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[en] The two-dimensional Saul’yev method of simulating processes at an ultramicrodisk electrode is compared with the fully implicit backward differentiation method started with a few backward implicit steps, and an alternating direction implicit method. 2D Saul’yev is convenient to program and although it is significantly slower in execution than the other two methods, it still executes in reasonable time, and yields equally good results with a suitable choice of discrete intervals, and despite its inherent propagation problem, and a certain restriction in the relationship of the spatial and temporal intervals. Saul’yev was implemented for the diffusion limited potential step experiment, as well as linear sweep voltammetry for a reversible system.
[en] Highlights: • Eco-friendly gelatin based electrolyte containing Iodide/triiodide I−/I3− redox mediator. • Integration in Electrochromic Device based on anchored-nanostructured TiO2-viologen. • White to Blue Switch for ECDs stable for thousand cycles. - Abstract: In the present study, a novel gel electrolyte composition combining lithium iodide LiI in 1-butyl-3-methylimidazolium iodide (BMII) ionic liquid,triiodide I3-/I- redox mediator and biodegradable gelatin is proposed for electrochromic devices (ECDs). More precisely, ECDs are assembled using viologen anchored − nanostructured TiO2 (deposited on FTO glass substrate by doctor blading at low temperature) as electrochromic material, FTO as counter-electrode and the gel electrolyte as redox mediator in between. Fast switching times and high cycling stability, up to 20000 cycles, are recorded. The optical reflectance modulation at 550 nm between white and blue color reaches a contrast value ΔR of about 19% in less than 4 seconds after 100 cycles.
[en] Highlights: • Numerical model for electrokinetic remediation of polluted soil with 2,4-D is shown. • Periodic polarity reversal processes has been included in the module M4EKR. • Improvements of the application of polarity reversal strategy has been studied. • Periodic polarity reversal at 6 h enhances the yield of EKR a 94.5%. - Abstract: This article presents a numerical study of the transport phenomena involved in the electrokinetic remediation of soils polluted with polar pesticides. 2,4-Dichlorophenoxyacetic acid is used as a representative of this pesticide type. A one-dimensional configuration with two facing electrodes placed in electrolyte compartments and a cathodic overflow pollutant extraction system has been used for that purpose. The conventional electrokinetic remediation process is evaluated by keeping the electrode polarity constant, and to obtain acceptable yields, it is necessary to extend the treatment for more than 250 days. The application of periodic polarity reversals is proposed to improve these results. This strategy maximises the pesticide concentration in the cathodic compartment, thus maximising the pollutant extraction rate. The results show that by applying polarity reversals over 6-h periods, it is possible to accelerate the treatment, thus improving its overall efficiency up to 94.5% compared with the treatment using a constant electrode polarity.
[en] Highlights: • The LiNiPO4@C powders were synthesized by microwave-assisted solvothermal process. • A diversified special type of microwave synthesis ‘low-level and long-time microwave synthesis’ was applied. • The formation of a perfect core–shell morphology about 6 nm thickness was achieved. • LiNiPO4 synthesized using isopropanol as the reaction medium shows the best electrochemical performance. • LiNiPO4@C (isopropanol) electrode reaches a discharge capacity of 157 mAh g−1 at 0.1 C-rate. - Abstract: Nanoscale, LiNiPO4-core and carbon-shell high voltage (>5 V) LiNiPO4@C cathode materials have been synthesized using a microwave & solvothermal methodology using different solvents, ethylene glycol, isopropanol, isobutanol and water as the reaction medium. The effects of these solvents on the crystal-quality, morphology and electrochemical qualification of the produced materials have been evaluated in terms of the heating efficiency in the microwave field by using various opto-analytical techniques and electrochemical measurements. The heating characteristics in terms of the absorption of the energy as part of the microwave-material interaction phenomenon is also discussed. X-ray diffraction analyses demonstrate that it is possible to synthesize substantially pure LiNiPO4 crystal using isopropanol as the reaction medium. High-resolution transmission electron microscopy analysis reveals that this combined methodology can provide core-shell morphology with a 5–6 nm coating thickness. The LiNiPO4@C cathode material produced in an isopropanol environment exhibits the best electrochemical properties, achieving a discharge capacity of 157 mAh g−1 at a 0.l C-rate, and shows almost 81% capacity retention at the end of the 80th cycle. Thus, this paper offers a perspective for solving the difficulties encountered in modifying a high voltage LiNiPO4 cathode, especially the deficiency in terms of cycle life behavior, and the further benefits are highlighted.
