Oxygen Vacancy‐Abundant Molybdenum Dioxide Electrodes with Minimal Interfacial Charge‐Transfer Resistance for Ultrafast Filter Electrochemical Capacitors

Electrochemical Capacitors (ECs) are considered capable of replacing bulky and low-capacitance aluminum electrolytic capacitors (AECs) in alternative-current filtering, yet regrettably, they have been plagued by slow ion migration and sluggish electrical response. Non-carbon-based electrode materials, while exhibiting significantly higher electric double-layer capacitance (EDLC) compared to carbon-based electrodes, still face the challenge of relatively high interfacial charge transfer resistance (R_ct) that needs to be overcome. Here, a charge-transfer kinetics enhancement strategy is demonstrated by utilizing the lattice oxygen deficiency in molybdenum dioxide (MoO_2- _x) to increase metallic electrical conductivity and the number of active sites. This strategy substantially reduces the R_ct, thereby upgrading the high-frequency performance of ECs, featuring the first high-performance and scalable metal oxide-based ultrafast ECs. The ECs with aqueous electrolyte achieve a phase angle (φ) of -80° and a specific capacitance of 966.8 µF cm^-2 (3.9 F cm^-3) at 120 Hz, while the surface-mountable capacitors incorporating NC@MoO_2- _x and EMImBF₄ demonstrate a φ of -80.3° and super-long cycle stability (1 400 000 cycles), surpassing commercial AECs in many key performance indexes. This approach aligns with modern embedded electronic component manufacturing processes, which is about to provide profound impact to the advancement of high-performance miniaturized components and emerging electronic technologies.