Oxygen Defect Modulated Titanium Niobium Oxide on Graphene Arrays: An Open‐Door for High‐Performance 1.4 V Symmetric Supercapacitor in Acidic Aqueous Electrolyte

Despite appealing supercapacitive properties, the acidic aqueous supercapacitors (SCs) are still suffering from low operating voltage (<1 V) leading to unsatisfactory energy densities. Herein, for the first time, it is reported that the oxygen defect modulated Ti 2 Nb 10 O 29− x (TNO x ) on interlinked graphene array (denoted as TNO x G) can achieve a wide potential window up to 1.8 V in 1 m H 2 SO 4 electrolyte and deliver an extremely high capacitance up to 368.9 F g −1 at 0.5 A g −1 . Accompanying the improved charge transfer efficiency and preferable H ion diffusion, the oxygen defects in TNO x G are capable of stimulating more pseudocapacitive behavior and simultaneously suppressing oxygen evolution reaction. Furthermore, a 1.4 V high voltage quasi‐solid‐state TNO x G‐based symmetric supercapacitor is demonstrated, yielding a maximum energy density of 0.58 mWh cm −3 at a power density of 0.57 W cm −3 and exceptionally excellent cycling durability. It is believed that this strategy of oxygen defect modulation to optimize reaction kinetics will lead to further improvements in the performance of high‐voltage aqueous SCs.