Double-layer Electrode Research Articles

Revealing the degradation mechanism of the lanthanum nickelates based double‐layer electrodes during long‐term tests in contact with chromium‐containing steel interconnects

This paper focuses on the long-term tests for 1000 hours of different Membrane-Electrode-Interconnect Assemblies (MEIAs), consisting of a steel interconnect and an asymmetrical solid electrochemical cell based on the Ce0.8Sm0.2O2−δ electrolyte, the double-layer working electrode with the La2NiO4+δ – Ce0.8Sm0.2O2−δ composite functional layer and the LaNi0.6Fe0.4O3−δ current collector layer, and the platinum reference electrode (O2, LaNi0.6Fe0.4O3−δ|La2NiO4+δ – Ce0.8Sm0.2O2−δ|Ce0.8Sm0.2O2−δ|Pt, O2). These tests were carried out on MEIAs with two types of Cr-based stainless steels, Crofer 22 APU and 08X17T, with and without protective coatings at 850°C in air. The electrochemical performance of MEIAs was studied without polarization as well as under cathodic and anodic polarization (current density was 0.5 A cm−2) by means of electrochemical impedance spectroscopy (EIS) and the distribution of relaxation times method (DRT). It was found that the proposed protective coatings for the stainless steels inhibit chromium poisoning without polarization and under anodic polarization: for Crofer 22 APU the degradation of the polarization resistance after ~1100 hours of exposure was 0.35 ± 0.05 Ω cm2, and for 08X17T it was from 0.40 ± 0.05 Ω cm2. In the case of cathodic polarization, the degradation of the polarization resistance remained at a very high level, comparable to uncoated samples: for Crofer 22 APU and 08X17T with coatings, it was about 0.6 to 0.8 Ω cm2 after ~1100 hours. Post-test analysis of the microstructure and chemical composition of the interconnect - double-layer electrode interface was carried out using scanning electron microscopy (SEM), wavelength dispersive X-ray spectrometry (WDS), and respective image analysis of the obtained data. The influence of chromium poisoning on the degradation was considered for different stages of the electrode performance. It was demonstrated that chromium predominantly accumulates in the current collector layer in the case of anodic polarization and in the functional layer in the cases of open circuit and cathodic polarization. For the first time, a combined electrochemical-chemical degradation mechanism of the La2NiO4+δ – Ce0.8Sm0.2O2−δ functional layer was discussed. Highlights Long-term tests of Membrane-Electrode-Inteconnect Assembles (MEIAs) were done. Chromium poisoning was detected on MEIAs with the interconnects without coating. Cathodic polarization terminates the protective properties of the coatings. Chromium poisoning decreases electrode activity to oxygen exchange and diffusivity. A combined electrochemical-chemical degradation mechanism of the functional layer was revealed.

Structural engineering for double-layer high-load LiFePO4 electrode with vertical imparity distribution of conductive additives

To improve the energy density of the batteries, constructing electrode structure should also be considered besides developing high specific capacity electrode materials. As the active material loading increases, the electrode rate performance worsens due to the long distance of electron transport and ion diffusion. This study proposes a simple and effective strategy to construct a high-load LiFePO4 electrode with excellent rate performance by using a double-layer structure. The bottom layer with more conductive additives forms a rich conductive network to improve the ability of electronic collection, the top layer with fewer conductive additives increases the porosity to facilitate ion diffusion. The capacity of the double-layer electrode (active material loading 11.4 mg cm−2) with imparity distribution of conductive additives achieves 98 mAh g−1 at 425 mA g−1 (2.5C). However, the capacity of the single-layer electrode is zero even at a lower loading (7.1 mg cm−2). The vertical imparity distribution of conductive additives in the double-layer structure can reduce the polarization and maintain the excellent rate performance of the high-load electrode. This strategy can be used not only in lithium-ion batteries but also for other energy storage systems possibly.

