N-Doped Hollow Mesoporous Carbon Nanospheres for Oxygen Reduction Reaction in Alkaline Media

Abstract

The replacement of precious metal catalysts with pyridinic and graphitic-N sites that are earth-abundant and of low-cost and enriched with a high concentration for oxygen reduction reaction (ORR) is highly desirable. Herein, we report a facile synthesis of N-doped hollow mesoporous carbon spheres (NHSs) using tetraethyl orthosilicate (TEOS) as a silica precursor and dopamine hydrochloride (DHC) as carbon and nitrogen precursors through which uniform hollow sphere mesopores can be attained by adjusting the temperature and DHC loading. At the optimum temperature of 900 °C, a concentration ratio (0.5 mL:0.4 g) of TEOS/DHC leads to high-surface-area (1452 m2/g) carbon with pore volume (0.3 cm3/g), enriched defect sites, and a large number of pyridinic and graphitic-N sites offering an outstanding activity toward ORR. Further electrochemical studies demonstrated a positive onset potential of 0.84 V, an excellent current density of 4.9 mA/cm2, and a four-electron pathway with a lower Tafel slope of 65 mV/dec, respectively.