A Study of 3D flake MnO2 nanoflower decorated hollow carbon spheres as cathode material for pseudo-capacitive deionization

Capacitive deionization (CDI) is an emerging brackish water desalination technology, Manganese dioxide (MnO2) is a promising material for CDI because of its good pseudo-capacitance performances. However, the agglomeration phenomenon of MnO2 nanosheets is serious in the application process. It is critical to improve the performance of MnO2 by increasing its dispersibility. In this work, the x-MnO2/HCS was prepared by in-situ growth of MnO2 on the surface of hollow carbon spheres (HCS), which were prepared with P123 and sodium oleate (SO) as templates and glucose as carbon precursor. The load of MnO2 in x-MnO2/HCS was controlled by adjusting the addition amount of KMnO4 (x is the mass ratio of KMnO4: HCS, x = 2, 4 and 8). Then put HCS and x-MnO2/HCS as anode and cathode respectively assembled into HCS||x-MnO2/HCS (H||x-M/H) asymmetric cells for CDI tests. The influence of different KMnO4 addition amount on the performances of x-MnO2/HCS electrodes were studied. Results show that HCS with good sphericity and uniform size, excellent electrical conductivity and hydrophilicity, which effectively reduces the agglomeration of MnO2 and makes more active sites to participate in ions intercalation, enhance the capacitive performance of the composites. Electrochemical tests show that the 4-MnO2/HCS exhibits the highest specific capacitance (264.75 F/g). And the CDI tests show that H||4-M/H cell has the largest adsorption capacity (30.86 mg/g), the highest charge efficiency (76%), the lowest energy consumption (0.018 kwh/mol) and excellent cycling stability (92.4%).