Dendrite-free lithium deposition on conventional graphite anode by growth of defective carbon-nanotube for lithium-metal/ion hybrid batteries

Full cell performance of conventional graphite and double-layer electrode of dCNT-G and G (dCNT-G/G) electrode at reverse designed N/P ratio (0.8). Inset images are schemes of each electrode at lithiated state with extra lithium layer.

Characterization of La0.65Sr0.35MnO3-based double-layered oxygen electrode for reversible solid oxide cells

Characterization of La0.65Sr0.35MnO3-based double-layered oxygen electrode for reversible solid oxide cells

Nelumbo nucifera Seed-Derived Nitrogen-Doped Hierarchically Porous Carbons as Electrode Materials for High-Performance Supercapacitors.

Biomass-derived activated carbon materials with hierarchically nanoporous structures containing nitrogen functionalities show excellent electrochemical performances and are explored extensively in energy storage and conversion applications. Here, we report the electrochemical supercapacitance performances of the nitrogen-doped activated carbon materials with an ultrahigh surface area prepared by the potassium hydroxide (KOH) activation of the Nelumbo nucifera (Lotus) seed in an aqueous electrolyte solution (1 M sulfuric acid: H2SO4) in a three-electrode cell. The specific surface areas and pore volumes of Lotus-seed–derived carbon materials carbonized at a different temperatures, from 600 to 1000 °C, are found in the range of 1059.6 to 2489.6 m2 g−1 and 0.819 to 2.384 cm3 g−1, respectively. The carbons are amorphous materials with a partial graphitic structure with a maximum of 3.28 atom% nitrogen content and possess hierarchically micro- and mesoporous structures. The supercapacitor electrode prepared from the best sample showed excellent electrical double-layer capacitor performance, and the electrode achieved a high specific capacitance of ca. 379.2 F g−1 at 1 A g−1 current density. Additionally, the electrode shows a high rate performance, sustaining 65.9% capacitance retention at a high current density of 50 A g−1, followed by an extraordinary long cycle life without any capacitance loss after 10,000 subsequent charging/discharging cycles. The electrochemical results demonstrate that Nelumbo nucifera seed–derived hierarchically porous carbon with nitrogen functionality would have a significant probability as an electrical double-layer capacitor electrode material for the high-performance supercapacitor applications.

Analysis of Decay of Photocatalytic Effect of Titanium Dioxide Electrode

Titanium Dioxide (TiO2) has been studied for its important photocatalytic semiconductor characteristics. Among many applicable areas of TiO2 photocatalysts, we have been studying to use as an anode electrode of the marine wet solar cells or marine microbial fuel cell. These studies include the analysis of TiO2 electrode prepared by the screen-printing method, and also the dye sensitizing effect on TiO2 electrode. In those studies, it was appeared that there is an open circuit potential that shifted to noble direction after TiO2 electrode was irradiated by the light source and measured its electrochemical properties. This phenomenon usually occurred after a few minutes the electrode showed its photocatalytic characteristics. It is unclear which caused the potential loss during the measurement. In this study, we have been trying to understand the mechanism affecting the potential degradation of the TiO2 electrode and the factors affecting that decay.The TiO2 electrodes were prepared by screen printing method. Type 329J4L stainless steel which exhibits duel phase properties was used as a base substrate for the electrode. Firstly, the surface of the substrate was polished and the substrate was cleaned with acetone using the ultrasonic cleaner for 10 minutes. Then, the substrate was passivated with 10% nitric acid (HNO3) solution at 60 ºC for 30 minutes. After that, the substrate was screen printed with TiO2 paste followed by heat treating for 60 minutes and the first layer of TiO2 was formed. For the second layer forming, the substrate was again screen printed with TiO2 paste and heat treated for 30 minutes. With these processes, double-layered heterojunction TiO2 electrode was prepared. The electrode was then coated with insulating epoxy resins and prepared ready for the electrochemical measurements and analysis.The electrochemical measurements of TiO2 electrodes were performed in an artificial seawater used as an electrolyte. The irradiation was carried out on the electrodes using a calibrated Xenon lamp with 150 W (wavelength ranging from 250 nm to 800 nm). The lamp was set to produce an output light intensity of 10.5 mW/cm2. The saturated calomel electrode (SCE) was used as the reference electrode. During the photopotential measurement, the potentials dropped to active direction as the electrodes were exposed to the light irradiation. But the potential values were ennobled rapidly after a few minutes the electrode was irradiated. Preliminary examinations showed that there is a relation between the rebounded potential values (open circuit potential loss) and the heat treatment temperatures of the electrodes. For example, the rebound rate of the electrode with second layer heat treatment temperature of 150 ºC was higher and longer compared to that of the electrode with 550 ºC one. Detailed mechanism was yet under investigation. Those investigation includes the photopotential measurement and the electrochemical impedance spectroscopy (EIS) analysis. The surfaces of the electrodes before and after the measurements of photopotential were compared and observed using the scanning electron microscope (SEM). The X-ray powder diffraction (XRD) analysis and differential thermal analysis (DTA) were also included for analysis of decay mechanism of photocatalytic on the TiO2 electrode. The results of those analyses and the mechanism affecting the open circuit potential decay in the TiO2 electrode will be presented to the upcoming ECS conference meeting.

