Low Cathodic Potentials Research Articles

Dual-signal immunosensor based on aggregation-induced electrochemiluminescence resonance energy transfer of La-MOF and low cathodic excitation potential of g-C3N4@AuNPs for the quantitation of human serum amyloid A

We report on the development of a dual-signal electrochemiluminescence (ECL) immunosensor for the quantitation of human serum amyloid A (SAA). The immunosensor comprises g-C3N4@AuNPs as the cathode and a lanthanum-based metal organic framework (La-MOF) as the anode, the latter of which utilizes aggregation-induced electrochemiluminescence (AIECL) to overcome the otherwise poor ECL intensity of H4TBAPy ligands at the electrode surface. Furthermore, the rigid MOF structure significantly improved the fluorescence quantum yield, as well as the fluorescence and ECL emission, of the La-MOF compared to H4TBAPy. The g-C3N4@AuNPs exhibits an ultrathin nanosheet structure with a low cathodic excitation potential of −0.72V. When the dual-signal ECL immunosensor was employed to detect SAA, the difference between the anodic and cathodic ECL signals exhibited a strong linear relationship with the logarithm of the SAA concentration in the range of 100 fg/mL–200ng/mL, with a detection limit of 24.5 fg/mL.

Energy-efficient CO(2) conversion to multicarbon products at high rates on CuGa bimetallic catalyst

Electrocatalytic CO2 reduction to multi-carbon products is a promising approach for achieving carbon-neutral economies. However, the energy efficiency of these processes remains low, particularly at high current densities. Herein, we demonstrate that the low energy efficiencies are, in part, sometimes significantly, attributed to the high concentration overpotential resulting from the instability (i.e., flooding) of catalyst-layer during electrolysis. To tackle this challenge, we develop copper/gallium bimetallic catalysts with reduced activation energies for the formation of multi-carbon products. Consequently, the reduced activation overpotential allows us to achieve practical-relevant current densities for CO2 reduction at low cathodic potentials, ensuring good stability of the catalyst-layer and thereby minimizing the undesired concentration overpotential. The optimized bimetallic catalyst achieves over 50% cathodic energy efficiency for multi-carbon production at a high current density of over 1.0Acm−2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$1.0 \\, {{\\rm{A}}} \\, {{\\rm{cm}}}^{-2}$$\\end{document}. Furthermore, we achieve current densities exceeding 2.0Acm−2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$2.0 \\, {{\\rm{A}}} \\, {{\\rm{cm}}}^{-2}$$\\end{document} in a zero-gap membrane-electrode-assembly reactor, with a full-cell energy efficiency surpassing 30%.

(Invited) Shunt-currents in Alkaline Water-Electrolyzers and Renewable Energy

Shunt-currents in bipolar cell stack design with a common electrolyte-feed and -outlet is an inevitable physical phenomenon governed by Ohms law that causes some extra challenges when alkaline water-electrolysers shall operate on renewable energy that is both dynamic and intermittent. Shunt-currents are also referred to as bypass-current or creep-current. The shunt-currents are to much degree governed by the electrolyte inside the cell stack manifold system that transports lye in and out of the cells. The electrolyte inside the manifold system also electrically connects the individual cells together and enables transport of ions/electricity in parallel to the cell stack. Thus, a small portion of the rectifier current is being shunted outside the cells and does not contribute to any production. Previous work on shunt-current modelling brought new insight on how to design the manifolds and raised the awareness on shunt-current and the use of metallic manifolds which both reduced the ohmic resistivity of the manifold system and was a source of secondary electrolysis.Classic alkaline water-electrolysers are typically using an internal manifold system where the inlet ports are located at the bottom of the cell stack and the outlet ports are located at the top, and where the ports connecting the cell-interior and the common manifold channel are short and straight. Such design has in the past worked satisfactory for alkaline water-electrolysers that have been working on a high nominal load and only being shut-down for maintenance a few times over the stack-lifetime, mainly causing a modest reduction in the current efficiency. Membrane-chlorine electrolysers on the other hand, are designed for very small shunt-currents by using an external manifold system, which enables a current protection system that protects electrodes from corrosion under shutdown conditions.Shunt-currents bypassing the cell stack does not contribute to any product and therefore constitutes a loss in current efficiency and, hence, an accordingly loss in the energy efficiency (the shunt-currents still adds to the electricity bill). The atmospheric alkaline electrolyser has a modest loss in current efficiency at nominal load where the high gas volume blocks much of the current path in the rather open outlet ports. The high-pressure alkaline electrolysers on the other hand, where the gas volumes are much smaller, the current efficiency can be as low as 89% at nominal load due to shunt-currents when using simple internal manifold system. For an electrolyser with already low current efficiency at the nominal load, the current efficiency will drop dramatically as the electrolyser is taken to lower load, severely compromising the energy efficiency. The impact on shunt-currents also dramatically increases for increased number of cells in a cell stack, and eventually limits the number of cells that can be assembled in one single cell stack operating on the same common lye system.Shutdown and discharge of the electrodes may further lead to corrosion and degradation of the electrodes, strongly influenced by the shunt-currents and the manifold system. Large cell stacks will discharge faster and deeper, eventually causing corrosion of the electrodes. As the cell stack is discharged the current in the cell stack is reversed where the hydrogen electrode is being polarized to anodic potentials, and the oxygen electrode is polarized to low cathodic potentials which eventually may challenging the material stability. Thus, evaluation of electrode potentials must be an integral part of development of industrial electrodes [LeRoy] and especially in intermittent operation where frequent shutdown will occur. A good integration of the manifold system into the cell stack can potentially mitigate both the loss of current efficiency under dynamic operation and the electrode corrosion under intermittent operation.

