Preferential electrosorption of anions by C/Na0.7MnO2 asymmetrical electrodes

In this work, an asymmetrical electrode system involving Na0.7MnO2 as negative electrode and activated carbon as positive electrode has been proposed for removal of anions from salty solutions. The Na0.7MnO2 has been prepared by facile hydrothermal reaction and the electrochemical analysis shows that the capacity of Na0.7MnO2 can attain 120 F/g at the scan rate of 1 mV/s in 1 M Na2SO4. Further, it is found that the electrosorption capacity of C/Na0.7MnO2 is 0.183 mmol/g in NaCl solutions with an initial conductivity of 500 μS/cm at cell voltage of 1.2 V, whereas it attains to 0.178 mmol/g in NaNO3 and 0.124 mmol/g in Na2SO4, respectively. Significantly, by normalizing the equivalent capacity, it is found that the electrosorption capacity of C/Na0.7MnO2 obeys the order of SO42− > Cl− > NO3−, indicating preferential ion electrosorption for anions due to different hydrated radius and valence regardless of initial solution concentration.