The Maximum Energy Density of Lithium Ion Capacitors

Recently, a new type of supercapacitor–lithium (Li)-ion capacitor (LIC) has attracted much attention, because LIC has not only the advantages of traditional supercapacitor, such as high specific power (e.g. >10 kW/kg) and extremely long cycle life (e.g. >250,000 cycles), but also much higher specific energy (e.g. 10-25 Wh/kg) than that of traditional supercapacitors. In additional, LIC also has high cell voltage, low leakage current, etc.LIC has an asymmetrical structure and is composed of a Li intercalation-type anode electrode (Faradic) and an electric double-layer capacitor-type cathode electrode (non-Faradic), operating in a Li-ion containing electrolyte. The cathode material is activated carbon, and anode material includes graphite, hard carbon, soft carbon, or Li titanate. Compared with ordinary electrochemical energy storage cells, LIC has two following unique characteristics: 1) the anode electrode must be pre-lithiated using a highly concentrated Li source such as Li metal since both electrodes without pre-doped Li-ion. The pre-lithiation can also compensate the active Li loss at anode in the first several cycles and 2) the capacity of anode is much larger than the capacity of cathode (e.g. 7-10× for using hard carbon and 10-15× for using graphite as anode). It is due to the distinct energy storage mechanisms of cathode (non-Faradic) and anode (Faradic), the high-rate performance and cycling durability of anode are not comparable to cathode, resulting in low power density and poor cycling lifespan. Therefore, a general method to improve the power density and cycling lifespan is to construct an ‘unbalanced system’, i.e. the capacity of anode is designed to be higher than that of cathode, which enables the anode to be working at low areal current density and experiencing a shallow charge and discharge to match the rate and cycle life of activated carbon cathode.In this talk, we will present a mathematical formula as Eq. (1) for the theoretical specific energy of LICs for the first time. The theoretical specific energy is only based on “active” materials including cathode, anode, extra Li source, and the required electrolyte during the charge. Other “non-active” materials such as separator, current collectors, binders, tabs, and case can be counted into a value of package efficiency (e.g. 50%). In the specific energy equation, the denominator is the sum of four terms, in which, the 1st term has been normalized by the specific capacitance of cathode, the 2nd term represents capacity ratio between anode and cathode, the 3rd term represents the pre-lithiation, and the 4th term represents the electrolyte consumption when the LIC is at fully charge state. In order to understand the impact of some important parameters to the specific energy of LICs, we vary just one parameter at once and fix all other parameters to default values. They are: cp=100 F/g is the specific capacitance of cathode, ca=372 mAh/g is the specific capacity of anode, cLi=3,860 mAh/g is the specific capacity of extra Li source, Vmax=3.8 V is the maximum cell voltage, Vmin=2.2 is the minimum cell voltage, Vc-max=Vmax+0.2 V vs. Li/Li+ is the maximum potential of cathode, Vc-OCP=3.0 V vs Li/Li+ is the open-circuit potential of cathode, co=1 M/L is the Li salt concentration in electrolyte, g=10 is the capacity ratio between anode and cathode, b=100% is the degree of lithiation for anode, and F=96,485 C/M is the Faraday constant. Fig. 1 shows the specific energy as functions of six different parameters. It can be seen that (a) when the capacity ratio decreased from a default value of 10 to 1, the specific energy can be increased by 54%; (b) when the specific capacity of extra Li source is much greater than that of anode (e.g. cLi>1,000 mAh/g), the specific energy is close to a constant value; (c) when the specific capacitance of cathode is doubled from 100 to 200 F/g, the specific energy increases only 17.5% because the masses of anode and electrolyte are doubled too; (d) when the specific capacity of anode is doubled from 372 to 744 mAh/g, the specific energy will increases 21.7%, which is limited by low capacity of cathode; (e) the specific energy increase rate is less than voltage increase rate (or ∆ε/ε<2∆V/V) because masses of anode, electrolyte, and extra Li source increase proportional to the maximum voltage as shown in Eq. (1); and (f) the specific energy doesn’t increase with decreasing the minimum cell voltage from a default value of 2.2 V due to the mass of anode increases to match the increase of the cathode capacity. Figure 1

