Multifunctional, Self-Activating Oxygen-Rich Holey Carbon Monolith Derived from Agarose Biopolymer

Agarose, a natural biopolymer, is carbonized to synthesize an economical lightweight (0.05 g cm^–3) mesoporous carbon monolith with large BET surface area (625 m² g^–1). The monolith prepared at different temperatures (700, 800, 900 °C) exhibits interesting morphologies without using any activating agent. The holey pattern appearing at 900 °C, besides increasing the meso/microporosity, confirms the self-activation at higher temperature. Most interestingly, the thick sheet-like morphology obtained at 700 °C is changed to nanoporous carbon flakes as the synthesizing temperature is increased to 800 and 900 °C. This synthesis approach affords an oxygen-enriched meso/microporous carbon monolith that constitutes high pseudocapacitance in addition to electric double layer charge. Lightweight carbon monolith exhibits excellent thermal and mechanical characteristics having a weight bearing capacity of ∼5900 times compared to its weight without developing any deformity. The electrochemical performance of carbonized agarose (CAR) tested in 1 M H₂SO₄ exhibits superior charge storage capacity in CAR 900 (302 F g^–1 at 5 mV s^–1) compared to that of CAR 800 (124 F g^–1) and CAR 700 (107 F g^–1). The symmetric cell (1 × 1 cm² area) fabricated using CAR 900 as electrodes exhibits excellent cell performance over 5000 charge/discharge cycles with ∼98% capacity retention. Three symmetric CAR 900 cells connected in series enable powering a red LED bulb (3 V) that indicates excellent sustainability of agarose-derived carbon in energy storage devices.