Evaluation of two potassium-based activation agents for the production of oxygen- and nitrogen-doped porous carbons
This work evaluates the use of potassium hydroxide (KOH) and potassium oxalate monohydrate (K₂C₂O₄•H₂O) for the formation of nitrogen- and oxygen-doped porous carbons. Based on molar equivalent amounts of potassium, we find that KOH activation generally produces porous carbons with larger fractions of mesopores (≥ 2 nm), while K₂C₂O₄•H₂O activation produces porous carbons with greater fractions of micropores (≤ 2 nm). Additionally, we investigate mechanisms of heteroatom loss during activation and find that nitrogen is exclusively sequestered in solid inorganic phases. Notably, differences in the surface properties of the resulting carbons are subtle. While surface nitrogen species are similar between both activation treatments, KOH activation produces materials with both a greater abundance and different types of surface oxygen species when compared to K₂C₂O₄•H₂O activation. Finally, we determine that the degree of carbon dioxide (CO₂) adsorbed in the activated carbons at pressures up to 1 bar is primarily determined by the volume of small micropores (≤ 1 nm). Overall, this study seeks to provide a roadmap to tailor the surface and textural properties of heteroatom-doped porous carbons for gas storage, separations, and energy storage applications.