Composition Tailoring via N and S Co‐doping and Structure Tuning by Constructing Hierarchical Pores: Metal‐Free Catalysts for High‐Performance Electrochemical Reduction of CO 2

A facile route to scalable production of N and S co‐doped, hierarchically porous carbon nanofiber (NSHCF) membranes (ca. 400 cm 2 membrane in a single process) is reported. As‐synthesized NSHCF membranes are flexible and free‐standing, allowing their direct use as cathodes for efficient electrochemical CO 2 reduction reaction (CO 2 RR). Notably, CO with 94 % Faradaic efficiency and −103 mA cm −2 current density are readily achieved with only about 1.2 mg catalyst loading, which are among the best results ever obtained by metal‐free CO 2 RR catalysts. On the basis of control experiments and DFT calculations, such outstanding CO Faradaic efficiency can be attributed to the co‐doped pyridinic N and carbon‐bonded S atoms, which effectively decrease the Gibbs free energy of key *COOH intermediate. Furthermore, hierarchically porous structures of NSHCF membranes impart a much higher density of accessible active sites for CO 2 RR, leading to the ultra‐high current density.