Double Electrode System Research Articles

Xylan derived carbon sphere/graphene composite film with low resistance for supercapacitor electrode

Reduced graphene oxide (rGO) films suffer from low capacitance for inner unreduced oxygen functional groups, restacking of sheets and high contact resistance. Herein, carbon spheres derived from renewable xylan were added to graphene oxide with large sheet area to fabricate film by gelation and filtration, followed by in situ reduction for high-performance flexible supercapacitor. rGO film with transverse size about 13 μm showed a good specific capacitance of 967 mF/cm2 at a scanning rate of 5 mV/s and increased to 1786 mF/cm2 by in situ reducing its inner part, which generally remained oxidized due to outer hindering from hydrophobic graphene. Then, by hydrothermal carbonization of xylan and activation with KOH, activated carbon sphere (aXCS) was prepared, which had a diameter of 150–200 nm and a specific capacitance of 270 F/g. The aXCS acted as spacer and connector to avoid restacking of graphene sheets and decrease interlayer contact resistance, resulting 94% increase in capacitance performance from rGO film to aXCS/rGO film. Therefore, combined in situ reduction and enhancement through compositing aXCS, the final film (aXCS/rGO-AA) showed a boosted specific capacitance of 755 mF/cm2 at 1 mA/cm2 in double electrode system, power density of 22.5–2250 mW/cm2, and energy density of 11.88–25.2 mWh/cm2. Meanwhile, aXCS/rGO-AA had outstanding cycling stability that its specific capacitance maintained 108.7% after 10,000 cycles of charge–discharge, showing promising potential in wearable and portable electronics.Graphical abstract

Improved supercapacitors and water splitting performances of Anderson-type manganese(III)-polyoxomolybdate through assembly with Zn-MOF in a host–guest structure

Enhancing performance through the combination of polyoxometalates (POMs) clusters with metal–organic frameworks (MOFs) that contain various transition metals is a challenging task. In this study, we synthesized a polyoxometalate-based metal–organic framework (POMOF) named HRBNU-5 using a solvothermal method. HRBNU-5 is composed of Zn[N(C4H9)4][MnMo6O18{(OCH2)3CNH2}2]@Zn3(C9H3O6)2·6C3H7NO, which includes two components: Zn[N(C4H9)4][MnMo6O18{(OCH2)3CNH2}2]·3C3H7NO ({Zn[MnMo6]}) and Zn3(C9H3O6)2·3C3H7NO (Zn-BTC). Structural characterization confirmed the host–guest structure, with Zn-BTC encapsulating {Zn[MnMo6]}. In a three-electrode system, HRBNU-5 exhibited a specific capacitance of 851.3 F g−1 at a current density of 1 A/g and retained high stability (97.2 %) after 5000 cycles. Additionally, HRBNU-5 performed well in aqueous-symmetric/asymmetric supercapacitors (SSC/ASC) in terms of energy density and power density in a double-electrode system. Moreover, it demonstrated excellent catalytic performance in a 1.0 M KOH solution, with low overpotentials and Tafel slopes for hydrogen and oxygen evolution reactions: 177.1 mV (η10 HER), 126.9 mV dec–1 and 370.3 mV (η50 OER), 36.3 mV dec–1, respectively, surpassing its precursors and most reported studies. HRBNU-5′s positive performance is attributed to its host–guest structure, high electron-transfer conductivity, and porous structure that enhances efficient mass transport. This work inspires the design of Anderson-type POMOF electrode materials with multiple active sites and a well-defined structure.

An enzyme-free glucose sensing device based on TiO2 nanorod array photoelectric catalysis

A simple one-step hydrothermal method is used to prepare an enzyme-free photoelectric combined glucose sensor based on TiO2NRs/FTO with low cost, sample two-electrode, and excellent detection. Under 380 nm light (0.5 mW cm−2) irradiation and a positive voltage, holes are accumulated on TiO2NRs surface, catalyzing glucose and forming a photocurrent without the need for an enzyme, such as Glucose oxidase (GOx). The designed sensor exhibits high sensitivity (about 0.96 μA mM−1 cm−2, without GOx) and excellent linear relationship in the glucose concentration range of 5–15 mML−1. The prepared glucose sensor performs better with a sensitivity of 1.48 μA mM−1 cm−2 when a certain amount of GOx is mixed in the detected solution. In addition, the sensor has excellent anti-interference resistance to non-reducing chitosan and reducing ascorbic acid with short response time (less than 5 s); thus, it can be used in quick detection with a double electrode system. This sensing device has the advantages of simple fabrication, easy storage, and reusability; therefore, it can be very promising in the portable and rapid monitoring of human blood glucose levels.

