Abstract
Nanoporous activated carbons-derived from agro-waste have been useful as suitable and scalable low-cost electrode materials in supercapacitors applications because of their better surface area and porosity compared to the commercial activated carbons. In this paper, the production of nanoporous carbons by zinc chloride activation of Washnut seed at different temperatures (400–1000 °C) and their electrochemical supercapacitance performances in aqueous electrolyte (1 M H2SO4) are reported. The prepared nanoporous carbon materials exhibit hierarchical micro- and meso-pore architectures. The surface area and porosity increase with the carbonization temperature and achieved the highest values at 800 °C. The surface area was found in the range of 922–1309 m2 g−1. Similarly, pore volume was found in the range of 0.577–0.789 cm3 g−1. The optimal sample obtained at 800 °C showed excellent electrochemical energy storage supercapacitance performance. Specific capacitance of the electrode was calculated 225.1 F g−1 at a low current density of 1 A g−1. An observed 69.6% capacitance retention at 20 A g−1 indicates a high-rate capability of the electrode materials. The cycling stability test up to 10,000 cycles revealed the outstanding stability of 98%. The fascinating surface textural properties with outstanding electrochemical performance reveal that Washnut seed would be a feasible agro-waste precursor to prepare nanoporous carbon materials as a low-cost and scalable supercapacitor electrode.
Highlights
Supercapacitors or electrical double-layer capacitors (EDLC), the most convenient and state-of-the-art electrochemical energy storage systems, with outstanding power density (>400 kW kg−1 ), unusually long cycle stability (>10,000), rapid charging-discharging with enhanced rate capability and poor internal resistance, and environmentally friendly and low-cost, have been extensively used for high power electronic devices [1,2,3,4,5,6,7,8,9,10]
Since the operating potential window is fixed in aqueous electrolyte (~1.2 V), it is important to improve the structure and properties of the materials to be used as supercapacitor electrodes so that introducing the novel and smart electrode materials could exhibit high specific capacitances and induces good combination with electrolyte [18,19]
All the chemically activated nanoporous carbon materials display more than 50% capacitance retention achieving outstanding 69.6% for the optimal sample (Figure 6e), which demonstrates the high rate capability of the electrode material required in supercapacitor devices
Summary
Supercapacitors or electrical double-layer capacitors (EDLC), the most convenient and state-of-the-art electrochemical energy storage systems, with outstanding power density (>400 kW kg−1 ), unusually long cycle stability (>10,000), rapid charging-discharging with enhanced rate capability and poor internal resistance, and environmentally friendly and low-cost, have been extensively used for high power electronic devices [1,2,3,4,5,6,7,8,9,10]. Nanoporous activated carbons have received considerable interest as the leading supercapacitor electrode materials because of the low production cost, outstanding cycle stability, and excellent surface specific surface area and porosity [21,22,23,24,25]. Biomass-derived nanoporous activated carbons exhibit very high surface area and offer large porosity because of their unique hierarchical micro- and meso-porous architectures, and have good electrical conductivity and excellent electrochemical stability, which are highly desired in the emerging electrochemical energy storage supercapacitors applications [31,32,33]. The biochar can be activated and transformed into high surface area hierarchical nanoporous carbon materials with well-developed porosity desired in supercapacitors by the direct carbonization and physical or chemical activation methods [34,35]. An outstanding cycling stability of 98% was recorded after 10,000 charging–discharging cycles demonstrating that Washnut seed could be an appropriate alternative low-cost biomass for the production scalable carbon electrodes for high-performance supercapacitors
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