Charge Transfer Reactions Research Articles

Carbon Nanotube Film Electrodes with Acrylic Additives: Blocking Electrochemical Charge Transfer Reactions.

Carbon nanotubes (CNTs) processed into conductive films by liquid phase deposition technologies reveal increasing interest as electrode components in electrochemical device platforms for sensing and energy storage applications. In this work we show that the addition of acrylic latex to water-based CNT inks not only favors the fabrication of stable and robust flexible electrodes on plastic substrates but, moreover, sensitively enables the control of their electrical and electrochemical transport properties. Importantly, within a given concentration range, the acrylic additive in the films, being used as working electrodes, effectively blocks undesired faradaic transfer reactions across the electrode–electrolyte interface while maintaining their capacitance response as probed in a three-electrode electrochemical device configuration. Our results suggest a valuable strategy to enhance the chemical stability of CNT film electrodes and to suppress non-specific parasitic electrochemical reactions of relevance to electroanalytical and energy storage applications.

Defect-induced anisotropic surface reactivity and ion transfer processes of anatase nanoparticles

Surface reactivity and ion transfer processes of anatase TiO2 nanocrystals were studied using lithium bis(trifluoromethylsulfone)imide (LiTFSI) as a probing molecule. Analysis of synthesized anatase TiO2 by electron microscopy reveals aggregated nanoparticles (average size ~8 nm) with significant defects (holes and cracks). With the introduction of LiTFSI salt, the Li+-adsorption propensity towards the surface along the anatase (100) step edge plane is evident in both x-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) analysis. Ab initio molecular dynamics (AIMD) analysis corroborates the site-preferential interaction of Li+ cations with oxygen vacancies and the thermodynamically favorable transport through the (100) step edge plane. Using 7Li nuclear magnetic resonance (NMR) chemical shift and relaxometry measurements, the presence of Li+ cations near the interface between TiO2 and the bulk LiTFSI phase was identified, and subsequent diffusion properties were analyzed. The lower activation energy derived from NMR analysis reveals enhanced mobility of Li+ cations along the surface, in good agreement with AIMD calculations. On the other hand, the TFSI– anion interaction with defect sites leads to CF3 bond dissociation and subsequent generation of carbonyl fluoride-type species. The multimodal spectroscopic analysis including NMR, electron paramagnetic resonance (EPR), and x-ray photoelectron spectroscopy (XPS) confirms the decomposition of TFSI– anions near the anatase surface. The reaction mechanism and electronic structure of interfacial constituents were simulated using AIMD calculations. Overall, this work demonstrates the role of defects at the anatase nanoparticle surface on charge transfer and interfacial reaction processes.

Shedding Light on the Molecular Surface Assembly at the Nanoscale Level: Dynamics of a Re(I) Carbonyl Photosensitizer with a Coadsorbed Cobalt Tetrapyridyl Water Reduction Catalyst on ZrO2

We present systematic kinetic studies of the interaction of a rhenium-based photosensitizer with a cobalt(II) tetrapyridyl water reduction catalyst coadsorbed on ZrO2 by transient IR and visible spectroscopies. The study focuses on the competition between the reduction of the excited photosensitizer by an electron donor in solution and nonproductive quenching between the photosensitizer and the catalyst, either by Dexter energy transfer or by electron transfer followed by ultrafast geminate recombination. The implications of both interactions for the charge transfer reactions on the surface are investigated. We find that the kinetics of the system as a whole and the achievable yield of reduced photosensitizer are determined by the inhomogeneous distribution of next neighbor distances between photosensitizers and the water reduction catalysts at the nanoscale level. This provides insight for rational design of heterogeneous water splitting systems with coimmobilized photosensitizers and catalysts.