Nanomaterial with Core–Shell Structure Composed of {P2W18O62} and Cobalt Homobenzotrizoate for Supercapacitors and H2O2-Sensing Applications

Designing and preparing dual-functional Dawson-type polyoxometalate-based metal-organic framework (POMOF) energy storage materials is challenging. Here, the Dawson-type POMOF nanomaterial with the molecular formula CoK4[P2W18O62]@Co3(btc)2 (abbreviated as {P2W18}@Co-BTC, H3btc = 1,3,5-benzylcarboxylic acid) was prepared using a solid-phase grinding method. XRD, SEM, TEM et al. analyses prove that this nanomaterial has a core-shell structure of Co-BTC wrapping around the {P2W18}. In the three-electrode system, it was found that {P2W18}@Co-BTC has the best supercapacitance performance, with a specific capacitance of 490.7 F g-1 (1 A g-1) and good stability, compared to nanomaterials synthesized with different feedstock ratios and two precursors. In the symmetrical double-electrode system, both the power density (800.00 W kg-1) and the energy density (11.36 Wh kg-1) are greater. In addition, as the electrode material for the H2O2 sensor, {P2W18}@Co-BTC also exhibits a better H2O2-sensing performance, such as a wide linear range (1.9 μM-1.67 mM), low detection limit (0.633 μM), high selectivity, stability (92.4%) and high recovery for the detection of H2O2 in human serum samples. This study provides a new strategy for the development of Dawson-type POMOF nanomaterial compounds.

The supercapacitor and photocatalytic supermolecule materials constructed by 4’4-pyridine and {PMo12O40}

A supramolecular compound with the molecular formula (Hbipy)3[PMo12O40]·3H2O(bipy ​= ​4,4-bipyridyl) (1) was prepared and characterized by one-step hydrothermal method. Single-crystal structure analysis shows, a cluster consists of 4,4-Hbipy bonded to four [PMo12O40]3- anions by hydrogen bonds, which forms two distinct two-dimensional structures through supramolecular interactions, then further extended to 4,4,12-connected {427·638·8}{45·6}{46}2 three-dimensional topology by π-π stacking and hydrogen bonds. The supercapacitor performance of compound 1 under different collector conditions was studied. In the three-electrode system, capacitance of nickel foam (263.9 ​F ​g-1, 1 ​A ​g-1) is higher than that of carbon cloth (60 ​F ​g-1, 1 ​A ​g-1). The energy density (5.34 ​Wh kg-1) and power density (399.67 ​W ​kg-1) of compound 1 are better in the nickel foam symmetric double-electrode system. Moreover, the compound 1 has a good photocatalytic degradation effect on methylene blue (MB) (95.8%) and rhodamine B (RhB) (93.54%).

Direct recovery of scrapped LiFePO4 by a green and low-cost electrochemical re-lithiation method

This study proposes a novel electrochemical method for recycling LFP based on a Zn//S-LFP double-electrode system, providing green and low-cost recycling technology for future industrial applications.

