Polymerizable ionic liquid as a precursor for N, P co-doped carbon toward the oxygen reduction reaction

Abstract

A polymerizable ionic liquid (PIL) is investigated as the precursor to produce nitrogen and phosphorus co-doped carbon toward the oxygen reduction reaction (ORR). The IL is functionalized with H₂PO₄⁻ anions, providing P heteroatoms in the final carbon. Simultaneously, the cations of the IL feature nitrogen in their structures, which dopes the carbon frameworks with nitrogen heteroatoms. Therefore, the N, P co-doped carbon material can be easily prepared with the PIL as the precursor via a one-pot process. The composition of the carbon makes it a potential metal-free electrocatalyst for ORR. As expected, the N, P co-doped carbon (C₁) exhibits an improved catalytic activity towards ORR compared with its N doped carbon (C₂) counterpart in alkaline solutions. The catalytic performance of C₁ toward ORR is also higher than that of the N, P co-doped carbon derived from a non-polymerizable ionic liquid. The results from scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET) measurement, etc. confirmed that the defective graphite carbon with limited porosity and doped with N, P can be obtained via the present process. Given its highest catalytic performance toward ORR, the C_VNP derived from the polymerizable ionic liquid possesses the best intrinsic catalytic activity due to the co-doping effects among the investigated samples, consistent with the density functional theory (DFT) calculation. The present work provides new opportunities for the application of polymerizable ionic liquids and the preparation of metal-free N, P co-doped carbon as an ORR catalyst. The prepared C₁ sample also shows some catalytic performance toward the oxygen evolution reaction and hydrogen evolution reaction.