Material design of biodegradable primary batteries: boosting operating voltage by substituting the hydrogen evolution reaction at the cathode.

Transient primary batteries (TPBs) degrade after use without leaving harmful toxic substances, providing power sources for developing low-invasive and environmentally benign sensing platforms. Magnesium and zinc, both abundant on Earth, possess low anodic potentials and good biodegradability, making them useful as anode materials. However, molybdenum, a biodegradable metal, causes the hydrogen evolution reaction (HER) at the cathode, reducing the operating voltage of cells because of its low cathodic potential. In this review, we examine recent material designs to increase the operating voltage by introducing alternative electrochemical reactions at the cathode, including the oxygen reduction reaction, metal-ion intercalation into transition metal oxides, and halogen ionization, all of which have higher cathodic potentials than the HER. After discussing the characteristics, constituents, and demonstration of TPBs, we conclude by exploring their potential as power sources for implants, wearables, and environmental sensing applications.

Impact of Dwell Time and Lower Potential Limit during Voltage Cycling on PEM Fuel Cells Catalyst Durability

Hydrogen proton exchange membrane fuel cells (PEMFC) are the most promising fuel cell technology for automotive applications. However, for full commercialization of the technology, the fuel cell stacks still need to overcome the durability issues caused by the degradation of the cathode electrode during load cycling. In fact, load cycling, which corresponds to high and low cathode potentials, causes oxidation of platinum (Pt) at upper potential limit (UPL) and reduction of this oxide layer to fresh Pt surface at lower potential limit (LPL), leading to dissolution and subsequent migration or redeposition of Pt ions that results in degradation of electrochemical surface area (ECSA) of Pt and loss of performance [1]. In order to simulate load cycling between relevant operation potentials and age the cells faster in the laboratories, appropriate voltage cycling (VC) based accelerated stress tests (ASTs) have been developed which mimic the Pt ECSA loss in the cathode electrode due to load variations. Various voltage cycle profiles in VC-ASTs, such as, LPL, UPL, and dwell time at each of these vertices could substantially impact the rate of cathode degradation [2]. In this work, the impact of LPL and UPL dwell time under different values of LPL on catalyst degradation is systematically investigated.In this regard, Kneel et al. [3] investigated the effect of exposure time to high potentials on degradation rate considering both symmetric and asymmetric (square wave cycles with a different dwell time at upper and lower voltage limits) square waves cycling between 0.6 and 0.9 V. They kept the cycle duration (sum of LPL and UPL dwell time) constant at 60 s while changing the LPL and UPL dwell time accordingly: 2 s-58 s, 30 s-30 s, and 58 s-2 s. As they observed greater degradation rate per cycle for longer dwell times at UPL, they concluded that the primary factor causing catalyst degradation is the dwell time at high potentials, rather than the cycle duration. Additionally, Young et al. [4] evaluated the impact of UPL dwell time when the LPL dwell time, instead of cycle duration, was kept constant at 30 s throughout the experiments. They varied the dwell time at high potentials (5, 20, 60, 300, and 600 s) during square wave voltage cycling between 0.6 and 1.4 V and found an increasing degradation per cycle with increasing dwell time at high potentials. However, at this high UPL (1.4 V), ECSA loss is not only caused by Pt dissolution but also by carbon corrosion. Indeed, when considering automotive applications, the upper potential is limited to the open circuit voltage (OCV), which is lower than 1.0 V during normal operation. Therefore, to ensure that the experiments are appropriate for these applications, in this work the degradation of the catalyst is studied under square wave voltage cycling between 0.6 to 0.95 V in a hydrogen/air atmosphere while keeping one of the dwell times fixed from one experiment to another. The LPL and UPL dwell times of the first three experiments are 3 s-3 s, 3 s-10 s, and 10 s-3 s, respectively. The ECSA loss is measured by cyclic voltammetry for each AST. The same set of experiments is then repeated for LPL of 0.8 V to examine the impact of complex interplay of the LPL and the dwell times on the ECSA degradation as the reduction rate of oxide layer in a VC-AST with a UPL near OCV (0.95 V) is expected to vary with different LPLs. These experiments could complete the previous findings in the literature by systematically changing potential limits and dwell times and therefore help better understand the underlying mechanism of Pt loss during load cycle operation. Acknowledgements This research was supported by the Natural Sciences and Engineering Research Council of Canada, Canada Research Chairs, and Simon Fraser University Community Trust Endowment Fund.

