Carbonization and H 3 PO 4 activation of fern Dicranopteris linearis and electrochemical properties for electric double layer capacitor electrode.

Today, the world's climate change is a growing problem, plant carbon sequestration is one of the effective ways to mitigate climate change by reducing greenhouse gases, mostly carbon gases. Dicranopteris linearis (D. linearis), a common fern species in the tropic or subtropic ecoregions, has been recently recognized as a potential feedstock to produce highly porous biochar. This study aims to enhance the specific surface area (SSA) and pore volumes of biochars derived from the D. linearis by H ₃ PO ₄ activation and examine electrical properties of the activated biochars and their possible usage for the electric double-layer capacitor (EDLC) electrode. The treated raw fern was activated with H ₃ PO ₄ 85% by the three different mixing ratios 1:0, 1:1, and 1:3 (w/w) and then pyrolysis under N ₂ flow maintained at 500 °C for 1 h. The performance as the electrode for an EDLC was evaluated in 1 mol L ^-1 H ₂ SO ₄ solution for the H ₃ PO ₄ -activated samples. The SSA and pore volumes were drastically increased after activation. The maximum SSA and pore volume were 1212 m ²  g ^-1 and 1.43 cm ³  g ^-1 , respectively for the biochar activated at 400 °C with a weight mixing ratio 1:3 (w/w) between the fern and H ₃ PO ₄ acid while these values of the biochar at 400 °C were 12 m ²  g ^-1 and 0.02 cm ³  g ^-1 , respectively. The biochar activated at 600 °C with the mixing ratio 1:1 (w/w) showed the maximum capacitance value, ca. 108 F g ^-1 at 1 mV s ^-1 . The activation using H ₃ PO ₄ showed a positive tendency to enhance electrochemical properties and it could be a premise toward a higher performance of EDLC from the D. linearis derived activated biochar.