Nitrogen-doped porous carbon derived from a bimetallic metal–organic framework as highly efficient electrodes for flow-through deionization capacitors

Abstract

Novel nitrogen-doped porous carbon has been synthesized from a bimetallic zeolitic imidazolate framework (BMZIF) based on ZIF-8 and ZIF-67 using a self-sacrificial template method and explored for application in flow-through deionization capacitors (FTDCs). The BMZIF itself provides the carbon and nitrogen sources as well as the porous structure. After carbonization and acid etching of BMZIF crystals, the obtained BMZIF derived nanoporous carbon (denoted as BNPC) not only maintains the original rhombic dodecahedron shape of the parent BMZIF, but also possesses a large surface area of 813 m² g⁻¹, a high N content of 8.00%, high graphitization degree, and good wettability. Electrochemical studies demonstrate that the BNPC electrode integrates the advantageous properties of carbons independently from ZIF-8 and ZIF-67, exhibiting high specific capacitance, lower inner resistance and good stability. Furthermore, the desalination performance of the BNPC electrode under different applied voltages, salty concentrations, and flow rates is investigated by the FTDC experiment. The BNPC electrode exhibits a high salt adsorption capacity of 16.63 mg g⁻¹ in a 500 mg L⁻¹ NaCl aqueous solution at a cell voltage of 1.4 V and a flow rate of 40 mL min⁻¹, which is higher than those of pure ZIF-8 carbon (12.25 mg g⁻¹), ZIF-67 carbon (11.38 mg g⁻¹), and commercial activated carbon (6.12 mg g⁻¹) under the same experimental conditions. Moreover, the BNPC electrode exhibits a high salt adsorption rate and good regeneration performance. The enhanced capacitive deionization performance of BNPC is ascribed to synergistic contributions of its unique hybrid structure, large surface area, rich nitrogen doping, and high graphitic degree. The results indicate that BNPC is a promising material for FTDCs.