Tamotsu Shirogami

Biochemical energy conversion using immobilized whole cells of Clostridium butyricum

Hydrogen producing bacteria, Clostridium butyricum, were immobilized in agar gel (2 per cent). The immobilized whole cells were employed for continuous production of hydrogen from alcohol factory waste waters. The hydrogen production rate became constant above BOD 1500 ppm when hydrogen production was performed with a batch system. The immobilized whole cells continuously produced hydrogen over a 20-day period. The amount of hydrogen produced was about 6 ml/min/kg wet gels. Hydrogen produced was supplied to the hydrogen-oxygen (air) fuel cells. The maximum cell voltage of cell I and II was about 0.55 and 0.66 V respectively when the flow rate of hydrogen was 6 ml/min. The limiting current density changed from 0.4 to 40 mA/cm2 as the resistance between the electrodes changed from 1 to 100 ohmz. The fuel cell was left on for 7 days and the current from 550 to 500 mA was obtained continuously over a 7 day period.

Long life sealed nickel-zinc cell using a new separator

Abstract Because of internal shorting due to zinc (Zn) dendrite formation at the Zn electrode, nickel-zinc (NiZn) secondary cell cycle life is somewhat less than the NiCd cell cycle life. To solve this problem, a new kind of separator was developed which consisted of nylon non-woven cloth coated with poly(vinyl alcohol) (PVA) containing boric acid. This separator has a high ionic conductivity, but is resistant to zincate ion penetration. A large number of additives, effective for Zn dendrite suppression, was also tested. From them, bismuth oxide (Bi 2 O 3 ) was selected and added, together with calcium hydroxide (Ca(OH) 2 ), to the Zn electrode. A charging method, applying an intermittent anodic pulse, was found to be effective to reduce the Zn electrode shape change and prolong the cycle life of this cell. By using these materials and investigating a cell construction containing an electrolytic solution and hydrogen gas absorber, sizes AA, C, and D sealed NiZn cells were developed whose charging and discharging cycle life achieved over 500 cycles, for a size C cell.

Solid state Li/MnO2 cells

The possibility of using MnO2 as the cathode material for a solid state lithium cell system has been studied. The cell system, where the mixture of MnO2 and LiI is directly in contact with the lithium anode without a solid electrolyte layer, showed high cell voltage and low internal impedance. Cell behaviour for this system and the discharge mechanism were investigated and discussed. It may be considered that the discharge process consists of two reactions: LiI + MnO2 → LiMnIIIO2 + (1/2)I2 Li + (1/2)I2 → LiI.The second reaction seems to determine the cell voltage.