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Amorphous carbon nitride thin fims, a-CN x , are potentially low cost candidates for electrochemical nitrate treatment by comparison to boron doped diamond electrodes. In aqueous media, a-CN x electrodes are characterized by a large potential window and, in acidic pH solutions, no surface charge capacitive contribution. In perchloric acid at pH 1, nitrate reduction occurs at the negative limit of a potential domain without any significant redox reaction over almost 1 Volt. In this domain, in the presence of a nitrate salt, a bell-shaped behaviour was observed for the interfacial capacitance. Differences were evidenced according to the solvation state of the cations (Na+, K+, Li+, Cs+, (CH 3) 4 N+, (C 2 H 5) 4 N+), depending on the cation size. Experimental capacitance data were simulated by using the phenomenological theory developed by Kornyshev in the case of ionic liquids. A good agreement was obtained assuming a compact layer in series with the highly structured diffuse layer and taking into account the short-range ion-ion interactions. Thus, at the a-CNx/aqueous electrolyte interface, nitrate anions are engaged into strong anion-cation interactions (ion pairing) especially with small sized cations, leading to nitrate anion trapping in the multilayered interfacial region with a possible negative effect on the nitrate ions electroreduction. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to show that it is possible to increase the diameter and length of the nanostructures of a framework formed of oriented polypyrrole nanowires that has been prepared by a templateless electrochemical method based on the use of a pyrrole solution containing a high concentration of weak-acid anion and a low concentration of non-acidic anion. The dimensions of the initial nanowires are increased by performing an additional electrosynthesis in a ‘classical’ monomer solution. Depending on the polarization time of this last synthesis (a few tens of seconds), wires with various diameters, from one hundred up to several hundred nanometers, are obtained. In addition to the variation of the nanowire size, these findings confirm, as outlined in the reaction mechanism we have proposed, that the base of the nanowires is surrounded by a thin non-conductive polymer i.e . by an overoxidized polypyrrole film. Actually this paper shows a proof-of-concept. Indeed one can imagine that the second polymeric electrodeposit could be performed using an organic monomer solution, using functionalized pyrrole monomer to fabricate a biosensor having large specific area, and/or using anions which could be drugs. [ABSTRACT FROM AUTHOR]

Abstract: Macromolecules like proteins are able to adhere to tin oxide electrodes at open circuit potential as proved by electrogravimetry experiments. In this work, electrochemical impedance studies were performed at aqueous electrolyte/F- or Sb-doped semiconducting tin oxide interfaces, including natural seawater. By this way, it was possible to characterize the potential dependence of the interfacial capacitance in various physicochemical conditions, without or in the presence of bovine serum albumin (BSA). In the potential range where tin oxide is in the depletion regime (blocking interface), a capacitance excess is evidenced which can be attributed to the formation of surface states which are the signature of chemical bonding. By simulating the so-called surface state capacitance, three states have been pointed out. They are centred at 0.7, 0.9 and 1.1eV in the tin oxide bandgap. On the basis of experimental arguments, the state at 1.1eV was ascribed to the OH-terminated tin oxide surface, the two other states were found to be specific of the interaction of organic matter with the oxide surface. In the presence of BSA, the density of surface atoms (about 1013 cm−2) involved in bonding is of the order of magnitude of the surface concentration of one BSA monolayer. The lasting character of these bonds was also shown. This finding shows the definitive protein immobilisation at the SnO2 surface. [Copyright &y& Elsevier]

Abstract: 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), SiMo12O40 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 SiMo12 reduction and re-oxidation. In a wide domain of potentials, only the HPA response is observed, the polymer remains in its conducting form. The SiMo12O40 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 SiMo12 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 SiMo12 ions in contact with solutions of pH higher than 4, on the contrary to what occurs when they are in solution. [Copyright &y& Elsevier]

