Journal of Electroanalytical Chemistry最新文献

The development and improvement of new transition metal-based catalysts to replace Pt/C electrodes in electrolytic water hydrogen evolution has attracted much attention. In this work, we used ammonium citrate as additive, mixed with cobalt nitrate, through hydrothermal and phosphating methods to get supported on carbon cloth catalyst with new morphology (referred to as E380-CoP/CC, E380 stands for ammonium citrate). Benefit from the dense and fine nanosheet structure, compared with cobalt phosphating alone, the catalyst E380-CoP/CC has a significant improvement in hydrogen evolution performance. In 1 M KOH, the overpotential is 57 mV at the current density of 10 mA cm⁻², and the Tafel slope is only 40 mV dec^-1, which is very close to the hydrogen evolution performance of Pt/C electrode. In addition, the catalyst has favorable stability and superior hydrogen evolution performance after undergoing CV 2000 cycles and 48 h i-t test. This work offers a reliable idea for realizing electrolytic water hydrogen evolution technology with high efficiency and energy saving.

The effects of a thin Ni-flash coating, tens of nanometers thick, on hydrogen evolution, ad/absorption, and permeation of advanced high-strength steel were examined for a deeper understanding of the hydrogen infusion behavior in the steel substrate during electro-Zn plating. The electrochemical permeation technique and impedance spectroscopy were used under cathodic polarization in a step-up manner. In addition to the electrochemical analyses, the hydrogen microprinting technique was employed to identify the distribution of Ag particles (locating hydrogen atoms) in the electro-Zn plated steels with and without a thin intermediate Ni-layer. The results revealed that despite the higher hydrogen evolution rate on Ni-flash coating layer than on bare steel, the intermediate Ni-layer decreased the hydrogen infusion considerably in the steel substrate during electro-Zn plating, due primarily to the lower hydrogen ad/absorption rate on the Ni-flash coating layer, and the predominant hydrogen trapping at the multi-interfacial areas of the Zn-layer/Ni-layer/steel substrate. These results could provide insights into the precise role of a thin (tens of nanometers) Ni-flash coating on the resistance to hydrogen embrittlement of ultra-high-strength steel alloys during electro-Zn plating.

The purpose of this study is to develop an electrode material with high electrocatalytic activity, good stability and low price for the degradation of the new pollutant - antibiotic levofloxacin (LEV). A novel modified Ti/SnO₂ electrode is prepared using a sol–gel method combined with spraying. The morphology of the Ti/SnO₂-Sb-Ni/SiO₂ electrode was performed by field emission scanning electron microscopy, which revealed a smooth and flat surface. It can be seen from the results of X-ray diffraction and electrochemical tests, the electrode possessed finer grain size (2.68 nm) and slightly higher oxygen evolution potential (OEP, 1.87 V). Electrochemical degradation experiments show that the removal rate of LEV in Na₂SO₄ and NaNO₃ solutions reached 100% after 10 min reaction, while in NaCl solution the reaction time (LEV 100% removal) was shortened to 3 min, indicating a faster removal rate. An electrical energy consumption per order of magnitude (EE/O) of LEV degraded by Ti/SnO₂-Sb-Ni/SiO₂ electrode was only 0.59 kWh m⁻³ for an initial concentration of 20 mg/L LEV with a volume of 400 mL. According to the changes of UV–visible absorption spectra during the LEV degradation, the damage degree of conjugated structures in LEV molecules varies with different electrolytes. The existence of hydroxyl radical (•OH) and sulfate radical (SO₄^•−) was confirmed by radical quenching experiment and EPR text with 100 mM 5,5-Dimethyl-1-pyrrolidine N-oxide (DMPO). In different electrolytes, SO₄^•− (in Na₂SO₄ solution), •OH (in NaNO₃ solution) and active chlorine(in NaCl solution) played a leading role in LEV degradation, respectively.

The anodizing in etidronic acid (HEDP) and oxalic acid (H₂C₂O₄) mixed electrolytes was conducted. The anodizing parameters were optimized based on the evaluation of energy consumption, growth efficiency, and hardness of PAA film. The results indicate that continuous and uniform PAA films can be fabricated in HEDP/H₂C₂O₄ solutions in any proportion, and both the anodizing voltages and roughnesses of PAA films decreased with the H₂C₂O₄ content. The moderate amount of H₂C₂O₄ could lead to an increase in the formation efficiency of PAA films. The hardness of the PAA film prepared in HEDP/H₂C₂O₄ electrolyte could reach up to ∼660 HV. Moreover, a surface resembling lotus leaves could be formed due to the corrosion of PAA films with sub-micron interpore distance by H₂C₂O₄ during anodizing, and a superhydrophobic surface with a contact angle of ∼153° could be obtained after it was modified via stearic acid.