Metallized Ni(OH)2·NiO/FeOOH on Ni Foam as a Highly Effective Water Oxidation Catalyst Prepared by Surface Treatment: Oxidation–Corrosion Equilibrium

The surface treatment method has a great influence on the structure and properties of applied materials for interface catalysis. In this study, we prepare Ni(OH)2·NiO/FeOOH by surface treatment in acid solution using oxidation–corrosion equilibrium (OCE). For comparison, we also treat Ni foam with the same process in alkaline solution. Ni(OH)2·NiO/FeOOH can achieve steady morphology and metallization by OCE and exhibits superior catalytic activity as a water oxidation catalyst. Ni(OH)2·NiO/FeOOH(OCE) needs only 232 mV to reach a current density of 10 mA cm–2, while it is 254 mV for a reference IrO2/Ni foam. The mechanism study shows that the small charge transfer resistance (2.04 Ω cm2) is favorable for the rapid interface electron exchange between Ni(OH)2·NiO/FeOOH(OCE) and reactive species in water oxidation. In addition, the results of X-ray photoelectron spectroscopy and series impedance show that the catalyst is metallic in property in virtue of the exposed metal Ni in Ni(OH)2·NiO/FeOOH(OCE). The volume ratio of hydrogen to oxygen (around 2:1) indicates overall water splitting by the double-electrode system. When the volume ratio of hydrogen to oxygen is 2:1, the Faraday efficiency of H2 or O2 is close to 100%. Ni(OH)2·NiO/FeOOH(OCE) exhibits good stability for 1 month. The research results provide a feasible approach for finding low-cost metallized catalysts to replace noble metals as water oxidation catalysts and improving the efficiency of water splitting.

Defect-engineered ultrathin NiMoO4 nanomeshes as efficient and stable electrocatalysts for overall water splitting

Defect-rich metal-based nanomeshes have been regarded as potential effective catalysts for electrocatalytic water splitting, in which nanopores are beneficial to increase active sites and enhance the mass transfer. However, facile synthesis of metal-based nanomeshes still remains a great challenge. Herein, we report the cost-efficient ultrathin nickel molybdenum nanomeshes (NiMoO4) for overall water splitting. The NiMoO4 possesses outstanding oxygen evolution reaction property (239 mV@10 mA cm−2), together with an exceptional cycling stability. Notably, phosphorus (P)-doping endows the NiMoO4 nanomeshes a superior hydrogen evolution reaction property (144 mV@−10 mA cm−2). We also prepare a double electrode system with NiMoO4 and P-doped NiMoO4, and evaluate the performance of overall water splitting (1.68 V @10 mA cm−2). The key point of the processing route developed here is the synergistic effect between defect engineering and element doping, which provide a guiding insight for the development of novel catalysts for their practical applications.

High-density Ag nanosheets for selective electrochemical CO2 reduction to CO

To increase the specific surface area, high-density (i.e. number per unit area) Ag nanosheets (ANS) with large electrochemically active surface area and rich edge active sites over Ag plates were synthesized via a facile electrodeposition approach in a double electrode system at a constant current of −1 mA for 1800 s. By adjusting the concentration of H3BO3 (0.5 M, 0.1 M and 0.05 M), which is used to control the growth direction of ANS, ANS-20, -50, -350 were obtained with varying thickness of 20 nm, 50 nm, and 350 nm, respectively. Notably, ANS-20 showed a remarkable current density of −6.48 mA cm−2 at −0.9 V versus the reversible hydrogen electrode (RHE), which is almost 1.6 and 2.4 times as high as those of ANS-50 and -350, respectively. Furthermore, ANS-20 exhibits the best CO selectivity of 91.2% at −0.8 V versus RHE, while the other two give 84.6% and 77.9% at the same potential. The excellent performance of ANS-20 is attributed to its rich edge active sites and large electrochemically active surface area (ECSA).

Ultrathin and dense Ag nanosheets synthesis under suppressed face (111) growth and surface diffusion

Ultrathin and dense Ag nanosheets (ANS) with large electrochemically active surface area and rich edge active sites over Ag foils are synthesized via a facile electrodeposition approach in a double electrode system. By adjusting the concentration of H3BO3 and changing deposition temperature, ANS with varying thickness are fabricated. Interestingly, ANS gradually become thinner with H3BO3 concentration increasing, as BO33- ions preferentially adsorb on the Ag (111) faces, thereby inhibit the growth of Ag on the (111) faces. Furthermore, the morphologies and dimensions of ANS are also found to strongly depend on the deposition temperature. Thinner and denser ANS are more easily obtained at low deposition temperature as it can suppress the surface diffusion of Ag atoms, while when the deposition temperature is high, thinner and denser ANS can only be obtained at high H3BO3 concentration. Especially, ANS fabricated with 0.5 M H3BO3 at 0 °C (ANS-0.5M-0°C) with an ultrathin thickness of about 11 nm exhibits a remarkable CO Faradaic efficiency of 97.11% and the total current density of −11.50 mA cm−2 at −0.9 V vs. the reversible hydrogen electrode towards CO2 electroreduction.