Electrocatalytic activity of nanoparticulate TiO2 coated onto Ta-doped IrO2/Ti substrates: Effects of the TiO2 overlayer thickness

The trade-off between short-term efficiency and long-term durability in electrocatalysis has always been a tough choice. This study examines the electrocatalytic activity of double-layered oxide electrodes comprising a ~1 μm-thick Ta-IrO2 underlayer (coated on a Ti plate) and ~3.5 μm- and 5.5 μm-thick nanoparticulate TiO2 overlayers (TEC-1 and TEC-2, respectively) in NaClO4 and NaCl solutions as non-active and active supporting electrolytes, respectively. The physicochemical features of both TEC samples, including the crystalline pattern, elemental states, morphology, and electrochemically active surface area, are very similar, except for the TiO2 overlayer thickness. The TEC-1 electrode shows ~54% lower electrode/electrolyte interfacial charge-transfer resistances than those of TEC-2. In the bulk electrolysis for the decomposition of ammonia, the current density with the TEC-1 electrode is two-fold larger than that with TEC-2 under the same potential, due to the relatively low interfacial charge transfer with TEC-1. Electron spin resonance spectroscopic analysis reveals that OH and O2−/HOO are the primary reactive oxygen species responsible for the ammonia decomposition in NaClO4. In the NaCl electrolyte, reactive chlorine species (i.e., free chlorines) decompose ammonia with significantly faster kinetics compared to the case with the reactive oxygen species. Regardless of the electrolyte type, TEC-1 is always more active than TEC-2. However, prolonged bulk electrolysis tests over 300 h show that TEC-2 is more durable than TEC-1, maintaining its electrocatalytic activity and faradaic efficiency. The effect of the TiO2 overlayer thickness on the efficiency and durability of the electrodes is discussed in detail.

Perovskite solar cell based on double-layer Ag/SnBi alloy as cathode

Herein, a low-melting point tin-bismuth (SnBi) alloy film combined with a silver layer was introduced to fabricate the inverted planar perovskite solar cells. SnBi alloy was prepared by high temperature melting method and was characterized by metallurgical microscope, XRD, SEM, DTA, XPS methods. The influence of silver thickness on the performance of perovskite solar cells was studied. The optimized perovskite solar cells based on 20 nm Ag and 80 nm SnBi show a power conversion efficiency of 13.52%, involving a 19.6% increase compared to the control device. The double-layer electrode can not only reduce the charge transfer resistance, increase the extraction efficiency of the charge, improve the photovoltaic performance of the device, but also improve the stability of the device in the environment.

