Article pubs.acs.org/JPCC
Nitrogen Doping Effects on the Physical and Chemical Properties of Mesoporous Carbons Huichao Chen, Fugen Sun, Jitong Wang, Wencheng Li, Wenming Qiao, Licheng Ling, and Donghui Long* State Key Laboratory of Chemical Engineering, East China University of Science and Technology, Shanghai, China S Supporting Information *
ABSTRACT: Nitrogen-doped mesoporous carbons (NMCs) with controllable nitrogen doping and similar mesoporous structures are prepared by a facile colloidal silica nanocasting method using melamine, phenol, and formaldehyde as precursors. Various physicochemical properties, such as the oxidation stability, the conductivity and the electrochemical capacitive performance, the CO2 adsorption, the basicity, and the metal-free catalytic activity of the NMCs, are studied extensively in relation to the incorporation amount of nitrogen in the carbon backbone. The dependence of the oxidation stability and the conductivity of the NMCs on the nitrogen content are similar; both of the biggest improvements are achieved at a low nitrogen content of ca. 4.2 wt %. While used as the supercapacitor electrodes, the NMCs with a mediate nitrogen content of ca. 8 wt % can take full advantage of the nitrogen-induced pseudocapacitance and the nitrogen-enhanced conductivity, delivering an excellent high-rate capacitive performance. The nitrogen content does not play an important role in the CO2 physical adsorption, where the effect of microporosity prevails over the nitrogen-doped carbon surface. However, the nitrogen content determines the basicity of the NMCs, which governs their CO2 chemical adsorption ability and the metal-free catalytic activity for direct oxidation of H2S. The higher the nitrogen content, the higher the basicity and the catalytic activity. Our studies give a reliable relationship between nitrogen doping and the physicochemical properties of mesoporous carbons, which should provide a useful guide to their practical applications. of the carbon.12The nitrogen doping generally provides basic properties, which can enhance the interactions between the carbon surface and acid molecules. Moreover, nitrogen doping could alter the electronic and crystalline structures of the carbons, enhancing their chemical stability, surface polarity, electric conductivity, and electron-donor properties.12−14 As a result, nitrogen-doped MCs (NMCs) show improved performance in their wide applications, such as CO2 capture, catalyst support, and electrochemical energy storage applications.15−18 Great efforts have been paid to dope nitrogen into MCs either by post-treatment of the carbons or by direct pyrolysis of the nitrogen-containing precursors. For the former, the MCs
1. INTRODUCTION Mesoporous carbons (MCs) have received significant attention owing to their excellent textural characteristics and mesoporous network that provide a highly opened 3D porous host with easy access for guest species, thus facilitating diffusion throughout the pore channels without pore blockage.1,2 These outstanding features enable them to be ideal candidates for applications in adsorption and separation,3,4catalysis,5−7 and electrochemistry.8−10 The properties of MCs depend to a large extent not only on the porosity but also on the heteroatoms that decorate their surface. The most important and widely introduced heteroatoms are oxygen and nitrogen atoms. The former related to the oxygen-containing surface groups generally contributed to the acidic character onto the carbon surfaces.11The latter can appear as amine-like surface functionalities, and more often directly dope into the backbone © 2013 American Chemical Society
Received: February 20, 2013 Revised: March 31, 2013 Published: April 1, 2013 8318
dx.doi.org/10.1021/jp4017773 | J. Phys. Chem. C 2013, 117, 8318−8328
The Journal of Physical Chemistry C
Article
us to focus on nitrogen doping on the properties of the resulting NMCs. Various properties, including the oxidation stability, the electronic conductivity, the basic properties, and the outspread electrochemical and catalytic applications, are investigated with respect to the amount of nitrogen atoms incorporated. We then explicitly establish, for the first time, a reliable relationship between nitrogen doping and the physicochemical properties in the NMCs. Such information should provide a useful guide for deliberately controlling the carbon surface chemistry to achieve high-performance MCs that can be extended to many different applications.
are subjected to a nitrogen-containing atmosphere, most often NH3 at high temperatures.19−23 The annealing in NH3 leads to the formation of nitrogen free radicals, which could attack the carbon to form nitrogen-containing functional groups.24 However, nitrogen-containing functional groups developed in such a way are often unstable and the nitrogen is mainly distributed on the surface with the highest nitrogen doping level reported so far of only
