Yasuhisa Maeda

The electrochemical response of highly boron-doped conductive diamond electrodes to Ce3+ ions in aqueous solution

The electrochemical response of highly boron-doped conductive diamond electrodes to Ce3+ ions in aqueous sulfuric acid, nitric acid and perchloric acid solutions was studied mainly by use of cyclic voltammetry. The diamond electrode shows a well-defined voltammogram indicating quasi-reversible behavior for the Ce3+/Ce4+ redox couple in aqueous acidic solution. The equilibrium redox potential of the Ce3+/4+ couple was derived from the cyclic voltammograms. The diffusion coefficients for Ce3+ were evaluated from the dependence of the cyclic voltammograms on the potential sweep rate. The kinetic parameters for the anodic oxidation of Ce3+ were measured at the diamond electrode from the relation between the overpotential and the logarithm of current.

Electrochemical synthesis of graphite intercalation compounds with nickel and hydroxides

Abstract Graphite intercalation compounds (GIGs) with nickel and iron hydroxides were synthesized from the corresponding GICs with metal chlorides by galvanostatic oxidation and also by repeated charge-discharge cycles in an alkaline secondary battery with KOH aqueous solution. The stage-one structure in the original chloride-GICs was found to disappear after the first charge-discharge process and the compounds kept the stage-two structure. A gradual increase in the capacity of the battery with charge-discharge repetition suggests a slow replacement of chloride ions by hydroxide ones in the graphite interlayer space.

Metal ion intercalation on graphite cathode in MgCl2DMSO and MnCl2DMSO solutions

Cathodic reduction behavior of pyrolytic graphite in MgCl2DMSO and MnCl2DMSO solutions was studied. The cathodic reduction in MgCl2DMSO solution caused the intercalation of DMSO solvated Mg2+ ion to form the graphite intercalation compound. The insertion of a little amount of DMSO solvated Mn2+ ion between layers near the edge part of the graphite was suggested on the cathodic reduction in MnCl2DMSO solution. These results led to an importance of relation between redox potential of metal/metal ion and threshold potential of beginning of cation intercalation on graphite.

Electrochemical intercalation of alkali metal ions on carbon fibers

Abstract Electrochemical intercalation of Li + , Na + and K + ions on carbon fibers heat-treated at various temperatures was examined by measurement of the cyclic voltammograms of them in LiClO 4 -DMSO, NaClO 4 -DMSO and KClO 4 -DMSO solutions.

Electrochemical Peltier heat in the polypyrrole-electrolyte system☆

Abstract The simultaneous detection of electrochemical and thermal responses of polypyrrole in 1 M NaClO 4 aqueous solution (pH = 5) was carried out. Thermal measurement with cyclic voltammetry and galvanostatic electrolysis revealed exothermic and endothermic changes due to anodic and cathodic currents, respectively, on the surface of the polypyrrole electrode. The proportional relation between the heat due to electrolysis and electric quantity or current was confirmed in both the exothermic and endothermic processes. This electrochemical Peltier heat could be attributed to the entropy change in the electrochemical doping and dedoping of ClO 4 − ions. It suggested the occurrence of a decrease and an increase in entropy in the doping and dedoping processes, respectively. The value of the entropy change in the dedoping of ClO 4 − ions could be evaluated on the basis of the entropy change in the anodic oxidation of Fe(CN) 6 4− ions.

A new carbon fiber and nitric acid cell with a temperature difference between electrodes

Abstract A new cell of polyacrylonitrile(PAN)-based carbon fibers and 30% nitric acid with a temperature difference between the cathode and anode has been developed. The open circuit voltage of about 150 mV and the short circuit current of about 1.6 mA were obtained by using the as-received carbon fibers of 1.55 g at both electrodes, when the cathode and anode were kept at 88.2 °C and 0.0 °C, respectively. The presence of carbon fibers at the electrodes was found to make the cathode potential more positive and the anode potential less positive. The electrode reaction was supposed to be the reduction of NO 30 − ions into N 2 O 4 gas at the cathode and the reverse reaction at the anode. The N 2 O 4 gas formed diffused from the cathode to the anode through the upper bridge, and NO 3 − ions transferred from the anode to the cathode through the lower bridge. This circulation of active materials leads to the continuous and steady generation of electric power.

Performance of a thermocell of carbon fibres and nitric acid

Abstract The performance of a thermocell of carbon fibres and nitric acid was studied. PAN-based carbon fibre cloths, heat treated at various temperatures, and 30% nitric acid were used as an electrode and an electrolyte, respectively. In this cell, the reduction of nitrate ion to nitrogen oxides occurs at the cathode, and the reverse reaction at the anode. The largest load current was obtained by using the 1300 °C-treated cloths. Oxidation treatment of the 2000 °C-treated cloths caused an increase in the load current. The load current dependence on the anode temperature showed a maximum value in the vicinity of 20 °C. The open circuit voltage was independent of the weight of the cloths. The load current increased linearly with the weight of the cloths up to 1.0 g. A test of durability confirmed stable performance for more than 190 days.