Rice straw-derived activated carbon/ZnO nanocomposite as a high-performance electrode for asymmetric supercapacitors

Area of Science:

• Materials Science
• Electrochemistry
• Renewable Energy

Background:

• Biomass waste utilization for sustainable energy storage materials is gaining traction.
• Activated carbon (AC) and zinc oxide (ZnO) are promising electrode materials for supercapacitors.
• Compositing AC with ZnO can enhance electrochemical properties.

Purpose of the Study:

• To synthesize an activated carbon-zinc oxide (AC-ZnO) composite from rice straw waste.
• To evaluate the electrochemical performance of the AC-ZnO composite as an electrode material for asymmetric supercapacitors.
• To investigate the synergistic effects of AC and ZnO in the composite.

Main Methods:

• Activated carbon was prepared from rice straw waste.
• Zinc oxide (ZnO) nanoparticles were composited with activated carbon.
• Electrochemical performance was characterized using techniques like cyclic voltammetry and galvanostatic charge-discharge.
• Surface area and pore size distribution were analyzed.
• Supercapacitor devices were assembled and tested for capacitance, energy density, and power density.

Main Results:

• The AC-ZnO composite exhibited a significantly higher specific surface area (578 m² g^-1) compared to AC (201 m² g^-1) and ZnO (255 m² g^-1).
• The composite demonstrated a superior specific capacitance of 244 F g^-1 at 0.5 A g^-1, with improved charge-transfer resistance (0.035 Ω).
• The assembled asymmetric supercapacitor using AC-ZnO achieved 149 F g^-1 capacitance, 20.66 Wh kg^-1 energy density, and 500 W kg^-1 power density at 1 A g^-1.
• The AC-ZnO composite electrode showed excellent cycling stability with 89.9% capacitance retention after 10,000 cycles and 97% retention after 5000 cycles in the assembled device.

Conclusions:

• The AC-ZnO composite derived from rice straw waste is a highly effective electrode material for asymmetric supercapacitors.
• The composite exhibits enhanced electrochemical performance due to the synergistic combination of electrical double-layer capacitance from AC and pseudocapacitance from ZnO.
• This approach offers a sustainable and cost-effective route for developing advanced energy storage solutions from biomass waste.