Performance of Li4Ti5O12-based reference electrode for the electrochemical analysis of all-solid-state lithium-ion batteries

The establishment of three-electrode cells for all-solid-state lithium-ion batteries is an important issue to clarify the electrochemical behavior of the battery components and solve problems for the practical applications. Here we prepared an all-solid-state three-electrode cell with a chemically-reduced Li4Ti5O12 reference electrode and investigated electrochemical properties of a LiCoO2 composite electrode in a Li-In|Li10GeP2S12|LiCoO2 cell. Plateau potentials in charge-discharge curves were coincident with reported values. Cell impedance measured with two-electrode configuration agreed well with the sum of the impedances of the positive and the negative electrodes measured with the reference electrode. These results show that chemically-reduced Li4Ti5O12 reference electrode was worked as a Li7Ti5O12|Li4Ti5O12 reference electrode and electrochemical properties of the LiCoO2 electrode and the Li-In electrode were separated. From the temperature and the state of charge dependences of LiCoO2 impedance, resistances related to interface or interphase and charge-transfer reaction were identified. These results show that all-solid-state cells with chemically-reduced Li4Ti5O12 reference electrodes are promising candidates for three-electrode cells for all-solid-state lithium-ion battery systems.

The effects of H2O, He, N2 and H2 on ion kinetic energies in inductively coupled plasma mass spectrometry

This study compares measurements of ion energy and the polyatomic species abundance in conventional solution inductively-coupled plasma mass spectrometry (ICP-MS) and laser ablation ICP-MS for multiple quadrupole instruments. Ion energy measurements in plasma sources have been used as a diagnostic tool for understanding processes occurring within the plasma during extraction of ions. Ion energy measurements have also allowed for determination of the nature of polyatomic species formation. In this study, ion energy measurements show that dry plasma conditions (laser ablation) result in a different ion energy distribution vs. mass compared to wet plasma (solution nebulization), suggesting a lower apparent temperature for dry plasma. The effect of helium and nitrogen or hydrogen additions to an argon plasma shows that helium is unlikely to ionize in the plasma or participate in charge transfer reactions, but primarily affects the interface pressure between the cones and the temperature of the plasma. Hydrogen addition to a dry plasma shows a slight increase in atomic ion energy, while nitrogen addition does not, and this suggests the two diatomic gases behave differently in the plasma. Investigation of ion energies with and without electrically shielding the torch shows no net benefit to using the shield for dry plasma. This behaviour, as well as differences in ion lens settings required for optimal ion beam properties, suggests different capacitive coupling between wet and dry plasma (un-shielded torch). This has implications for the optimal configurations of interface design of ICP-MS, which until now have been optimized primarily for wet plasma conditions.

Innovative wastewater treatment based on electrodeposited thin film: Systematic studies of interfacial processes between birnessite and Mn(II) for a better efficiency

Electrodeposited birnessite thin films have remarkable properties for spontaneous degradation of organic pollutants until mineralization via a complex mechanism of charge transfer reactions. But, birnessite may be transformed into passivated material by reaction with Mn(II) species generated during the reduction of birnessite due to oxidation of organic pollutants. Such modification could imply a possible inhibition of the degradation process, a depreciated condition for future applications. This paper focuses on the determination of the real robustness of electrodeposited birnessite thin films and their quality for innovative wastewater treatment. Systematical studies were performed with solutions containing different Mn(II) concentrations in presence and in absence of oxygen to have unfavorable conditions. Samples were characterized at macroscopic scales (SEM and XRD) in addition to a focused study on the chemical modification at the extreme near surface by XPS. Open circuit potential (OCP) was also followed to complete the study. Similar characterizations were performed after interaction with organic pollutants solutions. As a result, nature and structure of the bulk and the near surface of birnessite stay unchanged after long times even in absence of oxygen or in presence of organic pollutants at high concentrations, proving their very good robustness and real interests for future applications.

Redox-Active Vertically Aligned Mesoporous Silica Thin Films as Transparent Surfaces for Energy Storage Applications.

