Rate Of Electrochemical Oxidation Research Articles

Elucidating the Mechanism of Nickel-Mediated Electrochemical Alcohol Oxidation Using in-Situ X-Ray Absorption Spectroscopy and Microkinetic Modeling

Electrochemical alcohol oxidation (AOR) is an attractive replacement for oxygen evolution reaction (OER) in hydrogen production. Compared to OER, AOR has a lower thermodynamic potential and produces higher value products. Nickel-mediated AOR has been proposed to proceed through a chemical, redox pathway preferred by aldehydes (geminal diols in alkaline electrolyte), and a potential dependent pathway preferred by alcohols. The precise mechanism of these reactions and their effects on the material are not well understood. Using furfural and furfuryl alcohol as model molecules, we elucidate the mechanism of nickel-mediated AOR. In-situ tracking of the Ni K edge using x-ray absorption spectroscopy (XAS) reveals nickel is at a more reduced state during AOR compared to when no organic reactant is present. The nickel oxidation state profile, however, varies depending on the reactant present (furfural vs. furfuryl alcohol). Product analysis shows that competition for catalytic sites with OER at high potential could contribute to these differences. Microkinetic modeling explores the potential dependence of the Ni K edge position by studying the interplay between the rate of electrochemical nickel oxidation and its chemical reduction through reaction with alcohol. Understanding this relationship will identify rate-limiting steps and active (and inactive) phases for AOR. Insights from this model system will motivate novel guidelines for AOR catalyst design.

An investigation to enhance the performance of molten carbonate-direct coal/carbon fuel cells through improvements in anode layouts and the compositions of carbonate electrolyte

Two anode configurations are systematically tested in composite electrolytes of molten carbonate with Cs2CO3 at various temperatures using different carbon fuels, including bituminous coal, bituminous coal char, carbon black, and graphite powder. The results of electrochemical impedance spectroscopy show that electrolytes composed of (Li-K)2CO3 62:38 doped with 20 wt% Cs2CO3 and utilizing graphite powder as a fuel exhibit reduced ohmic and charge transfer resistance. This can be attributed to the decreased surface tension, which enhances the gas solubility of the reactants within the electrolytic matrix. The analysis of particle size distribution through laser diffraction reveals that the graphite specimen has the smallest mean particle size, resulting in an enhanced rate of electrochemical oxidation. The ultimate and proximate analysis indicates that graphite powder has a lower moisture and ash ratio along with a significantly higher fixed carbon content compared to other carbon fuels. Therefore, the obtained V-j &P-j curves in Anode 1 illustrate that graphite powder yields the highest current density and power density of 903 mA/cm2 and 172 mW/cm2, respectively, at an operating temperature of 680 °C under the laboratory conditions. These values surpass those reported in the existing literature. In contrast, Anode 2 exhibits low performance, due to ash particles regime-controlled at the lower part of the chamber during the coal pyrolysis. Based on results, we suggest that graphite powder is the promising fuel candidate for MC-DCFC to achieve the higher performance.

Stained Glass Effect in Anodic Aluminum Oxide Formed in Selenic Acid.

A combination of the unique porous structure and physical and chemical properties of anodic aluminum oxide (AAO) makes it widely used in cutting-edge areas of materials science and nanotechnology. Selenic acid electrolyte provides the ability to obtain AAO with low porosity and high optical transparency and thus is promising for the preparation of AAO photonic crystals (PhCs). Here, we show the influence of crystallographic orientation of Al on the electrochemical oxidation rate in 1 M H2SeO4 as well as on the growth rate, porosity, and the effective refractive index of AAO. The cyclic anodization regime is used to prepare AAO PhCs with photonic band gaps, their wavelength positions are used to measure the AAO growth rate. At an anodization voltage of 40-45 V, the growth rate varies by up to 22.6% with crystallographic orientation of Al grains, causing the stained glass effect, which can be seen with the naked eye.