Theoretically Designed Cu10Sn3-Cu-SnOx as Three-Component Electrocatalyst for Efficient and Tunable CO2 Reduction to Syngas.

Electrocatalytic transformation of CO2 to various syngas compositions is an exceedingly attractive approach to carbon-neutral recycling. Meanwhile, the achievement of selectivity, stability, and tunability of product ratios using single-component electrocatalysts is challenging. Herein, the theoretically-assisted design of the triple-component nanocomposite electrocatalyst Cu10Sn3-Cu-SnOx that addresses this challenge is presented. It is shown that Cu10Sn3 is a valuable electrocatalyst for suitable CO2 reduction to CO, SnO2 for CO2 reduction to formate at large overpotentials, and that the Cu-SnO2 interface facilitates H2 evolution. Accordingly, the interaction between the three functional components affords tunable CO/H2 ratios, from 1:2 to 2:1, of the produced syngas by controlling the applied potentials and relative contents of functional components. The syngas generation is selective (Faradaic efficiency, FE = 100%) at relatively lower cathodic potentials, whereas formate is the only liquid product detected at relatively higher cathodic potentials. The theoretically guided design approach therefore provides a new opportunity to boost the selectivity and stability of CO2 reduction to tunable syngas.

Electroreductive Defluorination of Unsaturated PFAS by a Quaternary Ammonium Surfactant-Modified Cathode via Direct Cathodic Reduction.

Remediation of per- and polyfluoroalkyl substances (PFAS) in groundwater remains a technological challenge due to the trace concentrations of PFAS and the strength of their C-F bonds. This study investigated an electroreductive system with a quaternary ammonium surfactant-modified cathode for degrading (E)-perfluoro(4-methylpent-2-enoic acid) (PFMeUPA) at a low cathodic potential. A removal efficiency of 99.81% and defluorination efficiency of 78.67% were achieved under -1.6 V (vs Ag/AgCl) at the cathode modified by octadecyltrimethylammonium bromide (OTAB). The overall degradation procedure started with the adsorption of PFMeUPA onto the modified cathode. This adsorption process was promoted by hydrophobic and electrostatic interactions between the surfactants and PFMeUPA, of which the binding percentage, binding mode, and binding energy were determined via molecular dynamics (MD) simulations and density functional theory (DFT) calculations. The step-wise degradation pathway of PFMeUPA, including reductive defluorination and hydrogenation, was derived. Meanwhile, C-F bond breaking with direct electron transfer only was achieved for the first time in this study, which also showed that the C═C bond structure of PFAS facilitates the C-F cleavage. Overall, this study highlights the crucial role of quaternary ammonium surfactants in electron transfer and electrocatalytic activities in the electroreductive system and provides insights into novel remediation approaches on PFAS-contaminated groundwater.

Enhanced Nitrogen Reduction to Ammonia by Surface- and Defect-Engineered Co-catalyst-Modified Perovskite Catalysts under Ambient Conditions and Their Charge Carrier Dynamics.

