Create Rich Oxygen Defects of Unique Tubular Hierarchical Molybdenum Dioxide to Modulate Electron Transfer Rate for Superior High‐Energy Metal‐Ion Hybrid Capacitor

Abstract

Metal‐ion capacitors could merit advantages from both batteries and capacitors, but they need to overcome the severe restrictions from their sluggish reaction kinetics of the battery type electrode and low specific capacitance of capacitor type electrode for both high energy and power density. Herein, we use the Kirkendall effect for the first time to synthesize unique tubular hierarchical molybdenum dioxide with encapsulated nitrogen‐doped carbon sheets while in situ realizing phosphorus‐doping to create rich oxygen vacancies (P‐MoO2‐x@NP‐C) as a sodium‐ion electrode. Experimental and theoretical analysis confirm that the P‐doping introduced oxygen defects can partially convert the high‐bond‐energy Mo–O to low‐bond‐energy Mo–P, resulting in a low oxidation state of molybdenum for enhanced surface reactivity and rapid reaction kinetics. The as‐prepared P‐MoO2‐x@NP‐C as an ion‐battery electrode is further used to pair active N‐doped carbon nanosheet (N‐C‐A) electrode for Na‐ion hybrid capacitor, delivering excellent performance with an energy density of 140.3 Wh kg−1, a power density of 188.5 W kg−1 and long stable life in non‐aqueous solution, which ranks the best among all reported MoOx‐based hybrid capacitors. P‐MoO2‐x@NP‐C is also used to fabricate a zinc‐ion hybrid capacitor, also accomplishing a remarkable energy density of 43.8 Wh kg−1, a power density of 93.9 W kg−1, and a long stable life@2A g−1 of 32 000 cycles in aqueous solutions, solidly verifying its universal significance. This work not only demonstrates an innovative approach to synthesize high‐performance metal ion hybrid capacitor materials but also reveals certain scientific insights into electron transfer enhancement mechanisms.