Effects of porosity on the electrochemical oxidation performance of Ti4O7 electrode materials

Ti4O7 is a kind of conductive ceramic material with a high electrical conductivity and excellent electrochemical performance, rendering it a potential candidate for electrode applications. Here, for the first time, we report the successful preparation of Ti4O7 electrodes with different porosities by adding a pore-forming agent. The results showed that the as-prepared Ti4O7 electrodes contained both mesoporous and macroporous structures. In addition, with an increase in the porosity of the electrodes, the electrochemical oxidation degradation of high-concentration methyl orange (MO) solution first increased, until reaching a critical point, and then decreased. The Ti4O7 electrode with a porosity of 34.9% and an electrical conductivity of 336.1 S cm-1 exhibited the highest electrochemical oxidation ability. The electrochemical oxidation rate constants for MO and chemical oxygen demand (COD) of the porous Ti4O7 electrode were 1.7 times those of the dense Ti4O7 electrode. Compared to commercial stainless steel, graphite, and Ti/RuO2 electrodes, the Ti4O7 porous electrode showed superior electrochemical oxidation performance under the same experimental conditions. The result of this study provide new directions for the application of Ti4O7 electrode materials.

Mosaic of Anodic Alumina Inherited from Anodizing of Polycrystalline Substrate in Oxalic Acid.

The anodizing of aluminium under oscillating conditions is a versatile and reproducible method for the preparation of one-dimensional photonic crystals (PhCs). Many anodizing parameters have been optimised to improve the optical properties of anodic aluminium oxide (AAO) PhCs. However, the influence of the crystallographic orientation of an Al substrate on the characteristics of AAO PhCs has not been considered yet. Here, the effect of Al substrate crystallography on the properties of AAO PhCs is investigated. It is experimentally demonstrated that the cyclic anodizing of coarse-grained aluminium foils produces a mosaic of photonic crystals. The crystallographic orientation of Al grains affects the electrochemical oxidation rate of Al, the growth rate of AAO, and the wavelength position of the photonic band gap.

Electrocatalytic performance of oxygen-activated carbon fibre felt anodes mediating degradation mechanism of acetaminophen in aqueous environments.

Carbon felts are flexible and scalable, have high specific areas, and are highly conductive materials that fit the requirements for both anodes and cathodes in advanced electrocatalytic processes. Advanced oxidative modification processes (thermal, chemical, and plasma-chemical) were applied to carbon felt anodes to enhance their efficiency towards electro-oxidation. The modification of the porous anodes results in increased kinetics of acetaminophen degradation in aqueous environments. The utilised oxidation techniques deliver single-step, straightforward, eco-friendly, and stable physiochemical reformation of carbon felt surfaces. The modifications caused minor changes in both the specific surface area and total pore volume corresponding with the surface morphology. A pristine carbon felt electrode was capable of decomposing up to 70% of the acetaminophen in a 240min electrolysis process, while the oxygen-plasma treated electrode achieved a removal yield of 99.9% estimated utilising HPLC-UV-Vis. Here, the electro-induced incineration kinetics of acetaminophen resulted in a rate constant of 1.54 h-1, with the second-best result of 0.59 h-1 after oxidation in 30% H2O2. The kinetics of acetaminophen removal was synergistically studied by spectroscopic and electrochemical techniques, revealing various reaction pathways attributed to the formation of intermediate compounds such as p-aminophenol and others. The enhancement of the electrochemical oxidation rates towards acetaminophen was attributed to the appearance of surface carbonyl species. Our results indicate that the best-performing plasma-chemical treated CFE follows a heterogeneous mechanism with only approx. 40% removal due to direct electro-oxidation. The degradation mechanism of acetaminophen at the treated carbon felt anodes was proposed based on the detected intermediate products. Estimation of the cost-effectiveness of removal processes, in terms of energy consumption, was also elaborated. Although the study was focussed on acetaminophen, the achieved results could be adapted to also process emerging, hazardous pollutant groups such as anti-inflammatory pharmaceuticals.