An electrocatalytic nitrogen reduction reaction is considered a potential approach for green ammonia production─a zero-carbon fertilizer, fuel, and energy storage for renewable energy. To harness the synergistic properties of perovskites, the inherent dipole moment due to their non-centrosymmetric structure (that facilitates better charge separation), oxygen vacancies, and the presence of Ni metal sites that permit activation and reduction of N2 efficiently, the NiTiO3-based nanoelectrocatalysts have been synthesized. Further, these catalysts have been modified with ultra-small metal nanocrystal co-catalysts to form heterointerfaces that not only aid to improve the charge separation but also activate N2 and lower overpotential requirements. The appearance of peaks corresponding to (012), (104), (110), (11-3), (024), (11-6), (018), (027), and (300) confirms the formation of rhombohedral NiTiO3. The shift in the XRD peak corresponding to the (104) plane to a smaller 2θ value and peak shifting and widening of Raman spectra imply the lattice distortion that signifies the formation of Pd-NiTiO3 and Pt-NiTiO3 heterojunction electrocatalysts with the loadings of 0.4 and 0.3 wt % of Pd and Pt, respectively, as confirmed by ICP-OES analysis. The detailed XPS analysis reveals the presence of Pd (0), Pd (II), and Pt (0), Pt (II) in respective electrocatalysts. The appearance of XPS peaks at 528.7 and 531.1 eV suggests the presence of oxidative oxygen species (O2-/O-) and the presence of oxygen defects due to oxygen vacancy. The detailed nitrogen reduction (NRR) investigation exhibits a 5-fold enhancement in ammonia yield rate (∼14.28 μg h-1 mg-1 at -0.003 V vs RHE), a faradic efficiency of 27% (at 0.097 V vs RHE) for Pd-NiTiO3 electrocatalysts than that for bare NiTiO3 (3.08 μg h-1 mg-1), and 9-folds higher than that of the activity shown by the commercial TiO2 (P25) (1.52 μg h-1mg-1). The formation of ammonia was further confirmed by using isotopic nitrogen as the feeding gas. Furthermore, the highest NRR is observed at lower cathodic potential (-0.003 V vs RHE) in the case of the Pd-NiTiO3 electrocatalyst than that of the Pt-NiTiO3 electrocatalyst (-0.203 V vs RHE), implying significantly reduced overpotential requirement. Such enhanced NRR activity with lower overpotential requirement in the case of the Pd-NiTiO3 electrocatalyst is due to efficient charge separation as shown by the semicircle Nyquist plot, decreased photoluminescence emission intensity, shorter average lifetime (∼29 ns) of excitons, appropriate band bending, and improved activation of N2 by the oxygen vacancies and heterointerface formed between Pd nanocrystals and NiTiO3. Furthermore, no change is observed in the current density, after stabilization in the initial few seconds, even up to 2 h, which signifies that these electrocatalysts are stable. The structural and morphological integrity of the optimized catalyst remained even after the nitrogen reduction reactions, as revealed by no significant change observed in FESEM, elemental mapping, and EDS analysis.

Electrochemical degradation and mineralisation of organic dyes in aqueous nitrate solutions

Electrochemical treatment of organic matter for environmental remediation necessitates the development of cheap and robust electrodes that are chemically and structurally stable. To address this challenging requirement, we demonstrate a new electrochemical approach using a simple copper electrode under cathodic conditions to electrochemically generate reactive nitrosonium ions for the degradation of different classes of synthetic organic dyes. This could be achieved in an aqueous HNO3/KNO3 electrolyte at a relatively low cathodic potential of −0.5 V RHE at room temperature. UV–visible absorption spectroscopy, Raman spectroscopy, liquid chromatography – mass spectrometry and total organic carbon measurements revealed the rapid decolorisation and mineralisation of several dye types such as triarylmethane dyes (crystal violet, cresol red), an azo dye (methyl orange) as well as a sulfur containing thiazine dye (toluidine blue). The total organic carbon content of a 50 mg L−1 methyl orange solution was found to decrease by 83% after 1 h of electrolysis. Promisingly, locally sourced river and creek water samples spiked with 50 mg L−1 methyl orange were also successfully treated for up to 6 cycles at a simple Cu electrode, demonstrating potential for the remediation of polluted waterways.

