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Liquid ammonia (NH 3 liq. ) provides an original electrochemical environment onto semiconductors electrodes (SC). Its particular interest is that water influences can be neglected in opposition to a lot of non-aqueous other solvents. Fundamentals electrochemistries of the SC are related to the energy diagram of the interface. In this paper it is established into NH 3 liq. , on both types, on p- and n-InP by flat band potential ( V fb ) measurements. The V fb are determined over the whole range of pH that reaches 33 pH units in this non-aqueous solvent. InP exhibits a pure nernstian behavior with a specific 44 mV/pH slope at 223 K. This is particular compare to the “under nernstian” dependency, observed in water onto InP. The actual band positions are related to the initial chemical state of the InP surface, since oxide free surfaces and thin native oxide covered surfaces differ slightly. Reproducible contrasted results from the acid–base equilibrium, which is supported by the V fb according to the pH, for singular interfacial chemistry. This aspect is confirmed by XPS measurements performed before and after InP immersion into NH 3 liq . They establish the perfect stability of the initial chemical composition of the semiconducting surface in contact with NH 3 liq. whatever its pH conditions. NH 3 liq. appears as an inert solvent which is able to create an acid–base equilibrium onto InP surfaces. Each InP surface chemistry support its own linear V fb vs. pH variation. In NH 3 liq. , the poor water control on the building of the Helmholtz layer is well shown by the perfect V fb alignment position from the intermediated pH buffered solution obtained from the addition of tetraethyl ammonium hydroxide ((Et) 4 N + ,OH − ) dissolved in water (20%).

This work reports – for the first time – the electrochemical anodic passivation of InP in a relevant nonaqueous solvent: liquid ammonia. A new route of InP passivation was clearly established by the coupling approach electrochemistry-XPS analyses. A specific P–N surface bond chemistry was evidenced and associated to a phosphinimidic amide-like electrodeposition. The efficiency of this new passivation route was supported by the high stability of the complete covering thin film since no air ageing effect is detected on InP surface for both types. The phosphazene surface termination offers new possibilities for further high-speed optoelectronic applications and functional molecular grafting. Keywords: III–V Semiconductor, InP, Passivation, Stability, Liquid ammonia

In this paper we report on galvanostatic pore formation on both n-InP and n-GaAs in acidic liquid ammonia (223 K). Quantitative analyses by atomic absorption have revealed two different dissolution mechanisms (involving 6 or 8 holes) without secondary reaction. Electrochemical behaviours have also shown diverse evolutions. Potential oscillations were observed onto InP while a constant voltage is measured for GaAs. Distinguished pore morphologies observed by scanning electron microscopy have confirmed the different porosification processes.

Porous structures have been anodically grown onto n -InP (100) in HCl. Surface chemistry and pore morphology have been respectively studied by X-ray photoelectron spectroscopy and scanning electron microscopy but in situ electrochemical investigations have been emphasized. Capacitance and photocurrent experiments have been performed while the porous etching occurred. No modifications of the electronic structure (flat band potential remains constant) are observed during the pore formation. However, for high dissolution charges, the photocurrent spectra are sharpened because the porous films behave like electrically “dead layers”. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The anodic electrochemical treatment in liquid ammonia of InP (n- and p-) leads to a simultaneous oxidation of both semiconductor and solvent. The oxidation of InP takes place through a passivating layer revealed as well by electrochemistry as by XPS. The chemical composition of InP surface is therefore gradually modified according the anodic charge. The composition of the film layer is supposed to be close to HN=P-NH2, a promising compound stable as well in liquid ammonia as in water.