Modeling of 1,2-Dibromoethane Biodegradation in Constant Electric Field

This study proposes a mathematical modeling approach for evaluating the effect of applying a permanent electric field on the biodegradation of 1,2-dibromoethane by bacterial cells of Bradyrhizobium japonicum 273. Two models for inhibited microbial growth including product inhibition were composed—one using the Monod–Yerusalimsky approach and another one—the Levenspiel kinetic equation. The models were used to process own experimental data obtained without an electric field and ones obtained at the application of an electric field. The experiments were carried out at an optimum anode potential of 0.8 V vs. the standard hydrogen electrode (SHE). Three initial concentrations of substrate were tested: 0.05, 0.1, and 0.15 g dm−3. The modeling takes into account the product inhibition on microbial growth assuming 2-bromoethanol as the first biodegradation product. It was found that the positive effect of the electric field is the enhancement of microbial growth, expressed by the increase in the maximum specific growth rate and the increase in the inhibition constant when the model of Monod–Yerusalimsky is applied. The main effect of the electric field is in the increase in the rate constant of 2-bromoethanol removal by electrochemical oxidation, enabling the enhancement the microbial growth and substrate conversion to the product. The obtained results show that the application of a permanent electric field leads to a higher electrochemical oxidation rate (with a rate constant up to 60% higher than for the control experiments) and complete substrate and 2-bromoethanol biodegradation. The model of Levenspiel is not so sensitive to the effects of the electric field on product inhibition.

Quantum Efficiency of Electrochemiluminescence Generation by Tris(2,2’‐bipyridine)ruthenium(II) and Tri‐n‐propylamine Revisited from a Kinetic Reaction Model

AbstractElectrochemiluminescence quantum efficiency (ECL‐QE) is an important parameter to evaluate the energy conversion ability of luminophores and analytical sensitivity of corresponding ECL systems. Herein, taking tris(2,2’‐bipyridine)ruthenium(II) (Ru(bpy)32+) and tri‐n‐propylamine (TPrA) coreactant system as an example, the ECL‐QE was evaluated in terms of a kinetic reaction model, in which Ru(bpy)33+ was considered to be the key intermediate in a reaction scheme consisting of competitive oxidative reduction and catalytic reaction routes. It was calculated as the product of electrochemical excitation efficiency (ηex) and light emission efficiency (i. e., photoluminescence quantum yield, PLQY). We used finite element simulations to examine the variation of ηex with the electrode material, applied potential, concentration and distance from the electrode surface. ηex was found to be largely determined by the electrochemical oxidation rate of TPrA that varied by several orders of magnitude with the electrode material. The estimation of ECL‐QE helped in selecting the appropriate conditions for efficient ECL generation and sensitive analysis.

Electrochemical Synthesis-Dependent Photoelectrochemical Properties of Tungsten Oxide Powders

A rapid, facile, and environmentally benign strategy to electrochemical oxidation of metallic tungsten under pulse alternating current in an aqueous electrolyte solution was reported. Particle size, morphology, and electronic structure of the obtained WO3 nanopowders showed strong dependence on electrolyte composition (nitric, sulfuric, and oxalic acid). The use of oxalic acid as an electrolyte provides a gram-scale synthesis of WO3 nanopowders with tungsten electrochemical oxidation rate of up to 0.31 g·cm−2·h−1 that is much higher compared to the strong acids. The materials were examined as photoanodes in photoelectrochemical reforming of organic substances under solar light. WO3 synthesized in oxalic acid is shown to exhibit excellent activity towards the photoelectrochemical reforming of glucose and ethylene glycol, with photocurrents that are nearly equal to those achieved in the presence of simple alcohol such as ethanol. This work demonstrates the promise of pulse alternating current electrosynthesis in oxalic acid as an efficient and sustainable method to produce WO3 nanopowders for photoelectrochemical applications.

