Single-site pyrrolic-nitrogen-doped sp2-hybridized carbon materials and their pseudocapacitance

Zhaopeng Xu,Fengyan Wang,Wei Yang,Shuhu Liu,Zhenbo Wang,Wei Li,Kesong Tian,Yanglong Hou,Haiyan Wang,Ling Cao,Junyan Wang,Wanchun Guo,Xueai Li

doi:10.1038/s41467-020-17727-y

Abstract

Integrating nitrogen species into sp2-hybridized carbon materials has proved an efficient means to improve their electrochemical performance. Nevertheless, an inevitable mixture of nitrogen species in carbon materials, due to the uncontrolled conversion among different nitrogen configurations involved in synthesizing nitrogen-doped carbon materials, largely retards the precise identification of electrochemically active nitrogen configurations for specific reactions. Here, we report the preparation of single pyrrolic N-doped carbon materials (SPNCMs) with a tunable nitrogen content from 0 to 4.22 at.% based on a strategy of low-temperature dehalogenation-induced and subsequent alkaline-activated pyrolysis of 3-halogenated phenol-3-aminophenol-formaldehyde (X-APF) co-condensed resins. Additionally, considering that the pseudocapacitance of SPNCMs is positively dependent on the pyrrolic nitrogen content, it could be inferred that pyrrolic nitrogen species are highly active pseudocapacitive sites for nitrogen-doped carbon materials. This work gives an ideal model for understanding the contribution of pyrrolic nitrogen species in N-doped carbon materials.

Highlights

Integrating nitrogen species into sp2-hybridized carbon materials has proved an efficient means to improve their electrochemical performance
We report the preparation of one kind of single nitrogen configuration-doped carbon materials, single pyrrolic N-doped carbon materials (SPNCMs), which are ideal model materials, based on a facile engineering process that combines the lowtemperature dehalogenation induced and alkaline-activated pyrolysis of 3-halogenated phenol-3-aminophenol-formaldehyde (X-APF, X = F, Cl-APF NCMs (Cl), and Br-APF NCMs (Br)) co-condensed resins; the pyrolyzed dehalogenation-induced coupling reaction occurring between adjacent benzene rings promotes enough graphitization of carbon materials at low temperature, and subsequent alkaline-activated pyrolysis induces the exclusive and complete transformation of sp3-hydrided nitrogen species into sp2-hydrided pyrrolic nitrogen species
The synthesis of the resulting crosslinked F-APF (1/1) resin involves the introduction of methylene, a few –CH2–NH– bridging groups and considerable –CH2–N(CH2OH)– bridging groups between 3-aminophenol and 3-fluorophenol monomers, which is achieved by both the ortho- and para-C–H substitution of phenols and N–H substitution of amino groups with methylol groups and the subsequent elimination of H2O and formaldehyde molecules

Summary

Introduction

Integrating nitrogen species into sp2-hybridized carbon materials has proved an efficient means to improve their electrochemical performance. We report the preparation of one kind of single nitrogen configuration-doped carbon materials, single pyrrolic N-doped carbon materials (SPNCMs), which are ideal model materials, based on a facile engineering process that combines the lowtemperature dehalogenation induced and alkaline-activated pyrolysis of 3-halogenated phenol-3-aminophenol-formaldehyde (X-APF, X = F, Cl, and Br) co-condensed resins; the pyrolyzed dehalogenation-induced coupling reaction occurring between adjacent benzene rings promotes enough graphitization of carbon materials at low temperature, and subsequent alkaline-activated pyrolysis induces the exclusive and complete transformation of sp3-hydrided nitrogen species into sp2-hydrided pyrrolic nitrogen species. The pseudocapacitance of carbon materials is positively dependent on the pyrrolic nitrogen content, as shown by the electrochemical analysis of our single pyrrolic nitrogen-doped carbon materials and nitrogen-absent carbon materials derived from the 3-fluorophenol resin (CMs (FPF)) samples used as ideal model materials, which exhibit both a similar ion diffusion capacity and electrical conductivity. This work presents an ideal model to fundamentally understand the mechanisms of pyrrolic nitrogen species in N-doped carbon materials for energy storage and conversion applications, offering a method for designing carbon materials doped with tunable structural nitrogen species for different energy conversion applications

Methods

Results

Conclusion