Synthesis of nano-porous carbon and nitrogen doped carbon dots from an anionic MOF: a trace cobalt metal residue in carbon dots promotes electrocatalytic ORR activity

Abstract

Metal–organic frameworks (MOFs) are effective self-sacrificial templates for the synthesis of carbon materials owing to their innate porosity, high carbon content and ease of heteroatom doping. A Mg^II based anionic MOF {[Mg₃(ndc)_2.5 (HCO₂)₂ (H₂O)]·[NH₂ Me₂ ]·2H₂O·DMF} (1) has been carbonized as a sacrificial template for the synthesis of high surface area nanoporous carbon as well as nitrogen doped carbon dots, simply by adjusting the carbonization temperature. The nanoporous carbon synthesized from the MOF precursor exhibits an exceptionally high surface area and high CO₂ uptake capacity. The anionic MOF contains dimethyl amine cations in its pores which, owing to their pre-bonded C–N moiety, act as a precursor for N-doping of the carbon dots. The N-doped carbon dots are held together by graphitic stacking and they show electrocatalytic activity as a metal-free catalyst for the oxygen reduction reaction (ORR). Trace amounts of metallic Co nanoparticles were post-synthetically incorporated into the N-doped carbon dots leading to enhanced electrocatalytic activity and stability for the ORR of the resulting material. The controlled design and synthetic strategy presented here offers a new platform for developing highly active and stable electrocatalysts.