International audience; Platinum nanoparticles (n-Pt), over-grafted with 2-thiophenecarbonyl chloride are assembled on gold electrodes, by the Langmuir Blodgett (LB) technique using behenic acid (BHA) as promoting agent. These layers are electrochemically active without any preliminary activation. The [Fe(CN)6]3−/4− redox couple was used as electrochemical probe. This paper reports on the influence of the number of deposited LB layers, and the n-Pt density on the electrochemical response. n-Pt density was modified by the change of the “BHA/n-Pt” ratio. Cyclic voltammograms of “[Fe(CN)6]3−/4−” were observed whatever the coating conditions. As soon as the first layer was deposited the electrochemical response was associated to the n-Pt coverage, its response slightly increased up to a steady state for five or seven layers. As expected, the increase of the Pt density favored the increase of the current density. XPS analysis performed before and after electrochemical cycling showed that 4-mercaptoaniline capped platinum nanoparticles, and their over grafting were chemically and electrochemically stable. Analysis of influence of the number or the n-Pt density of the layers showed that the electrochemically active part of LB electrodes was provided by the last layer plus a part of the underlying one.

Amine functionalized platinum nanoparticles have been modified by over-grafting two different molecules, 2-thiophenecarbonyl chloride (Pt-1) and 1-hexyl-4-(4-isothiocyanatophenyl)-bicyclo (2, 2, 2) octane (Pt-2). Cyclic voltammetry was performed at gold electrodes coated with Langmuir–Blodgett (LB) mixed films of Pt-1 and Pt-2 nanoparticles, and behenic acid. From five layers the electrochemical response was essentially provided by the last LB component. The electrochemical responses towards the [Fe(CN)6]3−/4− couple were strongly influenced by the nature of the over-grafted molecules: films of Pt-2 presented an almost complete blocking effect, while films of Pt-1 allowed the redox reaction to occur on Pt nanoparticles. In order to understand the reasons for such different behaviors we built up hetero-nanostructures by superposing Pt-1 and Pt-2 LB layers in different ways, yielding different kinds of “sandwich” structures. The electrochemical response depended on the electrode ending. When Pt-1 nanoparticles were in the outer layer, in contact with the electrolyte solution, the electrode was electroactive toward the redox probe, while when Pt-2 layers were in the outer layer no electroactivity was detected. For sandwiches made of Pt-1, with a variable thickness of an intercalated film of Pt-2, the electrode response to [Fe(CN)6]3−/4− was modulated by the thickness of the inter-layer: the thicker the layer, the lower the response.

Liquid ammoniates, which are highly conductive electrolyte (more than 100 mS.cm-1 at 20 °C), are proposed as solvents for a redox battery working around room temperature, and up 80 °C. In the negative compartment, the anolyte is NaI · 3.3NH3, and the Na+/Na couple is proposed. It is reversible, as determined by cyclic voltammetry and galvanostatic cycling. In the positive compartment, the catholyte NaI · 3.3NH3 enriched in silver cations is proposed too. The cathodic material is merely this compound and the cathode is the silver metal. The couple Ag+/Ag is reversible too, as determined by cyclic voltammetry and galvanostatic cycling. Metallic sodium is extremely stable in this electrolyte; therefore NaI · 3.3NH3 could be used in a redox battery of high energy density and high power density. The maximum working temperature, which is proposed, 70 °C, is lower than the melting point of sodium (98 °C), and avoids high pressures of ammonia.

It is shown that the conductivities of LiBF4, LiPF6, LiN(SO2CF3)2 (LiTFSI), NaPF6, KPF are abnormally high in two diamine solvents: ethylenediamine (EDA) and 1,3-diaminopropane (1,3 DAP). This is particularly evident for KPF6, κMAX(EDA) = 35 mS cm− 1 and κMAX(1,3 DAP) = 17.4 mS cm− 1. Compared to three other organic solvents having the same viscosity, η ≅ 1.6 cP, but higher relative permittivity, NMF e = 186.9, NMP e = 32, γ-Bu e = 39.1, the maxima of conductibility of EDA and 1,2 DAP, which have a low relative permittivity, e ≅ 13–11, are largely superior or equal to those of NMF, NMP, γ-Bu. For KPF6, κMAX(NMF) = 15.4mS cm− 1, κMAX(NMP) = 7.8 mS cm− 1 and κMAX(γ-BL) = 10.8 mS cm− 1. We assume that this is due to a non-Stokesian conductivity mechanism.