In the presence of α-SiMo12O404- ions dissolved in acidic solution and under laser irradiation, the electroless photoetching of n-type InP is achieved. At the laser impact, the semiconductor is oxidized while SiMo12O404- species are reduced. The shape of the pit formed, due to the photoanodic dissolution of the material, depends on the experimental conditions, notably on the presence or not of Cl- ions in the medium. It can have either a Gaussian shape or a flat bottom. To specify the charge transfer which occurs at the n-InP/solution illuminated interface, some electrochemical studies were performed on n- and p-type InP electrodes. In fact, the reduction of SiMo12O404- ions occurs by capture of electrons from the InP conduction band. Considering the energetic situation at the InP/electrolyte interface and some electrochemical results, it is concluded that the electron transfer from InP to SiMo12 is mediated by surface states. The influence of Cl- ions on the n-InP photodissolution process is also discussed. [Copyright &y& Elsevier]

A new process to locally photoetch n-type InP under electroless conditions is described. It is based on the use of a polyoxometalate, molybdenum heteropolyanion (SiMo12O404−), dissolved in acidic solution, as an oxidizing agent. The etching is confined to where the light is incident to the n-InP surface. The etch rate depends either on the heteropolyanion concentration or on the incident light intensity. The use of SiMo12O404− associated with light also makes it possible to perform dopant-type selective etching because either in the dark or under illumination p-InP does not undergo a dissolution process. This system should also provide a good means for n-InP defect revealing. [Copyright &y& Elsevier]

Reduced Graphene Oxide possesses numerous interesting properties, making it one of the most studied materials today. By this way, applications in various fields, including fundamental research, can be found. Nevertheless, the complexity of reduced Graphene Oxide lies in its fabrication process which defines their properties. In this paper, two fabrication methods -electrochemical and hydrothermal reduction of graphene oxide - were compared using physico-chemical and electrogravimetric analysis. Our findings reveal significant morphological differences between the two methods, accompanied by different electrochemical behaviors, when tested in aqueous electrolyte (i.e. 0.5 M Na 2 SO 4). Specifically, electrochemically reduced graphene oxide exclusively involves sodium (whether hydrated or not) in its charge compensation mechanism, whereas hydrothermally reduced graphene oxide also involves proton in sodium sulfate solution. [Display omitted] [ABSTRACT FROM AUTHOR]

In the presence of a high concentration of weak-acid anions, such as monohydrogenophosphate which confer to a pyrrole aqueous solution a pH around 9, an ultra thin non-conductive overoxidized polypyrrole film is deposited on the electrode under an anodic polarization. In the same experimental conditions, after addition of perchlorate anions (C > 0.5 mM) in the pyrrole solution the electrooxidation of the monomers leads to the synthesis of a superhydrophilic nanostructured conductive polypyrrole film (network of nanofibers or oriented nanowires, 50–120 nm in diameter). The aim of the present paper is to confirm the mechanism that we have previously proposed and so to explain the spontaneous nanostructuration of the electrogenerated polypyrrole films. We have assumed that this templateless formation of nanostructures is notably due to the oxidation of water with production of hydroxyl radicals and nanobubbles of dioxygen. Due to the fact that pyrrole polymerization is associated to the release of protons, we have first verified that the electrode/solution interfacial pH is compatible with the water oxidation potential. For this purpose, during the monomer oxidation the interfacial pH variation has been monitored using a pH electrode having a flat glass membrane which was covered with a Pt grid used as the working electrode. Secondly, the presence of dioxygen nanobubbles has been indirectly confirmed by rotating the working electrode. Indeed rotation of the electrode allows eliminating the nanobubbles present inside the polypyrrole film. For the highest rotation speed tested (94 rad s −1 ), a very thin overoxidized film was electrogenerated. Our results are in good agreement with the fact that the nanobubbles protect the PPy film against the action of the hydroxyl radicals which react with the polypyrrole film leading to its overoxidation. [ABSTRACT FROM AUTHOR]

