N-containing carbon-based materials have been employed with claimed improved performance as an adsorbent of acidic molecules, volatile organic compounds (VOC), and metallic ions; catalyst; electrocatalyst; and supercapacitor. In this context, the present work provides valuable insights into the preparation of N-doped activated carbons (ACs) by thermal treatment in NH₃ atmosphere (ammonization). A commercial AC was submitted to two kinds of pretreatment: (i) reflux with dilute HNO₃; (ii) thermal treatment up to 800 °C in inert atmosphere. The original and modified ACs were subjected to ammonization up to different temperatures. ACs with N content up to ~8% were achieved. Nevertheless, the amount and type of inserted nitrogen depended on ammonization temperature and surface composition of the starting material. Remarkably, oxygenated acidic groups on the surface of the starting material favored nitrogen insertion at low temperatures, with formation of mostly aliphatic (amines, imides, and lactams), pyridinic, and pyrrolic nitrogens. In turn, high temperatures provoked the decomposition of labile aliphatic functions. Therefore, the AC prepared from the sample pre-treated with HNO₃, which had the highest content of oxygenated acidic groups among the materials submitted to ammonization, presented the highest N content after ammonization up to 400 °C but the lowest content after ammonization up to 800 °C.

N-containing carbon-based materials have been employed with claimed improved performance as adsorbent of acidic molecules, VOC and metallic ions, catalyst, electrocatalyst and supercapacitor. In this context, the present work provides valuable insights into the preparation of N-doped activated carbons (ACs) by thermal treatment in NH3 atmosphere (ammonization). A commercial AC was submitted to two kinds of pre-treatment: (i) reflux with dilute HNO3; (ii) thermal treatment up to 800 oC in inert atmosphere. The original and modified ACs were subjected to ammonization up to different temperatures. ACs with N content up to 8% were achieved. Nevertheless, the amount and type of inserted nitrogen depended on ammonization temperature and surface composition of the starting material. Remarkably, oxygenated acidic groups on the surface of the starting material favored nitrogen insertion at low temperatures, with formation of mostly aliphatic (amines, imides, and lactams), pyridinic and pyrrolic nitrogens. In turn, high temperatures provoked the decomposition of labile aliphatic functions. Therefore, the AC prepared from the sample pre-treated with HNO3, which had the highest content of oxygenated acidic groups among the materials submitted to ammonization, presented the highest N content after ammonization up to 400 oC, but the lowest content after ammonization up to 800 oC.

Nine activated carbons (ACs) with hierarchical micro- and mesoporous textural structures and varied chemical compositions were evaluated as metal-free electrocatalysts for the Oxygen Reduction Reaction (ORR) under alkaline conditions. The base material was a commercial biomass-based carbon chemically activated with H3PO4, which possesses a hierarchical micro- and mesoporous structure. This material was modified by: oxidative treatment with HNO3 to increase the content of acidic oxygenated functional groups (OFGs); and by heat treatment in an inert atmosphere up to 800 °C to remove most of the acidic OFGs. Furthermore, the original and modified ACs were subjected to ammonization up to 400 or 800 °C to incorporate nitrogen. The results showed that there exists a synergistic effect among at least three critical factors that enhance the ORR performance of the materials: a high specific surface area (SSA); a high electrical conductivity (achieved by means of a well-developed carbon basal plane structure); and the presence of functional groups containing heteroatoms, mainly aromatic nitrogens. Notably, the ACs exhibited high tolerance to methanol crossover. Finally, as a proof-of-concept, a selected AC was tested in a single-cell Direct Methanol Fuel Cell (DMFC), yielding excellent performance. The results demonstrate the high potential of N-doped ACs as electrocatalysts, inexpensive and versatile materials that can replace costly Pt-based electrodes.