# Synthesis of Benzoxazine-Based N-Doped Mesoporous Carbons as High-Performance Electrode Materials
## 1 Introduction  
As a type of energy-storage device, supercapacitors offer a promising solution for the fast storage the excess electrical energy [1; 2]. Electrochemical double-layer capacitors (EDLCs) or supercapacitors have recently attracted the attention of many researchers due to their considerable capacity, high power density, wide operating temperature range, short charging time, and long cycle life [3; 4; 5; 6]. Energy is stored in supercapacitors via the electrostatic accumulation of charge at the electrode surface. As the most commonly used electrode materials for supercapacitors, carbon materials show excellent electrical and thermal conductivity, a large specific surface area, and high chemical stability [7; 8]. The limited specific capacity of carbon materials restricts its application as a good electrode material. This is shown to be ameliorated by doping heteroatoms, such as nitrogen (N), boron (B), phosphorus (P), and sulfur (S), into the carbon structures [9; 10]. Doped heteroatoms in carbon materials can effectively enhance the specific capacitance by adding pseudocapacitance, which arises from the redox reaction of the heteroatoms [11; 12]. Furthermore, doping could improve the wettability between the electrolyte and the electrode material [13]. Among the doped carbons, nitrogen-doped carbon materials (NCMs) have been shown to be promising at improving the capacitance via surface faradaic reactions without sacrificing the high rate capability and long cycle life. The new NCMs show good electronic conductivity and they can be easily prepared at low cost. To our knowledge, nitrogen has become the most-studied doped heteroatom for carbonaceous electrode materials [14; 15]. Two main methods for the preparation of heteroatom-doped carbon materials have been developed so far: in situ doping using nitrogen-containing precursors (such as urea-polymer [16], polyaniline (PANI) [17], cyanamide [18], dicyandiamide [19], melamine [20]) and the post-treatment of porous carbons (using NH\({}_{3}\) or amines). In in situ doping, heteroatoms usually enter directly into the skeleton of the carbon materials. This method could resolve the problem of nitrogen-containing functional groups on the surface of the porous carbons, which decrease the available surface area and pore volume [21; 22]. In our investigation, the heteroatom was introduced using benzoxazine as a carbon precursor. The benzoxazine-based porous carbon material introduces various organic elements, such as oxygen and nitrogen [23; 24; 25]. Meanwhile, the high surface area and ordered porous structure of electrode materials are also important factors that affect the performance of supercapacitors. The nanostructured porous materials synthesized using template mesoporous silica (e.g., SBA-15, MCM-41) usually meet the above material requirements. In this method, the carbon material can be obtained inside the pores of the silica template, which can easily be removed by the treatment of hydrofluoric acid or sodium hydroxide [26; 27]. The recovered carbon material, which keeps the morphology of the silica host, has a controlled pore size and ordered porous structure. Thus, the application of templating agents (e.g., SBA-15, MCM-41) provides a good idea for the design of electrode materials with a controllable morphology [28]. To date, benzoxazine-based, heteroatom-doped carbon materials that are synthesized using the hard template have not been well studied. In this paper, for the first time, we synthesized nitrogen-doped mesoporous carbons with two different precursors (aniline-phenol benzoxazine and aniline-cardanol benzoxazine). Through the hard template (SBA-15) synthetic method, we investigated the effect of these different phenol sources on the nitrogen content and the effect of the carbonization temperature on the structure of the carbon materials. The electrochemical properties were also investigated.