Dynamic Load Cycle Effects on PEMFC Stack CO Tolerance under Fuel Recirculation and Periodic Purge

This work presents first experimental evidence on the effects of dynamic load cycle on PEM fuel cell system CO tolerance, a topic which to date has not been comprehensively investigated. The experiments were performed with a 1 kW fuel cell system employing components, design, and operation conditions corresponding to automotive applications. To distinguish between the load cycle and other factors affecting the CO tolerance, the experiments were repeated with static and dynamic load cycles, as well as with pure and CO contaminated fuel. The measurement data showed that dynamic load cycle improves the CO tolerance in comparison to static load with the same average current density. Moreover, the cell voltage deviation data indicated that the difference could be explained by higher electrochemical CO oxidation rate under the dynamic load cycle. These results allow us to estimate the effect of the load cycle on CO tolerance and understand its origins, thus giving valuable input for fuel quality standardization and fuel cell system development work.

Optimized coupling of ammonia decomposition and electrochemical oxidation in a tubular direct ammonia solid oxide fuel cell for high-efficiency power generation

With high energy density both by weight and volume, ammonia (NH3) is a promising hydrogen carrier. Furthemore, NH3 has a mature industrial background, and in liquid form storage and transportation is not a problem. Adding the merit of zero CO2 emission, NH3-to-power by direct ammonia solid oxide fuel cells (DA-SOFCs) is an acceptable strategy to facilitate hydrogen usage. Nonetheless, to achieve efficacy, a high compatibility between operating temperature and catalytic materials for NH3 decomposition is needed. In this work, we developed a tubular DA-SOFC with an output power capability of > 3 W. By combining experimental measurements and multi-physics simulation, we comprehensively studies the related intrinsic processes. Based on experimental data, we developed a two-dimensional multi-scale electro-thermo model of tubular DA-SOFC. Separately we evaluated the effects of inlet fuel gas composition, inlet flow velocity, operating temperature, and operating voltage on the rate of NH3 catalytic decomposition and H2 electrochemical oxidation, as well as on NH3 conversion, H atom utilization, and electrical efficiency of the tubular DA-SOFC. The results suggest that high H atom utilization could be realized by matching the rate of NH3 decomposition with that of H2 electrochemical oxidation. It was observed that with the decrease of temperature, the rate of H2 oxidation decreases more rapidly than that of NH3 decomposition, suggesting that the flow velocity of NH3 should be appropriately lowered to optimize H atom utilization. Finally, we established a correlation between H atom utilization, operating voltage, and electrical efficiency for synergistic optimization of operating conditions. At 0.7 V and 800 ℃, the tubular DA-SOFC fueled with NH3 of 27 mL·min−1 is capable of offering 3.2 W, displaying an efficiency of 60%. Compared to that of a tubular H2-SOFC (only 51% efficiency), the efficiency is significantly higher on the basis of equal voltage and fuel utilization ratio. The outcome of the present study demonstrates the potential of tubular DA-SOFC as a device for high-efficiency power generation.

Bidentate Phosphonate‐Functionalized Ionic Liquid Exhibiting Better Ability in Improving the Performance of Lithium‐Ion Battery

AbstractIn this work, flame retarding phosphonate‐functionalized imidazolium ionic liquids (PFILs) were synthesized and employed as electrolyte additives for Li/LiFePO4 half‐cells. Physical and electrochemical properties, including ionic conductivity, electrochemical properties, electrochemical oxidation limit, electrochemical impedance spectroscopy (EIS) and lithium‐ion transference number (TLi+), were investigated. The results demonstrate that the addition of PFIL can improve the electrochemical performance of lithium‐ion batteries (LIBs). Hybrid electrolyte with 10 wt % bidentate phosphonate‐functionalized imidazolium ionic liquid (b‐PFIL) exhibits more excellent electrochemical oxidation stability (up to 4.77 V vs. Li/Li+), capacity retention (87.3 % after 400 cycles) and rate capability. These improvements can be ascribed to the enhanced lithium‐ion transference number (TLi+), which results from the stronger binding affinity between chelating b‐PFIL and LiPF6.

