Precursor modulated active sites of nitrogen doped graphene-based carbon catalysts via one-step pyrolysis method for the enhanced oxygen reduction reaction

Tuning active configurations of different nitrogen (N) species and elucidating their influence on the catalytic activity for oxygen reduction reaction (ORR) is important to develop N-doped carbon (N/C) as efficient metal-free catalysts. The challenge is to selectively control the active N sites of N/C. Herein, we approach this challenge by modulating N active species in graphene structured N/C with specific precursors via a one-step pyrolysis process. In this method, 5-aminouracil is selected as the N-containing precursor platform to modulate the pyridinic N (N_P), while 2,6-diaminopyridine and 1,3-diaminobenzene are used to modulate graphitic N (N_G) and pyrrolic N (N_PY), respectively. N/C materials with specific different N configurations such as N/CN_P+N_G, N/CN_P+N_P and N/CN_P+N_PY are successfully synthesized and identified by microstructure and phase characterization. Electrochemical results demonstrate that N/CN_P+N_G exhibits the best ORR performance, achieving an onset potential (E_onset) of 0.98 V and half-wave potential (E_1/2) of 0.86 V vs. RHE, respectively, which is comparable to that obtained on conventional Pt/C. By contrast, N/CN_P+N_PY exhibits the lowest activity for ORR. Density functional theory (DFT) simulation further validates that the N_P+N_G configuration produces strong electronic distribution on carbon matrix that leads to high charge and high spin density on surrounding carbon atoms. This work provides a facile approach to design N doped graphene structured carbon materials with active N configurations for ORR.