Surfactant‐in‐Polymer Templating for Fabrication of Carbon Nanofibers with Controlled Interior Substructures: Designing Versatile Materials for Energy Applications

A simple, scalable, surfactant‐in‐polymer templating approach is demonstrated to create controlled long‐range secondary substructures in a primary structure. A metal bis(2‐ethylhexyl) sulfosuccinate (MAOT) as the surfactant is shown to be capable of serving as a sacrificial template and metal precursor in carbon nanofibers. The low interfacial tension and controllable dimensions of the MAOT are maintained in the solid‐phase polymer, even during electrospinning and heat‐treatment processes, allowing for the long‐range uniform formation of substructures in the nanofibers. The MAOT content is found to be a critical parameter for tailoring the diameter of the nanofibers and their textural properties, such as size and volume of interior pores. The metal counterion species in the MAOT determine the introduction of metallic phases in the nanofiber interior. The incorporation of MAOT with Na as the counterion into the polymer phase leads to the formation of a built‐in pore structure in the nanofibers. In contrast, MAOT with Fe as a counterion generates unique iron‐in‐pore substructures in the nanofibers (FeCNFs). The FeCNFs exhibit outstanding charge storage and water splitting performances. As a result, the MAOT‐in‐polymer templating approach can be extended to combinations of various metal precursors and thus create desirable functionalities for different target applications. Adding only a functional surfactant to the polymer precursor leads to the creation of useful products with long‐range secondary substructures and functionality that can be expressed in the hierarchical structure. As a model case, carbon nanofibers with controlled interior iron phases are demonstrated as versatile electrode materials and electrocatalysts for charge storage and water splitting.