Single-precursor design and solvent-free nanocasting synthesis of N/S/O-doped ordered mesoporous carbons with trimodal pores for excellent oxygen reduction

Abstract

N/S-doped carbon materials hold great promise for the oxygen reduction reaction (ORR). Construction of uniform doping with desirable configurations and engineering of pore structure are essential to boost their performance. Herein, a single-precursor design and a solvent-free nanocasting approach are demonstrated to synthesize N/S/O-doped ordered mesoporous carbons (N/S/O-OMCs). The precursor cysteine (Cys) enables in-situ multiple doping. The special pyrolytic behavior of Cys confined in the ordered mesoporous silica (SBA-15) template enables efficient carbonization and structuration. The N/S/O-OMCs possess high surface areas (756–1339 m2/g), large pore volumes, trimodal pores (∼1.6, 4.6 and 7–100 nm), and high N/S/O contents. The influences of temperature and Cys/template mass ratio on the physicochemical properties of the N/S/O-OMCs are clarified. The N/S/O-OMCs are promising for ORR. The optimized sample shows high performance with high onset and half-wave potentials (0.95 and 0.87 V), a high limiting current density (5.9 mA/cm2), a high stability and excellent methanol tolerance. The correlations between the ORR performance and the physicochemical properties are elucidated. The high ORR performance of the optimized sample is attributed to its N/S/O doping with balanced graphitic-, pyridinic- and pyrrolic-N proportions and desirable C–S–C configuration, low charge transfer resistance, and hierarchical pore structure.