrodes and the poor conductivity of Si as well as the repeated rupture of solid electrolyte interface (SEI) lead to the rapid capacity decay of Si-based anode Li-ion batteries. The rational design of anode materials for the above problems is considered an effective solution. In this work, core-shell structured Si@Cu nanoparticles segregated in graphene-carbon nanotube networks (Si@Cu/CNT/rGO) is constructed by one-step hybrid and reduction self-assembly strategy. First, metallic copper was coated on silicon nanoparticles to improve the reaction kinetics of the cell during operation. The flexible reduced graphene oxide and rigid carbon nanotube are designed as a network structure for increasing the electrical conductivity and mechanical strength of the electrode material. This design not only provides sufficient buffering space for the volume change during cell operation, but also improves the electron migration effect of the composite Si@Cu/CNT/rGO. Thanks to this design, the composite electrode maintains a high lithium storage capacity of 1915.5 mAh/g (130 cycles) and 1486.7 mAh/g (200 cycles) after charging and discharging at 100 mA g⁻¹ and 1000 mA g⁻¹, respectively.

MnO has the advantages of high theoretical capacity, abundant resources and environmental friendliness, which is a potential material for lithium-ion storage. However, severe volume expansion and sluggish kinetics make MnO difficult to maintain long-term stability. In this study, MnO/C@CoPPc micro-rods composed of coral-like MnO/C nanobundles coated with CoPPc was synthesized via facile method. CoPPc impregnated into the empty space and simultaneously coated on the surface of the needles of MnO/C functions as an elastic layer to accommodate the mechanical stress caused by volume expansion of MnO/C, and simultaneously function as a buffering layer to keep electric disconnection on cycling. The volume of MnO/C is dramatically suppressed from 370% to 120%, and the reversible capacity is improved. Therefore, the configured MnO/C@CoPPc exhibits a high stability and delivers a high reversible capacity of 679.6 mAh/g after 200 cycles.

Sustainable materials with nanostructured architecture have made great strides in today’s energy storage technology. In this context, sustainable, environment-friendly SnO₂ are synthesised by hydrothermal method and its electrochemical performance as anode material for lithium and sodium-ion batteries are investigated. Structural analysis such as X-ray diffraction and Raman measurement validates the formation of the tetragonal rutile structure of pristine SnO₂. Scanning electron microscope image shows mixed, hollow spherical and rod- shape morphology. The Li⁺ and Na⁺ ion diffusion kinetics are conferred using cyclic voltammetry. The rate capability of pristine SnO₂ anodes are tested using charge–discharge measurements. SnO₂/Li half-cell shows the initial discharge capacity of 982 mAh/g at 0.1C rate and delivers the specific capacity of 219 mAh/g and 72 mAh/g at 10C and 20C rates. The SnO₂/Na half-cell delivers the initial discharge capacity of 600 mAh/g and maintains the specific capacity of 110 mAh/g (1C-rate) after 500 charge–discharge cycles. The mixed spherical and rod shape morphology increases the surface area and facilitates the Li⁺ and Na⁺-ion diffusion and minimizes pulverization. Post-mortem microstructural studies are performed after 500 cycles, confirming the formation of inert oxide phases and degradation of electrolyte by-products in both LIB and SIB.