Nitrogen-Doped Hierarchical Mesoporous/Macroporous Carbon (H-C) Prepared from the Combined Silica Templates with Different Size for Oxygen Reduction

The doped mesoporous carbon as the cathotdic electrode materials for oxygen reduction reaction (ORR) have drawn great attention due to the high specific surface area and porous structure, which can facilitate the accessible part of active sites and the transport properties of ORR-relevant species.^1,2 For obtaining the specified morphology and predetermined microstructure, the mesoporous carbon were usually synthesized using a sacrificial support method (SSM), during which the excess amount of hydrofluoric acid (HF) have to be added to vacate the silica and other metal-containing precursors.^2,3 The waste liquid generated in the process of centrifugal brings a lot of damage for the environment. Therefore, try to develop and/or find a green and effective method for the preparation of mesoporous/microporous carbon materical is no doubt an urgent issue.

Here, by combining a simple two-step graphitization of the impregnated carbon with sodium hydroxide (NaOH), a green and efficient  procedure has been demonstrated for the synthesis of nitrogen-doped hierarchical mesoporous/microporous carbon material using poly(ethyleneimine) (PEI) and ferrous sulfate (FeSO₄ 7H₂O) as precursors. The obtained doped mesoporous carbon shows very high catalytic activity toward oxygen reduction reaction (ORR). Additionally, the suction filtration can be adopted  rather than centrifuge and, 50% more yield of cathotdic electrode material can be obtained. Therefore we can completely use sodium hydroxide instead of hydrofluoric acid to vacate the silica, which is very green and environmentally friendly.