Reita Tamamushi

The electrochemical Peltier effect observed with electrode reactions of Fe(II)/Fe(III) redox couples at a gold electrode☆

Abstract The electrochemical Peltier effect was studied at a gold electrode in solutions containing some Fe(II)/Fe(III) redox couples by measuring the local temperature change in the electrode/solution interphase under controlled-potential and controlled-current polarization. Relative values of the electrochemical Peltier coefficient for the cathodic process at equilibrium potential, which is denoted by (Πc)I=0, were determined by analyzing the observed temperature change as a function of current. The values of (Πc)I=0 were found to be positive for the Fe(H2O)62+/Fe(H2O)63+ systems in HClO4 (1 M), HNO3 (1 M), H2SO4 (0.5 M), and HCl (1 M), their magnitudes being very similar in the first three acid solutions, but smaller in the HCl solution. On the other hand, a negative value of (Πc)I=0 was obtained in the case of a Fe(CN)64−/Fe(CN)63− couple in a H2SO4 (0.5 M) solution. Such a difference in the Peltier coefficient is considered to be due to the difference in the ionic species of iron involved in the electrode reaction.

Determination of electrochemical kinetic parameters by square-wave polarography: Polarographic reduction of Zn(II) in concentrated nitrate and perchlorate supporting electrolyte solutions

Abstract The electrochemical kinetic parameters for the polarographic reduction of Zn(II) at a dropping mercury electrode in concentrated supporting electrolytes consisting of sodium, ammonium, lithium, magnesium and calcium nitrates and sodium perchlorate have been determined at 25.0±0.1°C by the square-wave polarographic method. The rate parameter decreased with increase of radius of the alkali-metal cations present in the electrolyte and with increase of charge of the cation of the electrolyte in solution of the same ionic strength. It also decreases, passes through a minimum and then increases with the increase in the concentration of any of the supporting electrolytes. The initial decrease is ascribed to the Frumkin double-layer effect but the latter increase has been explained in terms of the change in the activity of water around the electrode.

Polarographic Study on the Electrode Reaction of Zinc Ion

The Polarographie reduction waves of Zn(U) in various solutions were analysed according to the theoretical equation for quasi-reversible currentpotential curves derived by Matsuda. In solutions of 1 M NaClOt or 1 M KNOs, the whole of the reduction wave of (11) can be explained approximately in terms of the kinetic parameters obtained by the above method. This is not the case, however, for the reduction in solutions containing halide ions. The effect of halide ions on the electrode reaction of Zn(H) appears to be due to a change of electrode surface resulting from the adsorption of the halide ions on the mercury electrode. From the present experimental results the following mechanism was proposed for the electrode reaction of Zìì(II) at the dropping mercury electrode in the solutions containing halide ions: the overall faradaie current is determined by two simultaneous reactions in parallel, i.e., one which proceeds at the naked electrode surface and the other which proceeds at that part of the electrode surface which is covered by the adsorbed halide ions. The standard rate constant hs and the cathodic transfer coefficient of the former are (2.3 ± 0.2) X 10~3 cm./sec. and 0.47 ± 0.02, respectively. The fact that polarographically reversible waves are obtained in solutions of 1 M KI or 5.25 M CaCl2 indicates that the rate constant of the electrode reaction at the covered electrode is much larger than at the naked electrode.

Current-time characteristics of the rapidly dropping mercury electrode

Summary The properties of the rapidly dropping mercury electrode (RADME) in stationary and flowing media were studied by measurement of the current-time curve during a drop-life. In the absence of surface-active substance (SAS), the limiting current observed at the RADME in the potential region where the maximum of the second kind appears, was shown to be controlled by both diffusion and convection. However, in the presence of a sufficient amount of SAS, the maximum of the second kind was completely suppressed and the characteristics of the limiting current at the RADME were similar to those at the conventional DME. It was also shown that the limiting current of lead(II) obtained with the RADME in 0.1 M potassium nitrate solutions containing 5.10−1M polyoxyethylene lauryl ether was almost independent of changes in flow rate of the solution up to about 3 cm/sec. These results suggest that the RADME is a suitable indicator electrode in d.c. polarography in flowing media.

