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

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.