Almond peel‐derived iron‐induced activated carbon for high energy and long‐life supercapacitor in organic electrolyte

Most carbon electrode materials for supercapacitors (SCs) are prepared by the conventional KOH activation method that entails several steps at higher temperatures resulting in low-energy density. Herein, we report one-step facile carbonization and low-concentration-activation aided synthesis of activated carbon (AC) from Prunus dulcis (almond) peel (AP) by using three activating agents, namely (a) KOH (AC-K1); (b) KOH with K3[Fe(CN)6] (AC-K2); (c) KOH with K3[Fe(CN)6] and K4[Fe(CN)6] (AC-K3) for high-performance symmetric supercapacitor (SSCs) applications in 6 M KOH and 1 M TEABF4 electrolytes. Detailed structural and chemical characterization studies were performed on the as-prepared AC-K1/K2/K3 samples and optimization studies revealed that AC-K3 electrode delivers the highest performance due to the presence of trace amount of iron salts in the carbon network that acts as a catalyst and induces fast charge-transfer for electrochemical reactions. The BET surface area of AC-K1, AC-K2, and AC-K3 are found to be 408.89 m2 g−1, 819.79 m2 g−1, and 1061.6 m2 g−1, respectively. AC-K3 electrode delivers an outstanding half-cell specific capacitance of 320 F g−1 at 1 A g−1 in 6 M KOH. The SC device with AC-K3 electrode delivers full-cell specific capacitance of 290 F g−1 and 370.37 F g−1 in 6 M KOH and 1 M TEABF4, respectively. The highest energy density of 41.24 Wh kg−1 at 1349 W kg−1 power with the extended potential of ~2.7 V is delivered by the AC-K3 electrode in 1 M TEABF4, which is considerably higher and unprecedented compared to other reported carbon materials. After 10 000 cycles, there is a ~100% capacitance retention. As a result of this study, the abundant bio-derived AC-K3 is found to be a potential long-term electrode material for high-energy SC applications. © 2022 John Wiley & Sons Ltd.