High yield self-nitrogen-oxygen doped hydrochar derived from microalgae carbonization in bio-oil: Properties and potential applications

[Display omitted] •High yield self-N-O dopedhydrochar was from microalgae in the aqueous bio-oil.•Hydrochar had a high solid yield (199.33%) and nitrogen content (7.84%).•Amino acids in chlorella, acetol, furfural in bio-oil were main reactants.•Polymer was formed via aldol condensation, esterification and repeated polymerization.•The CO2 absorption was 5.57 mmol/g and specific capacitance was 216.6F/g (at 0.2 A/g). In this work, the high yield self-N-O doped hydrochar had been prepared through the hydrothermal carbonization of microalgae in the aqueous bio-oil. The effects of temperature, residence time and the ratio of Chlorella and bio-oil on the solid yield were investigated. The results showed that the hydrochar had excellent thermal stability and abundant nitrogen and oxide functional groups, its solid yield reached 199.33%. After activated by KOH at high temperature, the hydrochar was transformed into a porous carbon material with high nitrogen content. The porous carbon showed high CO2 absorption of 5.57 mmol/g at 0 °C and 1 bar. It also exhibited a high specific capacitance of 216.6F/g at 0.2 A/g and a good electrochemical stability with 88% capacitance retention after consecutive 5000 cycles.