Unidirectionally Driving Nanofluidic Transportation via an Asymmetric Textile Pump for Simultaneous Salt-Resistant Solar Desalination and Drenching-Induced Power Generation

Solar-driven seawater desalination provides a promising technology for sustainable water energy harvesting. Although tremendous efforts have been dedicated to developing efficient evaporators, the challenge of preventing salt accumulation while simultaneously realizing high-performance steam-electricity cogeneration remains to be addressed. In this work, inspired by the water and solute transportation in plants via the wicking mechanism, a one-way asymmetric nanofluidic photothermal evaporator fabricated by disproportionately depositing photothermal MXene nanosheets on a hydrophilic cotton textile is reported for simultaneous freshwater and power production. By unidirectionally driving dynamic saline transportation via this photothermal cotton textile pump, this evaporator not only enables self-operating salt rejection for stable steam generation but also affords continuous electric power generation induced by the formation of an asymmetric double electrode layer within MXene nanochannels under the drenching state. Specifically, the solar-driven evaporation rate and voltage generation reach 1.38 kg/m2/h (with a conversion efficiency of 83.1%) and 363 mV under 1 sun irradiation, respectively. Notably, this designed nanofluidic system suffers negligible performance depreciation after 30 h of operation and washing 15 times, which indicates its outstanding stability and reusability. This facile design of the asymmetric nanofluidic photothermal system may provide prospective opportunities for scaling up sustainable freshwater and electric power production.

Decoupling Conductivity and Solubility in Electrolytes Using Microemulsions

Redox flow batteries have recently received considerable attention as possible large-scale energy storage devices, but their low energy density has inhibited widespread application. In this work, a novel strategy of decoupling conductivity and solubility of electrolytes using microemulsion is put forward to enhance ionic conduction of non-aqueous electrolytes, increase the selectivity of active species, improve the battery voltage, and eventually achieve the possibility of high energy density. We report a study of the electrochemistry of ferrocene in single phase Tween® 20/1-butanol/H2O/toluene microemulsion system at 20 °C. At low and intermediate surfactant to water weight ratios (<0.5/0.5), the voltammogram exhibits reversible electrochemical behavior, while at high surfactant levels the curves show lower levels of reversibility. The latter voltammograms have a form typically associated with high resistance in solution, consistent with a gradual transition in microstructure as surfactant levels increase. This change in structure is supported by correlations with conductivity results based on the literature. The voltammograms show little evidence of anomalies in double layer capacitance or electrode “blocking” by droplets, suggesting that the electron transfer is indeed occurring in a facile manner between the electrode and the ferrocene inside the oil phase.

Praperation of magnetic Fe,N co-doped nano-sized graphitized carbon aerogel with hierarchical porous structure and its electrochemical and adsorption performance

