Shaomin Zhou

In situ surface Raman study of the induced codeposition mechanism of Ni–Mo alloys

The induced codeposition of molybdenum with nickel on a Ni–Cu alloy electrode has been investigated by means of in situ surface Raman spectroscopy to obtain information about the codeposition mechanism during electrodeposition of Ni–Mo alloys. The experimental results show that, in the NiSO4-free solution, molybdate can only be reduced to a mixture of polyvalent molybdenum oxides and/or hydroxide, while, in the case where NiSO4 coexisted in the solution, molybdate is first reduced to Mo(IV) oxide, which, as an intermediate, subsequently is reduced to molybdenum in alloy under the catalysis of inducing nickel.

Current oscillations in the reduction or oxidation of some anions involving convection mass transfer

Abstract We have discovered a new kind of current oscillation during the reduction or oxidation of some anions, which appeared over the limiting reduction or oxidation current of the anions and was loaded on the current of hydrogen or oxygen evolution. The overlap of a positive feedback (convection mass transfer of the anions induced by hydrogen or oxygen evolution, and the increase of the potential difference in the cell when the current is smaller) and a negative feedback (depletion of the surface concentration of the anions by reduction or oxidation, and the decrease of the potential difference in the cell when the current is larger) between the bistable states accounts for the oscillations, and a ‘hidden’ negative impedance in the second ascending branch of the polarization curve was observed for the first time. Our model has also shed some light on the other systems reported in the literature, in which convection mass transfer also plays an important role in the current oscillations. In addition, the potential oscillations during the oxidation of Fe(CN) 6 4− are reported here for the first time, and are similar to the potential oscillations during the reduction of Fe(CN) 6 3− reported in our previous paper [Z. Li, J. Cai, S. Zhou, J. Electroanal. Chem., in press].

Effects of the magnetic field on the polyaniline film studied by in situ conductivity measurements and X-ray diffraction

Abstract Polyaniline (PANI) film formed under the effects of the magnetic field was characterized. In situ conductivity measurements with four microprobe electrodes were performed in acid aqueous solution. The electroactivity and potential dependent conductivity of the polymer film are much improved by use of a magnetic field. The results show that the upper value of conductivity for the PANI (Bp = 0.7 T) film prepared in the presence of the magnetic field parallel to the electrode surface is increased by a factor of three times that of a PANI film formed in the absence of the magnetic field, and the film has some anisotropic properties with a conductivity increase of 30% in the direction perpendicular to the magnetic flux compared with that in the parallel direction. The potential of the maximum conductivity is shifted negatively by 50 mV. The X-ray diffraction pattern of the polymer shows that the increase in crystallinity and structural order result from the magnetic alignment. It is suggested that the resulting polymer film formed under the magnetic field has a more ordered structure and better stability.

Improved conductivity and electrical properties of polyaniline in the presence of rare-earth cations and magnetic field

Abstract The influence of rare-earth cations on the preparation and properties of polyaniline (PANI) was investigated in the presence of a magnetic field. It was found that the addition of rare-earth cations can greatly increase the polymerization rate of PANI in the following order: Tb 3+ >Nd 3+ >Ce 3+ . When a parallel magnetic field ( B p ) was imposed with respect to the electrode surface, the maximum polymerization rate was obtained at B p =0.5 T. Whereas, in a perpendicular magnetic field ( B s ), the rate was accelerated as the magnetic flux density rose. The conductivity of PANI/Tb 3+ / B p =0.7 T film was 115.4 S cm −1 which, as expected, is higher by about an order of magnitude as compared to the parent PANI film without the effects of rare-earth cations and magnetic field. Meanwhile, the X-ray diffraction patterns and electrochemical impedance spectroscopy indicated an increase of crystallinity and a more-ordered arrangement of the polymer chains with a concurrent increase in the capacitance, and a decrease in the charge transfer resistance and the ohmic resistance in the presence of rare-earth cations and magnetic field.

Surfactant effects on the polyaniline film

Abstract Polyaniline (PANI) film prepared in the presence of surfactant anions, such as sodium dodecylbenzenesulfonate (SDBS) and sodium dodecylsulfate (SDS), was characterized. The conductivity of PANI/SDBS film was 65.9 S cm −1 , which is five times higher than that of the parent PANI film without the influence of surfactants. The UV–Vis spectra and X-ray diffraction pattern of the PANI/SDBS film showed increase of polaron delocalization, structural order of polymer chains and higher crystallinity, resulting from the decreased degree of degradation due to the hydrophobic effect of the surfactant molecules on the film growth, and the large surfactant anions immobilized in the polymer backbone and the stabilized polymer chain.