Organic-inorganic hybrid membranes, made of a high density of redox active moieties covalently bonded to the internal surfaces of vertically aligned mesoporous silica thin films, are relevant for applications in transparent energy storage devices. This is demonstrated here on the basis of functionalized transparent mesoporous silica thin films prepared on the indium-tin oxide electrode from the combination of an electrochemically induced self-assembly method (to generate azide-functionalized silica) and a copper-catalyzed azide-alkyne click reaction (to derivatize the material with electroactive groups). The very small thickness (105 nm) and the uniformly distributed vertical mesochannels with ultranarrow diameter (2 nm) make the hybrid film a promising substrate that not only achieves a transparency of 82% but also provides large surface area to accommodate a high density of redox active species such as ferrocene. In such rigid and insulating porous membranes, the charge transfer reactions take place through a pure electron-hopping mechanism between adjacent redox sites, which are favored by the ordered and oriented mesostructure containing large amounts of uniformly distributed ferrocene functions in the mesochannels. Their performance results from both high charge transfer rates (electron hopping) and easy mass transport (fast diffusion of counter ions). The most effective system is the ferrocene-functionalized silica film prepared from 40% organosilane, which is able to deliver a capacity of 105 C cm-3 (1.10 mC cm-2) at a current density of 0.4 A cm-3 (with up to 48% capacity retention achieved at a charging time as short as 2.8 s). Such an electrode can be associated to an electrodeposited graphene anode in a solid-state battery-capacitor hybrid device, which can deliver 0.74 mC cm-2 at a potential scan rate of 20 mV s-1. The azide-functionalized mesoporous silica film is actually a versatile platform that can be functionalized with different redox molecules, as shown here for cobaltocenium moieties, which may broaden its application field.

FexP/biochar composites induced oxygen-driven Fenton-like reaction for sulfamethoxazole removal: Performance and reaction mechanism

Fe-based phosphide has shown tremendous potential for heterogeneous catalysis due to its superior activity. Herein, a series of FexP/biochar composites were successfully prepared through a simple pyrolysis process. Iron species (FeOOH) was pre-loaded on the surface of phosphorus-containing biomass (yeast), which was subsequently converted to FexP/biochar with the assistance of in-situ produced reducing gases (H2, CO, PH3, etc.). When applied for typical antibiotic pollutant (sulfamethoxazole, SMX) removal, the optimal material (FexP/BC-5) performed well with a 99% removal efficiency in 30 min via the synergistic effects of adsorption and degradation by activation of dissolved oxygen (DO). Reactive oxygen species, including H2O2, ·OH, O2− and 1O2, were generated in FexP/BC-5/DO system by charge transfer and Fenton-like reaction. FexP/BC-5 was applicable in a broad pH range from 3.0 to 9.0 and exhibited good reusability in five recycle runs after regeneration. Moreover, the primary reactions in SMX degradation process were discussed based on identified intermediates by liquid chromatography–mass spectrometry (LC–MS). This work not only develops a simple approach to construct iron phosphides/biochar using green and sustainable phosphorus source but also bring new insights for environmental pollutants remediation by oxygen activation.

(Invited) Designing SOC for Power-to-X Applications: A Multi-Physical Modelling Approach

In the current global energy transition, the Solid Oxide Cell (SOC) represents a promising technology for stationary energy generation and storage, since it facilitates highly efficient and low-emission energy conversion. Besides converting hydrogen or hydrocarbon fuels directly into electricity in fuel cell mode, the SOC can also be operated in a reverse mode as a Solid Oxide Electrolyzer Cell (SOEC). By operating the SOC as an electrolyzer, any surplus electrical energy produced from fluctuating renewable energy sources (e.g. solar or wind energy) can be utilized to synthesize syngas and subsequently hydrocarbon fuels. The outlet syngas composition is directly correlated to the applied operating conditions as H2O/CO2-ratio, temperature and current. Therefore, it is of utmost importance to gain a deep understanding of these relationships in order to establish optimal operational strategies for different applications.During electrolyzer operation the key component of the SOC is the fuel electrode (anode), since it facilitates the (i) electrochemical charge transfer reaction and (ii) the chemical reaction kinetics (cf. Fig. 1(c)). In state-of-the-art, anode-supported SOCs the anode relies on two porous, Ni / stabilized zirconia layers with specified phase compositions and microstructural characteristics: (i) the highly porous and catalytically active anode substrate (AS) and (ii) the electrochemically active anode functional layer (AFL) (cf. Fig. 1(a)). To raise fuel conversion efficiency, we must first gain a profound understanding of the optimal double-layer design for the desired application. Numerical simulations enable an efficient variation of geometrical, microstructural and material parameters over wide ranges and provide correlations between anode design and SOEC performance.In this contribution, we demonstrate a multi-physical modelling approach to predict the SOC performance in both fuel cell and electrolyzer operation. To do so, we combine two of our recently published modelling approaches: (i) the physically meaningful, three-channeled transmission line model for double-layered cermet anodes [1,2] and (ii) the non-isothermal FEM stacklayer model [3,4]. For the first time, a powerful mode framework is realized (cf. Fig. 1(b)), which is capable of spatially resolving all of the above mentioned processes, in both anode layers, within a complete stacklayer. The model considers the complex interplay of (i) multi-component gas transport coupled with (ii) catalytic reforming reactions, (iii) charge carrier transport, (iv) electrochemical charge transfer, (v) coupled heat release and consumption as well as (vi) heat transport in the individual stack components.We demonstrate a comprehensive, model-based optimization of Ni-based cermet anodes in a SOC stack layer with respect to (i) the selection of the electrolyte material, (ii) the modification of the microstructure and (iii) adapting of the layer thicknesses. Furthermore, the impact of the operating conditions on the optimal cell configuration will be discussed. Finally, we derive operational strategies for efficient SOEC operation by investigating the impact of (i) the inlet gases, (ii) the operating temperature and (iii) the applied current on the produced syngas composition.[1] S. Dierickx, J. Joos, A. Weber, E. Ivers-Tiffée, Advanced impedance modelling of Ni/8YSZ cermet anodes, Electrochim. Acta. 265 (2018) 736–750.[2] S. Dierickx, T. Mundloch, A. Weber, E. Ivers-Tiffée, Advanced impedance model for double-layered solid oxide fuel cell cermet anodes, J. Power Sources. 415 (2019) 69–82.[3] H. Geisler, A. Kromp, A. Weber, E. Ivers-Tiffée, Stationary FEM Model for Performance Evaluation of Planar Solid Oxide Fuel Cells Connected by Metal Interconnectors, J. Electrochem. Soc. 161 (2014) F778–F788.[4] N. Russner, S. Dierickx, A. Weber, R. Reimert, E. Ivers-Tiffée, Multiphysical modelling of planar Solid oxide fuel cell stack layers, J. Power Sources (in press). Figure 1

