Tunable Carbon Surface from Mono- to Multi-Metallic Single Atoms

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 (Fe³⁺), cobalt (Co³⁺), ruthenium (Ru³⁺), palladium (Pd²⁺), indium (In³⁺), iridium (Ir²⁺), and platinum (Pt²⁺) . As illustrated in Figure 1, the carbon surface can be tuned with different level of compositional complexities, including unary Pt₁@NC, binary (MSAC-2, (PtFe)₁@NC), ternary (MSAC-3, (PtFeIr)₁@NC), quaternary (MSAC-4, (PtFeIrRu)₁@NC), quinary (MSAC-5, (PtFeIrRuCo)₁@NC), senary (MSAC-6, (PtFeIrRuCoPd)₁@NC), and septenary (MSAC-7, (PtFeIrRuCoPdIn)₁@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_metal^-1 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.