High performance asymmetric capacitive mixing with oppositely charged carbon electrodes for energy production from salinity differences

Abstract

Capacitive mixing (CapMix) is an emerging technique that uses supercapacitors for harvesting salinity gradient energy. Here, positively charged quaternized poly(4-vinylpyridine) coated activated carbon and negatively charged nitric acid oxidized activated carbon are employed as electrodes for asymmetric CapMix (Asy-CapMix), enabling the production of electricity via four-step or two-step energy generation cycles without using an external power source and selective membranes. The voltage rise of this capacitor is 150.0 mV, and the average power density can reach as high as 65.0 mW m⁻². Both values are higher than those of CapMix using symmetric electrodes and an external power source or selective membranes and better than those of previous Asy-CapMix, including those with external power supplies. Such superior performance can be attributed to the high surface charge density and the good conductivity of the chemically modified activated carbon electrodes, which may give insight into the design of electrodes for high performance Asy-CapMix.