Heterogeneous Damage in Li-Ion Batteries: Experimental Analysis and Theoretical Modeling

We assess the heterogeneous electrochemistry and mechanics in a composite electrode of commercial batteries using synchrotron X-ray tomography analysis and microstructure-resolved computational modeling. We visualize the morphological defects at multi-scales ranging from the macroscopic composite, particle ensembles, to individual single particles. Particle fracture and interfacial debonding are identified in a large set of tomographic data of active particles. Mechanical failure in the regime near the separator is more severe than toward the current collector. The active particles close to the separator experience deeper charge and discharge over cycles and thus are more mechanically loaded. The difference in the Li activity originates from the polarization of the electrolyte potential and the non-uniform distribution of the activation energy for the charge transfer reaction. We model the kinetics of intergranular fracture and interfacial degradation to confirm that the various Li activities are the major cause of the heterogeneous damage. The interfacial failure may reconstruct the conductive network and redistribute the electrochemical activities that render a dynamic nature of electrochemistry and mechanics evolving over time in the composite electrodes. We further quantify the influence of the mechanical damage on the metrics of battery performance. We simulate the electrochemical impedance profile to build a relationship between the interfacial debonding and the impedance of electron transport and surface charge transfer. The mechanical failure disrupts the conduction path of electrons and results in significant polarization and capacity loss in batteries.

Controllable Vacancy Redistributions in Embedded Thin Films Under Concentrated Electric Fields

The redistribution and accumulation of oxygen vacancies under electric field underpins both the functionality and degradation of electrical and electrochemical devices comprising oxide layers. Interfacial accumulations of oxygen vacancies form defect dipoles, significantly reduce the breakdown strength, increase the breakdown path area, yet facilitates charge transfer reactions. Confinement of both oxygen vacancy redistributions and their mobility remains critical to preserving function in oxide systems.Here we study one of the most important, yet random transport processes: the redistribution of oxygen vacancies in binary oxides under high local electric fields. The ability to identify or predefine the shape, size, and location of vacancy distributions is critical to controlling interfacial properties of functional oxides. We achieved superior uniformity in HfO2 films by embedding highly-ordered metal nanoisland (NI) arrays to act as electric field concentrators. Embedded films exhibit significant reduction in operating voltages while displaying enhanced uniformity of resistance states. This behavior is attributed to the concentration of electric fields along Pt and Ti NIs and their interactions with the surrounding oxide film matrix environment, which induce separate and distinct filamentary formation mechanisms that affect the stability. A comparison of the density and distribution of the oxygen vacancies responsible driving filament dynamics is made via combined electrostatic force microscopy (EFM) and conductive atomic force microscopy (c-AFM) studies. Finally, the morphological evolution of conducting vacancy filaments is enabled by three-dimensional (3-D) c-AFM nanotomography and cross-sectional scanning transmission electron microscopy – energy dispersive spectroscopy (STEM-EDS) to provide direct correlations of nanoisland-oxide interactions with overall switching performance. The application of these exciting results to other vacancy-mediated electronic and electrochemical processes will also be discussed.