Abstract: The electrochemical reduction of nitrate ions at a copper electrode in an unbuffered neutral aqueous solution is studied. Using a two compartment electrochemical cell, three stationary cathodic waves, noted P1, P2 and P3, were evidenced by cyclic voltammetry at −0.9, −1.2 and −1.3V/SCE, respectively. By comparing the electrochemical response of nitrate and nitrite containing solutions, P1 was attributed to the reduction of nitrate to nitrite. In order to assign P2 and P3 features by determining the number of electrons involved at the corresponding potential, rotating disk electrode experiments at various rotation speeds, combined with linear sweep voltammetry, were performed. Current data analysis at a given potential was carried out using Koutecky–Levich treatment taking into account water reduction. Confident values of the diffusion coefficient D of nitrate ions were assessed by electrochemical impedance spectroscopy for nitrate concentrations of 10−3, 10−2 and 10−1 M. For a nitrate concentration of 10−2 M, D was found to be 1.31×10−5 cm2 s−1 allowing the number of electrons to be determined as 6 for P2 and 8 for P3, in accordance with nitrate reduction into hydroxylamine and ammonia, respectively. The formation of hydroxylamine was confirmed by the observation of its reoxidation at a Pt microelectrode present at the Cu electrode/nitrate solution interface. [Copyright &y& Elsevier]

The electrochemical response of GaAs, n- and p- type, in the presence of a Keggin-type heteropolyanion—SiMo12O404−—has been studied in order to determine the reactions which take place at the GaAs/SiMo12O404− solution interface. The behavior of the GaAs electrodes, in the dark and under illumination, allowed us to determine the nature of the semiconductor carriers involved in the charge transfer. All the charge transfers occur via the GaAs valence band (VB). At open circuit potential, the SiMo12O404− ions are reduced at the GaAs surface which therefore undergoes an anodic dissolution process. Under polarization, when the reduction current is maximum, no GaAs oxidation reaction takes place. The SiMo12O404− reduction current densities are the same at a platinum electrode and at a GaAs electrode. These observations imply that at a GaAs/SiMo12O404− solution interface, under electroless conditions, the GaAs anodic dissolution occurs via a purely electrochemical process, by consumption of the holes injected during SiMo12O404− reduction. [Copyright &y& Elsevier]

The development of highly efficient catalysts using inexpensive and earth-abundant metals is a crucial factor in a large-scale commercialization of direct methanol fuel cells (DMFCs). In this study, we explored a new catalyst based on copper nanodendrites (CuNDs) supported on carbon nanofibers/poly (para -phenylenediamine) (CNF/P p PD) nanocomposite for methanol oxidation reaction (MOR). The catalyst support was prepared on a carbon paste electrode by electropolymerization of para -phenylenediamine monomer on a drop-cast carbon nanofibers network. Afterwards, CuNDs were electrodeposited on the nanocomposite through a potentiostatic method. The morphology and the structure of the prepared nanomaterials were characterized by transmission electron microscope, scanning electron microscope, energy dispersive X-ray, X-ray diffraction, and X-ray photoelectron spectroscope. The results suggested that a three-dimensional nanodendritic structure consisting of Cu 2 O and Cu(OH) 2 formed on the hybrid CNF/P p PD nanocomposite. The catalytic performance of CuNDs supported on CNF, P p PD and CNF/P p PD was evaluated for MOR under alkaline conditions. The CNF/P p PD/CuNDs exhibits a highest activity (50 mA cm−2) and stability toward MOR over 6 h, with respect to CNF/CuNDs (40 mA cm−2) and P p PD/CuNDs (36 mA cm−2). This inexpensive catalyst with high catalytic activity and stability is a promising anode catalyst for alkaline DMFC applications. • 3-D Cu 2 O–Cu(OH) 2 dendrites supported on CNF/PpPD were prepared via simple process. • Good synergy in CNF/PpPD promotes electron transport and increases surface area. • CNF/PpPD/CuDs exhibits outstanding catalytic activity and stability toward MOR. • Efficient catalytic activity attributed to powerful synergy between CNF/PpPD and CuDs. [ABSTRACT FROM AUTHOR]

