Charge Compensation Process Research Articles

Exploiting charge/ions compensating processes in PANI/SPANI/reduced graphene oxide composite for development of a high sensitive H2O2 sensor

The present work describes the development of a polyaniline/polyaniline-2-sulfonic acid/reduced graphene oxide composite (PANI/SPANI/rGO) modified electrode by electropolymerization to detection of hydrogen peroxide. The ionic transport at the PANI/SPANI/rGO film was evaluated by the investigation of the protonic and anionic participation in the charge compensation processes. The sulfonic group and reduced graphene oxide in the composite film contribute to suppression of the anionic transportation and improve the composite ability to fixing cytochrome c redox protein (Cytc). The ability of the PANI/SPANI/rGO film in absorbing the Cytc resulted in a high sensitivity (0.45μALμmol−1), high linear range (from 0.1μmolL−1 up to 1000μmolL−1) and low limit of detection (0.04μmolL−1) to hydrogen peroxide. Indeed, the hybrid organic–inorganic sensor exhibited a good reproducibility and stability to H2O2 reduction at an applied potential of −200mV vs. Ag/AgCl.

High-capacity electrode materials for rechargeable lithium batteries: Li3NbO4-based system with cation-disordered rocksalt structure

Rechargeable lithium batteries have rapidly risen to prominence as fundamental devices for green and sustainable energy development. Lithium batteries are now used as power sources for electric vehicles. However, materials innovations are still needed to satisfy the growing demand for increasing energy density of lithium batteries. In the past decade, lithium-excess compounds, Li2MeO3 (Me = Mn(4+), Ru(4+), etc.), have been extensively studied as high-capacity positive electrode materials. Although the origin as the high reversible capacity has been a debatable subject for a long time, recently it has been confirmed that charge compensation is partly achieved by solid-state redox of nonmetal anions (i.e., oxide ions), coupled with solid-state redox of transition metals, which is the basic theory used for classic lithium insertion materials, such as LiMeO2 (Me = Co(3+), Ni(3+), etc.). Herein, as a compound with further excess lithium contents, a cation-ordered rocksalt phase with lithium and pentavalent niobium ions, Li3NbO4, is first examined as the host structure of a new series of high-capacity positive electrode materials for rechargeable lithium batteries. Approximately 300 mAh ⋅ g(-1) of high-reversible capacity at 50 °C is experimentally observed, which partly originates from charge compensation by solid-state redox of oxide ions. It is proposed that such a charge compensation process by oxide ions is effectively stabilized by the presence of electrochemically inactive niobium ions. These results will contribute to the development of a new class of high-capacity electrode materials, potentially with further lithium enrichment (and fewer transition metals) in the close-packed framework structure with oxide ions.

EPR study of the ground state of Mn2+ impurity ions in alumoborates MAl3(BO3)4 (M = Y, Eu, Tm)

New data about the ground state of the Mn2+ impurity ions in a series of single crystals of alumbrados MAl3(BO3)4, where M = Y,Eu,Tm were obtained. The electron paramagnetic resonance (EPR) spectra of the Mn2+ spectra were studied, the parameters of the spin Hamiltonian describing the angular dependence of the spectrum were defined. It was shown that Mn2+ ions substitute trivalent ions of rare earth metals without changing the symmetry of the substitution site. The charge compensation process was found to be a nonlocal one. The cooling of the crystals leads to the increase of the splitting of the ground state, which is associated with the anisotropy of the thermal expansion coefficient. It was shown that an application of the superposition model to explain the distortions induced by an impurity Mn2+ ion has some limitations. The EPR linewidth of the Mn2+ ion in the TmAl3(BO3)4 crystal increases with increasing temperature as a result of the dipole–dipole and exchange interactions with the excited states of the host lattice Tm3+ ion.

Effect of annealing atmosphere on the cerium valence state and F+ luminescence center in Ca‐codoped GGAG:Ce single crystals

GGAG:Ce crystals with various Ca concentrations were grown by the Czochralski technique. The introduction of Ca2+ ions into a trivalent site results in a change in the Ce valence state as well as an additional F+ luminescence center. The changes of Ce valence state could be affected by various annealing atmospheres and were investigated via measuring the Ce3+ absorbance and observing the color change of the sample. Photoluminescence spectra and photoluminescence decay were used to reveal the occurrence of F+ center related to the oxygen vacancies during the annealing. A redox mechanism and a charge compensation process are proposed to explain the change in Ce state charge and F+ center during the annealing.

