Selective lithium extraction using capacitive deionization with fabricated zeolitic imidazolate framework encapsulated manganese oxide carbon electrode

Abstract

Presently, substantial research focus is being placed on alternative lithium (Li) extraction from natural water sources such as seawater and salt brine to meet the growing demand for Li, a crucial component for energy storage. Electrochemical capacitive deionization (CDI) shows promising capacity to rapidly extract Li from brine solutions with selective electrodes. This study fabricated activated carbon (AC)-based Li-selective electrodes with hydrogen manganese oxide (HMO) ion-exchange nanomaterial, HMO@AC, and zeolitic imidazolate frameworks encapsulated HMO (HMO@ZIF-AC) electrodes. The incorporation of HMO@ZIF-AC electrode into CDI resulted in rapid Li-ion adsorption and a notable reduction in Mg-ion uptake compared to HMO-AC electrode. In mixed solutions, HMO@ZIF-AC displayed promising Li selectivity over other ions (ρNa+Li+ = 13.14, ρK+Li+ = 6.60, ρMg2+Li+ = 1.69). Also, HMO@ZIF-AC exhibited enhanced Li selectivity in highly saline conditions (Na: Li molar ratio of 96:1). The high performance of HMO@ZIF-AC compared to HMO-AC was attributed to its higher surface area that provided higher vacant sites and the presence of Zn. This was evident as a significantly higher Li uptake (46–48 %) was achieved with a Zn doped HMO electrode (Zn-HMO-AC) compared to HMO-AC and HMO@ZIF-AC electrodes. Meanwhile, compared to HMO-AC, the high Li to Mg selectivity of HMO@ZIF-AC was attributed to the small cavity size of the activated ZIF, creating specialized pathways for Li ions and impeding the ion conduction of Mg2+.