It is shown that not only the relative permittivity or the dynamic viscosity, but also the chemical nature of the salt and that of the solvent can be taken into account to predict the most important properties of electrolytes: the conductivity maximum κMAX and the equivalent conductivity at infinite dilution Λ0. For taking into account the chemical nature of the salt and of the solvent, we assumed that solvation reactions could be expressed in terms of the absolute chemical hardness of the salt, ηACH salt, and that of the solvent, ηACH solvent (or their absolute difference, ∣ΔηACH∣). Relations are proposed for κMAX and the equivalent conductivity at infinite dilution Λ0. Their validity is supported by our own conductivity data and by equivalent conductivity at infinite dilution data from the literature for a wide range of different systems. The accuracy of our predictions seems to be ±20%.

The aim of this work was to elaborate on a thin polymeric film for coating transparent fluorine-doped tin oxide (FTO) electrode supported on a glass substrate for trapping Cu 2 + ions. Possible applications are the easier detection of Cu 2 + ions due to complexation on the FTO surface or could be the making up of electrochromic devices using copper(I)-salt based electrolytes to avoid diffusion of Cu 2 + ions formed at the anode toward Cu(0) deposited on the cathode. These thin polymeric films proposed here as complexing material candidates toward copper ions belong to polyalkyleneimine polymers. They were obtained by anodic electropolymerization of aliphatic polyamines (with at least two primary amino groups) such as ethylenediamine, 1,3-diaminopropane, or diethylenetriamine on FTO electrode surfaces and characterized by IR attenuated total reflectance spectroscopy. Moreover, we have shown that polyalkyleneimine-type polymers used here present good chelating properties towards Cu 2 + ions due to the amino groups they contain. © 2004 The Electrochemical Society. All rights reserved.

The cathodic decomposition of InP at pH 9 was studied by cyclic voltammetry and X-ray photoelectron spectroscopy (XPS). Under cathodic conditions, the modified surface layer consists mainly of elemental indium (In). In the anodic range, In is converted into In(OH)3. The subsequent cathodic reduction of In(OH)3 to In does not take place to completion, and the amounts of In(OH)3 and In increase irreversibly during cyclic potential scanning.

p-Si electrodes coated with linear polyethylenimine (L-PEI) allow the fabrication of a pH sensitive film for potentiometric transducers. The coating is realized in one step through the anodic oxidation of pure ethylenediamine (EDA) charged with 0.1 M LiCF3SO3 (Lithium Triflate). Such an electrochemical procedure leads to the thickness control of the coating. The best silicon surface pre-treatment before any coating is obtained with potassium dichromate in sulfuric acid, which leads to OH-terminated p-Si. This pre-treatment allows a uniform thin coating. In this work, the thickness is 2.6 nm. The pH response is high and close to 50 mV per pH unit.

Electrochemical oxidation of ethylenediamine leads to the coating of different electrode surfaces by a thin polymeric film. This film was characterized as a polyethylenimine one using both spectroscopic methods such as infrared-attenuated total reflection or infrared absorption spectroscopy and ab initio calculations. More, since the polymeric coating changes the electrochemical behavior of different surfaces, this film can be used successfully to make new chemical sensors.

For nonaqueous electrolyte solutions, we correlated the equivalent conductance Λ 0 at infinite dilution and the conductivity maximum κ MAX with only two intrinsic parameters of the pure solvents: the dielectric constant and the viscosity. On the basis of two new handy empirical formulas, predictions of Λ 0 and κ MAX can now be made for a given salt in any solvent on the basis of only one Λ 0 or κ MAX measurement in only one solvent.

The cathodic electrochemical behavior of InSb was studied in liquid ammonia. In neutral unbuffered media, in spite of strong negative polarization no electrochemical modification of the interface was observed. However, in acidic media, a cathodic decomposition was detected after scanning InSb in the potential range of hydrogen evolution. Hydrogen embrittlement results from a strong interaction of hydrogen radical (H . ) and indium surface. A coated film of indium results from this cathodic decomposition.