The rapidly dropping mercury electrode in direct current and alternating current polarography

Abstract The characteristics of the rapidly dropping mercury electrode (RADME) in direct current and alternating current polarography have been investigated. The RADME gives a maximum of the second kind on the D.C. current-voltage curve because of the “Spuleffekt”. This maximun is suppressed upon the addition of a large amount of surface-active substance, and typical currentvoltage curves similar to those at the DME are obtained. The limiting current at the RADME is proportional to the concentration of the electroactive substance. In A.C. polarography the RADME gives the peak current more accurately than the conventional DME. The height of the peak current is not affected by the “Spuleffekt”, and is proportional to the concentration of the electroactive species.

Mediating effects of ferric chelate compounds in microbial fuel cells

Abstract The performance of bio-fuel cells containing Escherichia coli, glucose and a series of ferric chelate reagents was studies. The measured coulombic outputs indicate that the most of the compounds work effectively as electron-transfer mediators in the fuel cells. These outputs were compared with measured rate constants for the reduction of ferric chelates by E. coli and the electrochemical reaction of these compounds at a carbon electrode. The results suggest that a good mediator for microbial fuel cells is one which shows fast reduction by E. coli, together with a fast electrode reaction. In regenerative fuel cells which were run for 5 days, coulombic yields over 70 % were obtained on the basis of complete oxidation of added glucose.

Instrumental study of electrolytic conductance measurements using four-electrode cells

Summary A new apparatus was presented for the electrolytic conductance measurement by a four-electrode cell under controlled-current or controlled-potential conditions. The four-electrode cell method enables us to dry the whole cell without altering the cell constant and to use electrodes of any material unless they are attacked by the solution. The direct reading of solution resistance can be made with an accuracy of ±0.2%. When the resistance is measured by the null method and calibrated by the method of substitution, the accuracy is increased to better than 0.1% at frequencies less than 1500 Hz, provided that the resistance is less than several kiloohms. It was shown that the d.c. conductance can be determined with a reasonable accuracy by the same measuring apparatus. The present method can be applied to the absolute determination of electrolytic conductivity without calibrating the cell constant by using standard solutions of known conductivities. Because of these advantages, the present method is expected to be very useful in the conductance study of solutions where the conventional two-electrode methods fail to give reliable data.

Determination of electrochemical kinetic parameters by square-wave polarography: Polarographic reduction of Zn(II) in 1 M KCl, KBr, and KNCS solutions

Abstract A new method of determining electrochemical kinetic parameters by square-wave polarography was presented, in which the faradaic current at θ/2, θ being the half-period of superimposed square-wave voltage, was used for the analysis. The method gave the following kinetic parameters for the electrode reaction, Zn(II) + 2 e (Hg), in aqueous solutions at 25° C: k c θ =0.0052 cm s −1 and α c =0.36 in 1 M KCl, k c θ =0.011 cm s −1 and α c =0.30 in 1 M KBr, and k c θ =0.020 cm s −1 and α c =0.52 in 1 M KNCS. Induced adsorption of Zn(II) on the dropping mercury electrode was suggested in solutions containing thiocyanate ions.

Potential-dependent transfer coefficients of the Zn(II)/Zn(Hg) electrode reaction in aqueous solutions

The electrochemical kinetic parameters of the Zn(II)/Zn(Hg) reaction at the DME were determined by phase-sensitive a.c. and square-wave polarography in a sufficiently wide potential range to test the Marcus prediction on the potential dependence of transfer coefficients. In 1 mol dm−3 solutions of perchlorate, nitrate, chloride, bromide, and thiocyanate, the apparent cathodic transfer coefficient was found to be a linear function of the electrode potential, the potential dependence being in agreement with the Marcus theory.

Nuclear magnetic resonance and thermal studies of concentrated aqueous solutions of lithium chloride

The nuclear spin relaxation times, T1 and T2, of 7Li nuclear magnetic resonance have been investigated over a wide range of temperatures in 14 mol kg–1 aqueous lithium chloride solution, whose thermal behaviour was examined with differential thermal analysis. The relaxation is mainly attributed to dipolar coupling between water protons and lithium ions, and T1 and T2 at temperatures higher than the glass transition point are governed by the translational motion of the hydrated lithium ions. The activation parameters of the motion were found to be Ea= 33.5 ± 0.8 kJ mol–1, τ0=(1.2 ± 0.5)× 10–17 s. The Ea values are similar to those for molecular self-diffusion in a plastic-crystalline phase of globular molecules.