Current Generation from Na2SO3 and H2SO3 by Using Carbon Fiber Anode

Current generation from Na2SO3 aqueous solution was found to occur by using PAN-based carbon fibers with heat treatment at 700 °C. Sixty mL of 0.1 M Na2SO3 and 80 mL of 0.5 M H2SO4 were added into the anode cell and cathode cell, respectively, and current generation was performed for 10 h. As a result, the current value increased from background current of 0.04 to 22.3 mA after 5 min. Afterward, the current was almost constant, and decreased a little in the final stage, accompanied by decrease of the amount of Na2SO3. The current efficiency was calculated to be 91%. The mechanism of the current generation is assumed to be described by the equation: SO32− + 2OH− → SO42− + H2O + 2e−. In the current generation using a 30 Ω resistor, the current was 11.3 mA, so that the voltage is calculated to be 0.339 V. The maximum electric power of this cell is calculated to be 3.83 mW. Next, 60 mL of 0.02 M H2SO3 was added to the anode cell, and current generation was performed for 4 h as well as in the case of Na2SO3. As a result, the current was 8.25 mA after 6 min. Afterward, the value linearly decreased, and the value was 3.80 mA after 3 h. The current generation almost finished after 4 h. In this case, the current efficiency was 28%. Furthermore, chemical groups on the surface of carbon fibers with heat treatment were measured by X-ray photoelectron spectroscopy. The element analysis on the surface resulted in: C, 82 atom %; N, 7.2 atom %; and O, 10.9 atom %; the existence of COO, C=O, C–O, C–C, C=C, C–N, and C=N groups was thus suggested.