Role of Nitrogen-doping in porous carbon for enlarging working voltage window of aqueous supercapacitors in neutral electrolyte

• A set of NOPC free-standing electrodes with adjustable N-doping level was designed. • Rationally manipulating N-doping level can enlarge working voltage window. • In situ experiments and DFT calculations have revealed the mechanism. • The generalizability of our conclusion has been verified by other N-doped carbons. The fundamental mechanism on enlarging working voltage window of carbon-based aqueous supercapacitors is still unclear owing to the indistinct principles in inhibiting water splitting occurred at the electrochemical interface. Herein, we design a set of N, O co-doped porous carbon (NOPC) free-standing electrodes with adjustable N-doping level, and establish that N-doping (N-content and specific N-configuration) governs neutral HER and OER. The NOPC electrode with a lower N-doping level can possess a wide working potential window of − 1–1 V, and thus the corresponding aqueous symmetric supercapacitors showcase a wide working voltage window of 2 V in LiCl aqueous solution. In situ spectroscopy evidences and theoretical simulation demonstrate that the low N-doping (N-content and percentage of pyrrolic nitrogen) level can weaken the interaction between the electrode and interfacial water molecules and suppress the formation of *OOH intermediate during the charge–discharge process, and thus significantly decreasing the HER and OER activities to inhibit water splitting. The finding can shed light on the fundamental understanding of mechanism on enlarging working voltage window of carbon-based aqueous supercapacitor.