First-principles study of native defects in LiTi2O4

In this study, we report on a fundamental first-principles investigation of native point defects in spinel LiTi2O4, an alternative electrode material for lithium ion batteries (LIBs). Under O-rich conditions, Ti vacancy (VTi) and Li antisite (LiTi) are energetically favorable, but Ti interstitial (Tii) has highest formation energy and is hence unstable. While Li interstitial (Lii) is the most stable configuration in O-poor conditions, and O vacancy (VO), Ti interstitial (Tii), Li antisite (LiTi) and Ti antisite (TiLi) have almost the same formation energies, suggesting spontaneous formation of defect complexes. According to the calculated electronic structures of defects, no localized states are found in the gap between the O 2p and Ti t2g states, which is considerable related to the charge compensation process between O and Ti ions. Besides, Li vacancy (VLi) and Li interstitial (Lii) are the most stable defect types with negligible structural changes, while other defects will induce large octahedral disorders and suppress Li ions mobility. These results not only reveal the original defect information of LiTi2O4, but also provide practical guidance to the development of this material.

Lithium ion electrochemical insertion in vanadium pentoxide/cucurbit[6]uril intercalates

Cucurbit[6]uril (CB[6]) and its complex with VO2+ (CB[6]VO) were intercalated into lamellar vanadium pentoxide in several proportions, generating a series of hybrid pillarised intercalates in the form of xerogel films. These different guests dramatically affect Li+ insertion/expulsion from the composites during redox processes. Our results show that CB[6] has little effect or may even impair charge compensation by Li+, while CB[6]VO exerts the opposite effect, enhancing this process when compared to pure vanadium pentoxide. This is clear evidence that CB[6] binds these ions retaining them in the bulk structure, and when the oculi are blocked by VO2+ ions, the macrocycle acts as a non-coordinating pillar in the structure favoring ion traffic, and charge compensation processes become easier. Specific charge capacities for pure vanadium pentoxide, CB[6] and CB[6]VO intercalates correspond to 158, 168 and 230 mA h g−1 respectively.

Application of horseradish peroxidase/polyaniline/bis(2-aminoethyl) polyethylene glycol-functionalized carbon nanotube composite as a platform for hydrogen peroxide detection with high sensitivity at low potential

Polyaniline/O,O′-bis (2-aminoethyl) polyethylene glycol-functionalized multiwalled carbon nanotube (PANI/PEG–MWCNT) composite-modified electrode was successfully prepared by electropolymerization. The ionic transport in PANI/PEG–MWCNT film and its effects on the composite performance are presented. Both protonic and anionic participation in the charge compensation processes were calculated and they indicated that the presence of the PEG–MWCNT in the PANI film suppress the anionic transportation and improve the composite ability in fixing horseradish peroxidase enzyme. Finally, the adsorption between the negatively charged PANI/PEG–MWCNT nanocomposite and the positively charged Horseradish peroxidase resulted in a high sensitivity (1.01 μA L cm−2 μmol−1) to hydrogen peroxide. This sensor exhibited a good reproducibility and stability at an applied potential of −100 mV vs Ag/AgCl.

Effect of Na-, K-, Mg-, and Ga dopants in A/B-sites on the optical band gap and photoluminescence behavior of [Ba0.5Sr0.5]TiO3 powders

In this work, the role of the representative metal dopants (Na, K, Mg and Ga) in A/B-sites of [Ba0.5Sr0.5]TiO3 powders (in short BST) synthesized by sol–gel method have been investigated. As revealed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and UV–visible spectroscopy, Na and K can be occupied into A-site, while Mg and Ga can be substituted on B-site of BST powders. It was found that the optical band gap energies of modified B-site are higher than modified A-site of BST powders. The possible mechanisms of intermediate energy levels between optical band gaps were suggested by photoluminescence (PL) behavior. The four major optical emissions in visible range were found to be 2.95, 2.80, 2.55, and 2.33eV. The 2.95eV in violet PL emissions is related to the electron transfer in octahedral [TiO6] clusters. Moreover, this energy level is attributed to the charge compensation process due to acceptor substitution defects in order to preserve the overall charge neutrality in the BST crystal. The 2.85eV in blue PL emissions is attributed to the fully-ionized oxygen vacancy (VO••) in BST powders. The 2.55 and 2.33eV in green PL emission are assigned to the charge-transfer of singly-ionized oxygen vacancy (VO•) and the charge transfer vibronic excitons (CTVE) in BST perovskite, respectively. In additional, as revealed by electron paramagnetic resonance (EPR), modified B-site of BST powders facilitated titanium vacancy more than modified A-site. The X-ray photoelectron spectroscopy (XPS) results indicated that modified B-site of BST powders were easily created oxygen deficiency than modified A-site. However, the oxygen deficiency significantly affected on A-site of the Sr atoms site more than A-site of the Ba atoms, it might be a result of the strength of chemical bond of Sr–O bonds which is lower than Ba–O bonds.

