Distributed direct air capture by carbon nanofiber air filters

The rising atmospheric CO2 concentration is one of the biggest challenges the human civilization faces. Direct air capture (DAC) that directly removes CO2 from the atmosphere provides great potential in carbon neutralization and even reverses the CO2 concentration in the long run. However, the massive land use and capital investment of centralized DAC plants and the energy-intensive process of adsorbent regeneration limit its wide employment. Here, we develop a distributed carbon nanofiber (CNF)-based DAC air filter capable of adsorbing CO2 downstream in indoor ventilation systems. The DAC air filter not only has the potential to remove 596 MtCO2 yr−1 globally but can also decrease the energy consumption in existing building heating, ventilation, and air-conditioning (HVAC) systems. The CNF-based adsorbent has a high capacity of 4 mmol/g under a humid atmosphere and excellent lifetime cyclability. More importantly, the CNFs can be regenerated either via solar thermal or electrothermal method with extremely low carbon footprints, owing to their superior solar absorptivity of 94.4%, electrical conductivity, and low heat capacity of 1.3 J/(g·˚C). The ultrafine nanofiber has a low pressure drop of 66 Pa at a face velocity of 76 cm/s, minimizing the additional energy load to the ventilation system. Through life cycle assessment, the CNF air filter shows an excellent carbon removal efficiency of 92.3% from cradle to grave with low environmental impacts, such as land use and ecotoxicity.