<p indent=0mm>Nano-sized carbon materials have received intensive preoccupation owing to their extraordinary properties such as high specific surface area, abundant porous structure, and excellent electronic properties. Doping non-metallic element N can effectively modulate the electronic properties of graphene, and doping metallic element Fe can further improve their catalytic activity. To date, applications of Fe-N/C materials are mostly concentrated in supercapacitors, electrochemical double layer electrode materials or adsorption. In this communication, we present a novel route for fabricating Fe,N co-doped nano-sized graphitized carbon materials (FeNC aerogels) by a chelate-carbonization-activation process using chitosan-Fe³⁺ chelate and KOH as precursor and activator respectively. Chitosan-Fe³⁺ chelate aerogel was first formed via sol-gel process, and Fe³⁺ was chelated by chitosan and evenly distributed in 3D networks of aerogel. Then in a nitrogen atmosphere, Chitosan-Fe³⁺ chelate aerogel was pyrolyzed at elevated temperature, and Fe³⁺ was reduced to Fe nanoparticles under the control of chitosan molecular in this carbonization process. At the last stage of KOH activation process, most of the amorphous carbon was etched, and abundant nanoscale pores appeared. Upon mild heating at 70°C in air, core@shell Fe@Fe₃O₄ nanoparticles were formed due to the reaction of Fe nanoparticles inside the Fe-N/C aerogels with oxygen in air. The morphology, structure, and properties of the obtained FeNC aerogels were characterized using field emission scanning electron microscope (FESEM), high-resolution transmission electron microscope (HRTEM), element mapping, Raman spectra, X-ray diffraction analysis (XRD), X-ray photoelectron spectroscopy (XPS), and vibrating-sample-magnetometer (VSM). FeNC aerogels were confirmed to be Fe,N-contained carbon aerogels with 3D hierarchical porous scaffold including macropores, micropores and mesopores, displayed low density and good magnetic response. The as-prepared FeNC(1-100)-K800 showed extremely large specific surface area <sc>(3103 m²/g),</sc> low density <sc>(27 mg/cm³),</sc> and high nitrogen content (4%). The magnetic response ability of FeNC aerogels increased with the increase of Fe content, and Fe was doped as Fe@Fe₃O₄ and Fe-N. FeNC aerogels exhibited good electrocatalytic oxidation-reduction activity, which increased with the increase of Fe doping amount, graphitization degree, and specific surface area. The obtained FeNC(1-20)-K800 with the highest Fe doping amount showed the highest initial potential of <sc>0.98 V,</sc> half-wave potential of <sc>0.82 V</sc> in<sc>0.1 mol/L</sc> KOH electrolyte saturated with O₂, and the highest initial potential of <sc>0.92 V,</sc> half-wave potential of <sc>0.62 V</sc> in<sc>0.05 mol/L</sc> H₂SO₄ electrolyte, respectively. Meanwhile, FeNC aerogels showed good performance of the electric double layer capacity and good cycling stability, and the specific capacitance enhanced with the increase of specific surface area. The specific capacitance, energy density, and power density of FeNC(1-40)-K800 was <sc>253 F/g,</sc> 35.1 W h/kg, and <sc>249.7 W/kg</sc> respectively. And its specific capacitance retention rates were 92.9% and 88.6% respectively after 6000 times and 10000 times continuous charge-discharge cycles at a current density of <sc>10 A/g.</sc> Furthermore, The saturated adsorption capacities of four kinds of dyes: Methyl orange (anionic dye), Rhodamine B (neutral dye), crystal violet and malachite green (cationic dyes), on FeNC(1-20)-K800 all exceeded <sc>400 mg/g,</sc> and the saturated adsorption capacity of malachite green reached up to <sc>816 mg/g.</sc> FeNC aerogel prepared here is a new type of carbon materials with application potential in the field of new energy and environmental remediation. The novel aerogel preparation process we preposed is suitable for large-scale industrial preparation without environmental risks because complex nitrogen and iron treatment steps and expensive equipments are not needed.

Changes in Microstructure of NiCo-Dispersed SDC Hydrogen Electrodes for the Improvement of Durability via Reversible Cycling Operation Between SOEC and SOFC-Modes

We have examined changes in microstructure of double-layer hydrogen electrodes for solid oxide cells, consisting of a samaria-doped ceria (SDC) scaffold with highly dispersed Ni–Co nanoparticles as the catalyst layer (CL) and a thin current collecting layer of Ni–YSZ cermet, whose durability we recently found to undergo a remarkable improvement via reversible cycling operation between electrolysis and fuel cell-modes. The lower parts of many Ni‒Co particles were found to be anchored tightly on the SDC support after the cycling operation, probably due to a strong interaction between Ni‒Co and SDC. It was demonstrated by focused ion beam–scanning electron microscopy (FIB–SEM) that the Ni content in the CL was nearly fully maintained by the cycling operation, compared with a significant depletion of Ni after SOEC single-mode operation. Such a stabilization of the microstructure is proposed to contribute to the improved durability.