The lack of robust interphases between carbon and most metals prevent the exploration of the full scope potential of carbon-based metal matrix composites. Here, we demonstrated a scalable and straightforward way to produce strong interphase between copper (Cu) and carbon fibers (CFs) by designing a tailored titanium oxide-carbide coating (TiO y -TiC x) on CFs in a molten salt process. The oxide-carbide composition in the graded layer strongly depends on the coating temperature (800–950 °C). A coating with a high TiO y content obtained at a low coating temperature (800 °C) contributes to better molten-Cu wetting and strong adhesion energy between CFs and Cu during a subsequent exposure at 1200 °C. The Cu wetting angle for the TiO y -TiC x -CF sample obtained at 800 °C was ∼80° ± 5° with a Cu surface coverage of ∼50% versus ∼115° and ∼10% for the TiC x -CF sample made at 950 °C. The kinetic analysis of the coating process step by step suggests a growth rate limited by the mass-transfer through the coated layer. This method provides a novel approach to improve the thermal conductivity of Cu/C composite for thermal management applications. Image 1 [ABSTRACT FROM AUTHOR]

Sensitive and simple electroanalytical methods were developed for the determination of the loop diuretic furosemide (FUR) in pharmaceutical formulations and synthetic urine samples by coupling square-wave voltammetry (SWV) with polished basal-plane pyrolytic graphite (BPPG) or cathodically pretreated boron-doped diamond (BDD) and amorphous carbon nitride (a-CN x ) as working electrodes. The analytical parameters obtained with the three methods were compared. With BPPG, best results were attained using 0.10 mol L −1 H 2 SO 4 as supporting electrolyte, whereas with BDD and a-CN x , this was attained using a 0.040 mol L −1 BR buffer (pH 4.5). Cyclic voltammograms obtained for FUR evidenced an irreversible behavior (with two oxidation peaks), in agreement with the literature. On the BDD and a-CN x electrodes, the electrooxidation of FUR is a purely diffusion-controlled process, whereas on the BPPG electrode some degree of adsorption is also involved. The obtained linear response ranges (detection limits) for the BPPG, BDD, and a-CN x electrodes were 0.60–4.8 (0.47), 0.30–13 (0.30), and 0.50–99 (0.39) μmol L −1 , respectively. The proposed methods were successfully applied in the determination of FUR in pharmaceutical formulations (tablets), with results similar to those obtained using a reference spectrophotometric method (at a confidence level of 95 %), and in the recovery of FUR in synthetic urine samples. The analytical conditions obtained with the novel SWV methods here reported are comparatively better than those for other electrochemical methods in the literature. As the pretreatment procedures are much simpler for BDD and a-CN x than for BPPG, one can conclude that the former two materials can be advantageously used to determine FUR with good sensitivity and selectivity. [ABSTRACT FROM AUTHOR]

Abstract: In this work, the role of convective mass transport in two ionic liquids (ILs) that differ by the anions 1-butyl-2,3-dimethyl-imidazolium bis(trifluoromethanesulfonyl)imide ([BMMI][Tf2N]) and 1-butyl-2,3-dimethyl-imidazolium tetrafluorborate ([BMMI][BF4]) were studied in the presence of ferrocene (Fc) as a redox tracer. A rotating disk electrode (RDE) system was used, and the use of electrochemical (EIS) and electrohydrodynamic (EHD) impedance spectroscopies allowed for a deeper analysis of mass transport and charge transfer at the surface of the electrode. The two ILs showed a viscoelastic character that was observed using a parallel plate geometry viscometer with a high storage-to-loss modulus ratio in a frequency domain where the RDE response was characterized by significant elongational flow kinematics. As a general conclusion, the observed effects were interpreted as unbalanced contributions of the elongational flow close to the electrode surface, which induced an anisotropic diffusivity that increased along the flow lines, and the effect of Fc and Fc+ as structure breakers or strengtheners in the diffusion layer. Finally, from EIS analysis, it was established that increasing the overpotential in the anodic direction yielded an increased Schmidt number, which indicated a detrimental effect on the mass transport of Fc+, whose production rate was also increased under the same conditions. EIS showed that the anion had an effect on the reaction rate of Fc oxidation and on the double-layer capacitance value. [Copyright &y& Elsevier]

