Fundamentals of lead-acid cells: Part XI. Phase formation at solid and porous lead electrodes

The development of lead sulphate on lead (charged) electrodes (massive and porous) has been examined by the potential-step technique. The behaviour of the solid electrode conforms to control by nucleation and growth processes. The exact form of the process is potential-dependent and becomes two-dimensional at more positive potentials. The behaviour of the porous electrode can be interpreted in terms of well-established theory for porous materials assuming that the same crystallisation processes are observed as for the case of solid electrodes.     

Electrochemical behaviour of organolead compounds: Part I. Triphenyl-lead acetate

The electrochemical behaviour of triphenyl-lead acetate in 50% (v/v) ethanol has been investigated using various electrochemical techniques including polarography, cyclic voltammetry and controlled potential coulometry. It has been found to give three/four polarographic waves. The first normal wave involves an one-electron irreversible reduction of triphenyl-lead ions giving triphenyl-lead free radicals which are strongly adsorbed at the DME giving rise to an adsorption prewave. The triphenyl-lead free radicals produced in the normal reduction step immediately react with mercury of the DME producing phenylmercury radicals and metallic lead. Wave II has been ascribed to the simultaneous reduction of triphenyl-lead free radicals and phenylmercury free radicals. The metallic lead produced in these processes undergoes oxidation at the electrode and “distorts” the “normal” adsorption prewave of step I. A mechanism of reduction is proposed and polarographic methods have been developed for determining triphenyl-lead compounds at ordinary level and down to submicromolar level.     

Heterogeneous Electron Transfer and Oxygen Reduction Reaction at Nanostructured Iron(II) Phthalocyanine and Its MWCNTs Nanocomposites

Electron transfer and oxygen reduction dynamics at nanostructured iron(II) phthalocyanine/multi‐walled carbon nanotubes composite supported on an edge plane pyrolytic graphite electrode (EPPGE‐MWCNT‐nanoFePc) platform have been reported. All the electrodes showed the category 3 diffusional behaviour according to the Davies–Compton theoretical framework. Both MWCNTs and MWCNT‐nanoFePc showed huge current responses compared to the other electrodes, suggesting the redox processes of trapped redox species within the porous layers of MWCNTs. Electron transfer process is much easier at the EPPGE‐MWCNT and EPPGE‐MWCNT‐nanoFePc compared to the other electrodes. The best response for oxygen reduction reaction was at the EPPGE‐MWCNT‐nanoFePc, yielding a 4‐electron process.     

Anisotropic Conductivity at the Single‐Molecule Scale

In most junctions built by wiring a single molecule between two electrodes, the electrons flow along only one axis: between the two anchoring groups. However, molecules can be anisotropic, and an orientation‐dependent conductance is expected. Here, we fabricated single‐molecule junctions by using the electrode potential to control the molecular orientation and access individual elements of the conductivity tensor. We measured the conductance in two directions, along the molecular plane as the benzene ring bridges two electrodes using anchoring groups (upright) and orthogonal to the molecular plane with the molecule lying flat on the substrate (planar). The perpendicular (planar) conductance is about 400 times higher than that along the molecular plane (upright). This offers a new method for designing a reversible room‐temperature single‐molecule electromechanical switch that controllably employs the electrode potential to orient the molecule in the junction in either “ON” or “OFF” conductance states.     

3D-printed porous electrodes for advanced electrochemical flow reactors: A Ni/stainless steel electrode and its mass transport characteristics

Porous electrodes have shown high performance in industrial electrochemical processes and redox flow batteries for energy storage. These materials offer great advantages over planar electrodes in terms of larger surface area, superior space time yield and enhanced mass transport. In this work, a highly ordered porous stainless steel structure was manufactured by 3D-printing and coated with nickel from an acidic bath by electrodeposition in a divided rectangular channel flow cell. Following the electrodeposition, the volumetric mass transport coefficient of this electrode was determined by the electrochemical reduction of 1.0×10⁻³ mol dm⁻³ of ferricyanide ions by linear sweep voltammetry and chronoamperometry. The convection diffusion characteristics are compared with other geometries to demonstrate the novelty and the advantages of 3D-printed porous electrodes in electrochemical flow reactors. Robust porous electrodes with tailored surface area, composition, volumetric porosity and flow properties are possible.     

