Fe-N and Fe-P dual active centers in MOF-derived carbon electrode for efficient capacitive deionization: Abundant defects and superior electrochemical properties

Carbon-based compounds play a significant role in achieving efficient capacitive deionization (CDI) desalination. However, the adsorption capacity is usually restricted by single spatial structures and limited number of ion adsorption sites. Heteroatom doping, especially multiple doping is an effective strategy to augment the surface functionalities of electrodes to improve the capacitive activity. In this work, Fe, N, P tri-doped hierarchically porous carbon (FeNPCs) were successfully fabricated via a facile one-step pyrolysis procedure. The FeNPC30 electrode demonstrated an outstanding electrosorption capacity of 40.42 mg g−1 within 15 min at 1.2 V and good cyclic regeneration capability with little decrease in charge storage during 200 charge/discharge cycles. The systematic results revealed that a reasonable ratio of Fe, N, and P yielded a synergistic effect, which not only improved the defective level and hydrophilicity, but enhanced the specific capacitance and decreased the charge transfer resistance, resulting in superior adsorption capacity and rate. The unique coordination structures of Fe-N and Fe-P modulated the charge density distribution and served as additional active sites for ions trapping, thus improving the desalination performance. This work gives deep insight into Fe-N and Fe-P dual active sites in CDI and provides a new perspective on multiple heteroatoms doped electrodes.