Effect of Reduction Agent on ZnO Reduction by Radio-frequency Dielectric Heating

Abstract

Metal air battery attracts attention as an automobile battery, because of its high energy density. In order to reuse the battery, it is necessary to undertake reduction of metal oxide which is generated at the cathode without large environment load. We conducted the reduction of ZnO powder by radio-frequency dielectric heating. The ZnO powder and a reducing agent of organic liquid is put into a reaction vessel, and the tip of the electrode inserted from the top of the vessel is in contact with the surface of the powder. By measuring the spectrum of the blackbody radiation, the temperature was found to be approximately 2000 K. The reduction amount of ZnO increased remarkably when 0.7 to 1.4 mL of methanol was added as a reduction agent to 2.0 g ZnO powder, with a maximum of 27.6 mg at 1.1 mL reached. The reduction amount was smaller when ethanol, acetone, furfural, cyclohexane or dodecane were added as a reduction agent. The maximum energy efficiency is 3.3% without taking the reaction energy of the reduction agent into consideration, whereas it becomes 1.0% when taking it into consideration.