In liquid ammonia, the anodic behavior of n- and p-type III-V semiconductors are strongly different from those observed in aqueous media. For both types, the anodic process in liquid ammonia involves the formation of an adsorbed film, onto the semiconductor surface just before its dissolution. This film results from the chemisorption of N atoms, issued from the oxidation of the solvent.

New conductive materials involving Cu+ ions are proposed for electrochromic devices. They are liquid ammoniates which can be used from room temperature up to 80°C, and whose conductivity and p(NH3) can be modulated according to requirements. The synthesis does not require strong acids or complexing agents such as halide ions. The principle of operation of the electrochromic material is the reduction of Cu+ to Cu at the transparent cathode while Cu+ is oxidized to Cu2+ (thus developing a blue color) at the transparent anode. The bleaching is realized by the reverse reactions.

In acidic liquid ammonia, the anodic behaviour of the p-GaAs semiconductor is strongly different than in aqueous media. The anodic process in liquid ammonia involves the formation and adsorption of a thin film onto the p-GaAs surface. This thin film leads to the oxidation of the solvent. The initial state of the semiconductor electrode was recovered by photoreduction of the thin film.

The electrical response of Pt microelectrodes, with a radius of 10 μm, was studied in liquid ammonia (−50°C). The question of a suitable time scale for steady state measurements in liquid ammonia is important. The proton reduction currents were measured for different scan rates. A suitable experimental time scale of 20 mV s −1 was determined to reach a stationary state. The diffusion coefficient of protons in liquid ammonia was deduced from these electrochemical results: D (NH 4 + ) NH 3 =(3.8±0.4)×10 −9 m 2 s −1 .

The use of buffered neutral liquid ammonia medium for the first time provided evidence for a current doubling effect on p-InP during oxygen photoreduction. Unlike results in aqueous medium, a common mechanism of O2 reduction was observed at p-InP and p-GaAs electrodes. When protons were added to the solution, two different oxygen reduction mechanisms occurred at these electrodes. This study emphasizes the important results of the hydrogenated p-InP surface and revealed that liquid ammonia (at 223 K) was perfectly appropriate to understand the mechanism of O2 reduction at InP electrodes.

For nonaqueous electrolytes, using the HSAB principle, we tried to correlate the conductivity maxima κMAX, vs. only two intrinsic parameters: chemical hardness η of the solvent and that of the salt. Thus, not only the nature of the solvent but also that of the salt were taken into account. We were able to predict for a given solvent the variation of κMAX as a function of the hardness of the salt and that of the solvent: κMAX = K(1 − |Δη|/ηSOLVENT) with |Δη| = |ηSOLVENT − ηSALT| and K a constant in S-cm−1 independent of the salt, but not of the solvent.

In liquid acidic ammonia, the mechanism of oxygen reduction begins as in acidic aqueous solutions, by the successive contribution of the conduction band and then of the valence band (doubling effect). However, unlike in the acidic aqueous solutions, soon after the oxygen photoreduction, an activation process of the p-GaAs surface is initiated, tied to the presence of protons in the solution. This activation of the surface allows the passage from a reduction mechanism via a conduction band to a reduction mechanism via a valence band (oxygen reduction in the dark).

We report an attempt to provide evidence for the doping-dedoping of lithium cations into an F−-doped SnO2 transparent conductive substrate. The investigation was performed in anhydrous acetonitrile charged with alkaline salts containing Li+ ions: 0.1 M LiBF4 and 0.1 M LiSO3CF3. After polarization in a potential range sufficiently positive to ensure that Li deposition does not occur, the material was analyzed by scanning electron microscopy and energy-dispersive X-ray analysis, and the chemical composition of the surface layers was determined by X-ray photoelectron spectroscopy.

A new family of electrolytes is described. It is obtained from liquid ammoniates prepared with mixtures of three selected lithium salts, in which small amounts of amines (compounds derived from ammonia) are added. These electrolytes possess high ionic conductivities (10 −2 S cm −1 at room temperature) even at low temperature (above 10 −3 S cm −1 at −20°C) within a large operating temperature range (−20°C, +60°C) and under a low vapor pressure (below 1 bar at +60°C).