An Evaluation of Carbon Steel Corrosion in Nitrate Solution Using Electrochemical and Solution Analysis Methods

Nuclear power reactors offer a long term, cost efficient and sustainable method to produce electricity with very low greenhouse gas emissions. As nuclear reactors age and their lifetimes are extended, accurate assessment of the integrity and longevity of the reactor structural materials is increasingly important. Corrosion in the vicinity of a nuclear reactor core happens in the presence of high energy, ionizing radiation, which needs to be considered. In particular, the potential for accelerated (galvanic) corrosion attack on carbon steel (CS) adjacent to the dissimilar metal weld between CS (SA 36) and stainless steel (SS) (Type 304L) at the periphery of the annular gap must be addressed.The initial environment inside the gap of structural support for End Shield Cooling (ESC) System could be humid due to trapped water in its annular gap. The pH of the ESC System water is adjusted to around 10.4, but when it condenses onto the weld region the pH might change. The oxygen level, the humidity, and many other factors will change with time. In addition, ionizing radiation decomposes water into a range of redox active species ranging from highly oxidizing (e.g., •OH and H2O2) to highly reducing (e.g., •eaq -) whose concentrations evolve with time (1-4). Humid-air radiolysis produces nitric acid (HNO3), that can dissolve into the water (5). The radiation products will lower the pH of the water in the droplet.In this work, corrosion of CS is evaluated carefully, and the effect of all solution reactions on interfacial charge transfer reactions is considered.The effect of [NO3 -] and solution pH is studied by using potentiodynamic polarization experiments and corrosion potential measurements (Figure 1), along with solution analysis. The results of polarization measurements in the presence of 0.01 M and 0.1 M [NO3 -] (with initial pH 2.0) show that the oxidation reactions are implicitly influenced by the mass transfer of metal cations from the CS surface into the solution. Also, the comparison of the rate of corrosion measured using Tafel extrapolation method and those obtained from ICP measurements suggests that the Tafel extrapolation method enormously underestimate the corrosion rate (in this case by about 100 times for 8 h corrosion) and must be applied more carefully.In order to study the effect of pH, we have compared the electrochemical results in pH 2.0 and pH 6.0 obtained in different concentrations of nitrate. The results show that solution pH is a rate controlling factor and the metal oxidation is limited by the metal transfer even at potentials close to/at the corrosion potential, and this influence the rate of corrosion.The results of this work imply that solution reactions can alter the corrosion behavior of carbon steel and hence, its galvanic coupling with stainless steel.

First-Principles Study for Fluorination/Defluorination Reaction Mechanism in Fluoride-Shuttle Batteries