Three-dimensional manganese cobaltate: a highly conductive electrocatalyst for paraoxon-ethyl detection.

The synthesis of manganese cobaltate (MnCo2O4) with the hybrid three-dimensional architecture has beendeveloped as an electrocatalyst for the electrochemical sensing of paraoxon-ethyl (PEL). The detailed physicochemical and structural characterization of MnCo2O4 is meticulously examined. The MnCo2O4-modified screen-printed carbon electrode (SPCE) exhibits good electrocatalytic activity for the reduction of PEL compared with the bare SPCE due to numerous unique properties. By profiting from these advantages, the proposed MnCo2O4/SPCE shows superior sensing performance toward the determination of PEL, including low cathodic peak potential (- 0.64V), wide detection range (0.015-435µM), low limit of detection (0.002µM), high detection sensitivity (2.30 µA µM-1cm-2), excellent selectivity, and good reproducibility. Notably, the electrochemical performance of the MnCo2O4-based electrocatalyst is superior to those previously reported in the literatures. The practical application of the MnCo2O4/SPCE is effectively assessed in the analysis offood and water samples with satisfied recoveries of 96.00-99.35%. The superior performance of the proposed MnCo2O4 electrocatalyst holds considerable potential for future development of electrochemical sensing platforms.

Chemical and Morphological Changes of Graphite Electrodes at Low Cathodic Potentials and Its Relevance to Li-Ion Batteries

Lithium-ion (Li-ion) batteries have become ubiquitous to modern-day electronics and electric vehicles. A detailed understanding regarding the reversible and irreversible nature of Li-ion electrode processes is a prerequisite to rationally delineate the factors affecting device performance and clarify degradation mechanisms. This includes, for instance, the role of electrode cracking and solid solid-electrolyte-interphase (SEI) formation which can contribute toward irreversible capacity loss. In terms of experimental approaches, aside from the high surface area electrodes used in practical systems, one powerful approach is to incorporate the study of well-defined electrodes and surface science techniques.1 Herein, we employ highly oriented pyrolytic graphite (HOPG) as a well-defined model anode in Li-ion batteries and reveal the chemical and morphological changes at low cathodic potentials prior to the potentials of bulk SEI formation.2 To achieve this, we employ the use of X-ray photoelectron spectroscopy (XPS) and ultrahigh vacuum scanning tunneling microscopy (UHV-STM). We utilize a so-called UHV-EC setup to provide a snapshot-like analysis of the electrode surface without the involvement of electrode washing or exposure to air.Upon cathodic polarization at ca. 1.75V (Figure 1), STM imaging shows the onset and occurrence of graphite exfoliation which can originate from the intercalation of solvated Li+ ions. Meanwhile, XPS shows a minimal amount of residual electrolyte along with the observation of LiF indicating the decomposition of the Li salt (LiPF6). The future extensions of our methodology and additional details will be provided at the presentation. Figure 1. (a) Cathodic linear sweep voltammogram in 1.1 M LiPF6 EC/DMC. Following polarization at ca. 1.75 V (b) STM imaging, and (c) XPS F 1s and Li 1s spectra.

Degradation rate at the Solid–Solid interface of sulfide-based solid Electrolyte–Cathode active material

All-solid-state lithium-ion batteries with sulfide-based solid electrolytes (SEs) are leading candidates for next-generation batteries because of the high lithium-ion conductivity and thermoplasticity of the SE. However, the cathode slowly degrades in harsh environments. Therefore, the degradation rate of the cathode is analyzed in this study using the “root law” for the half-cell. An argyrodite-type sulfide SE, LiNi0·5Co0·2Mn0·3O2 with LiNbO3 coating as a working electrode, and In–Li alloy as a counter electrode is used. The floating tests help determine the degradation under various potentials (4.25–4.55 V vs. Li/Li+) and temperatures (45–100 °C). The “root law”, explained by the decomposition layer growth on active material, is applicable under all durability test conditions. The results of the secondary-ion mass spectrometry showed that the increasing tendency of the normalized POx− fragment changes depending on the cathode potential. X-ray photoelectron spectroscopy revealed that the electrochemical decomposition of the SE is dominant at low cathode potentials, and the LiNbO3 coating is involved in a side reaction, which produces decomposed species such as phosphates and sulfates at higher potentials. These two side reactions control the cell performance of the cathode.

Response of Methanogen Communities to the Elevation of Cathode Potentials in Bioelectrochemical Reactors Amended with Magnetite.