Colour control in SrS:Cu,Cl powder phosphor

Abstract By controlling the concentration of defects and their type in strontium sulphide phosphor, a broad range of colours in the visible spectrum can be achieved. Photoluminescence (PL) spectrum in the blue to green range of SrS:Cu,Cl is presented and explained on the basis of charge compensation process and coordination about the Cu + ion. Analysis of lattice parameter, strain and grain size were carried out on the basis of X-ray diffraction (XRD) data. From the study of diffuse reflectance spectra (DRS), red-shift in band-gap was observed with increasing doping concentration, which is due to the presence of doping induced tail states.

Effects of electrolyte composition on the electrochemical activation of alkali-treated soft carbon as an electric double-layer capacitor electrode

The electrochemical behavior of alkali-treated soft carbon (ASC) has been investigated in organic electrolyte solutions with different compositions. So-called electrochemical activation phenomena, in which higher capacitive currents are observed after certain anodic or cathodic polarization in the electrolyte solutions, depended on the electrolyte composition as well as its polarization condition. The anodic polarization in tetraethylammonium tetrafuruoroborate (TEABF 4) solutions induced higher capacitive currents in the positive potential region where the electrochemical adsorption/desorption of anion acts as a charge compensation process, while the activation by cathodic polarization in TEABF 4 solutions increased the capacitive currents associated with the cation adsorption/desorption. The electrolyte solvent also affected the activation process, especially for the cathodic activation. Larger sizes of ions and solvent molecules were generally effective for the activation, while the smaller sizes of them were preferable to obtain higher capacitance for the resulting electrochemically activated carbon.

Ionic and Free Solvent Motion in Poly(azure A) Studied by ac-Electrogravimetry

This work is focused on the mechanistic aspects of the redox behavior of poly(azure A) taking advantage of the controlled modulation of their oxidation states by ac-electrogravimetry. The originality of this technique is its ability to discriminate between cation and anion involved in the charge compensation process and the accompanying free solvent transfer, directly or indirectly. Two processes were proposed where the faster ionic exchange is considered to be the participation of the anion species acting as counterions whereas the slower one is related to the proton transfer. The proton is implied as reactants for the two electroactive sites identified in the polymer chain, the intermonomeric amino links and the aromatic rings. The ac-electrogravimetry technique was used to study the kinetic aspects of the transfer of proton (H+), anion (NO3– or Cl–), and free solvent in KNO3 and KCl aqueous solutions.

Resonant inelastic X-ray scattering and X-ray absorption spectroscopy on the cathode materials LiMnPO4 and LiMn0.9Fe0.1PO4––a comparative study

We present a study of the charge-state behavior of the Li-ion battery cathode materials Li(x)MnPO(4) and Li(x)Mn(0.9)Fe(0.1)PO(4) using X-ray absorption spectroscopy (XAS) and resonant inelastic X-ray scattering (RIXS). A set of six identical battery cathodes for each material have been cycled and left in different charge states in the range of x = 0.2…1.0 before disassembly in an Ar glove box. Unexpectedly, we find that the Mn 3d-bands are almost inert to the delithiation process, suggesting that Mn ions participate to a very small extent in the charge compensation process. In Li(x)Mn(0.9)Fe(0.1)PO(4) the Fe 3d-band shows much more response to delithiation than the Mn 3d-band. The O 2p-band hybridizes with the bands of the other ions in Li(x)MnPO(4) and Li(x)Mn(0.9)Fe(0.1)PO(4) and thus, indirectly, carries useful information about the effects of delithiation at all ion sites. We conclude that the redox reactions during lithiation/delithiation of these materials are complex and involve repopulation of charges for all constituent elements.

