Abstract
The synthesis of biomass-derived porous carbons (PCs) for supercapacitors by conventional two-steps method (chemical activation after carbonization) is complicated and time-consuming. In this study, we present a one-step microwave activation strategy to prepare hierarchically PCs from waste palm boosted by activated carbons (ACs). ACs with various specific surface areas (14, 642, and 1344 m2·g−1) were used for the first time to fast absorb microwave energy for converting waste palm into hierarchically PCs, that is, PC1, PC2, and PC3, respectively. The morphological and structural characterizations of PCs were studied. Also, the electrochemical performances of supercapacitors based on PCs as electrodes were further investigated. The results showed that the PC (PC1) boosted by AC with the lowest specific surface area possessed a porous structure (containing micro-, meso-, and macro- pores) with the largest specific surface area (1573 m2·g−1) and the highest micropore volume (0.573 cm3·g−1), as well as the suitable mesoporosity (29.69%). The as-prepared PC1 supercapacitor even in a gel electrolyte (PVA/LiCl) exhibited a high specific capacitance of 226.0 F·g−1 at 0.5 A·g−1 and presented excellent charge-discharge performance with an energy density of 72.3 Wh·kg−1 at a power density of 1.4 kW·kg−1 and 50.0 Wh·kg−1 at 28.8 kW·kg−1. Moreover, this promising method exhibited a simple, rapid, and cost-effective preparation of carbon materials from renewable biomass for energy storage applications.
Highlights
Driven by the increased concern about environment and energy issues, renewable materials-based energy storage devices are increasingly demanded [1,2,3]
As shown in the figure, the abundant pores in all porous carbons (PCs) display irregular shapes and have the interconnected channels, showing a 3D distribution. This observation is due to the fact that KOH and carbon can react as following: 6KOH + 2C → 2K + 3H2 + 2K2CO3, to generate PCs by washing with hydrochloric acid (HCl) [35,36]
The PC1 with hierarchical porous structure is apparently favorable for the rapid transportation of electrolyte ions
Summary
Driven by the increased concern about environment and energy issues, renewable materials-based energy storage devices are increasingly demanded [1,2,3]. Three-dimensional (3D) structures of carbon materials as electrode materials can further facilitate the rapid diffusion of ions [14,15], and doping with heteroatoms (e.g., oxygen, nitrogen) can promote the wettability of carbon surface and participate in the Faradaic reaction contributing to pseudo-capacitance [16,17,18]. To fabricate this hierarchical porous carbon (PC) with heteroatom doping, hard templates (e.g., SiO2), complicated subsequent synthesis, and chemical agents (e.g., urea) are often required [19,20]. It is essential to find a cost-effective and simple method to prepare this hierarchical PC for supercapacitor
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