Electromethanogenesis refers to the process whereby methanogens utilize current for the reduction of CO2 to CH4. Setting low cathode potentials is essential for this process. In this study, we tested if magnetite, an iron oxide mineral widespread in the environment, can facilitate the adaptation of methanogen communities to the elevation of cathode potentials in electrochemical reactors. Two-chamber electrochemical reactors were constructed with inoculants obtained from paddy field soil. We elevated cathode potentials stepwise from the initial -0.6 V versus the standard hydrogen electrode (SHE) to -0.5 V and then to -0.4 V over the 130 days of acclimation. Only weak current consumption and CH4 production were observed in the bioreactors without magnetite. However, significant current consumption and CH4 production were recorded in the magnetite bioreactors. The robustness of electroactivity of the magnetite bioreactors was not affected by the elevation of cathode potentials from -0.6 V to -0.4 V. However, the current consumption and CH4 production were halted in the bioreactors without magnetite when the cathode potentials were elevated to -0.4 V. Methanogens related to Methanospirillum were enriched on the cathode surfaces of magnetite bioreactors at -0.4 V, while Methanosarcina relatively dominated in the bioreactors without magnetite. Methanobacterium also increased in the magnetite bioreactors but stayed off electrodes at -0.4 V. Apparently, the magnetite greatly facilitates the development of biocathodes, and it appears that with the aid of magnetite, Methanospirillum spp. can adapt to the high cathode potentials, performing efficient electromethanogenesis. IMPORTANCE Converting CO2 to CH4 through bioelectrochemistry is a promising approach to the development of green energy biotechnology. This process, however, requires low cathode potentials, which entails a cost. In this study, we tested if magnetite, a conductive iron mineral, can facilitate the adaptation of methanogens to the elevation of cathode potentials. In two-chamber reactors constructed by using inoculants obtained from paddy field soil, biocathodes developed robustly in the presence of magnetite, whereas only weak activities in CH4 production and current consumption were observed in the bioreactors without magnetite. The elevation of cathode potentials did not affect the robustness of electroactivity of the magnetite bioreactors over the 130 days of acclimation. Methanospirillum strains were identified as the key methanogens associated with the cathode surfaces during the operation at high potentials. The findings reported in this study shed new light on the adaptation of methanogen communities to the elevated cathode potentials in the presence of magnetite.

Research on the stress corrosion and cathodic protection of API X80 steel under AC stray current interference

Purpose The corrosion of buried steel pipelines is becoming more serious because of stress corrosion, stray current corrosion and other reasons. This paper aims to study the various alternating current (AC) interference densities on the stress corrosion cracking behaviors of X80 steel samples under cathodic protection (CP) in the simulated soil electrolyte environment by using an electrochemical method. Design/methodology/approach The change of corrosion rate and surface morphology of the X80 steel samples at various AC current densities from 0 to 150 A/m2 or CP potential between −750 and −1,200 mV in the soil-simulating environment was revealed by the electrochemical methods and slow strain rate testing methods. Findings The results revealed that with the increase of interference density, the corrosion potential of the X80 steel samples shifted to the negative side, and the corrosion pitting was observed on the surface of the sample, this may cause a danger of energy leak. Moreover, the corrosion rate was found to follow a corresponding change with the stress–strain curve. Besides, with the introduction of the CP system, the corrosion rate of the X80 steel working electrode decreased at a low cathodic potential, while showed an opposite behavior at high cathodic potential. In this study, the correlation between AC stray current, cathodic potential and stress was established, which is beneficial to the protection of oil and gas pipeline. Originality/value Investigation results are of benefit to provide a new CP strategy under the interference of AC stray current corrosion and stress corrosion to reduce the corrosion rate of buried pipelines and improve the safety of pipeline transportation.

Polymethylolacrylamide/AuNPs Nanocomposites: Electrochemical Synthesis and Functional Characteristics.