The Influence of Charge Trapping on the Electrochromic Performance of Poly(3,4-alkylenedioxythiophene) Derivatives

This paper describes the electrochromic properties of a series of poly(3,4-alkylenedioxythiophene) (PXDOT) derivatives featuring various ring sizes and substitutions. The presence of a bulky group on the monomer resulted in a polymer possessing a more-open morphology, which promoted reversible ionic transfer. We used an electrochemical quartz crystal microbalance and cyclic voltammetry to investigate the properties of these polymers. We found that both cations and anions were involved in the charge compensation process. Furthermore, PXDOT derivatives possessing larger ring sizes and/or longer alkyl substituents exhibited less trapping of ions within the polymer during the redox process. The long-term electrochromic stability of these PXDOTs depended strongly on the number of trapped ions. Although the transmittance attenuation of poly(3,4-ethylenedioxythiophene) (PEDOT) decreased from 53 to 42%, we observed no significant decay for poly(diethyl-3,4-dihydro-2H-thieno[3,4-b]-[1,4]dioxepine) (PProDOT-Et(2)) after 400 cycles.

Electrostatic Layer-by-Layer Deposition and Electrochemical Characterization of Thin Films Composed of MnO2 Nanoparticles in a Room-Temperature Ionic Liquid

Thin films of MnO(2) nanoparticles were grown using the layer-by-layer method with poly(diallyldimetylammonium) as the intercalated layer. The film growth was followed by UV-vis, electrochemical quartz crystal microbalance (EQCM), and atomic force microscopy. Linear growth due to electrostatic immobilization of layers was observed up to 30 bilayers, but electrical connectivity was maintained only for 12 MnO(2)/PPDA bilayers. The electrochemical characterization of this film in 1-butyl-2,3-dimethyl-imidazolium (BMMI) bis(trifluoromethanesulfonyl)imide (TFSI) (BMMITFSI) with and without addition of a lithium salt indicated a higher electrochemical response of the nanostructured electrode in the lithium-containing electrolyte. On the basis of EQCM experiments, it was possible to confirm that the charge compensation process is achieved mainly by the TFSI anion at short times (<2 s) and by BMMI and lithium cations at longer times. The fact that large ions like TFSI and BMMI participate in the electroneutrality is attributed to the redox reaction that occurs at the superficial sites and to the high concentration of these species compared to that of lithium cations.

Spectroscopic characterization and investigation of the dynamic of charge compensation process of supramolecular films derived from tetra-2-pyridyl-1,4-pyrazine ligand

This work describes the infrared spectroscopy characterization and the charge compensation dynamics in supramolecular film FeTPPZFeCN derived from tetra-2-pyridyl-1,4-pyrazine (TPPZ) with hexacyanoferrate, as well as the hybrid film formed by FeTPPZFeCN and polypyrrole (PPy). For supramolecular film, it was found that anion flux is greater in a K+ containing solution than in Li+ solution, which seems to be due to the larger crystalline ionic radius of K+. The electroneutralization process is discussed in terms of electrostatic interactions between cations and metallic centers in the hosting matrix. The nature of the charge compensation process differs from others modified electrodes based on Prussian blue films, where only cations such as K+ participate in the electroneutralization process. In the case of FeTPPZFeCN/PPy hybrid film, the magnitude of the anions’s flux is also dependent on the identity of the anion of the supporting electrolyte.

Ac-Electrogravimetry study of ionic and solvent motion in polypyrrole films doped with an heteropolyanion, SiMo 12O 404−

One way to immobilize heteropolyanions on an electrode is to entrap them into a film of conducting polymer. In the present work, a polypyrrole film doped with a Keggin-type heteropolyanion, SiMo 12O 40 4−, obtained by electrochemical way was studied. We focus on the charge compensation process, which occurs when the heteropolyanions entrapped into the polymer are reduced or re-oxidized. First, electrochemical quartz crystal microbalance analyses were performed, then, to determine if solvent motion takes place, ac-electrogravimetry measurements were carried out. In fact, in concentrated acidic solution, only protons are involved in the charge compensation. In low acidic solution (pH 3) having a high potassium concentration (0.5 M) both proton and potassium ions are involved whereas at pH 5.2 only potassium motion takes place. These findings are in good agreement with the acido-basic properties of SiMo 12O 40 6−. In all cases, no solvent motion was pointed out.

