Investigating Economic Methods to Synthesize Wood Biochar for Supercapacitor Electrodes*

We investigated economic methods for producing bur oak biochar to replace fossil fuel-derived activated carbons as electrode materials for supercapacitors. Three synthesis methods were evaluated by their operating temperatures, mass yield, setup cost, ease of use, and their performance in supercapacitor electrodes: a top-lit updraft gasifier, distillation of wood, and a biochar kiln. The resultant biochars were fashioned into electrodes of coin-type supercapacitors and tested for their specific capacitance, cycling stability, and electrical conductivity. The gasifier demonstrated the best electrode material, with a median specific capacitance of 70.14 F/g, cycling stability of 97.37% after 250 cycles, and an internal resistance drop of 5.58 Ω (all tested at a 0.5 mA charging current). This is close to commercially available carbons (83.55 F/g, 98.99%, 9.3 Ω), and outperforms the kiln (40.79 F/g, 123.03%, 23.98 Ω) and distillation methods (20.57 F/g, 97.72%, 11.22 Ω). The gasifier also possessed high operating temperatures (>550℃), low setup costs (~$50), a mass yield of 18.84%, and user-friendly operation. Future work will optimize composition of the gasifier biochar, explore different wood species, and search for more sustainable chemical activation agents.