Ultra-microporous biochar-based carbon adsorbents by a facile chemical activation strategy for high-performance CO2 adsorption

The new adsorption-enhanced compressed CO2 energy storage technology uses high-performance adsorbents to adsorb and store CO2 in low-pressure tanks, reducing vessel costs while significantly increasing energy storage density. In this paper, porous biochar with excellent CO2 adsorption capacity is prepared by carbonization combined with KOH chemical activation using pine nut shells, which can be used for the energy storage system. The influence of pore structure is revealed by changing the activation temperature. The results show that the activity of KOH is moderate at 700 °C, which can promote the formation of ultramicropores. The specific surface area of the obtained porous biochar is 1027 m2·g−1, the distribution center of ultramicropores is about 0.65 nm, and the microporosity can up to 91.7%, which is very suitable for CO2 adsorption under atmospheric pressure and room temperature. The CO2 adsorption capacities are 6.05 mmol·g−1 and 3.96 mmol·g−1 at 1 bar, 273 K and 298 K with the pore volume is only 0.56 cm3·g−1. The material also has a low value of isosteric heat of adsorption about 25 kJ·mol−1. These findings suggest that pine nut shells can be used to design highly porous biochar for the system of new adsorption-enhanced compressed CO2 energy storage.