INTRODUCTIONRechargeable batteries with energy densities higher than those of the present Li-ion batteries (LIBs) are required for electric vehicles. We focus on fluoride-ion (F−) transfer batteries whose electrodes are composed of metal/metal fluoride (M|MF n ) combinations. Electrochemical charge-transfer reactions occur during the discharge/charge processes at the two electrodes. Defluorination of the metal fluoride MF n and fluorination of another metal M’ occurs at the positive and negative electrodes, respectively, during the discharging process asM1/n F + e− → M1/n + F− (1),M’1/m + F− → M’1/m F + e− (2).This type of battery is called a fluoride-shuttle battery (FSB), which is expected to produce high voltage and have large capacity.1 In 2017, Okazaki et al. fabricated a Bi|BiF3 electrode with a liquid electrolyte prepared by dissolving an organic fluoride in an ionic liquids (ILs) at room temperature. 2 In 2018, Davis et al. reported another type of liquid electrolyte composed of a simple organic solvents (OSs) with F−conductivity greater than 1 mS/cm.3 From the development of these liquid electrolytes, the F− conductivity has been dramatically increased in recent years. After improvement of the electrolyte conductivity, the fluorination and defluorination reactions at the electrodes are considered to be the rate-determining steps in FSBs. However, the mechanism of the fluorination and defluorination reactions in FSBs has not been clarified in contrast to the well-investigated Li-intercalation reaction in LIBs.METHODSIn this study, we classify the fluorination and defluorination reactions into two possible reaction pathways from a thermodynamic point of view: reaction through the solid-solution state and reaction through the two-phase state. It is possible to find which reaction pathway is realized from the free energy difference. Selection of these reaction pathways can be determined from the enthalpies of all of the intermediate states, since the entropy term in the free energy is fairly cancelled when we consider the difference of free energies. Selection rule for the fluorination and defluorination reactions in FSBs is schematically illustrated in Figure 1. The solid-solution states of M1/n F x for x ≈ 0 and for x ≈ 1 are assumed to be formed by introducing an interstitial and a vacancy defect, respectively. In this case, the free energy relation for the selection can be described as G ss(x) < G tp(x) → H I(M1/n ) < H(M1/n F) or H(M1/n F) < −H V(M1/n F) (3),where G ss(x), G tp(x), H (M1/n F), H I(M1/n F) , H V(M1/n F) are the free energy of the solid-solution state of M1/n F x , that of two-phase state, the formation enthalpy of M1/n F, that of interstitial defect in M1/n , and that of vacancy defect in M1/n F, respectively. We use the energies from first-principles calculations for the enthalpy differences, whose accuracy is validated by comparing them with experimentally obtained thermodynamic enthalpy data.4 The first-principles calculations were performed with the configurations of the bulk crystal systems using Quantum Espresso package.5 The crystal data were taken from the AtomWork database.6 RESULTSThe relative formation enthalpies of typical, transition, and relativistic metal fluorides are well reproduced by first-principles calculations within 0.1, 0.2, and 0.4 eV, respectively. By comparing the formation enthalpies of H, H V, and H I, the relation H I > H > −H V is always satisfied in all of the calculated metal and metal-fluoride combinations (M = Li, Mg, Ca, Al, Co, Ni, Cu, Pb, Bi). Thus, the selection rule of eq. (3) strongly suggests that fluorination and defluorination in FSB electrodes occur by two-phase reaction.7 This fluorination and defluorination mechanism will be useful to clarify the rate-determining step in FSBs.AcknowledgmentsThis work was supported by the Research and Development Initiative for Scientific Innovation of New Generation Batteries 2 Project (RISING2) administrated by the New Energy and Industrial Technology Development Organization (NEDO).REFERENCES1) F. Gschwind, G. Rodriguez-Garcia, D. Sandbeck, A. Gross, M. Weil, M. Fichtner, N. Hörmann, J. Fluorine Chem. 182, 76 (2016).2) K.-I. Okazaki, Y. Uchimoto, T. Abe, Z. Ogumi, ACS Energy Lett. 2, 1460 (2017).3) V. K. Davis et al., Science 362, 1144 (2018).4) Handbook of Chemistry: Pure Chemistry, 5th ed.5) P. Giannozzi et al., J. Phys.: Condens. Matter. 29, 465901 (2017).6) National Institute for Materials Science (NIMS) AtomWork <http://crystdb.nims.go.jp/>7) J. Haruyama, K.-I. Okazaki, Y. Morita, H. Nakamoto, E. Matsubara, T. Ikeshoji, M. Otani, “Two-Phase Reaction Mechanism for Fluorination and Defluorination in Fluoride-Shuttle Batteries: A First-Principles Study” in revision. Figure 1. Two reaction pathways considered in this study. In the fluorination and defluorination reactions, the solid-solution (M1/n F x , 0 < x< 1) and two-phase (M1/n and M1/n F) states are considered to be possible intermediate states. Figure 1

Fabrication of bionic flower-like g-C3N4/Bi4O5I2 photocatalyst with enhanced photocatalytic performance

The g-C3N4/Bi4O5I2 bionic flower-like structure was facilely synthesized by one step calcination method, and the as-prepared samples were characterized by XRD, UV-vis DRS, photoelectron chemical analysis etc. There obviously exists the phenomenon of a certain right shift for absorption edge of bionic composites according to UV-Vis DRS tests. The mercury removal efficiency of NB-1 (the doping content of g-C3N4 is 1 mmol) can be improved by 76%, which is higher than that of g-C3N4 and Bi4O5I2. Electrochemistry confirms that the bionic structure is beneficial to facilitate the migration efficiency and suppress the surface charge recombination, in turn improve the photocatalytic performance. In addition, the heterostructure between g-C3N4 and Bi4O5I2 are built for efficient modulating the charge transfer channels in the interface/surface to enhance photocatalytic efficiency of Hg0. On the basis of experiment and characterization, a reasonable and convincing mechanism of charge transfer and photocatalytic reaction on Hg0 was proposed.

