A bottom-up puzzle strategy for P/B co-doped carbon nanosheets as efficient oxygen reaction electrocatalysts

Preparing metal-free and non-N-doped carbon-based electrocatalysts via pyrolysis encounters a significant challenge of low controllability for microstructure modulation and limited electrocatalytic activity. Herein, a bottom-up puzzle strategy is proposed to fabricate a series of phosphorus and boron co-doped carbon (P-BC) nanosheets. These P-BC nanosheets manifest diverse morphologies and distinct heteroatom doping levels, achieved through the innovative utilization of four similar P onium salts featuring varying benzene ring arrangements, coupled with a fixed B onium salt. Among them, the flat 4P-BC nanosheets with abundant P/B heteroatoms exhibit the optimal oxygen reduction reaction (ORR) performance (E1/2 = 0.79 V, jL = 5.77 mA cm−2), and the assembled zinc-air battery displays a large power density (163 mW cm−2) and excellent long-term durability (450 cycles), which is attributed to the high specific surface area, enhanced defects or disorder, and ample P/B-doping induced active sites for electrochemical reaction. The assembly mechanism of functional units in solution and their intricate evolution at high temperature are elucidated for various P-BC nanosheets. This work elaborates the influence of precursors functional units on the resulting microstructure attributes and active sites properties, providing a novel avenue for the rational design and optimization of metal-free and heteroatom-doped carbon electrocatalysts.