Biomass Organs Control the Porosity of Their Pyrolyzed Carbon

In most electrochemical energy storage and conversion devices, nanostructured carbon materials play essential roles. One-step carbonization of some biomass materials has recently been demonstrated as a promising route to produce high surface area carbon without introducing extra activation agents. Here, this study shows the importance of physiologic function of plant organs in the microstructure and porosity of formed carbon nanomaterials. The lotus stem pyrolyzed carbon at 800 °C presents a specific surface area of 1610 m2 g−1, about 55% higher than the porous carbon from the leaves. A similar organ-dependent effect in the porosity of the pyrolyzed carbon is also observed in other plants with wide disparity in the stems and leaves, such as celery and asparagus lettuce, largely due to the higher metal ion content in the stems, which plays the role of ion transportation for plants. Furthermore, optimizing the celery stem pyrolyzing condition can produce carbon with specific surface area as high as 2194 m2 g−1 without any extra activation process. As a supercapacitor electrode, the porous carbon pyrolyzed from lotus stems exhibits a specific capacitance of 174 F g−1 at a scan rate of 5 mV s−1 in 6 M KOH aqueous electrolyte, with 72% capacitance retention at a high scan rate of 500 mV s−1 and good stability over 10 000 cycles.