Sulfur‐Deficient Bismuth Sulfide/Nitrogen‐Doped Carbon Nanofibers as Advanced Free‐Standing Electrode for Asymmetric Supercapacitors

The use of free‐standing carbon‐based hybrids plays a crucial role to help fulfil ever‐increasing energy storage demands, but is greatly hindered by the limited number of active sites for fast charge adsorption/desorption processes. Herein, an efficient strategy is demonstrated for making defect‐rich bismuth sulfides in combination with surface nitrogen‐doped carbon nanofibers (dr‐Bi2S3/S‐NCNF) as flexible free‐standing electrodes for asymmetric supercapacitors. The dr‐Bi2S3/S‐NCNF composite exhibits superior electrochemical performances with an enhanced specific capacitance of 466 F g−1 at a discharge current density of 1 A g−1. The high performance of dr‐Bi2S3/S‐NCNF electrodes originates from its hierarchical structure of nitrogen‐doped carbon nanofibers with well‐anchored defect‐rich bismuth sulfides nanostructures. As modeled by density functional theory calculation, the dr‐Bi2S3/S‐NCNF electrodes exhibit a reduced OH− adsorption energy of ‐3.15 eV, compared with that (–3.06 eV) of defect‐free bismuth sulfides/surface nitrogen‐doped carbon nanofiber (df‐Bi2S3/S‐NCNF). An asymmetric supercapacitor is further fabricated by utilizing dr‐Bi2S3/S‐NCNF hybrid as the negative electrode and S‐NCNF as the positive electrode. This composite exhibits a high energy density of 22.2 Wh kg−1 at a power density of 677.3 W kg−1. This work demonstrates a feasible strategy to construct advanced metal sulfide‐based free‐standing electrodes by incorporating defect‐rich structures using surface engineering principles.