Potential oscillations during the reduction of Fe(CN)63− ions with convection feedback

Potential oscillations, which were observed during Fe(CN)63− reduction under galvanostatic conditions in 1 mol dm−3 NaOH solution on a platinum electrode, are described. The bifurcation boundaries were measured in the parameter plane of applied current vs. Fe(CN)63− concentration. A broad limiting current plateau (zero slope) occurring in the current-potential curve in combination with a negative real impedance is a typical characteristics for this kind of oscillation, and the oscillation amplitudes are within that region. The bistability, i.e., Fe(CN)63− reduction and hydrogen evolution at different potentials, coupled with convection feedback induced by hydrogen evolution, accounts for the oscillations. The sequence of chaotic-quasiperiodic-periodic-quasiperiodic oscillations, which appeared when the applied current was increased monotonously, was characterized by time series, power spectra, phase portraits and one-dimensional maps.

In situ surface Raman study of the phosphorus incorporation mechanism during electrodeposition of Ni-P alloys

Abstract Codeposition of phosphorus with nickel on an Ni–Ag alloy electrode has been investigated by means of in situ surface enhanced Raman spectroscopy (SERS) to obtain information about the phosphorus incorporation mechanism during electrodeposition of Ni–P alloys. The experimental results showed that in the solution without NiSO4, hypophosphite was reduced only to a Ni–phosphine compound, while in the case where NiSO4 coexisted in the solution, the Ni–phosphine compound, as an intermediate, was oxidized by Ni2+ to elemental phosphorus in alloys with nickel acting as the catalyst.

An ESR study of the electrocatalytic oxidation of hypophosphite on a nickel electrode

Abstract The electrocatalytic oxidation of hypophosphite on a nickel electrode has been studied by means of electron spin resonance spectroscopy (ESR) to obtain information about the anodic oxidation mechanism. A 16-line ESR spectrum was observed in the process of the electrocatalytic oxidation of hypophosphite when spin trap α-pyridyl- N -tert-butyl nitrone (PBN) was added in the electrolytic solution. The spectra-line patterns and hyperfine coupling parameters were greatly consistent with those in the solution composed of Ti 3+ (0.01 mol / l )+ H 2 O 2 (0.05 mol / l )+ H 2 PO 2 − (0.01 mol / l )+ PBN , in which reactions Ti 3+ + H 2 O 2 → Ti 4+ + OH + OH − and OH + H 2 PO 2 − → PHO 2 − + H 2 O take place and PHO 2 − from the reactions formed spin adduct with PBN. Therefore, the spin adducts formed in the process of electrocatalytic oxidation of hypophosphite could be ascribed to an adduct belonging to PHO 2 − and PBN. Accordingly, the electrocatalytic oxidation of hypophosphite might undergo an H abstraction of hypophosphite from the P–H bond to form the phosphorus-centered radical PHO 2 − , which is subsequently reacted with water to form the final product, phosphite.

In situ surface Raman investigation on induced-codeposition of an Fe-Mo alloy

Abstract In situ surface Raman spectroscopy was used for investigation of induced-electrodeposition of Fe–Mo alloy. The results of Raman spectra showed that in the electrolyte without FeSO 4 , the Mo(VI) species reduction occurred at a potential more negative than −0.5 V (vs SCE) as indicated by the appearance of a new peak (ca. 730 cm −1 ) which corresponded mainly to a Mo(IV) species.The broadening of the peak was attributed to a Mo(IV) species deposited on the electrode surface existing in the form of a ‘molybdenum blue’ compound. This compound was not further reduced even at the potential up to −1.9 V, while in the case where FeSO 4 coexisted in the electrolyte, the formation of the ‘molybdenum blue’ became easier and the peak blue shifted to 740 cm −1 . Moreover, this peak faded away gradually in the potential region from −1.5 to −1.9 V and a bright Fe–Mo alloy deposited on the electrode surface was observed. These results showed that in situ surface Raman spectroscopy was a useful tool in the study of the induced-electrodeposition of this alloy.

The effects of tetraphenylporphyrin and its metal coordination compounds on H+ ion transfer across the water / nitrobenzene interface

Abstract The effects of tetraphenylporphyrin (H 2 TPP) and its first transition-metal coordination compounds (MTPP) on H + ion transfer across the liquid/liquid (L/L) interface have been investigated by cyclic voltammetry and UV spectroscopy. The results show that H 2 TPP and MTPP assist H + ion transfer across the water/nitrobenzene (W/NB) interface to a different extent, and that the transfer process is reversible and diffusion-controlled. As far as MTPP is concerned, the sequence of activity is NiTPP > MnTPP > CoTPP, CuTPP > ZnTPP, FeClTPP; this order corresponds to the sequence of their stabilities. On the basis of the interfacial tension measurement results and the characteristic structural features of H 2 TPP and MTPP, the ionophores were specifically adsorbed at the interface; coordination was likely to occur in the mixed-solvent layer. An apparent kinetic mechanism of H + ion transfer across the W/NB interface facilitated by H 2 TPP is proposed.