In-situ etching activation towards flexible carbonized paper-supported electrode with transition-metal oxides embedded into carbonized cellulose fibers.

Cellulose paper is considered to be a promising substrate of energy materials for energy storage device due to its flexible, porous, renewable, degradable, and environmental-friendly feature. However, the large weight and low conductivity of cellulose fibers limit the specific capacitance and energy density of the paper electrodes. Converting cellulose fibers into conductive carbon fibers (CCF) by high temperature carbonization is an effective strategy for improving the electrochemical performance of paper electrodes. But the brittleness of carbonized paper limits its application in flexible supercapacitors. In addition, stable loading of energy materials on CCF is another challenge. Here, KNO 3 in-situ etching activation method is used to construct the embedded structure of transition-metal oxides (TMOs) on CCF. And the embedding degree of TMOs on CCF can be adjusted by controlling the amount of KNO 3. The embedded structure releases the mechanical stress from bending of CCF, endowing good flexibility for carbonized paper. In addition, embedded structure can anchor TMOs into CCF, and increase the porosity and specific surface area of CCF, promoting a rapid ion diffusion and electron transport for high capacitance contributions. The KNO 3 -etched Co 3 O 4 @CCF paper as an electrode exhibits a high volume specific capacitance of 72.3 F cm−3 at current density of 0.5 mA cm−2 (more than three times higher than that of Co 3 O 4 /CCF paper) and shows good rate capability (capacitance retention of 83.3% with 10 times current density) and long lifetime (charge-discharge stability of 94.8% after 10000 cycles). Even in bending state, the composite paper still maintains stable electrochemical performances, which can broaden potential application in flexible supercapacitors. [Display omitted] • A flexible carbonized paper was fabricated for supercapacitors electrode. • KNO 3 in-situ etching activation method was used to embed TMOs into CCF. • The embedded structure released the mechanical stress from bending of CCF. • The embedded structure increased the porosity of CCF for rapid ion diffusion. • The flexible carbonized paper exhibited excellent electrochemical performances. [ABSTRACT FROM AUTHOR]