• Capacity fading of composite electrodes over cycling in Aqu-LIBs is investigated. • Water-assisted Li+ intercalation persists during cycling. • No mechanical degradation of LiCoO 2 composite electrode is observed. • Surficial evolution from LiCoO 2 to CoO results in the capacity fading. • Structural evolution of interface significantly slows down Li+ insertion kinetics. Unravelling the underlying reasons for degradation mechanism of battery materials is of great fundamental and practical importance. For a classical electrode consisting of an active material, a conductive additive, and a polymeric binder, its capacity fading is commonly related with (i) mechanical degradation of polymeric binder and/or (ii) structural and compositional degradation of active materials. The former is more relevant for electrodes showing volume expansion and represented by the progressive breakage of polymeric binder network during battery operation, leading to the dissolution of the other two components into electrolytes. The latter is generally reflected by an irreversible phase transition in active materials, which may affect the species exchanged at the electrode/electrolyte interface and their interfacial transfer dynamics. By employing a coupled methodology pairing electrochemical techniques with piezoelectric probes derived from quartz crystal microbalance (QCM), this work reports on the evolution of the interfacial processes during electrochemical cycling and correlates to the performance degradation of the electrodes. Shown on a LiCoO 2 (LCO) composite electrode as a model system, it was revealed that bare Li+ without a hydration sheath plays a dominant role in charge balance irrespective of the aging degree of the electrode under the experimental conditions of this work. However, Li+ transfer is closely accompanied with free H 2 O molecules with a Li+:H 2 O ratio around 10:1 at a polarization state close to LCO redox potential (0.65 V vs. Ag/AgCl). This ratio persists in all cycled electrodes with gradually faded interfacial transfer kinetics of Li+ and H 2 O along cycling. Such fading in species interfacial transfer kinetics driven by the surficial evolution from LiCoO 2 to CoO plays a major role in the electrode performance degradation during cycling. [Display omitted] [ABSTRACT FROM AUTHOR]

In an aqueous electrolyte under an anodic polarization, most of the conductive polymers could undergo an overoxidation due to the hydroxyl radicals formed during water oxidation. Regarding poly(3,4-ethylenedioxythiophene) (PEDOT) only a few reports studied its overoxidation. In this paper, we propose a facile and rapid strategy to prepare an ultrathin (15 nm), pinhole-free and non-conductive overoxidized PEDOT film by electropolymerization of EDOT under potentiostatic conditions in the presence of solely weak-acid anions in the monomer solution. The influence of the pH of this solution as well as the applied potential was studied notably by electrochemical impedance spectroscopy. It was pointed out that the PEDOT film is overoxidized when its electrosynthesis is performed in an aqueous monomer solution of pH 10.5, at 1.1 V/SCE, the monomer solution containing only weak-acid ions as anions (phosphates or carbonates). XPS analyses show that some C and S atoms of the film are oxidized leading to a break of the polymer conjugation and therefore to a decrease of its electronic conductivity. Finally, after adding in the monomer phosphate solution of pH 10.5 perchlorate ions that allow to avoid total overoxidation of the film formed at the very beginning of the process, PEDOT nanowires were obtained. [Display omitted] [ABSTRACT FROM AUTHOR]