Sulfur & nitrogen co-doped electrospun carbon nanofibers as freestanding electrodes for membrane capacitive deionization

• S and N co-doped porous carbon nanofibers were obtained by the electrospinning process. • Flexible and monolithic SCNFs can be used directly as MCDI electrode materials. • SCNFs-6 exhibited a salt adsorption capacity as high as 27.48 mg g −1 , twice that of the pristine CNFs. • Theoretical calculations demonstrated the synergistic effect of S，N co-doping. Capacitive deionization (CDI), especially membrane capacitive deionization (MCDI) technology, is an energy-efficient and environmentally friendly water desalination technology. Tremendous efforts have been devoted to designing and preparing high-performance and applicable electrode materials for CDI and MCDI. In this work, sulfur and nitrogen co-doped carbon nanofibers (SCNFs) are prepared by a facile co-electrospinning strategy coupled with subsequent high-temperature heat treatment, and directly used as monolithic and binder-free electrodes for MCDI. Benefiting from the integrated structural and compositional merits, i.e. 3D network composed of disorderly stacked 1D nanofibers and uniform distribution of nitrogen and sulfur atoms, the as-obtained SCNFs exhibit superior electrosorption ability and excellent cycling stability, with the salt adsorption capacity up to 29.50 mg g −1 and the current efficiency higher than 80% when desalting 500 mg L −1 NaCl solution at the voltage of 1.4 V. The doped nitrogen and sulfur atoms in SCNFs not only effectively improve their electrical conductivity and wettability but also tailor the pore structure, thus providing more active sites for ions adsorption. The heteroatom doping strategy could shed new light on the design of high-performance carbon-based electrodes for the electrochemical MCDI application.