Controllable Transmation Of Doping Nitrogen Configuration In Carbon Materials And Electrochemical Properties

Nitrogen-doped carbon materials could fully adjust the local electronic structure and surface wettability of carbon materials to improve the electrochemical activity of carbon materials due to their abundant nitrogen doped configurations.However,the doping process always involves high-temperature thermal treatment,resulting in uncontrollable conversion between different nitrogen configurations,which makes it difficult to fine control nitrogen doped configurations,limiting the accurate identification of electrochemical reactive nitrogen species configurations and in-depth research on reaction mechanisms,and further limiting the development of high-performance nitrogen doped carbon materials in the field of electrochemistry.Therefore,establishing a precise regulatory mechanism for nitrogen configuration in carbon materials remains a fundamental scientific issue in the field of nitrogen doped carbon materials.A clear nitrogen configuration control mechanism was established through low-temperature pyrolysis and subsequent alkali activation of hydroxypyridine-3-halophenol-formaldehyde resins with well-defined structure.For the first time,a complete conversion from pyridine nitrogen to pyrrole nitrogen has been achieved in carbon materials,and single pyrrolic nitrogen configuration-doped carbon materials have been prepared.（1）Firstly,4-hydroxypyridine-3-fluorophenol formaldehyde resin was synthesized by hydrothermal method,and the initial carbon material was formed through defluorination pyrolysis at 600°C.Meanwhile,carbonyl and hydroxyl functional groups were removed,resulting in the conversion of pyridone and hydroxypyridine with poor thermal stability into pyridinic and pyrrolic nitrogen,respectively,to obtain pyridinic and pyrrolic nitrogen co-doped carbon materials.Subsequently,micropores were introduced into the carbon material during KOH activation at 500 ^oC,while hydroxyl groups were also introduced into the carbon material,enabling the conversion of pyridinic nitrogen to be converted into tautomeric hydroxypyridine and pyridone,and further into pyridinic and pyrrolic nitrogen,respectively.Excessive alkali ensures complete conversion of pyridinic into pyrrolic nitrogen,and single pyrrolic nitrogen configuration-doped carbon material was ultimately prepared.（2）The secondary pyrolysis and Na OH activation of pyridinic and pyrrolic nitrogen co-doped carbon materials,as well as the direct KOH activation of model compounds such as acridine,phenanthridine,and acridone,further confirmed that the alkali activation process promoted the complete conversion of pyridinic into pyrrolic nitrogen through hydroxypyridine and pyridone tautomerism intermediates in carbon materials.（3）When 4-hydroxypyridine and 3-fluorophenol monomers were extended to2-hydroxypyridine and 3-chloro/bromophenol,the hydrothermally synthesized resins also achieved controllable conversion of pyridine to pyrrole nitrogen in carbon materials through low-temperature pyrolysis and alkali activation strategies,thereby achieving fine regulation of nitrogen configuration in carbon materials.（4）When single pyrrolic nitrogen-doped carbon materials were used as electrode materials for supercapacitors,due to their rich pseudocapacitive active pyrrolic nitrogen and quinone/hydroquinone configurations,as well as their high specific surface area and rich micropores,they can exhibit a high specific capacity of 396 F g^-1 at 1 A g^-1.After10000 cycles at 10 A g^-1,the capacity retention rate reaches 96%,demonstrating excellent cycling stability.