<p>Herein, we develop a non-selective charge
compensation strategy to prepare multi-single-atom doped carbon (MSAC) in which
a sodium p-toluenesulfonate (PTS-Na) doped polypyrrole (S-PPy) polymer is designed
to anchor discretionary mixtures of multiple metal cations, including iron (Fe<sup>3+</sup>),
cobalt (Co<sup>3+</sup>), ruthenium (Ru<sup>3+</sup>), palladium (Pd<sup>2+</sup>),
indium (In<sup>3+</sup>), iridium (Ir<sup>2+</sup>), and platinum (Pt<sup>2+</sup>)
. As illustrated in Figure 1, the carbon surface can be tuned with different level
of compositional complexities, including unary Pt<sub>1</sub>@NC, binary
(MSAC-2, (PtFe)<sub>1</sub>@NC), ternary (MSAC-3, (PtFeIr)<sub>1</sub>@NC),
quaternary (MSAC-4, (PtFeIrRu)<sub>1</sub>@NC), quinary (MSAC-5, (PtFeIrRuCo)<sub>1</sub>@NC),
senary (MSAC-6, (PtFeIrRuCoPd)<sub>1</sub>@NC), and septenary (MSAC-7,
(PtFeIrRuCoPdIn)<sub>1</sub>@NC) samples. The structural evolution of carbon
surface dictates the activities of both ORR and HER. The senary MSAC-6 achieves
the ORR mass activity of 18.1 A·mg<sub>metal</sub><sup>-1</sup> at 0.9 V (Vs
reversible hydrogen electrode (RHE)) over 30K cycles, which is 164 times higher
than that of commercial Pt/C. The quaternary MSAC-4 presented a comparable HER
catalytic capability with that of Pt/C. These results indicate that the highly
complexed carbon surface can enhance its ability over general electrochemical
catalytic reactions. The mechanisms regarding of the ORR and HER activities of
the alternated carbon surface are also theoretically and experimentally
investigated in this work, showing that the synergistic effects amongst the
co-doped atoms can activate or inactivate certain single-atom sites.</p>
A novel fluorescent sensor based on sulfur and nitrogen co-doped carbon dots with excellent stability for selective detection of doxycycline in raw milk