Development of g-C3N4 activated hollow carbon spheres with good performance for oxygen reduction and selective capture of acid gases

Abstract

A variety of nitrogen-doped hollow carbon nanospheres (A–NHCN–Ts, where T stands for activation temperature) with abundant microporosity were developed by us in this work. The A–NHCN–Ts were synthesized from carbonization of silica-resorcinol formaldehyde core-shell composites (silica@RF). The resulting silica@carbon core-shell composites were then treated with KOH to enrich microporosity, fast activation with g-C3N4 to improve nitrogen-doping, and etched with HF to removal silica core. The silica@RF was synthesized from coating of silica nanosphere with resorcinol-formaldehyde resin in presence of hexamethylenetetramine crosslinker. A–NHCN–Ts exhibit hollow and uniform sphericity, large BET surface areas (704–1043 m2/g) and hierarchical porosity. Abundant nitrogen sites (11.6–14.8 wt%) with high percentages of pyridinic-N (55–70%) were doped in A–NHCN–Ts. As a result, A–NHCN–Ts can be used as high-efficient and long-lived electrocatalysts in oxygen reduction reaction (ORR). The reduction potential of A–NHCN–Ts activated at 800 °C (A–NHCN–800) is 0.8 V versus reversible hydrogen electrode (vs. RHE) in alkaline electrolyte, with a half-wave potential of 0.81 V (vs. RHE), an onset potential of 0.9 V (vs. RHE) and a limiting current density of 3.63 mA cm−2 at a rotation of 1600 rpm, respectively. A–NHCN–800 exhibits comparable ORR activity, enhanced methanol tolerance and superb stability in comparison with commercial Pt/C (20%). A–NHCN–Ts also show competitive properties in the capture of acid gases of SO2 and CO2, and the CO2 can be mildly catalyzed into cyclic carbonates over metalized A–NHCN–Ts. This work provides a novel g-C3N4 fast activation strategy for designing of high-efficient, multiple functional nanocarbon materials in both ORR, acid gases selective capture and conversion.