Investigations of nanometric films of doped polyaniline by using electrochemical surface plasmon resonance and electrochemical quartz crystal microbalance

In the present work, the ionic transport in copper tetrasulfonated phthalocyanine doped polyaniline (PANI/CuTsPc) film and its effects on the optical properties of the polymer is presented. The studies were performed in situ and in real time by using electrochemical surface plasmon resonance (ESPR) and electrochemical quartz crystal microbalance (EQCM). The electropolymerization was performed by potentiodynamic method and the EQCM experiments showed that the PANI/CuTsPc films behave rigidly validating the use of the Sauerbray equation. Both protonic and anionic participation in the charge compensation process were calculated and showed that the presence of the CuTsPc in the PANI film suppress the anionic transportation. Finally, the ESPR experiments showed that changes in the optical properties of the PANI/CuTsPc film were more expressive in the same potential range where the protonic transport was dominant.

Investigation by EQCM of the electrosynthesis and the properties of polypyrrole films doped with sulphate ions and/or a Keggin-type heteropolyanion, SiMo 12O 404−

The first part of this paper describes in detail the electrochemical synthesis of polypyrrole (PPy) films monitored by electrochemical quartz crystal microbalance (EQCM). These films are either doped only with a Keggin-type heteropolyanion (HPA), SiMo 12O 40 4−, or co-doped with such polyanions and sulphate ions. It is evidenced that this HPA catalyses the electropolymerisation of the pyrrole since it is able to oxide pyrrole monomer, and on the other hand, that HPAs are definitively entrapped into the polypyrrole film as shown by their electrochemical response. All the PPy film is electroactive. When the co-doped film is obtained by potentiodynamic method, its anion composition is not homogeneous in depth, there is a concentration gradient of the doping anions. In the second part of this paper, the morphology of the films is shown as well as their electrochemical characterisations that were carried out by EQCM in order to focus on the charge compensation process that occurs during SiMo 12 reduction and re-oxidation. In a wide domain of potentials, only the HPA response is observed, the polymer remains in its conducting form. The SiMo 12O 40 4− doped PPy films are cationic films. When several types of cations are present in the medium, the influence of the pH on the nature of the cations implied in the charge compensation that occurs during SiMo 12 reduction and re-oxidation is important. When the PPy film is co-doped, it is possible to obtain a mixed PPy film. Another important finding is the stability of trapped SiMo 12 ions in contact with solutions of pH higher than 4, on the contrary to what occurs when they are in solution.

Raspberry-like composite polymer particles by self-assemble heterocoagulation based on a charge compensation process

Nano-sized poly(ethylene glycol dimethacrylate- co-acylic acid) (poly(EGDMA- co-AA)) were effectively self-assembled on poly(divinylbenzene- co-styryl methylpyridinium chloride) (poly(DVB- co-StMPyCl)) surfaces to form the raspberry-like composite by a charge compensation mechanism through the affinity complex between carboxylic group and pyridinium group. The effects of pH and salt electrolyte on the morphology of the self-assembled polymer composites were investigated. The resulting heterocoagulates were highly stable in water and acid solution. These heterocoagulates were reversible through the self-assembly in acidic or neutral media and the dissociation in the basic medium due to the charge compensation through the strong affinity complex between hydroxide anion and pyridinium group cation. The resulting heterocoagulates were characterized with scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM) and Fourier transform infrared spectroscopy (FTIR). As a result, a new method for tuning the structure of a charge compensation directed polymer composite was developed.

Optical spectroscopy of SrWO4:Nd3+ single crystals

The optical properties of SrWO4 crystals doped with Nd3+ have been investigated at temperatures ranging from 10 to 300 K. The scheme of the energy levels up to20 000 cm−1 has been deduced from low temperature measurements and reproduced bytheoretical calculations based on a parametric Hamiltonian including Coulombic,spin–orbit and crystal field terms. The spontaneous transition probabilities, thebranching ratios and the radiative lifetime have been calculated in the frameworkof the Judd–Ofelt theory and compared with the experimental results for the4F3/2 emitting level. The optical bands are broadened because of crystal field inhomogeneitiescaused by charge compensation processes accompanying the substitution ofNd3+ for Sr2+. This fact and the high emission cross section values obtained for the emission from the4F3/2 multipletindicate Nd:SrWO4 as a possible active medium for tunable laser operation.