The solvates based on combinations of lithium salts with ammonia (called liquid ammoniates) form highly conductive and low cost electrolytes. The generalizing of this fact is possible with amines. Like ammoniates, their solvates possess properties which can widely vary with the composition, the nature of the amine and the anion. Mixtures of NH3, amine(s) and lithium salt(s) were also investigated. These properties include the glass-transition temperature, the conductivity, the vapour pressure and the corrosion rate of lithium. The conductivity can be as high as 1 × 10−2 Ω−1 cm−1 at 60 °C. The lithium stability depends on the anion and on the nature of the amines: with n-propylamine and isopropylamine charged with lithium triflate (only 1.5 M) lithium metal is very stable even at +70 °C during several months.

The interface structure of the semiconductor/electrolyte junctions in nonaqueous solvents is an open question, and as in water, the study of the influence of pH on the flat band potential can lead to an important part of its knowledge and to applications such as pH measurements. In water, the flat band potential shifts of many semiconducting materials can be connected with pH shifts. In this paper we show it is the case for nInP electrodes in acetonitrile and methanol (96% in weight in water) at room temperature, and in liquid ammonia at low temperature, −55°C. Therefore this material can be used as a probe of pH. Using this property we were able to find again, for example, the values of the self-ionization constants of the studied solvents and the acidity constants of water in liquid ammonia and of acetic acid in methanol.

The linear dependency of the n-InP photocurrent on the level of illumination is indepedent of the solution composition, the type of illumination, the exposed crystalline face, or the level of doping. The photodissolution mechanism (for photocurrents between 1.1 and 65 mA cm−2) utilizes six charges to dissolve one molecule. In the absence of an insoluble oxide layer, the ratio between photogenerated holes and injected electrons is independent of the exposed crystalline face, the photon flux, the solution composition and the level of doping. Solutions containing oxygen bearing mineral anions (such as ClO−4, H2PO−2, or SO−24) are predisposed to the formation of an insoluble oxide layer on the surface of the InP under strong illumination.

The use of buffered neutral liquid ammonia medium for the first time provided evidence for a current doubling effect on p-InP during oxygen photoreduction. Unlike results in aqueous medium, a common mechanism of O2 reduction was observed at p-InP and p-GaAs electrodes. When protons were added to the solution, two different oxygen reduction mechanisms occurred at these electrodes. This study emphasizes the important results of the hydrogenated p-InP surface and revealed that liquid ammonia (at 223 K) was perfectly appropriate to understand the mechanism of O2 reduction at InP electrodes.

The linear dependency of the n-InP photocurrent on the level of illumination is indepedent of the solution composition, the type of illumination, the exposed crystalline face, or the level of doping. The photodissolution mechanism (for photocurrents between 1.1 and 65 mA cm−2) utilizes six charges to dissolve one molecule. In the absence of an insoluble oxide layer, the ratio between photogenerated holes and injected electrons is independent of the exposed crystalline face, the photon flux, the solution composition and the level of doping. Solutions containing oxygen bearing mineral anions (such as ClO−4, H2PO−2, or SO−24) are predisposed to the formation of an insoluble oxide layer on the surface of the InP under strong illumination.

The electrical conductivities, viscosities and NH3 vapor pressure data for lithium salts ammoniates are reported. These measurements allow the apprehension of the nature of the solvation shell of ions by ammonia and the quantification of the NH3- Salt bonding energy which are essential for application of ammoniates as non aqueous electrolytes in lithium batteries.