Differential pulse voltammetric determination of selected nitrophenols on novel type of porous silver working electrode prepared by powder metallurgy

Nitrophenols are important environmental pollutants and their monitoring is important because of their genotoxic and ecotoxic properties. Easy electrochemical reduction of nitro groups can be used for their voltammetric determination using mercury based electrodes. However, requirements of green analytical chemistry prompted us to investigate a novel type of silver porous electrode (AgPE) prepared by powder metallurgy compatible with both “green” and “white” analytical chemistry requirements. In this paper, AgPE was for the first time successfully used for differential pulse voltammetric determination of micromolar concentrations of 2-nitrophenol (NP), 2,4-dinitrophenol (DNP), and 2,4,6-trinitrophenol (TNP) in aqueous media. The main advantage of the novel method is the possibility to use small sample volume (down to 25 μL) and to work in the presence of oxygen when using supporting electrolyte of pH 3. This advantage partially compensates the fact that the obtained sensitivity and limit of detection are not better than with the previously investigated electrodes.     

Powder Microelectrodes Applied to NO_2 Detection

TheelectrochemicalbehaviorsandthedetectionofNO2-haveattractedincreasingattentionrecentlybecauseoftheimportantrolesplayedbyNO2-inenvironmentandlifeprocesses.Thus,advancedtechniquesforthedetermination,especiallyon-sitedetermination,ofthenitriteinfoods...     

Continuous potentiometric determination of sulphate in a differential flow system

Continuous monitoring of sulphate in a differential flow system equipped with two lead ion-selective electrodes is described. All solutions contained 75% methanol and were adjusted to pH 4. In the flow cell, a standard solution of lead(II) is pumped past the first sensing electrode and is mixed with the sample stream containing sulphate in a small mixing chamber; the mixture containing excess of lead(II) and lead sulphate precipitate then flows through the second sensing electrode chamber. The potential difference depends on the sulphate content in the sample. The effects of lead electrode passivation and the interferences of calcium and chloride are discussed. The system is useful for routine sulphate determination in the range 30–400 mg l^-1 with an accuracy of ±5%     

Silica-Derived Nanostructured Electrode Materials for ORR,OER, HER,CO2RR Electrocatalysis,and Energy Storage Applications: A Review**

Silica-derived nanostructured catalysts (SDNCs) are a class of materials synthesized using nanocasting and templating techniques, which involve the sacrificial removal of a silica template to generate highly porous nanostructured materials. The surface of these nanostructures is functionalized with a variety of electrocatalytically active metal and non-metal atoms. SDNCs have attracted considerable attention due to their unique physicochemical properties, tunable electronic configuration, and microstructure. These properties make them highly efficient catalysts and promising electrode materials for next generation electrocatalysis, energy conversion, and energy storage technologies. The continued development of SDNCs is likely to lead to new and improved electrocatalysts and electrode materials. This review article provides a comprehensive overview of the recent advances in the development of SDNCs for electrocatalysis and energy storage applications. It analyzes 337,061 research articles published in the Web of Science (WoS) database up to December 2022 using the keywords “silica”, “electrocatalysts”, “ORR”, “OER”, “HER”, “HOR”, “CO₂RR”, “batteries”, and “supercapacitors”. The review discusses the application of SDNCs for oxygen reduction reaction (ORR), oxygen evolution reaction (OER), hydrogen evolution reaction (HER), carbon dioxide reduction reaction (CO₂RR), supercapacitors, lithium-ion batteries, and thermal energy storage applications. It concludes by discussing the advantages and limitations of SDNCs for energy applications.     

