Phase transition–induced electrochemical performance enhancement of hierarchical CoCO3/CoO nanostructure for pseudocapacitor electrode.

Phase transition of active electrode materials for pseudocapacitors always plays a pivotal role during the energy storage/release process. Here, large-scale hybrid CoCO 3 /CoO nanostructure arrays were obtained on carbon fiber paper substrate in a mild environment and tested as pseudo-capacitor electrode. After several cycles’ activity, the as-prepared electrodes exhibited good energy storage performance with maximum specific capacitance of 0.77 F/cm 2 in area and 510 F/g in gram at a discharge current of 1 A/g, and 82% of the capacity is retained when the discharge current increased to be 10 A/g from 0.2 A/g, indicating high power capability. Most interestingly, the electrode showed excellent cycling durability with gradually increased capacitance along with cyclic voltammetry at first 5,000 cycles and then maintained at least more than other 15,000 cycles. The initial phase transition of CoCO 3 /CoO to Co(OH) 2 /CoO induced by alkaline electrolyte was demonstrated to be the critical factor for the capacitance enhancement. The phase transition before and after long cycles was discussed through ex-situ X-ray diffraction, Raman and high resolution transmission electron microscope analysis. [ABSTRACT FROM AUTHOR]