Design of hierarchical double-layer NiCo/NiMn-layered double hydroxide nanosheet arrays on Ni foam as electrodes for supercapacitors

Reasonably designing the structure of composite materials and effectively increasing electroactive sites of electrode materials are considered as the promising approaches to enhance the electrochemical performance for supercapacitors. Herein, a double-layer layered double hydroxide nanosheet array grown on Ni foams is constructed through a facile two-step hydrothermal method. The as-prepared double-layer electrode materials including Ni, Co, and Mn elements possess large surface area and porosity; thus, it can increase the contact between electrolytes and the electrode materials, which leads to an increase in electroactive sites and high electrochemical performance. The double-layer electrode shows a high capacitance performance (2950 F/g at 1 A/g) and superior cycling stability (79% retention after 10,000 cycles at 10 A/g). In addition, the asymmetric NiCo/NiMn-LDHs//AC device is fabricated and manifests good capacity with excellent cyclic stability of 82.2% after 10,000 cycles.

Electronically conductive MXene clay-polymer composite binders for electrochemical double-layer capacitor electrodes

Electrochemical double-layer capacitors recently attract strong attention because of their fast and stable charge/discharge characteristics and their high-power density. To improve the performance of EDLCs, it is necessary to conduct comprehensive studies on electrode, including the binder. An ideal binder for an EDLC must have high adhesion ability to the electrode components and should be electronically conductive. Here, we synthesize a composite binder consisting of MXene clay and poly(acrylonitrile-co-butyl acrylate) using an in-situ emulsion polymerization. This is a first report of an in-situ polymerization method to make a conducting composite binder with good mechanical, adhesion, and electronic conducting properties. An EDLC containing electrodes of activated carbon and MXene clay/poly(acrylonitrile-co-butyl acrylate) composite binder shows a high specific power of 8510 W kg−1 with a high specific energy of 23.6 Wh kg−1. This is a significant improvement over EDLC electrodes containing only activated-carbon and poly(acrylonitrile-co-butyl acrylate). The excellent performance is attributable to the binder's high conductivity and toughness due to improved interactions among the electrode components.

Design of all-solid-state chloride and nitrate ion-selective electrodes using anion insertion materials of electrodeposited poly(allylamine)-MnO2 composite

All-solid-state ion-selective electrodes as potentiometric ion sensors for the determination of chloride (Cl−) or nitrate (NO3−) ions were designed by inserting an electrodeposited composite layer consisting of manganese dioxide and poly(allylamine), a polymeric cation, as the inner solid-contact layer between the electrode substrate and poly(vinyl chloride) (PVC)-based ion-sensitive membrane containing the corresponding ionophores for Cl− or NO3− ions. The double-layered ion-selective electrodes exhibited selective and quick (≤10 s) potential response for the anions; moreover, the Nernstian slopes of the calibration curves of the electrodes were adequate, and the electrodes presented a wide detection range (10−5–10−1 mol dm−3). As the poly(allylamine)-manganese dioxide composites presented anion-insertion redox activity, the insertion of composite layers was highly effective in stabilizing the membrane potential of PVC because it lowered the impedance at the electrode interface, resulting in quicker responses to the anion activity in analytes than those of the corresponding electrodes without composite layers.

Precursor of Pr2NiO4+δ as a highly effective catalyst for the simultaneous promotion of oxygen reduction and hydrogen oxidation reactions in solid oxide electrochemical devices

The electrochemical behaviour of a Sr2Fe1.5Mo0.5O6–δ based double-layer electrode decorated with a “symmetric” catalyst by the wet impregnation technique for the simultaneous acceleration of cathodic and anodic reactions was investigated for the first time. As a “symmetric” catalyst, a solution of precursor for the synthesis of praseodymium nickelate (Pr2NiO4+δ) was considered. Since the catalyst consists of NiO and Pr6O11 in an oxidizing atmosphere and of Ni and Pr2O3 in a reducing atmosphere, it effectively accelerates the rate of oxygen reduction at the cathode and hydrogen oxidation at the anode of solid oxide fuel cells with symmetric electrodes. It was shown that the rate of oxygen reduction after introduction of the catalyst into the electrode increased due to an increase in the rate of oxygen interfacial exchange between the electrode and the gas phase. The rate of hydrogen oxidation increased due to an increase in the rate of dissociation of adsorbed hydrogen. During tests of the fuel cell with a 300 μm LaGaO3-based supporting electrolyte and decorated electrodes, a maximum power density of about 0.83 W cm−2 at 800 °C under wet hydrogen/air condition was obtained.

