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[en] A model of a non-polarizable interface is developed and considered in terms of the specific adsorption of charged redox species and the nonspecific adsorption of the supporting electrolyte. The adsorption coefficients of charged redox species depend on their charges and the potential at the inner Helmholtz plane. The adsorbed amounts of the redox species and supporting electrolyte are estimated using the Frumkin isotherm and Gouy–Chapman theory, respectively. The potential dependence of the adsorbed amount of either one or both of the oxidized and reduced forms of the redox species is maximized near its standard potential. The electrocapillary equation at a non-polarizable liquid metal–solution interface under an externally controlled potential is revisited. The derived electrocapillary equation facilitates calculating the electrocapillary curve of the non-polarizable interface based on the quantity of adsorbed ions. The electrocapillary curve calculated based on the model may have a concave part, which would indicate that the interface is thermodynamically forbidden, near the standard redox potential of the redox couple.
[en] In this study, a symmetrical poly (3, 4-ethylenedioxythiophene) (PEDOT) coated on poly (vinyl alcohol) (PVA)-graphene oxide (GO)-manganese oxide (MnO2) microfibers (PVA-GO-MnO2/PEDOT) supercapacitor was successfully prepared using a combination of two facile techniques; electrospinning and electropolymerisation. The FESEM analysis revealed the uniform distribution of manganese oxide nanoparticles on the surface of cross-linking PVA-GO microfibers and a cauliflower-like morphology was observed upon deposition of PEDOT on the surface of PVA-GO-MnO2 microfibers. The chemical composition of PVA-GO-MnO2/PEDOT and oxidation state of manganese were characterised using Raman and X-Ray photoelectron spectroscopies. The inclusion of MnO2 and PEDOT in the microcomposite proved the enhancement of specific capacitance where PVA-GO-MnO2/PEDOT exhibited a specific capacitance of 144.66 F/g compared to PVA-MnO2/PEDOT (107.22 F/g), PVA-GO/PEDOT (94.73 F/g) and PEDOT (62.86 F/g). A wide potential window (1.8 V) was achieved for PVA-GO-MnO2/PEDOT with an excellent capacitance retention of 91.18% suggesting an ideal capacitive behaviour and good cycling stability. PVA-GO-MnO2/PEDOT microcomposite also showed an improved specific energy and specific power with small equivalent series resistance (34.5 Ω) and charge transfer resistance (0.62 Ω). This demonstrated that symmetric electrode of PVA-GO-MnO2/PEDOT can offer a great promise in producing high-performance supercapacitors.
[en] Lithium Phosphorus Oxynitride glass (LiPON) is the most used electrolyte for lithium solid-state microbatteries. The current main challenge is improving its ionic conductivity without deteriorating its very low electronic conductivity, wide electrochemical window and stability with Li. While the chemical mechanisms of ionic conduction have been intensively studied, they still are controversial and not fully understood to date. Therefore, it is particularly important to well define and understand the influence of the keys parameters acting on the ionic conductivity. In this study, LiPON is deposited by reactive radio frequency (RF) sputtering of Li3PO4 under nitrogen by two ways. LiPON deposited with a non-standard method exhibits an exceptionally high ionic conductivity (6.7 × 10−6 S cm−1) compared to the standard method (1.4 × 10−6 S cm−1). The chemical composition and structure are compared using RBS/NRA and FTIR, respectively. The electrical properties as ionic and electronic conductivities, charge mobility and carrier concentration are measured by impedance spectroscopy. It is demonstrated the positive influence of the disorder created by the phosphate groups on the mobility. This high mobility creates a depletion area at the interfaces which can be suppressed by adding a buffer layer. The interfacial properties are also investigated from both chemical and electrical point of view using ToF-SIMS and impedance spectroscopy.
[en] Highlights: • The SrSc0.175Nb0.025Co0.8O3-δ perovskite was evaluated for proton conducting SOFC. • Polarization resistance of SSNC decreased obviously via introducing H2O in gas phase. • The symmetrical cell showed the lowest Rp of 0.26 Ω cm−2 at 600 °C in 3% H2O-air. • This study suggests that in situ creation of H+ is possible at the SSNC cathode. - Abstract: Proton-conducting solid oxide fuel cells (H+-SOFCs) have attracted considerable interest recently. However, the overall cell performance of H+-SOFCs is still low due to the lack of a promising cathode material. In this study, SrSc0.175Nb0.025Co0.8O3-δ (SSNC) was synthesized for evaluation as a cathode material in H+-SOFCs based on a BaZr0.1Ce0.7Y0.2O3-δ (BZCY) electrolyte. The chemical compatibility and stability of the SSNC cathode with the BZCY electrolyte in humidified air were studied. In addition, the electrochemical behavior of the SSNC cathode on the BZCY electrolyte was investigated using SSNC/BZCY/SSNC symmetrical cells at 600 °C in dry air and humidified air at various H2O partial pressures. Promising electrocatalytic activity was observed for the SSNC cathode in humidified air. The area specific resistance obtained on symmetrical cells at 600 °C in a 10% H2O-air atmosphere was 0.26 Ω cm2. A promising peak power density of 498 mW cm−2 was obtained using an anode-supported cell with a 46 μm-thick BZCY electrolyte layer at 700 °C.