[en] Highlights: • Mn silicate hollow spheres are enclosed in reduced graphene oxide (rGO). • Manganese silicates provide advantageous de-/lithiation potentials with regard to energy density. • Mn silicate hollow spheres remain unaltered even after 350 full dis-/charge cycles. • The incorporation of rGO enhances the achievable capacity and rate capability. - Abstract: Herein is presented a new composite material consisting of nanostructured Mn silicate hollow spheres enclosed in a matrix of reduced graphene oxide (rGO), synthesized via a facile and low-cost hydrothermal method. The hollow structure provides free space to accommodate the volume expansion occurring upon lithiation, while the rGO facilitates the electron transport, thus enhancing the lithiation kinetics. Remarkably, the composite provides a continuously increasing reversible capacity up to ca. 1300 mAh g−1 after 350 cycles. This increase in capacity is ascribed in part to the steadily rising fraction of Mn2+/Mn3+ being oxidized to Mn4+ as well as the reversible formation of the solid electrolyte interphase. The particle morphology, in fact, remains unaltered, as evidenced by ex situ scanning electron microscopy – even after 350 cycles. Additionally, the implementation of manganese as transition metal for the reversible conversion reaction appears advantageous with regard to the overall electrochemical performance and the relatively lower lithiation potential.
[en] Highlights: • Porous BDD/Ta sensor constructed using a Ni-assisted plasma etching method. • Sensor was applied to detection of dopamine and pyridoxine in human serum. • Electrochemical sensor has high sensitivity, selectivity, and long-term stability. • Selectivity of sensor is dependent on plane activity and surface chemistry. - Abstract: A porous boron-doped diamond (PBDD)/Ta sensing electrode was prepared for the fast, sensitive, stable, and discriminative detection of dopamine (DA) and pyridoxine (vitamin B6) in human serum. All the exposed surfaces of the diamond grains of the BDD layer were etched into a porous form, with pore sizes of less than 500 nm and an average depth of about 200 nm. The electrochemical performance characteristics of the PBDD layer and the reaction mechanisms enabling the detection of DA and vitamin B6 were studied. Large numbers of oxygen-containing groups on the PBDD surface, as well as the activity difference of the different planes, enabled us to successfully distinguish between DA and B6 by using the PBDD/Ta electrode. The low background current of PBDD, the large active area of the porous surface, and the high electron transfer properties led to the PBDD electrode having a high sensitivity. Therefore, this sensor can be used to stably detect DA and B6 in serum. Aberrant levels of DA and vitamin B6 in body fluids are key risk indicators for some diseases; thus, monitoring the levels of both and other species in serum is of great significance to clinical diagnoses.
[en] Highlights: • The LiFePO4/porous graphene oxide/C was prepared by a hydrothermal method and a spray dry process. • The porous graphene oxide was prepared through an activation method. • The discharge capacity of the SP-LFP/1%PGO/C is 107 mAh g−1 after 1000 cycles at 10C rate. • The SP-LFP/PGO/C material shows promising candidate for high-power Li-ion battery in EV. - Abstract: A 3D spray-dried micro/mesoporous LiFePO4/porous graphene oxide/C (denoted as SP-LFP/PGO/C) composite material is synthesized via a three-step process, i.e., hydrothermal process, carbon coating, and spray dry method in sequence. The 2D porous graphene oxide (denoted as PGO) material is first prepared through an activation method. The galvanostatic charge-discharge measurements of LFP composites without graphene oxide, with 1 wt% graphene oxide, and 1 wt% PGO are conducted in the potential range of 2–3.8 V at various rates (0.1–10C). It is revealed that the SP-LFP/PGO/C material shows the best performance among three samples. The discharge capacities of the SP-LFP/PGO/C composites are observed to 160, 152, 151, 149, 144, 139, 127 mAh g−1 at 0.1C, 0.2C, 0.5C, 1C, 3C, 5C and 10C rate. In particular, the discharge capacity of the SP-LFP/PGO/C composite with 1 wt% PGO is 107 mAh g−1 after 1000 cycles at a 10C rate, and its capacity retention is ca. 97%. It is due to the unique structural and geometrical feature of SP-LFP/PGO/C composite, there the diamond-like (rhombus) LFP nanoparticles are embedded in porous GO matrix which forming a porous three-dimensional network for fast electronic and ionic transport channels.
[en] Highlights: • Cathodic reduction becomes a feasible alternative to activate persulfate. • A synergistic effect of electro-PS with heat activation improve the DB3 mineralization. • Complete decolorization within 30 min was achieved at 70 °C in the synergic process. - Abstract: This work assesses the role of the operational conditions upon the electro-activation of persulfate (electro-PS) using Ti/IrO2Ta2O5 electrode for the decolorization of anthraquinone azo dye Disperse Blue 3 (DB3). The studied variables include current density (j) (5–80 mA cm−2), persulfate concentration based on the stoichiometric dose for complete DB3 mineralization (20–100%), temperature (30–90 °C) and pH (3–12) as well as the influence of dissolved oxygen. The persulfate activation from cathodic reduction was confirmed by linear sweep voltammetry (LSV). The increase in j enhanced the PS decomposition and, consequently, decolorization efficiency, because of the greater production of sulfate radicals (SO4• −). Besides, the combination of electro-PS with thermal activation resulted in a synergistic effect upon the DB3 mineralization. In the range 30–70 °C, electro-PS led to a significantly higher TOC conversion (above 60% at 40 mA cm−2) than sole heat-activated PS. This difference steeply decreased as temperature increases, achieving similar TOC conversion at 90 °C after 60 min.