The oligocondensations of methane, ethane and propane have been studied by allowing an excess of these hydrocarbons to react on carbenium ions, derived from these alkanes (and obtained by their gentle oxidation at an anode) dissolved in HSO 3 F + HF mixture (1:1) which is a good non-nucleophilic solvent. Since these three compounds are not chemically oxidized by HSO 3 F into the corresponding carbenium ions, unlike all the other saturated hydrocarbons, an activation method has been developed. Thus the electrooxidation of these gases was conducted successfully in the mixture HSO 3 F + HF (1:1) with anodes made of platinum or vitreous carbon “V10”. Ethane was formed from methane and propane, isobutane and isopentane were formed from ethane. The oligocondensation of methane comes to a stop, to give predominantly ethane due to the low electrooxidation rate of this last compound compared with that of methane. In the case of propane, isobutane, isopentane and a mixture of branched-chain hexanes were obtained. A high pressure electrolysis cell has been developed.

The ammoniates of lithium perchlorate LiClO4, nNH3 (2,2 < n < 4) undergo sharp transitions of their conductive and mechanical properties as a function of the temperature. The study of the conductivity in the range of temperature [+ 10°C, + 90°C] shows a transition insulator-conductor in agreement with a percolation theory.

Mixed Langmuir–Blodgett (LB) films based on crown derivatized platinum nanoparticles (NPs) and fatty acid showed a direct electrochemical activity toward oxygen reduction reaction (ORR) in acidic medium. This paper reports on the original and strong effects observed in the electrochemical response of these two-phase systems towards oxygen reduction by varying the Pt amount in the mixed LB films. The easy manipulation of pre-synthesized organically capped nanoparticles, combined with the features of the Langmuir–Blodgett technique allows good control of the platinum loading in the films. Pt loadings are set by changing the number of deposited monolayers and/or their nanoparticle density. Loading variations induce strong modifications in the voltammograms and are considered in terms of the relative weight of the two phases: platinum nanoparticles and fatty acids. We point out the strong influence of the environment of platinum nanoparticles towards their electrocatalytical behaviour. Various effects, such as electrical resistance of the nanostructures are considered. Evolution of the peak current density ratios from O2 and [Fe(CN)6]3−/4− probes as a function of platinum loading in mixed films could suggest a possible change in the dominating number of electrons exchanged in the ORR. The effect of the fatty acid phase is definitely demonstrated by the leveling of the electrochemical responses after its elimination from the thin film structures. The electrochemical response is then likely governed by only the organic crown of the particles, which controls the ultimate local environment of the platinum particles. In such a situation, the optimized platinum loading is found to be 2.4 μg cm−2.

We report on the behavior of Pt nanoparticles functionalized with 4-mercaptoaniline over-grafted with 2-thiophenecarbonyl chloride. Stable Langmuir–Blodgett (LB) mixed films were built up from these particles with behenic acid (BHA). Such ultra-thin films were transferred onto gold substrates, which allowed the study of their electrochemical response towards Fe[(CN)6]3− and their XPS chemical analysis before and after the BHA removal. After washing, XPS analysis showed that the signals corresponding to the metal core and the capping agent were almost unchanged. Moreover, the layers became more compact, as shown by the Pt/Au intensity ratio decrease, because of the apparent decrease of length escape of electrons coming from gold, evidencing the removal of the fatty acid in the LB film structure. After BHA removal, the resulting electrochemical activity slightly increased. This result, in agreement with XPS analysis, showed the structural rearrangement within the film that facilitated the percolation between the particle domains.

International audience; 4-mercaptoaniline functionalised platinum particles of 2 nm diameter were synthesised and over-grafted with 2-thiophenecarbonyl chloride. The derivative particles were dispersed in DMSO and gave long term stable suspensions. The Langmuir-Blodgett technique was then used to build up stable Langmuir-Blodgett films and the electrochemical behaviour of these ultra-thin films towards oxygen reduction was investigated in an acidic medium. It revealed direct activity without any previous activation treatments despite of the presence of the organic shell at the particle surface. Furthermore, XPS experiments revealed that the organic crown was not significantly destroyed on prolonged cycling. The results open a way to study original and versatile platinum-based nanocomposites.

