Naturally derived porous carbon with selective metal- and/or nitrogen-doping for efficient CO₂ capture and oxygen reduction

A heterogeneously porous "green carbon" structure was derived from abundant London plane leaves and shows excellent performance for both CO₂ capture and Oxygen Reduction Reaction (ORR). The carbonised and KOH-activated carbon possesses a high level of micropores, a specific surface area exceeding 2000 m² g^-1 and a large pore volume of over 1 cm³ g^-1, leading to an excellent CO₂ uptake of 19.4 wt% under ambient conditions and fast four-electron transfer in an alkaline medium for ORR. Furthermore, XPS and X-ray analyses reveal well-dispersed metal elements (such as Mg and Ca) in the porous carbon, which are naturally doped and inherited from the leaf structure, and can help to enhance CO₂ adsorption. On the other hand, these metal elements do not positively affect catalytic ORR performance. Hence, a purpose-specific cleaning approach after KOH activation, i.e. by water or acid, has been devised to obtain optimal functionalities for CO₂ capture or ORR.