Abstract
Capacitive deionization (CDI) is an energy saving and environmentally friendly technology for water desalination. However, classical CDI is challenged by a low salt removal capacity. To improve the desalination capacity, electrode materials utilizing the battery mechanism for salt ion removal have emerged as a new direction more recently. In this work, we report a study of amorphous iron phosphate (FePO
) as a promising electrode material for pseudocapacitive sodium ion removal. Sodium ions can be effectively, reversibly intercalated and de-intercalated upon its electrochemical reduction and oxidation, with an excellent sodium ion capacity under half-cell testing conditions. By assembling a hybrid CDI (HCDI) system utilizing the FePO
electrode for pseudocapacitive sodium ion removal and active carbon electrode for capacitive chloride ion removal, the cell exhibited a high salt removal capacity and good reversibility and durability, which was attributed to the advantageous features of amorphous FePO
. The HCDI system achieved a high deionization capacity (82 mg g
) in 10 mM NaCl, a fast deionization rate (0.046 mg g
s
), and good stability and cyclability.