Designing NiFe-metal organic frameworks@NiFe-layered double hydroxide/carbon fiber self-supporting electrode for enhanced capacitive deionization

Abstract

Self-supporting electrode benefits to enhance the desalination capacity and maximize the capacitance retention by avoiding the usage of organic binders and conductive additives in capacitive deionization (CDI). In this work, we design a self-supporting electrode of NiFe-metal organic framework@NiFe-layered double hydroxides/carbon fiber (MOF@LDH/CC) for highly efficient CDI. The cross-linked CC provides a unique network structure to promote the diffusion of salty ions, leading to high desalination kinetics. On the other hand, the NiFe-MOF acts as seed to induce the growth of NiFe-LDH which not only block the agglomeration of NiFe-LDH layers, but also strengthen the linkage between the CC and NiFe-LDH. As expected, the optimized MOF@LDH/CC//activated carbon CDI system achieves high initial salt removal capacity of 0.033 mg/cm2 in 1000 μS/cm NaCl solution, which decreases to 0.026 mg/cm2 after 30 cycles. The capacity decline is ascribed to the salt deposition during the cycling, which can be observed from the structural evolution. Further, the X-ray photoelectron spectra verifies the reversible chloride ions electro-adsorption/desorption by MOF@LDH/CC. Meanwhile, the porous fibrous structure of MOF@LDH/CC electrode is remaining after few cycles, highlighting the robust structure.