Suppressing Water Electrolysis via Pb Single Atoms in Nitrogen‐Doped Carbon for High‐Energy‐Density Supercapacitors

ABSTRACT Aqueous supercapacitors (SCs) are attractive energy storage devices owing to their high power density and operational safety; however, their practical deployment is constrained by the limited operating voltage window imposed by water electrolysis, which restricts the attainable energy density. Herein, we report a lead (Pb) single‐atom anchored on nitrogen‐doped carbon (SA‐Pb/NC), where Pb, as a p‐block metal, modulates the adsorption strength of H * /H 2 O species at Pb‐N 4 sites. Such modulation effectively suppresses water‐electrolysis reactions, thereby expanding the electrochemical operational voltage window and enhancing energy storage performance. SA‐Pb/NC delivers a specific capacitance of 530.07 F g −1 , nearly twice that of bare NC. A symmetric SA‐Pb/NC device further achieves an energy density of 38.67 Wh kg −1 within an ultrawide voltage window of 1.50 V. Remarkably, no detectable H 2 evolution is observed for the SA‐Pb/NC device even after 48 h of continuous operation, whereas the NC‐based device generates 0.09 µmol of H 2 within only 12 h. Theoretical calculations further reveal that SA‐Pb sites optimize K + adsorption–desorption kinetics while weakening the affinity for H 2 O‐derived intermediates, thereby enabling efficient charge storage and effective suppression of water electrolysis. This work provides a general strategy for designing high‐energy‐density aqueous supercapacitors through voltage‐window expansion enabled by lead single‐atom sites.