[en] Present investigation deals with electrochemical determination of copper(II), lead(II) and mercury(II) ions, using ethylenediaminetetraacetic acid (EDTA) chelating ligand modified polyaniline (PANI) and singe walled carbon nanotubes (SWCNTs) based nanocomposite (PANI/SWNCTs). Stainless steel (SS) electrode was modified with PANI and SWCNTs based nanocomposite. PANI/SWCNTs nanocomposite was electrochemically synthesized using potential cycling technique. Further it was modified with EDTA in the presence of 1-ethyl-3(3-(dimethylamin propyl)carbodiimide (EDC) as activating agent, using dip coating technique at room temperature. The EDTAPANI/SWCNTs/SS electrode was characterized by cyclic voltammetry in 0.5 M H2SO4, which was complemented with electrochemical impedance spectroscopy (EIS). AFM and SEM analysis was applied for the morphological studies of EDTAPANI/SWCNTs nanocomposite structure. FTIR analysis was applied for the structural and compositional analysis of EDTAPANI/SWCNTs nanocomposite. All the characterizations were performed before and after the modification of PANI/SWCNTs nanocomposite structure with chelating ligand. Differential pulse voltammetry (DPV) was used for the determination of Cu(II), Pb(II) and Hg(II) ion concentrations. Analytical characteristic such as selectivity and sensitivity of here above-mentioned metal ions was studied. The limit of detection the EDTAPANI/SWCNTs/SS toward Cu(II), Pb(II) and Hg(II) was determined as 0.08 μM, 1.65 μM and 0.68 μM respectively.
[en] While lithium bis(fluorosulfonyl) imide (LiFSI) is widely used in current Li-ion batteries (LIBs), the role of LiFSI in the LIB performance remains elusive. We herein elucidate the effects of LiFSI on the electrochemical performance of graphite anodes in comparison with those of lithium hexafluorophosphate (LiPF6). An in-depth electrochemical analysis using graphite/Li half cells and graphite/graphite symmetric cells confirms that LiFSI provides little improvement to the cyclability of the graphite anode at 25 °C, but enables far better performance in cycle and storage tests at 60 °C. The superior thermal stability of the graphite anode in LiFSI electrolyte is attributed to the formation of a thin, inorganic-rich solid electrolyte interphase (SEI) layer as indicated by differential scanning calorimetry (DSC) and X-ray photoelectron spectroscopy (XPS) measurements.
[en] A major portion of the existing literature on TiO2 nanotubes modified by CdS and CdSe report an enhanced photoelectrochemical (PEC) performance using electrolytes with inorganic sacrificial electron donors where a dominant sulfite oxidation occurs. In this study, we distinguish the PEC performance arising entirely from water splitting to that originated by sulfite oxidation in the TiO2 nanotube system modified by CdS/CdSe nanoparticle depositions. The photocurrent density measured under the AM1.5G simulated spectra, 1 sun (100 mWcm−2) intensity for the TiO2 nanotubes modified by CdS/CdSe nanoparticles and using an aqueous alkaline electrolyte (1 M NaOH) was observed to be 0.92 mAcm−2 at 1.23 V vs. RHE which was 8-fold lower than in the case for sulfite oxidation (Jph/SO = 7.4 mAcm−2 at 1.23 V vs. RHE) using an Na2S/Na2SO3 aqueous electrolyte. A maximum STH efficiency of 0.71% and water splitting efficiency of 12.4% was determined for water oxidation using an aqueous alkaline electrolyte. To rationalize such device efficiency, we propose that the ‘water splitting efficiency’ parameter is much more meaningful since it correlates the PEC activity specifically to water splitting and not to other pathways that produce an artificially enhanced photocurrent through the use of sacrificial reagents. The incident photon-to-current conversion efficiency spectrum measured at 1.23 V (vs. RHE) bias for the TiO2 photoanodes modified by CdS/CdSe nanoparticles revealed that the current conversion efficiency is lower (∼17% or less) when absorption occurs solely from the external CdSe layers indicating higher recombination during charge transport. The increase of dark current observed in the linear sweep voltammetry plots for the voltage range of −0.25 V to +0.15 V vs. RHE was attributed to anodic dissolution of the photoanodes in aqueous electrolytes containing no sacrificial reagents. The photocurrents and onset potentials for the CdS/CdSe modified TiO2 photoanodes improved under acidic conditions showing a slightly increased PEC activity and faster reaction kinetics.
