High-performance capacitive deionization electrodes through regulated electrodeposition of manganese oxide and nickel-manganese oxide/hydroxide onto activated carbon

Capacitive deionization (CDI) can directly produce freshwater from brackish water through electrostatic force which is applied to porous electrodes for ion adsorption. The adsorption capacity can be extended by not only physical surface area but also pseudocapacitive behavior on metal oxide. Here, we enhanced CDI performance of microporous activated carbon (AC) electrode by regulated electrodeposition of Ni and Mn metal hydr(oxide). Metal hydr(oxide) coating increases the electrosorption capacity (Mn only: 6.81 mg g−1 and Mn with Ni: 6.46 mg g−1) and CDI performance compared to pristine AC electrode (3.67 mg g−1) due to synergistic influence of an electric double layer-based and pseudocapacitive-based capacitance. By comparing capacitance depending on the ratio of Mn to Ni, we revealed that incorporation of small Ni amount in Mn oxide matrix contributes to increase electrochemical capacitance. Furthermore, Ni also plays a role in improving adsorbed salt desorption, achieving higher long-term stability compared AC and only Mn-coated AC electrodes.