Zeolite ZSM-5 and zeolite β were modified by aqueous ion exchange with cerium and then calcined (cal) to obtain Ce-ZSM-5, Ce-ZSM-5 cal, Ce-β, and Ce-β cal electrocatalysts. X-ray powder diffraction analysis, Fourier Ttransform infrared spectroscopy, scanning electron microscopy with energy dispersive spectroscopy, X-ray photoelectron spectroscopy, fluorescence spectroscopy, and Brunauer-Emmett-Teller method revealed changes in the structure and porosity of zeolites upon calcination. Voltammetry, chronoamperometry, and electrochemical impedance spectroscopy were used for testing four zeolites for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) in alkaline media. OER starts the earliest at Ce-β cal with onset overpotential 50, 70, and 110 mV lower than Ce-ZSM-5 cal, Ce-ZSM-5, and Ce-β. Ce-β cal further showed the lowest OER Tafel slope (114 mV dec⁻¹). Consequently, the highest OER current density was recorded in the case of Ce-β cal, followed by Ce-β, Ce-ZSM-5 cal, and Ce-ZSM-5. Regarding ORR, Ce-ZSM-5 cal showed the lowest Tafel slope (70 mV dec⁻¹) with the highest current densities that remained constant during the chronoamperometry test with a negligible decrease of 4%. It could be concluded that calcined forms exhibit better performance for OER and OER than their parent, non-calcined forms due to more active sites available for OER/ORR and decreased charge-transfer resistance.

For long-term energy storage and conversion, the design of commercial and high-performance catalysts for bifunctional electrocatalytic water splitting is critical. We report the efficient method to prepare Cu_xNi_1-xS Nanoflakes (NFs) on binder-free and large area plastic chip electrodes. Cu_xNi_1-xS NSs show superior overall water splitting with optimized Cu-amount. The synthesized catalysts perform well in 1.0 M KOH alkaline media for simultaneous hydrogen and oxygen evolution, with relatively low overpotential, efficient kinetics, and sustained electrolysis durability. Impressively, it is found that Cu-doping enhances the chemical and environmental stability, beneficial for the practical application. By modifying the electronic structure, Cu-atom doping promotes the easy flow of electrons, which leads to incredible rise in the electrocatalytic activity with over potential of 152 mV for HER and 189 mV for OER on Cu_xNi_1-xS. Bi-functional water splitting cell generates 10 mA/cm² current density at cell voltage of 1.74 V. Encouragingly, current density of 80 mA/cm² can be generated at potential of 2.61 V with optimized chemical composition of Cu_xNi_1-xS based electrodes. Cu_xNi_1-xS demonstrates excellent stability for bi-functional water electrolysis at 20 mA/cm² for more than 18 h. This research lays forth a viable technique for developing enhanced bi-functional electrocatalysts that can be used to substitute noble metals in a range of renewable energy applications.

Rechargeable Li-O₂ batteries show great potential due to their superior high energy density. However, the practical application is still limited by the sluggish kinetics, resulting in poor cycling performance and high overpotentials. Herein, highly dispersed Co nanoparticles embedded into porous N-doped carbon matrix (DCo-NC) with carbon nanotubes is explored through the pyrolysis of a bimetallic leaf-shaped ZnCo-ZIFs. The evaporation of Zn species and porous carbon matrix derived from ZIFs prevents the Co nanoparticles aggregation, exposes more Co-N active sites and provides abundant pores. They facilitate Li⁺ and electron transfer, prevent Co nanoparticles from deactivation and provide enough space for Li₂O₂, thereby accelerating oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) kinetics. Accordingly, the Li-O₂ batteries with DCo-NC cathode exhibit reduced overpotential, high discharge capacity (10,490 mA h g⁻¹ at 100 mA g⁻¹ current density) and improved cycling performance (258 cycles at 500 mA g⁻¹ with a limited capacity of 500 mA h g⁻¹, 103 cycles at 500 mA g⁻¹ with a limited capacity of 1000 mA h g⁻¹).