Characteristics of Impulse Arc Discharge in the Circuit of a Powerful Capacitive Energy Storage Device

Within the framework of the engineering approach and channel model of the electric arc, a new variant, impulse air arc discharge between metal (graphite) electrodes of an air double-electrode system (DES), which is part of the heavy-current discharge circuit of a powerful high-voltage capacitive energy storage (CES), was investigated. The amplitude–time parameters (ATPs) formed by the storage device of the current aperiodic pulse in the plasma channel of the air arc discharge corresponded to the slow current C-component of the artificial lighting intended for testing the elements of aircraft for the electrothermal lighting resistance. With respect to the rated ATP of the discharge current, the calculated ratios were obtained, in the plasma channel of the pulse electrical arc in an air DES, for determination of such main characteristics as the equivalent resistance, the released thermal energy, the maximum intensity of the longitudinal electric field, the linear power of thermal losses, the channel current density and the maximum electronic temperature. Distinctive features and general properties of pulse arc discharge in the air DES as compared with heavy-current pulse spark-discharge in similar DES were revealed. The offered ratios allow specifying the energy balance in the CE discharge circuit. The results of the approximate calculations proved the efficiency of the calculated ratios.

Tuning Ni-Foam into NiOOH/FeOOH Heterostructures toward Superior Water Oxidation Catalyst via Three-Step Strategy.

Splitting of water into hydrogen and oxygen has become a strategic research topic. In the two semi-reactions of water splitting, water oxidation is preferred to the four-electron-transfer process with a higher overpotential (η) and is the decisive step in water splitting. Therefore, efficient water oxidation catalysts must be developed. IrOx and RuOx catalysts are currently the most efficient catalysts in water oxidation. However, the limited reserve and high prices of precious metals, such as Ir and Ru, limit future large-scale industrial production of water oxidation catalysts. In this study, we tune inert Ni-foam into highly active NiOOH/FeOOH heterostructures as water oxidation catalysts via three-step strategy (surface acid-treating, electroplating, and electrooxidation). NiOOH/FeOOH heterostructures as water oxidation catalysts only require η of 257 mV to reach a current density of 10 mA cm–2, which is superior to that of IrO2/Ni-foam (280 mV). The high electrochemically active surface area (72.50 cm2) and roughness factor demonstrate abundant interfaces in NiOOH/FeOOH heterostructures, thus accelerating water oxidation activity. The small value (4.8 Ω cm2) of charge transfer resistance (Rct) indicate that fast electronic exchange occurs between NiOOH/FeOOH heterostructures catalyst and reaction of water oxidation. Hydrogen-to-oxygen volume ratios (approximately 2:1) indicate an almost overall water splitting by the double-electrode system. Faraday efficiency of H2 or O2 is close to 90% at 2:1 hydrogen-to-oxygen volume ratio. NiOOH/FeOOH heterostructures exhibit good stability. The results provide significance in fundamental research and practical applications in solar water splitting, artificial photoelectrochemical cells, and electrocatalysts.

APPROXIMATE CALCULATION OF ACTIVE RESISTANCE AND TEMPERATURE OF THE PULSE ELECTRIC ARC CHANNEL IN A HIGH-CURRENT DISCHARGE CIRCUIT OF A POWERFUL HIGH-VOLTAGE CAPACITOR ENERGY STORAGE

