Nitrogen and Oxygen-Doped Hierarchical Porous Carbons from Algae Biomass: Direct Carbonization and Excellent Electrochemical Properties

Herein, the algae pollutants of Enteromorpha prolifera were applied as precursors to obtain nitrogen and oxygen co-doped hierarchical carbons with major pores at around 1.5 and 5.0nm through direct carbonization at 700 and 900°C after freeze-drying treatment. Physical properties of porous carbons including morphology, elemental analysis, and pore size distribution were evaluate by transmission electron microscopy, X-ray photoelectron spectroscopy and N2 sorption. In both cases, surface areas were only close to 450m2g−1 with 70% areas inherited from mesopores, resulting in high density materials. The carbon derived at 700°C had the highest capacitance of 234Fg−1 at a current density of 0.5Ag−1 in 6M KOH electrolyte and also had excellent cycling stability with 95% of capacitance after 2000 cycles, owing to the naturally heteroatoms and unique hierarchical nanopores contributed pseudo-capacitance and provided active sites for facilitating electrolyte ions diffusion. In addition, the carbon derived at 900°C had CO2 uptake of 6.48mmolg−1 at 20bar and 25°C.