Strategic Design and Synthesis of N, S, P Tridoped Carbon: A Highly Efficient Metal-Free Catalyst for Oxygen Reduction Reaction

Doping multiple nonmetal heteroatoms into carbon materials is a promising avenue for boosting the catalytic performance of carbon-based metal-free catalysts (CMFCs) for the oxygen reduction reaction (ORR). Nevertheless, selecting appropriate precursors and doping processes to synthesize high-performance CMFCs for the ORR remains challenging. Herein, N-doped carbon (N-C) and N,S-codoped carbon (NS-C) catalysts were first prepared via in situ doping. Then, based on these catalysts, N, P codoped carbon (NP-C) and N, S, P tridoped carbon (NSP-C) catalysts were synthesized by ex situ phosphorus doping. Characterization shows that the number of varieties is more important than the content of the doped heteroatoms in determining the ORR performance of the CMFCs. Theoretical calculations and in situ attenuated total reflectance surface-enhanced infrared absorption spectroscopy reveal that doping S and P atoms can create more active sites, promote OOH* formation, adjust the adsorption energy of oxygenated intermediates, and lower the thermodynamic limiting potential. Consequently, the performance of the dual-doped NS-C and NP-C is superior to that of N-C, while the tridoped NSP-C exhibits the highest activity with half-wave potentials of 0.898 and 0.766 V vs RHE under alkaline and acidic media, respectively. Furthermore, the NSP-C-assembled Zn-air battery achieves a peak power density of 119 mW cm^-2 and a specific capacity of 800 mAh g_Zn^-1. This study introduces an innovative strategy to synthesize CMFCs highly efficient for the ORR.