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Heteroatom-doped porous carbon (HDPC) materials have bloomed as a popular supporting material for metal catalysts used in oxygen reduction reaction (ORR). However, their intrinsic activity and catalytic mechanism are not well understood. Herein, hierarchically porous S, N-doped carbon flower (H-SNF) was synthesized and investigated as an ORR catalyst. Through a systematic electrochemical measurement technique, it is confirmed that H-SNF with abundant hierarchically porous structures shows improved electrochemical mass transport and favorable diffusion of O 2 and OH − . The optimal H-SNF shows outstanding ORR performance with an onset potential of 0.97 V (vs. RHE) and half-wave potential of 0.81 V. The H-SNF-based zinc-air battery yields a high open circuit voltage of 1.40 V, peak power density of 161.4 mW cm −2 . Density functional theory (DFT) calculation reveals that the pyridinic-N/graphitic-N atomic pair boosts the catalytic efficiency by optimizing the absorption/desorption of ∗OOH. The dual atomic site structure can enable a bifunctional mechanism where the pyridinic-N site acts as the “quick-start” triggering site to convert O 2 to ∗OOH, with ∗OOH transfer to the adjacent graphitic-N site and is converted to ∗O immediately. This work provides a unique HDPC material towards ORR, reveals their intrinsic catalytic mechanism, and sheds light on the design of high-performance carbon materials.
Chen et al. (Sat,) studied this question.
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