Purpose. To obtain calculation correlations for active resistance Rce and maximal temperature Tme of plasma channel of pulse electric arc in the air double-electrode system (DES) with metal (graphite) electrodes, and also practical approbation of the obtained correlations for Rce and Tme in the conditions of high-voltage laboratory on the powerful capacity energy storage (CES) of electric setting, intended for reproducing on the electric loading of protracted C- component of current of artificial lightning with the USA rationed on normative documents by amplitude-temporal parameters (ATP). Methodology. Electrophysics bases of high-voltage impulse technique, scientific and technical bases of development and creation of high-voltage high-current impulse electrical equipment, including powerful CES, and also measuring methods in discharge circuits of powerful high-voltage CES of pulse currents of millisecond temporal range. Results. On the basis of engineering approach the new results of approximate calculation of values of Rce and Tme are resulted in the plasma channel of pulse electric arc discharge in air DES of atmospheric pressure with metallic (graphite) electrodes. Practical approbation of results of calculation of values of Rce and Tme is executed as it applies to air DES, to connected in a discharge circuit of powerful high-voltage CES with protracted C- of component current of artificial lightning, characterized rationed ATP. It is shown that calculation of numeral value Rce approximately in 100 times exceeds the proper value of active resistance for the plasma channel of impulsive spark of electric discharge in air DES other things being equal, and a calculation of numeral value Tme well corresponds with the known thermodynamics information for classic electric arc in air DES of atmospheric pressure with graphite electrodes. Originality. New engineering approach is developed for the approximate calculation of values of Rce and Tme in electron-ion plasma of channel of pulse electric arc, arising in air DES of high-current discharge circuit of powerful high-voltage CES of proof-of-concept of electric setting of the technological setting. A formula is first obtained for the approximate calculation of equivalent active resistance of Rce of channel of pulse electric arc in air DES, remaining unchanging in the process of high-current discharge on RL- load of indicated CES. Practical value. Drawing on the got calculation results for the values of Rce and Tme in high-voltage impulse technique provides the rational choice of own electric parameters and construction elements of basic devices of powerful high-voltage CES of technological of electric setting, and also account of influence of electrical engineering descriptions of air DES on electromagnetic processes, taking place in the high-current discharge circuit of indicated CES with protracted C- of component current of artificial lightning.

Double electrode systems with microelectrode arrays for electrochemical measurements

AbstractMicroelectrode arrays-based double electrode systems possess the property of diffusion layer overlapping between the two sets of electrodes. They have received increased attention in recent years in the field of electrochemistry and electroanalytical chemistry. This review introduces the fabrication, characterization, and applications of microelectrode arrays-based double electrode systems. The progress of photolithography enables and benefits microfabrication of the electrode systems with various geometries. As an essential step before electrochemical applications, various characterization methods are addressed to monitor the quality of the fabricated electrodes. Following that, applications as electrochemical sensors in generator-collector mode are discussed. Then, electrochemical sensors in bipolar mode, an interesting phenomenon existing in double electrode systems, are also introduced. Finally, applications of double electrode systems to the measurement of fundamentally electrochemical parameters are demonstrated.

In-Situ Monitoring of Platinum Dissolution under Potential Cycling by a Channel Flow Double Electrode

Submonolayer dissolution of platinum (Pt) nanoparticles under potential cycling is specified by a channel flow double electrode system. Dissolution of Pt2+ starts at 0.6 V (vs. standard hydrogen electrode) in an anodic scan. The amount of dissolved Pt2+ below 1.0 V was calculated using collector current (IC) and was confirmed by ex-situ inductively coupled plasma mass spectrometry. The amount of Pt2+ and Pt4+ dissolved in different potential regions during potential cycling was quantified by IC for the first time. A mechanism of Pt dissolution under potential cycling in 0.5 M H2SO4 was proposed, and an in-situ system capable of quantitatively monitoring submonolayer dissolution of Pt2+ and Pt4+ was established.

Generator-collector double electrode systems: A review

A variety of generator-collector systems are reviewed, from the original rotating ring-disc electrodes developed in the 1950s, to very recent developments using new geometries and microelectrodes. An overview of both theoretical and experimental aspects are given, and the power of these double electrode systems in analytical electrochemistry is illustrated with a range of applications.