This work presents a comprehensive degradation study of two types of large lithium-ion pouch cells; 26 NMC532/Graphite (64 Ah) and 9 NMC433/Graphite (31 Ah) pouch cells. The cells were degraded under different cycling conditions and periodically characterized at room temperature. Specifically, the effect of different ambient temperatures and constraining the cells by clamping was studied. Incremental capacity analysis is an in situ, non-invasive characterization technique that allows the identification of battery degradation modes, and is a technique that does not require additional and advanced equipment. Therefore, in this study we also look into applying the analysis technique on an existing data set. This is done by combining incremental capacity analysis on a qualitative level with the tracking of features of interest in the incremental capacity curve as a function of State of Health and utilizing the simulation of different degradation modes for a more in-depth analysis. We combine simulation and experimental incremental capacity analysis with conclusions from capacity loss and resistance changes with a focus on understanding the benefit and limitations of the incremental capacity analysis for large cells. This is important, as incremental capacity analysis is a relatively fast analysis to qualify large commercial batteries for 2nd life applications. Specifically in this study, we found that degradation and capacity loss do not always correlate. For the 64 Ah Cells cycled at 15 °C and 25 °C, the rate of capacity loss appeared to be similar, although the degradation modes and mechanisms are found to be very different. The clamping was the most important factor for impeding degradation. The 31 Ah Cell cycled at low temperatures showed a very poor cycling performance, where the incremental capacity analysis revealed that Loss of Lithium Inventory from fast and irreversible plating was responsible.

11,12-dihydrodibenzo[c,g][1,2]diazocine (Diazocine, 12), a molecular switch capable of reversible interconversion between (at least) two states by light, has been widely used in pharmacology and biochemistry. However, most of the synthetic methods so far have been limited by tedious steps, complicated derivatives, and long reaction times, resulting in poor synthetic yields of 12. Here, we propose a green, effective, and controllable strategy for synthesizing 12. The intramolecular cyclization (8-membered ring) of 2,2′-dinitrodibenzyl (1) was achieved by electrochemical reduction in the presence of CO₂, and 12 and its derivatives 11,12-dihydrodibenzo[c,g][1,2]diazocine-N-oxide (DDCG-N, 11) were synthesized. The electrochemical reduction mechanism of 1 in the presence of CO₂ was investigated by cyclic voltammetry (CV) and in situ FT-IR spectroelectrochemistry. The molecular structures of the electrolytic product (12) and intermediate (11) were confirmed by single-crystal X-ray diffraction, NMR, and MS. The results show that the electrochemical behavior of 1 in acetonitrile (AN) changes from a reversible two-step 1-electron transfer process (in the absence of CO₂) to an irreversible 8-electron transfer process (in the presence of CO₂). The 12 and 11 can be obtained by controlling the electrolytic potential and time. Under the optimum conditions, the yields of 12 and 11 were 84% and 71%, respectively.

Wearable electronic devices have become a preferred choice for health monitoring, but suffer from low capacitance of planar electrodes. This work aims to improve the capacitive performance through the combination of porous boron-doped diamond (BDD) and MnO₂ modification. BDD film was deposited on the substrate of titanium foam using hot-filament chemical vapor deposition (HFCVD). Constant-voltage deposition was then employed to deposit MnO₂ on the BDD, and the deposition time was adjusted to evaluate the influence of MnO₂ modification on the electrode capacitance. Porous structure formed by titanium foam enables BDD electrode to exhibit larger specific surface area, and reach a capacitance of 67.9 mF/cm². Porous BDD/MnO₂ film (MnO₂ deposited for 1500 s) shows pea-like morphology and has optimal capacitive performance. BDD/MnO₂-1500 s electrode displays a maximum capacitance of 1383.6 mF/cm² at a current density of 2 mA/cm², which is about 195 times that of the planar BDD electrode (7.1 mF/cm² at a current density of 2 mA/cm²) along with a minimum R_ct value of 2 Ω. This allows us to see the fact that improvement mechanism of combining porous structure and MnO₂ modification may result from common effect of three following aspects: (1) Porous structure gives BDD superior specific surface area and favorable ion transport channels than planar electrode; (2) Pseudocapacitance effect of MnO₂ increases the capacitance density; (3) Pea structure of MnO₂ may markedly increase the specific surface area of the film and shorten ion/electronic diffusion distances.