Performance enhanced of Ni Ce0.8Sm0.2O1.9 hydrogen electrode for reversible solid oxide cells with cadmium substitution

Ni1-xCdxO-SDC composite materials are prepared and investigated as the hydrogen electrodes for reversible solid oxide cell (RSOC). XRD, SEM, XPS and Raman techniques have been used to characterize structural properties, textural and mobility of adsorbed oxygen and lattice oxygen. After reduction, Cd is incorporated into the lattice of Ni and formed NiCd alloy. The reduced Ni0.9Cd0.1O-SDC possesses the most oxygen vacancies, resulting in the highest catalytic activity for the electrochemical oxidation of H2 and the electrolysis of H2O. The electrochemical oxidation process of H2 on the hydrogen electrode in solid oxide fuel cell (SOFC) mode is investigated with a symmetric cell under various H2 partial pressures. The surface diffusion of adsorbed H atom on the reduced Ni1-xCdxO-SDC composite hydrogen electrodes is the rate-determining step (RDS) for H2 electrochemical oxidation reaction and the reduced Ni0.9Cd0.1O-SDC shows the highest electrochemical oxidation rates. The maximum power densities (Pmax) of the cells with reduced Ni0.9Cd0.1O-SDC as hydrogen electrode is 796.2 mW cm−2 when using H2 as the fuel at 700 °C. Furthermore, in solid oxide electrolysis cell (SOEC) mode, the cell with reduced Ni0.9Cd0.1O-SDC as hydrogen electrode exhibits the best electrolysis performance under various H2O concentrations and the current densities remain stable during the test at different voltages for a total period of 10 h under 47%H2O + 53%H2O atmosphere at 700 °C.

Electrochemical Oxidation of Guanines of DNA Loaded on Carbon Nanomaterials

Investigating the interactions of biomolecules DNA/RNA with carbon nanomaterials is very important for applications in bioassay and bioanalysis. Graphene and graphene oxide (GO) and carbon nanotube have been successfully adopted by exploiting the binding affinity difference between single-stranded oligonucleotides (ssDNA) and double-stranded oligonucleotides (dsDNA) to graphene sheets. In this work, we describe the electrochemical DNA oxidation with [Ru(bpy)3]2+ to understand the interaction between dsDNA (and corresponding ssDNA) and reduced graphene oxide (rGO). The electrochemical oxidation rate of guanine bases of ssDNA bound to rGO by electrochemically generated [Ru(bpy)3]3+ was much slower than that unbound to rGO. Our study revealed that ssDNA constrained on rGO was significantly protected from the electron transfer to [Ru(bpy)3]3+ because of π,π-stacking interaction between nucleobases and rGO. On the other hand, the oxidation rates of 11-, 20-, and 27-mer dsDNA bound to rGO increased relative to those of dsDNA alone, demonstrating that the guanine bases of dsDNA on interacting with rGO became more accessible to [Ru(bpy)3]3+. Our electrochemical data illustrated that dsDNA could be totally or partially dehybridized and bind to rGO to form ssDNA/rGO. Furthermore, absorption, circular dichroism spectra, and fluorescence measurements of ethidium bromide using ssDNA and dsDNA with rGO supported the dehybridization of dsDNA in the presence of rGO and CNT.

Study of the Mechanism for Forming a Passivating Layer under Electrochemical Oxidation of Copper (I) Sulfide

In this study the patterns of anodic oxidation of copper (I) sulfide were considered. It was shown that during the crystallization of copper sulfide, the formation of both the chalcosine (Cu2S) phase and the jarleite (Cu31S16) phase is possible, which is characterized by a deficiency of copper in the crystal lattice and deviation from the stoichiometric composition. The electrochemical oxidation of the sample in a solution of sulfuric acid was carried out. During oxidation, intermediate non-stoichiometric sulfides (Cu1 74S, Cu1.8S) were formed in the following sequence: Cu2S (Cu31S16) → Cu1.81S → Cu1.74S → Cu1.6S → CuS → S + Cu2+. The process was accompanied by the transition of copper cations into solution. As elemental sulfur and copper sulfides accumulated on the reaction surface of the sample and, as a result, the rate of electrochemical oxidation decreased due to the difficulty of the product removal and the reagent supply to the reaction zone.

