Enhancement of charge transport in porous carbon nanofiber networks via ZIF-8-enabled welding for flexible supercapacitors

Lightweight, self-supporting, and flexible carbon nanofiber membranes are desirable electrode candidates for flexible supercapacitors. At present, inadequate electrical contact between adjacent nanofibers, poor wettability with electrolyte, and limited specific surface area are still challenges for further improving the capacitive property. In this work, a novel porous N-doped carbon nanofiber network membrane in which continuous ZIF-8-derived carbon layers welding adjacent carbon nanofibers is synthesized through bifunctional ZnO nanoparticles contained in the nanofibers. Here, ZnO nanoparticles not only serve as the pore-forming agent to create multiscale pores, but also provide zinc sources for in-situ growth of ZIF-8 nanoparticle layer. Because of highly interconnected networks, special spider-web-like surface nanostructure, and hierarchical pores, the as-prepared carbon membrane reveals superior electrical conductivity, high specific surface area and excellent wettability. An excellent rate performance with 75.5% capacitance retention even with 70-times current density increase and extraordinary cycling stability (98.8% capacitance retention after 100,000 cycles at 10 A g(-1)) could be found, when the optimized hierarchically porous N-doped welded carbon network membrane is used as the electrode. The quantitatively electrochemical kinetic analysis of the electrode indicates that fast double layer capacitive behavior is dominant at high current densities. Meanwhile, the flexible quasi-solid-state devices display excellent electrochemical stability in severely bending states.