Sol–gel synthesis of porous inorganic materials using “core–shell” latex particles as templates

Here we report on the sol–gel synthesis of porous inorganic materials based on manganese, molybdenum, and tungsten compounds using the “core–shell” siloxane-acrylate latex as a template. The chemical composition and structural characteristics of the materials obtained have been investigated. It was shown that temperature conditions and gaseous media composition during the template destruction controlled the composition and structure of porous materials. To obtain porous inorganic materials for catalytic applications, the “core–shell” latex template was preliminarily functionalized by gold and palladium nanoparticles obtained by thermal reduction of noble metal ions-precursors in a polycarboxylic “shell”. Upon the template removal, noble metals nanoparticles of a size of dozens of nanometers were homogeneously distributed in the material porous structure. The evaluation of the catalytic activity of macroporous manganese, tungsten, and molybdenum oxides under the conditions of liquid phase catalytic oxidation of organic dyes has been performed. The prospects of employing macroporous oxide systems with immobilized nanoparticles of noble metals in the processes of hydrothermal oxidation of radionuclide organic complexes in radioactive waste decontamination have been demonstrated.     

Fundamentals of lead acid cells: Part IV. The reduction of porous PbO2 electrodes in sulphuric acid

The reduction behaviour of porous lead dioxide electrodes is shown to be independent of rotation speed in a large excess of 5 M H₂SO₄. The reduction peak is broadened by the porosity. This porosity broadening is interpreted in terms of the reaction being driven more deeply into the pore structure as the front of the electrode becomes progressively more ressstive. The effect of different potential sweep rates on the current response and the effects of progressive redox cycles can be fully explained on this model.     

Phase transition in porous electrodes

It is shown by Monte Carlo simulation that electrochemical thermodynamics of electrolytes in a porous electrode is qualitatively different from that in the bulk with a planar electrode. In particular, first order phase transitions occur in porous electrodes when the pore size is comparable to the ion size of the electrolytes: as the voltage is increased from zero, the surface charge density and the ion density in the porous electrodes discontinuously change at a specific voltage. The critical points for those phase transitions are identified.     

铅及铅锑合金阳极膜中硫酸铅的氧化过程

应用电位阶跃和交流阻抗法分别研究铅和Pb-5wt% Sb合金在4.5mol·dm^-^3H~2SO~4(30℃)中于1.3V(vs. Hg/Hg~2SO~4, 下同)生长20min后的阳极膜在0.9V还原5min后再在1.4V将膜中硫酸铅氧化的过程。实验结果表明在0.9V还原二氧化铅而得到的硫酸铅能在1.4V于1min内氧化为二氧化铅。这是由于此种硫酸铅处于硫酸铅颗粒表层的缘故。至于颗粒内部由铅直接生成的硫酸铅的氧化为二氧化铅就要缓慢得多。合金中的锑能使二氧化铅晶核形成和生长速率显著降低。     

Inhibition of copper corrosion in acidic sulphate media by eco-friendly amino acid compound

This investigation aimed to study a “green” non-toxic biodegradable copper corrosion inhibitor in an acidic sodium sulphate solution. The methods used in the investigation of cysteine as a copper corrosion inhibitor in an acidic sodium sulphate solution were: potentiodynamic measurements, open circuit potential measurements, and chronoamperometric measurements. Optical microscopy was used in addition to electrochemical methods. Potentiodynamic measurements show that cysteine has good inhibitory properties in an acidic medium. Polarisation curves indicate that the presence of cysteine in a sulphate solution decreases the current density and that using various cysteine concentrations results in the formation of a protective film on the surface of the electrode due to the formation of the Cu(I)-cys complex. These results are confirmed by chronoamperometric measurements. Furthermore, it is clear from microphotographs that a protective film does form on copper electrode in the presence of cysteine. The Langmuir adsorption isotherm indicates that cysteine is chemisorbed on the surface of the electrode.     