Unraveling Polymorphic Pyrrhotite Electrochemical Oxidation by Underlying Electronic Structures

Metal sulfide oxidation is a common, yet poorly understood, phenomenon that significantly affects surface properties. In this paper, we studied the electrochemical oxidation of polymorphic pyrrhotites (Fe1–xS) to gain insights into the relationship between their electrochemical oxidation rate and electronic structures. Surface composition of oxidized pyrrhotites, as shown by time-of-flight secondary ion mass spectrometry (ToF-SIMS) and X-ray photoelectron spectroscopy (XPS), suggested that one key step for pyrrhotite oxidation is the outward diffusion of metal cations to form polysulfide and oxides. This diffusion process involves the rupture of Fe–S bonds and, hence, depends on the Fe–S bond strength. According to the ToF-SIMS, the Fe–S bond strength in the defective layer (>100 nm), the layer right underneath the polysulfide layer (∼20 nm), was modified by the incorporation of oxygen atoms, which mainly existed in the form of OH– and H2O. It was found that oxygen anions are much more abundant in the def...

Electrochemical oxidation of methyl orange by a Magnéli phase Ti4O7 anode.

In this study, high quality Magnéli phase Ti4O7 bulks with electrical conductivity up to 961.5 S cm-1 were successfully prepared by spark plasma sintering (SPS) and then served as electrode materials for electrochemical oxidation of azo dye methyl orange (MO). The influences of current density and initial dye concentration on the removal rates of MO and chemical oxygen demand (COD) were studied. Removal of MO and COD exhibited an increase with increasing current density and decreasing initial concentration of MO. Complete removal of MO was realized within a short time under all experimental conditions. The removal rate of COD reached 91.7% when current density was 10 mA cm-2 and initial dye concentration was 100 mg L-1. In addition, the electrochemical oxidation rate could be described through a pseudo-first-order kinetic constant k, and the obtained experimental results could be well fitted with a proposed kinetic model in all the examined conditions. Possible degradation mechanisms for electrochemical oxidation of MO by Ti4O7 electrode were proposed on the basis of intermediate products analysis. Tests were also conducted with other commercial electrodes for comparison, including commercial graphite, stainless-steel and dimension stable anode (DSA) electrodes. The results showed that Ti4O7 anode exhibited the fastest electrochemical oxidation rates than those of the other electrodes. This study provides a feasible method for realizing high efficiency of electrochemical oxidation degradation by Ti4O7 electrode.

Bioinspired Architecture of a Hybrid Bifunctional Enzymatic/Organic Electrocatalyst for Complete Ethanol Oxidation

Enzymatic biofuel cells utilize enzymes to electrochemically catalyze the anodic oxidation of a fuel or the cathodic reduction of an oxidant due the high volumetric catalytic activity towards oxidation of biofuels, providing clean and renewable energy, besides presenting great potential as alternative power sources for low-power electronic devices. One way to amplify the electrocatalytic activity of the biosystem and also extend its service life is mix the proper enzyme with organic oxidation catalysts. This hybrid system enables improvement at the rate of electrocatalytic oxidation of several biofuels[1-3].Herein, we describe the development of a hybrid catalytic architecture combining OxOx with a recently developed TEMPO-modified linear poly(ethylenimine) (TEMPO-LPEI) coupled with carboxylated multi-walled carbon nanotubes (MWCNT-COOH) to transform ethanol into CO2, extracting 12 electrons per ethanol molecule at a single bioanode. We identify and quantify the products from electrochemical ethanol oxidation by high performance liquid chromatography (HPLC). The electrochemical experiments were carried out using an AUTOLAB potentiostat / galvanostat (Software NOVA 1.11) with a three-electrode standard cell. The cascade oxidation of ethanol was performed by the chronoamperometric technique (electrolysis) with applied potential of 0.600 V and analysis time of 43,200 s (12 hours). The products obtained after 12 hours of electrolysis were analyzed by HPLC-UV / RID in Full-Scan mode. On the basis of chromatographic results, the catalytic hybrid electrode system completely oxidized ethanol to CO2 after 12 h of electrolysis. The fact that the developed system can catalyze ethanol electrooxidation at a carbon electrode confirms that organic oxidation catalysts combined with enzymatic catalysts allow up to 12 electrons to be collected per fuel molecule. The Faradaic efficiency of the hybrid system investigated herein lies above 85%. Complete ethanol electrooxidation was achieved by using a hybrid bifunctional enzymatic/organic electrocatalyst, MWCNT-COOH/TEMPO-LPEI/OxOx, This new hybrid system represents a good alternative as compared to previous systems [1], not to mention its excellent selectivity, the high yields of CO2 as the final product, and the high electrochemical oxidation rates. This system also represents an example of a hybrid multifunctional catalyst that may be valuable and open up a number of exciting opportunities to fabricate new hybrid bioanode architectures as energy conversion/storage devices and also as part of multistep reaction cascade systems.