Synthesis and electrochemical properties of Na0:67Mn0:75Ni0:25O2 in carbonate-based electrolytes

In this work, a single phase of P2-Na0:67Mn0:75Ni0:25O2 (NaMNO) material was successfully synthesized via a coprecipitation method with the size varying from 2 to 4 mm. According to the atomic absorption spectroscopy (AAS), all the metallic elements were uniformly distributed in the bulk material with the desired ratio Mn¸Ni = 3¸1. The electrochemical properties of P2-NaNMO were investigated in carbonate-based electrolytes using 1M NaClO4 or 1M NaPF6. Among these electrolytes, this cathode exhibited the best electrochemical performance with initial capacity up to 205.7 mAh/g and capacity retention reaches 63.2% during 60 cycles when using 1M NaClO4/PC + 2% (v/v) VC. Indeed, vinylene carbonate (VC) additive plays an important role in improving the performance of NaMNO cathode through the formation of a stable cathode electrolyte interphase layer (CEI). Electrochemical impedance spectroscopy (EIS) was performed to demonstrate CEI layer formation indicated by the elevation of the electrode surface film and double layer impedance in the initial cycle. During cycling, galvanostatic intermittent titration technique (GITT) helps to calculate the Na+ ion diffusion coefficient, which was increased clearly at the working voltages of Mn3+/Mn4+ and Ni3+/Ni4+ redox couples.

Are activated carbon pore structure parameters linearly positively related to its mass-specific capacitance?

Despite considerable achievements in the use of porous carbon in electrochemical double-layer capacitor or electrode of supercapacitor over the past few years, understanding the relationship between pore structure parameters and electrochemical performance has long been highly desirable. Herein, apricot shell lignin (ASL) was used to prepare activated carbon, after which the galvanostatic charge–discharge (GCD) test was performed. Meanwhile, the pore structure parameters of AAC were determined by the nitrogen adsorption–desorption test. The results confirmed that the AAC pore structure parameters were consistent with the inherent law of activation. Besides, in the low current density ranging from 0.50 A/g to 10.00 A/g, the micropore surface area density of AAC rather than other pore structure parameters (e.g., mesoporosity, micropore specific surface area, mesopore specific surface area) was linearly positively related to its mass-specific capacitance. Additionally, the average of linear fit coefficients between micropore surface area density and mass-specific capacitance was 0.92. Consequently, when using a three-electrode configuration with a 6 M KOH electrolyte, the micropore surface area density of activated carbon can be employed as a universal predictor of mass-specific capacitance in a low current density range 0.50–10.00 A/g.

Energy storage performance of electric double layer capacitors with gradient porosity electrodes

• Novel gradient and double-layered porous electrodes are applied. • ELDC performance is related to the location of electrolyte accumulation at large discharge rate. • More advantage occurs in EDLC of the electrode with stepwise and linear increasing porosities. • Porosity variation amplitude serves as an important factor. The variations of porosity in porous electrode influence the performance of electric double layer capacitor (EDLC) greatly. Four kinds of novel porous electrode structure, i.e. linear increasing porosity, linear decreasing porosity, stepwise increasing porosity, stepwise decreasing porosity are applied in the EDLCs. The numerical simulations are conducted to study the effect of porosity distribution in porous electrode on the electrolyte concentration, voltage, specific capacitance and energy in EDLC. In comparison to the electrode with fixed porosity, the higher specific capacitance, higher specific energy and less voltage loss caused by non-uniform electrolyte distribution occur in the EDLC with the porous electrodes in stepwise or linear increasing porosity distributions. The ELDC performance is related to the location of electrolyte accumulation in the electrodes at large discharge current density. The variation amplitude of porosity, whole electrode thickness and initial electrolyte concentration influence the behaviors of EDLC greatly. Thus, the high performance of electric double layer capacitor can be obtained in its porous electrodes with stepwise or linear increasing porosity.