Study of oxygen electrode reactions on symmetrical porous SrTi0.30Fe0.70O3-δ electrodes on Ce0.8Gd0.2O1.9 electrolyte at 800 °C–500 °C

Iron doped strontium titanates (SrTi1-xFexO3-δ) are an interesting mixed ionic-electronic conductor model used to study basic oxygen reduction/oxidation reactions. In this work, we performed an impedance spectroscopy study on symmetrical porous SrTi0.30Fe0.70O3-δ (STF70) electrodes on a ceria-based electrolyte. The sample was measured in varying oxygen concentration: from 0.3% to 100% in 800 °C–500 °C temperature range. Low polarisation resistance (e.g. <125 mΩ cm2 at 600 °C in the air) values were obtained, showing an overall high performance of the STF70 electrode. Impedance data analysis was assisted by the distribution of relaxation times method, which allowed an equivalent electrical circuit to be proposed comprising of two resistance/constant phase element sub-circuits connected in series. The medium frequency contribution, with a characteristic frequency of ∼2000 Hz at 800 °C in air, originates most probably from possible surface diffusion followed by charge transfer reaction limitation, whereas the lower frequency contribution (characteristic frequency <10 Hz) is due to gas-phase diffusion.

Direct dissolution of uranium oxides in deep eutectic solvent: An insight using electrochemical and luminescence study

Nuclear energy is going to be the most potential option for solving the global energy crisis owing to its cost efficiency and environment friendliness. This work was carried with objective to propose a cheap, non-toxic and green solvent for dissolution of actinide oxide which is highly relevant from nuclear fuel reprocessing point of view. This prompted us to take the challenging research problem of investigating the dissolution behavior of different Uranium oxides (UO3, UO2 and U3O8) in p-Toluenesulfonic acid monohydrate (PTSA) based deep eutectic solvent (DES) and investigating its redox behavior and speciation using cyclic voltammetry (CV) and photoluminescence spectroscopy. We initiated with synthesis of relatively new class of DES consisting of Choline chloride (ChCl) and PTSA using mechanochemical route. The metal concentration dissolved was determined by EDXRF and it was found that PTSA: ChCl (1:2) was better in terms of solubility for uranium oxides as compared to PTSA: ChCl (1:1) and Malonic acid: ChCl (1:1). The formation of DES consisting of Hydrogen bonding network is confirmed using attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy. It could also be found that uranium oxide dissolution doesn’t distort the H-bonding network of DESs. Based on CV results it was proposed that U(VI)/U(V) reduction is controlled not only by diffusion of U(VI) ion in PTSA:ChCl (1:2), but also by the kinetics of the charge transfer reaction occurring at the electrode-electrolyte interphase. Luminescence spectroscopy suggested U(VI) in DES has U–O single bond moiety, having UO66− local coordination with excited state lifetime of 9.5 μs.

High Voltage Electrodes for Li-Ion Batteries and Efficient Water Electrolysis: An Oxymoron?

We demonstrate that key parameters for efficient electrocatalytic oxidation of water are the energetics of the redox complexes associated with their ionization and electrochemical potentials coupled to the change of metal-oxygen band hybridization. We investigate the catalytic activity of the LiCoPO4-LiCo2P3O10 tailored compound, which is a 5 V cathode material for Li-ion batteries. The reason for the weak catalytic activity of the lithiated compound toward the oxygen evolution reaction is a large energy difference between the electronic states involved in the electrochemical reaction. A highly active catalyst is obtained by tuning the relative energetic position of the electronic levels involved in the charge transfer reaction, which in turn are governed by the lithium content. A significant lowering of the overpotential from >550 mV to ∼370 mV at 10 mA cm-2 is achieved via a decrease of the ionization potential and shifting the electrochemical potential near the electronic states of the molecule, thereby facilitating water oxidation.

