Tailoring atomically dispersed cobalt-nitrogen active sites in wrinkled carbon nanosheets via "fence" isolation for highly sensitive detection of hydrogen peroxide

Stable and highly sensitive determination of hydrogen peroxide (H2O2) is needed in various fields ranging from disease prevention to environmental protection. The construction of inexpensive and highly active transition-metal-based nitrogen-doped carbon (TM-N/C) electrocatalysts is a promising strategy for highly sensitive enzyme-free electrochemical detection of H2O2. Deriving the TM-N/C electrocatalysts with abundant active sites and uniform micro/mesopores from rationally designed metal-organic frameworks (MOFs) as self-sacrificing templates has been demonstrated as one of the most effective ways. However, the phenomenon of spontaneous aggregation of metal atoms often occurs in the synthesis of TM-N/C electrocatalysts, which reduces the density of the TM-N moieties and destroys the original active sites in the catalyst. For converting the metal atoms in the precursor directly into TM-N atomically active moieties, we present a straightforward approach, which is based on the pyrolysis of a complex of nanosized Zn/Co bimetallic ZIF crystals (0-8% Co) and carbon nitride (g-C3N4). This approach enables the controllable synthesis of nitrogen-doped carbon nanosheets anchored with atomically dispersed cobalt-nitrogen active sites (Co-N/CNSs). Particularly, the Co (4%)-N/CNS synthesized using Zn/Co ZIF (4% Co) and g-C3N4 precursors possesses a maximized Co atom utilization and favorable degree of graphitization. The Co (4%)-N/CNS exhibits excellent sensing performance towards H2O2 reduction with a wide linear current response ranging from 1 x 10(-6) to 0.5 x 10(-3) M and from 0.5 x 10(-3) to 1 x 10(-1) M, high sensitivity of 468.95 and 605.50 mu A mM(-1) cm(-2), a low detection limit of 6.18 x 10(-9) M, and good anti-interference, stability, and reproducibility. Hence, the Co (4%)-N/CNS has practical application potential for precisely detecting the concentration of H2O2 at a trace level.