[en] Highlights: • A rapid microwave-heated method was used to form cobalt-iron phosphates nanosheets. • The peculiar structure composed of nanosheet is like the appearance of tremella. • The tremella-like catalyst exhibits an extraordinary electrocatalytic performance. • The as-made catalyst is more suitable for commercial water electrolyzers than RuO2. - Abstract: Electrochemical water splitting involves two half-cell reactions, that is oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), and the overall reaction is severely restricted by the OER sluggish kinetics. Hence, to design and develop superior active and low-cost OER electrocatalyst is of significant necessary. In this study, the bimetallic cobalt-iron phosphates nanosheets (denoted as Co-Fe-P-O) with high activity toward OER has been constructed via a rapid microwave-assisted process using sodium hypophosphite and ethylene glycol as the phosphorus source and reaction solvent, respectively. Due to the structural feature of a larger electrochemical active surface area, the catalyst exerts a small overpotential of 267 mV at a current density of 10 mA cm−2 and a low Tafel slope of 30 mV dec−1 in 1.0 M KOH solution. The as-prepared catalyst also shows an outstanding stability with a current density retention of 94% at a constant water oxidation for almost 10 h. All of the results suggest that the performance of the catalyst prepared in our work is better than the state-of-the-art commercial RuO2 and even can rival most of transition metal-based material.
[en] Highlights: • Porous ZnCo2O4 nanoribbon arrays were synthesized on nickel foam. • A versatile binder-free electrode for both SCs and LIBs was obtained. • The porous nanostructured largely enhanced cycling stability and rate capability. • A high specific capacitance of 1957.7 F g−1 at 3 mA cm−2 was obtained for SCs. • A large reversible capacity of 1422 mA h g−1 was obtained after 80 cycles for LIBs. - Abstract: In order to meet the growing need for energy, much effort has been devoted to develop the powerful electrodes for electrical energy storage devices. Herein, we offer a facile and effective strategy to synthesize a versatile binder-free electrode for both supercapacitors and lithium-ion batteries, which are regarded as two major electrical energy storage devices. Using a one-step hydrothermal strategy followed by calcination treatment, the porous ZnCo2O4 nanoribbon arrays are successfully synthesized on nickel foam. With the favorable composition and three dimensional porous nanostructure, this advanced electrode demonstrates excellent cycling stability and rate capability. Moreover, a high specific capacitance of 1957.7 F g−1 (3 mA cm−2) is obtained for supercapacitors and a large reversible capacity of 1422 mA h g−1 is retained after 80 cycles at 200 mA g−1 for lithium-ion batteries. Our results suggest that the versatile ZnCo2O4 nanoribbon arrays/nickel foam electrode possesses great electrochemical performance and shows promising potential for large-scale application.
[en] Highlights: • The membrane-free structure benefits electrochemical performance and decolorization. • The bio-cathode can accelerate electron transfer and obtain a lower potential. • Decolorization efficiency will be enhanced while batch running without solution renewal. • The electrons that decolorization required are provided from two different approaches. - Abstract: A membrane-free microbial electrolysis cells (MFMEC) with bio-cathode was applied to enhance azo dye Congo red decolorization by the improvement of cathodic action and membrane abandon. To reveal the advantages of MFMEC, a membrane-free electrolysis cell (MFEC) without microorganism and a microbial electrolysis cell (MEC) with membrane were set as comparisons. The electrochemical characteristics of MFMEC and its relation with decolorization were analyzed by measuring cathode potential, EIS and current change. The results showed that MFMEC with bio-cathode acquired lower cathode potential than MFEC. The charge transfer resistance of MFMEC was 5.2 Ω which was lower than MEC (43.6 Ω). The decolorization efficiency of MFMEC with different voltages (0.3 V, 0.6 V and 0.9 V) were nearly identical and stable at 87.9%, 85.1%, and 86.7% respectively in 24 h. In batch tests without solution renewal, the decolorization had a remarkable increasing (25%) in cycle 2 and 3, then it had declined since cycle 4. The main degradation product was benzidine which produced by azo bond cleavage. More CH4 was produced with 0.9 V as a side reaction that restricted further increase of decolorization rate. The result demonstrated that both the act of co-substrates and accepting electrons from cathode were the main decolorization approaches of MFMEC.