Charge and Discharge Characteristics of Thermochargeable Galvanic Cells with an [ Fe ( CN ) 6 ] 4 − / [ Fe ( CN ) 6 ] 3 − Redox Couple

Abstract

We present the thermocharge and discharge characteristics and long‐term cycling performance of a thermochargeable galvanic cell with carbon fiber electrodes, a ferro/ferricyanide ion redox couple incorporating a cation‐exchange membrane, and an extra pair of electrodes on each side of the membrane. This cell is a rechargeable concentration cell. No external charger is needed, and the cell can be used while it is being charged. It also functions as a thermoenergy conversion system, which can store energy. The ratio of discharge capacity to thermocharge capacity was more than 90% when there was a temperature difference between the main electrodes during thermocharging and discharging. When the temperature difference was removed after thermocharging and the cell was discharged, the ratio remained above 80% when the difference during thermocharging was greater than 35°C. Thermocharge and discharge capacities were almost constant for over 40 cycles. The cell retained the advantage of the conventional thermocell with a ferro/ferricyanide ion redox couple; its voltage was constant as long as constant thermal energy was supplied. The cell was discharged from the main electrodes at 0.5 mA/cm2 and constant voltages of the main and extra electrodes for over 1000 h while simultaneously thermocharging from the extra electrodes at the same current density. As a thermoenergy conversion system, our cell showed nearly the same thermal efficiency and power density as the conventional thermocell.