Electropolymerization growth of an ultrathin, compact, conductive and microporous (UCCM) polycarbazole membrane for high energy Li–S batteries

Abstract Rationally constructing an interlayer to suppress the lithium polysulfide (LiPS) shuttling but allow fast transport of Li-ions is of great significance for high-density Li–S batteries. Despite numerous nanomaterials have been explored, an effective approach to fabricate an ideal interlayer is still elusive. Herein, we developed a new electropolymerization strategy to grow in-situ a polycarbazole-type interlayer with a number of merits to boost the reversible capacity. Firstly, the membrane is microporous but compact with uniform 0.82 nm nanochannels that can effectively suppress the diffusion of polysulfide species. Secondly, using the CNT (700 nm) as conductive substrate, the electropolymerized membrane is ultrathin (60 nm), which facilitates fast transport of lithium ions and rate performance. Thirdly, the membrane is electron conductive (23 S m−1) that benefits the charge transfer and redox reaction. Li–S batteries configured with such an UCCM type of interlayer have showed enhanced sulfur utilization by threefold, with a reversible capacity of 920 mA h g−1 after 600 cycles at 0.2 C, and a high areal density of 10 mAh cm−2 at 11.2 mg cm−2 sulfur loading. A safer lithium-ion sulfur full-cell with lithiated graphite anode demonstrated a stable capacity over 4 mAh cm−2 under a low electrolyte/sulfur ratio of ~10 μL mg−1.

Co-deposition of silica and proteins at the interface between two immiscible electrolyte solutions

In this work, we have simultaneously examined, electrochemically driven deposition of three proteins (haemoglobin, acid phosphatase, and α-amylase) and silica films at a polarized liquid–liquid interface. The interfacial adsorption of the proteins occurs efficiently within the acidic pH range (pH = 2–4). The interfacial charge transfer reactions recorded in the presence of fully positivity charged macromolecules were followed with cyclic voltammetry on the positive side of the potential window. Faradaic currents attributed to the presence of proteins in the aqueous phase appeared for concentrations equal to ca. 0.1 µM for haemoglobin and acid phosphatase and ca. 1 µM for the α-amylase. Concomitant deposition of silica films was achieved via the addition of tetraethoxysilane molecules to the organic phase (1,2-dichloroethane). The hydrolysis and condensation reactions of tetraethoxysilane were controlled via the interfacial transfer of H+ coinciding with the potential for protein adsorption. The effect of tetraethoxysilane concentration – up to 50% by volume – revealed significant shrinkage of the potential window (the region where capacitive currents are recorded). The optimized platform was then used to prepare silica-proteins co-deposits. These could be easily collected from the interface and further analyzed with infrared spectroscopy and transmission electron microscopy.

Synthesis of natural deep eutectic solvents using a mixture design for extraction of animal and plant samples prior to ICP-MS analysis

Solvents with both low density and viscosity have the advantage of higher extraction efficiency due to lower diffusivity and consequently higher mass transfer. In this study, a mixture design was performed for the synthesis of three different natural deep eutectic solvents (NADES) using citric acid, malic acid, and xylitol. The optimized proportion for each of the three solvents synthesized was selected based on density and viscosity values. The NADES were characterized by infrared spectroscopy analysis, that showed characteristic bands of the initial reagents and the presence of hydrogen bonds confirming the formation of each deep eutectic solvent. Then, the NADES were used as solvents in ultrasound-assisted extraction (UAE) and microwave-assisted extraction (MAE) of biological tissue and plant material samples for the determination of As, Cd, Hg, Pb, Se, and V by inductively coupled plasma mass spectrometry (ICP-MS). The results for the proposed methods were compared to microwave-assisted acid digestion (MW-AD). The extraction recoveries ranged from 80 to 120% for most of the elements determined. The use of NADES as carbon sources improved the sensitivity of the As and Cd analyses, due to charge transfer reactions between the analyte and C+ and/or other carbon species. In addition, the Analytical Eco-Scale was used to assess the greenness of the proposed analytical procedures (UAE and MAE). It showed that the UAE and MAE methods provided excellent green analyses, while the MW-AD method was rated as an acceptable green procedure.