In this study the advantages of the electrochemical approach to the formation of polymer/metal nanoparticle composites are demonstrated. The method enables one to simplify the multistage processes of traditional technologies for the production of such materials through combining all intermediate processes in one stage and reducing the total formation time to 3–10 min. The possibility of a single-stage formation of a polymethylolacrylamide/AuNPs composite through including AuNPs into an electrically non-conducting polymethylolacrylamide film (carrier) formed by electropolymerization through potentiostatic electrolysis is also demonstrated for the first time. It is established that the addition of tetrachloroauric acid (HAuCl4·4H2O) into a monomeric composition containing acrylamide, formaldehyde, N,N′-methylene-bis-acrylamide, zinc chloride, and H2O results in simultaneous electrochemical initiation of polymerization with the formation of a polymer film on the cathode, electrolytic reduction of gold ions to Au0, and immobilization of AuNPs particles into the growing polymer matrix. It was found that the formation of the PMAA / AuNPs composite is energetically more favorable than the synthesis of the main PMAA film, since it proceeds at a lower cathodic potential. The inclusion of AuNPs into the polymethylolacrylamide film was confirmed visually, as well as by X-ray phase analysis, small-angle X-ray scattering, microscopy, and element analysis. The gold content in the composite increases along with the increase of the concentration of HAuCl4 in the electrolyte. The radius of the AuNPs particles was found to range between 3 and 7 nm. The AuNPs particles are spherical in shape and can combine into larger clusters containing up to 10 or more particles. The dynamics of formation, structure, and morphology of the polymethylolacrylamide/AuNPs composite were investigated. It was revealed that gold nanoparticles are mainly concentrated in the near-electrode and near-solution layers of the composite. We found that the composite has electrocatalytic activity. The possibility of its use as a sensor for hydrogen peroxide is demonstrated.

Effect of sodium diisopropylnaphthalene sulfonate on Zn-Mn alloys electrodeposition

A novel additive sodium diisopropylnaphthalene sulfonate (SDIPNS) was investigated in Zn-Mn electrodeposition on steel from chloride bath. To this end, cyclic voltammetry was performed in absence and presence of SDIPNS to study different electrochemical systems. Electrochemical data showed that SDIPNS increases Zn deposition overpotential, resulting from strong adsorption of SDIPNS molecules on the cathode surface. The effects of scan rate, switching potentials on the electrochemical behavior of Zn-Mn co-deposition were investigated. The variation of scan rate reveals that the Zn-Mn co-deposition is associated with charge transfer coupled with the mass transfer. SDIPNS concentration was investigated with regard to the Mn content in the final coatings. The chemical composition result showed that Mn-rich deposits, containing 20 wt.% of Mn, are successfully deposited under low cathodic potential (E = − 1.52 V vs. Ag/AgCl). The surface characterization of Zn-Mn coatings was explored by scanning electron microscopy (SEM). The presence of SDIPNS in the electrolytic bath permits to obtain compact, well adherent, and fined grain Mn-rich alloys.

Electrochemical calcareous deposition in seawater. A review

Pollution and climate change issues are calling for advanced techniques of pollutant sequestration to decrease toxicity, of coral and costal remediation, and of carbon sequestration to decrease atmospheric CO2 levels. For that, calcareous deposition appears as an overlooked, but potentially efficient technique. The calcareous deposit is a well-known precipitation by-product of cathodic protection in seawater. The deposit is made of a mixture of CaCO3 and Mg(OH)2. A calcareous deposit is formed electrochemically when a metal connected to an electrical power source is immersed in seawater. So far, electrochemical calcareous deposition has seldomly found applications, except for speedup of coral growth, prevention of shore erosion, reinforcement of artificial marine structures and remediation of polluted seawater. Here, we review the principles and mechanisms of electrochemical calcareous deposition. The growth, composition and mechanical properties of calcareous deposits are controlled by several factors such as 1) the impact of electrochemical parameters on the Ca/Mg ratio. For instance, CaCO3 formation is favoured at low cathodic potentials and low currents, whereas Mg(OH)2 precipitates preferentially at high cathodic potentials and high applied current; 2) the nature of the metallic electrode: although lime could be deposited onto any metallic surface at a fixed potential, electrochemical reactions and deposit composition are controlled by the metal nature. Moreover, the state of the electrode surface, e.g. with the presence of oxides or biofilms, modifies the kinetics of deposit formation; and 3) electrolyte composition, pH, temperature and stirring. For instance, in seawater, Ca2+ and Mg2+ concentrations control the allotropic variety of CaCO3 formed, e.g. Mg2+ inhibits the formation of calcite and vaterite. Hydrodynamic conditions near the electrode also influence the deposit composition since conditions regulate the mass transport at the electrode–solution interface. Below 10 °C, aragonite is not formed and the deposit stays thin. In the first stage of the deposit formation, an Mg-based compound is formed, followed by the growth of a Ca-based compound with time.