Acceleration of Processes on Positive Electrode of Lithium–Oxygen Battery: Electrocatalyst or Redox Mediator?

The approaches to increasing the efficiency of lithium–oxygen battery (LOB), which are based on the use of PtCo/carbon nanotubes (CNT) catalyst and iodine-containing liquid-phase mediator, are compared. It is found that, when 1 M LiClO4/DMSO electrolyte is used, the 20PtCo/CNT catalyst provides an increase of the capacity of a Swagelok LOB model in the complete discharge to a voltage of 2 V as compared to the CNT-based LOB. During the cycling of LOB with each of the materials, the charging voltage increases to 4.5 V. This leads not only to an increase in the rate of electrochemical oxidation of lithium peroxide, but also to an acceleration of corrosion of the electrolyte and active material. In the presence of iodine compounds in the electrolyte, Li2O2 is oxidized by the chemical mechanism, which reduces the charging voltage. In the 0.05 M LiI + 1 M LiClO4/DMSO electrolyte, 85 successive cycles were obtained at a capacity of 500 mA h/gС in the LOB discharging stage and a final charging voltage of not more than 3.8 V. When scaling the LOB to the size of the positive electrode (5 × 5 cm2), the complete discharge capacity close to this characteristic of Swagelok model (as calculated for the geometric electrode surface area) was reached. An introduction of iodine-containing additive into the electrolyte enabled us to obtain up to 100 cycles at a capacity of 300 mA h/gC. The results of the work show that the use of iodine-based redox mediator is more effective from the viewpoint of stability of characteristics of LOB of this type as compared with the use of the platinum-containing catalyst.

The influence of oxygen vacancy concentration in nanodispersed non-stoichiometric CeO2-δ oxides on the physico-chemical properties of conducting polyaniline/CeO2 composites

Cerium oxide (CeO2-δ) ultrafine nanoparticles, with the lower (CeO2-δ-HT) and higher (CeO2-δ-SS) fraction of oxygen vacancies, were used as anchoring sites for the polymerization of aniline in acidic medium. As a result, polyaniline-emeraldine salt (PANI-ES)-based composites (PANI-ES@CeO2-δ-HT and PANI-ES@CeO2-δ-SS) were obtained. The interaction between CeO2-δ and PANI was examined by FTIR and Raman spectroscopy. The PANI polymerization is initiated via electrostatic interaction of anilinium cation and Cl− ions (adsorbed at the protonated hydroxyl groups of CeO2-δ), and proceeds with hydrogen and nitrogen interaction with oxide nanoparticles. Tailoring the oxygen vacancy population of oxide offers the possibility to control the type of PANI-cerium oxide interaction, and consequently structural, electrical, thermal, electronic and charge storage properties of composite. A high capacitance of synthesized materials, reaching ∼294 F g−1 (PANI-ES), ∼299 F g−1 (PANI-ES@CeO2-δ-HT) and ∼314 F g−1 (PANI-ES@CeO2-δ-SS), was measured in 1 M HCl, at a common scan rate of 20 mV s−1. The high adhesion of PANI with cerium oxide prevents the oxide from its slow dissolution in 1MHCl thus providing the stability of this composite in an acidic solution. The rate of electrochemical oxidation of emeraldine salt into pernigraniline was also found to depend on CeO2-δ characteristics.