La jonction semiconducteur/électrolyte est un système permettant de détecter aisément les processus d'injection de charges associées à des espèces chimiques en liaison avec le réseau cristallin. Ces phénomènes interviennent lors de réactions électrochimiques très diverses, comme les réactions de réduction multiélectroniques (oxygène, eau oxygénée) ou d'oxydation (décomposition des matériaux). Dans cet article, une comparaison entre InP et GaAs permet de discuter, dans le processus global, du rôle des intermédiaires réactionnels et des films de surface.

The interface formation of the junction (n and p) InP/liquid ammonia is examined in terms of acid base equilibrium of adsorbed species (issued from the solvent) from impedance measurements recorded in basic (potassium amide) and acidic (ammonium bromide) solutions.

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This paper reports on the original and promising electrocatalytic properties of thiol-capped platinum nanoparticules toward O2 reduction in acidic medium. The nanoparticles were initially functionalized by 4-mercaptoaniline, and were further derivatized with 2-thiophenecarbonyl chloride leading to high stabilization of the organic crown. Ultrathin films of these particles were built up by the LB technique on gold. Their electrochemical behavior was studied. These assemblages were also characterized by X-ray photoelectron spectroscopy before and after oxygen reduction experiments. An electrocatalytic activity was established without any activation treatment. Our results show that the organic crown of the nanoparticles does not prevent their electrochemical activity

Using cyclic voltammetry, for both p- and n-type GaAs, an anodic peak is observed just before an unlimited anodic current, in acidic, neutral, or basic media in liquid ammonia. This anodic peak is due to an adsorption/precipitation phenomenon. It led to the passivation of the SC surface regardless of pH. After passivation of the electrode, a reduction wave appeared in acidic medium as well in unbuffered neutral medium, but in this last case only for high scan rates. In basic medium, no reduction wave appeared. The initial electrochemical state of GaAs, corresponding to the presence of the anodic peak, is recovered by reduction of the adsorbed film in acidic media, in unbuffered neutral medium, or in buffered neutral medium. No recovery is observed in basic media. These last results show that this recovery occurred only when protons came from the medium (acidic medium) or protons came from the anodic reaction associated to the anodic peak, or if a proton donor was present. Quantitative analysis of gallium and arsenic elements released in solution showed clearly that a dissolution happened without limitation as soon as the unlimited anodic current was reached. Coulometric measurements point out that the efficiency of dissolution increased with current density in the anodic unlimited current, showing that ammonia oxidation and material oxidation were concomitant reactions. The anodic wave may be considered as the result of the precipitation of a nitrogenous-based complex (i.e., amide complex) which implies the superficial lattice contribution. The passivation film may be initiated by the formation of strongly adsorbed atoms of nitrogen, intermediaries arising from ammonia oxidation, which can behave as site poison at the interface during nitrogen evolution.

It is demonstrated that films of heteropolyanions (HPAs) can be electrodeposited onto different metallic electrode surfaces in nonaqueous media such as N,N-dimethylformamide (DMF) or N-methyl-2-pyrrolidinone (NMP) by reduction of Keggin-type (NEt 4 ) 3 PMo 12 O 40 . For both DMF and NMP, electrodeposition gives rise to a coating. In DMF, the electrodeposition takes place during the first and second reduction steps of HPA, while in NMP, the electrodeposition takes place only during the second reduction step, which demonstrates that electrodeposition strongly depends on the solvent nature, possibly because of a process of coadsorption of the solvent during electrodeposition.

Til 4 is soluble in the liquid ammoniate Nal.3.3NH 3 . Ti(IV) can be reduced to Ti(III) at a smooth Pt electrode at - 1.63 V vs. ferrocene/ferricinium ([Fc] 0/+ ) couple. This reduction seems to be a quasi-reversible reaction. No further reduction to metallic titanium is observed.

Studies of the oxygen reduction mechanism were performed in acidic liquid ammonia at 223 K. Pt microelectrodes and III-V semiconductors were used as probes. With both types of electrode it was found that two electrons are required for oxygen reduction and a chemical reaction involving two ammonium ions (NH + 4 ) is essential.