Poisoning effects of sulfur dioxide in an air stream on spatial proton exchange membrane fuel cell performance

The paper examines spatial and temporal proton exchange membrane fuel cell (PEMFC) performance under exposure to SO2 in an air stream at low and high operating currents. Cathode poisoning by 2 ppm SO2 resulted in cell voltage losses of 60 and 295 mV for overall cell currents of 0.2 and 1.0 A cm−2, respectively. The voltage drop was accompanied by localized current redistributions, which depend on the operating current hold. The observed spatial PEMFC behavior is attributed to different electrochemical reactions of adsorbed SO2 occurring at high and low cathode potentials. SO2 is mainly oxidized at potentials corresponding to 0.2 A cm−2, while reduction to zero-valent sulfur takes place at 1.0 A cm−2, as confirmed by XPS. Full self-recovery was not observed for either operating current hold, and only potential cycling recovered the performances. Moreover, comparison of the initial and after-poisoning electrochemical PEMFC parameters revealed that SO2 exposure led to a decrease in Pt electrochemical surface area due to growth of the Pt particle size and caused final performance losses of 20–30 and 25–50 mV for low and high current operations. A physics-based mathematical model was successfully developed and applied for analysis of SO2 effects on PEMFC performance.

Influence of current density on the adhesion of seedless electrodeposited copper layers on silicon

Electrodeposition of metals directly on non-metal substrates without any seed layer reduces process steps; however, adhesion of the electrodeposited layer is a challenge. In this work, the influence of current density during seedless electroplating on the adhesion of Cu layers on Si substrates was investigated. Cu was electrodeposited on phosphorus-doped Si samples having different orientations in two stages. During the first stage, higher current densities were used for a few minutes to reach instantaneous nucleation and maximize the number of Cu islands on the substrate. The second stage had the goal of growing the nuclei previously formed. Therefore, lower current densities were used to create progressive nucleation. Adhesion values of Cu layers on Si were derived from scratch tests and tensile measurements. Higher adhesion was obtained either at higher current densities or at lower cathodic potentials at the beginning of potentiostatic or galvanostatic processes. To study the influence of hydrogen evolution on the adhesion of seedless electrodeposited Cu on Si, the transition time which indicates the moment when transferred charges are used to create hydrogen at the cathode, was determined experimentally. The transition time shows a strong dependence on current density. Therefore, control and optimization of adhesion by an appropriate choice of current densities within the two-stage process is possible.

Highly conductive Faradaic artificial muscle based on nanostructured polypyrrole-bis(trifluoromethylsulfonyl)imide synthesized onto electrospun polyurethane nanofibers

Conductive polymer-based artificial muscles have attracted enormous interest in various fields due to their unique properties such as electroactivity and biocompatibility. In this study, a bending artificial muscle was fabricated by chemical synthesis of polypyrrole (PPy) onto nanofibrous polyurethane (PU) structures using bis(trifluoromethylsulfonyl)imide (TFSI) anions as dopant. First, PU nanofibers were prepared by electrospinning and then coated with a layer of polypyrrole via in-situ polymerization to produce core-shell nanofibers of PU/PPy-TFSI. The actuation performance of the PU/PPy-TFSI nanofibers in 1M LiClO4 aqueous solution was analyzed based on their cyclic voltammetric, coulo-voltammetric, dynamo-voltammetric, coulo-dynamic and chronopotentiometric responses. FESEM images showed that the surface of all PU nanofibers has been coated with a uniform layer of PPy in the form of semi-spherical nanostructures. Doping using TFSI anions resulted in an excellent electrical conductivity in nanofibers (314.55 S/cm). The examination of electrochemomechanical properties showed that for the produced electroactive nanofibers, reversible oxidation and reduction processes occur under the potential cycle between -0.8 V and 0.5 V. It was demonstrated that during the oxidation and reduction reactions, the dominant volume variation mechanism can be best explained based on the exchange of perchlorate anions, which yields a reversible angular displacement of 160°. However, a weak mechanism involving the absorption of small lithium cations was also observed at low cathodic potentials. The results demonstrated that the produced nanofibrous artificial muscle could be considered as a Faradaic motor, as its bending angle and velocity are completely controlled by the consumed charge and the applied current, respectively.