Three-dimensional nitrogen-doped carbon materials are prepared using thermally decomposable polystyrene(PS) and mussel-inspired polydopamine(PDA), as a sacrificial template and a nitrogen-doped carbon precursor, respectively. By virtue of the versatile coating ability associated with the high nitrogen content, dopamine was demonstrated to be an effective precursor for the preparation of nitrogen-doped carbon. In previous studies, PDA has been used as a nitrogen source by coating its layer onto a main carbon source. Herein, however, the PDA is utilized not only for the nitrogen precursor but also for the carbon source, without any additional carbon source, in order to achieve the higher nitrogen content and simple synthetic procedure. As a result, nitrogen content on carbon increased to over 4 at. %, which was limited to under 1 at. % when PDA was just coated onto the other carbon source. Moreover, due to highly moldable characteristics of polymer ingredients, three-dimensional carbon structures with various configurations could be prepared such as micron-sized hollow carbon fiber.

First, nitrogen-doped hollow carbon fiber with μm-sized diameter was synthesized by coating PDA around the electrospun PS fiber and following pyrolysis for PS removal and PDA carbonization. The length of hollow carbon fiber was also able to be controlled from several μm to hundreds of μm, using ultra-sonication. Completely hollow carbon fiber with about 3-μm diameter was successfully obtained and analyzed its physical characteristics from XPS, Raman and Mercury porosimeter. Nearly 4 at. % of nitrogen was detected on the hollow carbon fiber and the over 68 % of nitrogen-doping structure is revealed to be graphitic-N, which is known as the most effective nitrogen-doping structure for oxygen reduction reaction.

Since both PDA-derived carbon materials have relatively high nitrogen content and can form a self-supporting network, endowing high applicability as a binder-free electrode, they can be effectively applied to electrochemical energy device, specifically polymer electrolyte membrane fuel cell (PEMFC) and Li-O₂ battery system where the oxygen reduction reaction is the dominant reaction.