Cohydrothermal carbonization of defatted microalgae and glucose for the production of supercapacitor carbon material

Most research on the utilization of microalgae resources is the preparation of biodiesel, but this method will produce a large amount of defatted microalgae waste. This paper mainly studies the resource utilization of defatted microalgae waste, that is, through the cohydrothermal carbonization (C-HTC) of defatted Chlorella pyrenoidosa (DFCP) and glucose (G), to prepare nitrogen-containing carbon materials for the preparation of supercapacitor electrodes. The effects of feedstock, temperature, time, and G:DFCP mass ratio on the yield and properties of the hydrochar produced from the C-HTC of G and DFCP were examined. The hydrochar yield produced from the C-HTC of G and DFCP was 43 wt%, which is much higher than that of the HTC of G (34.0 wt%) and DFCP (25.5 wt%) alone due to the promotion of Maillard reactions between the derivatives produced from G and DFCP. The specific area and micropore volume played important roles in the specific capacitances of the activated hydrochars rather than the effect of heteroatomic doping. At a current density of 1 A/g, the activated hydrochar produced from the C-HTC of G and DFCP at 200 °C for 5 h (AHC-DFCP+G-200-5) achieved a specific capacity of 220.95 F/g. After 20,000 cycles at a charge density of 2 A/g, this kind of activated hydrochar still maintained an outstanding coulomb efficiency of 100 % and a good capacitance retention of 98.26 %. This study provides a new solution to the high-value-added utilization of defatted microalgae waste and the improvement of the economics of microalgae biorefinery.