Channel-Flow Double-Electrode Study on the Dissolution and Deposition Potentials of Platinum under Potential Cycles

A channel-flow double-electrode system has been employed to determine the potential regions of Pt dissolution and redeposition during a cyclic voltammetry (CV) measurement in 0.5 M solution at . The double-electrode system consists of a Pt plate as a working electrode (WE) placed upstream and a Au plate as a collector electrode (CE) placed downstream with a separation gap of 0.1 mm. Pt ions dissolved at the WE during CV have been detected at the CE by employing an appropriate reduction potential and have been analyzed by using an electron probe microanalyzer (EPMA). The EPMA results show that the deposition of Pt from hydrated Pt ions occurs below 0.60 V vs the standard hydrogen electrode. When CV is carried out between 0.0 and 1.4 or 1.6 V, dissolution of Pt occurs during both the anodic and cathodic scans of the CV. When CV is carried out between 0.0 V and an upper potential limit of 1.2 V, the dissolution of Pt could be observed only in the anodic scan. The dissolution mechanism of Pt during CV is proposed.

Modelling homogeneous kinetics in the double channel electrode

Concentration profiles of electrochemically generated species are simulated in a channel flow cell containing two electrodes, where a species produced upstream at the generator electrode is detected downstream by the collector electrode. The model is extended for simulation of the currents produced at each electrode when a homogeneous reaction takes place involving the species produced at the generator. For specific cell dimensions and homogeneous mechanism there is a maximum rate constant for the homogeneous reaction that can be measured using the double electrode system, which is a function of the flow rate, the cell geometry and the relative concentrations of the species initially present. The results presented function as a guide to selecting suitable cell geometries and experimental parameters in order to measure homogeneous kinetics using the double channel electrode.

Spinal cord stimulation (SCS) using an 8-pole electrode and double-electrode system as minimally invasive therapy of the post-discotomy and post-fusion syndrome--prospective study results in 34 patients

Therapy of a pronounced post-discotomy (PDS) and post-fusion syndrome (PFS) is often unsatisfactory because of the complexity and multifactorial pain genesis. If surgical interventions cannot promise relief and if the entire interdisciplinary spectrum of conservative treatment measures is inadequate, the area of neuromodulative procedures offers spinal cord stimulation (SCS). The objective of this study was to examine the therapeutic possibilities of SCS using an 8-pole electrode and double electrode system in PDS and PFS with extensive back-leg pain areas. An appropriate SCS system was implanted in 34 patients with PDS and PFS. Follow-up examinations were made prospectively over a period of 24 months using general criteria and psychometric test measuring instruments validated for German-language use. An 8-pole double electrode system was implanted 23 times, a single electrode sufficed in 11 cases. The area of pain was covered in all patients. This required special technical capabilities of the SCS system. The results remained constant over 24 months. The morphine dose could be reduced by at least 50 %. All measuring instruments confirmed a clear reduction in pain and improvement in quality of life as a result of SCS implantation. The SCS is an minimally invasive surgical procedure which can enlarge the therapeutical possibilities of pronounced PDS and PFS resistant to other modes of treatment. Special technical possibilities of parameter setting are required to cover the pain areas.

Mechanistic studies of oxygen reduction at La 0.6Ca 0.4CoO 3-activated carbon electrodes in a channel flow cell

The mechanism of the oxygen reduction reaction ( orr) was studied in alkaline media at La 0.6Ca 0.4CoO 3-activated carbon electrodes in a channel flow cell (CFC). The electrodes were made by depositing a mixture of the perovskite (La 0.6Ca 0.4CoO 3) powder as the catalyst, Vulcan XC 72 as the carbon, and Triton X-100 as the binder on Ti substrates. The collection efficiency, N, of the double-electrode system in the CFC was evaluated in advance using the ferro–ferricyanide couple. The results obtained for the orr show that the mean number of electrons transferred per O 2 molecule, n g, remains around 2, while the ratio k 1/ k 2 (the rate constants for direct reduction to OH − and indirect reduction to HO 2 −) is much smaller than 1, both at nonactivated and perovskite-activated carbon electrodes. This indicates that most of the oxygen was reduced via the two-electron pathway to HO 2 −. The hydrogen peroxide ions appear to be stable at Vulcan, but are further reduced and/or chemically decomposed in part in the presence of the metal-oxide catalyst.