Void-size-matched hierarchical 3D titania flowers in porous carbon as an electrode for high-density supercapacitive charge storage

Abstract Porous carbon has been a commercial choice as supercapacitor electrode; however, a large fraction of micrometer-sized voids limits the charge storability. Here, we show that porous carbon derived from an agricultural byproduct (palm kernel shell) with their voids filled by flower-shaped 3D nanostructure of TiO2 (TiO2@AC) acts as a low-cost electrode material for high energy density lithium ion capacitors (LIC) and supercapacitors. The size of the TiO2 flowers here is ideally suited to fit in the voids (∼1 μm); thereby, the TiO2@AC offers larger available surface area than its components, enhanced cyclic stability due to the larger particle volume and enhanced ion diffusion pathways due to the hierarchical structure. The LIC fabricated using the TiO2@AC electrode with a lithium plate as counter electrode showed impressively larger potential window (2.0–4.5 V vs. Li/Li+) than that fabricated using pure porous carbon (2.0–4.0 V vs. Li/Li+), a high specific energy (ES) at high specific power (PS) (ES ∼113 W h kg−1 @ PS ∼3.3 kW kg−1). Symmetric supercapacitors fabricated using the TiO2@AC in a neutral aqueous electrolyte (1 M Na2SO4) showed three times higher energy density than that fabricated using pure porous carbon with similar power density.