Electrochemistry of quinizarine adsorbed on a glassy carbon electrode in aqueous solutions

The electrochemistry of quinizanne in aqueous solutions, adsorbed on electrochemically pretreated glassy carbon electrodes, is described. The anodic and cathodic reversible reactions are followed by physical and chemical processes, respectively. The desorption of the fully oxidized species from the electrode was assigned to the follow-up process in the anodic region. The follow-up reaction at the more negative potentials is ascribed to tautomerization. in which the central hydroxyl group(s) participate. When the range of the reduction is expanded, two additional irreversible reduction waves are observed. A full mechanism of the electrode reactions is proposed. Intramolecular hydrogen bonds and the pH of the aqueous solutions play an important role in the rationalization of the overall mechanism. The “electro-chemical label” concept is used to study the progress of the electrode reactions, and to evaluate the intermediates and the products which are confined to the electrode surface.     

锡钴合金电沉积层的结构与锂离子嵌脱行为

应用电沉积方法制备Sn-Co合金镀层.X-射线衍射和扫描电子显微镜分析表明,该Sn-Co合金镀层为六方固溶体结构,含Co量为20%的Sn-Co合金,其沉积层呈现(110)择优取向.表面微孔随沉积层Co含量的增加而增多.以Sn-Co合金镀层作锂离子电极材料,电化学性能测试表明,其首次充电曲线表现出锡钴合金、锡及锡氧化物与锂合金化的多个反应综合特征,随后的充电曲线趋于稳定,呈现L i-Sn-Co合金化反应特征;具有择优取向和多孔结构的Sn-Co合金电极材料的充放电性能较好,首次库仑效率为63.9%,经过20次充放电循环后,其充电容量为461mAg/h,库仑效率为99%.     

The Influence of Electrode Porosity on Diffusional Cyclic Voltammetry

A simple generic model to predict the influence of electrode porosity on the cyclic voltammetric response of an electrode is presented. The conditions under which deviation from the behavior of a perfectly flat, planar electrode can be expected are predicted. The scope for misinterpretation when conventional flat electrode theory is applied to porous electrodes is highlighted, especially in respect to the extraction of electrode kinetic parameters and the influence of ‘electrocatalysis’.     

Phase transition in porous electrodes. II. Effect of asymmetry in the ion size

The electrochemical thermodynamics of electrolytes in porous electrodes is qualitatively different from that in the bulk with planar electrodes when the pore size is comparable to the size of the electrolyte ions. In this study, the effect of the ion size asymmetry on the thermodynamics in porous electrodes was studied by using Monte Carlo simulation. We used the electrolyte ions for which the size of the cations and that of anions is different. Due to the asymmetry in the ion size, the ionic structure and the way the surface charge is distributed on the electrode surfaces were found to be qualitatively different in the cathode and in the anode. In particular, for some ranges of applied voltage, the distribution of the surface charge induced on the electrode planes shows inhomogeneity, which is not intrinsic to the structure of the porous electrodes. The transition from the homogeneous to the inhomogeneous distribution of surface charge on changing the voltage is a second order phase transition.     

Textile electrodes as substrates for the electrodeposition of porous ZnO

Metal-coated polyamide threads and filaments were chosen as substrate electrodes to deposit highly porous ZnO films for photovoltaic application. The films were electrodeposited at 70 degrees C from oxygen-saturated aqueous zinc salt solutions containing EosinY as a structure directing agent. The current density during deposition was increased compared with planar electrodes by enhanced diffusion at the filaments operating as cylindrical microelectrodes. Analysis by scanning electron microscopy showed an influence of geometrical constraints within the textiles and the hydrodynamic flow rate in the deposition solution on the film morphology. Photoelectrochemical characterization of sensitized films revealed the feasibility of the presented approach and indicated further steps needed for electrode optimization.     

Application of the superposition principle to the study of multistep electrode processes and systems with several components in chronopotentiometry with programmed current. Part I

Summary In this paper we present the solution to the differential equations system corresponding to the problem of multistep processes and systems with several components when a programmed current-time function is applied to planar and spherical electrodes. The analytical solutions have been obtained in both cases, by a recurrent procedure, which facilitates the numerical determination of results. This solution has been found for an expanding spherical electrode, since by using simple substitutions it is transformed into that corresponding to a stationary spherical electrode, to an expanding plane electrode or to a stationary plane electrode.