Potassium Citrate-Activated Porous Carbon Nanostructures for CO2 Adsorption and Electroreduction

Abstract

CO2 capture via adsorption has been widely explored and is viewed as one of the most effective and green solutions to address the high CO2 concentration globally. However, the formation of intermediates during CO2 adsorption and the synthesis of the adsorbent, activated carbon, still need to be resolved. In this study, potassium citrate-activated carbon (ACK) samples were prepared. The synergistic effects of the potassium content and reaction temperature (600 and 1000 °C) were examined. In the synthesis of potassium citrate-activated carbon, potassium citrate was converted to KOH, K2CO3, and K2O and evaporated as metallic potassium vapor followed by intercalation into the activated carbon lattice, forming a micro- and mesoporous nanostructure, which is advantageous for CO2 capture and electrocatalytic reduction. In addition, trace potassium in the ACK sample acted as a reactive site to redistribute and facilitate electron transfer, enabling enhanced CO2 activation and reduction. The ACK samples exhibited strong dual-site bonding of CO2 to the Lewis basic sites, forming b-CO32– intermediates by the physical adsorption through the abundant porous structure of the ACK sample and chemical adsorption by its strong Lewis basicity. In summary, our work presents detailed analyses to understand the mechanism of CO2 adsorption using activated carbon as an effective adsorbent.