Significantly Enhanced Electrochemical Redox for High-Performance Electrochemical Capacitor via Active Ion-Tunnel Oriented BaCoF_4 Electrodes

摘要

Active plane and specific morphology with reduced particle sizes have long been considered a promising strategy to achieve superior electrochemical properties, but the active sites involved may not be sufficiently utilized or the surface atomic configurations may obscure the activity. Herein, a novel structural "active orientation" strategy is developed to overcome the aforementioned shortcomings and improve the efficiency at active sites. A transition-metal fluoride BaCoF4 is well controlled to thin the dimensions along an active [31 over bar 0] orientation through a sodium dodecyl benzene sulfonate assisted solution chemistry route. The active orientation facilitates the opening of the ionic pathways, for example, OH- in the electrolyte, to take full advantage of the redox activity of the electrochemically active Co2+/Co3+ cations in [31 over bar 0]-BaCoF4, resulting in significantly enhanced electrochemical redox performance. A high specific capacitance (692 F g(-1) at 1 A g(-1) in 6 m KOH electrolyte) is achieved owing to active-tunnels orientation, approximate to five-fold higher compared to its bulk counterpart. Strikingly, the asymmetric electrochemical capacitor (AEC) fabricated with [31 over bar 0]-BaCoF4 and activated carbon exhibits an ultrahigh energy density of 147.7 Wh kg(-1) at a power density of 1.025 kW kg(-1) (also 100 Wh kg(-1) at 5 kW kg(-1)), much higher than the majority of existing AEC systems.