Novel CdFe bimetallic complex-derived ultra-small Fe and N codoped carbon as a highly efficient oxygen reduction catalyst

During the development of oxygen reduction reaction (ORR) electrocatalysts, transition metal nanoparticles embedded in N-doped graphene have attracted increasing attention due to their low cost, minimal environmental impact and satisfying performance. In this study, a new organic-Cd complex formed through Cd2+ coordination with P-phenylenediamine (PPD) was used to prepare highly active Fe-embedded N-doped carbon catalysts for the first time. It is significant that with the decreasing molar ratio of Cd/Fe, an obvious microstructure evolution was observed in Cd-Fe-PPD from diamond-like blocks to thick flakes, and further bloomed into flower-like shapes with ultrathin petals and then eventually exhibited large block starfish-like shapes. After carbonization treatment, Cd was removed, slack and porous N-doped carbon was formed, and Fe was assembled in N-doped carbon. Similar phenomenon was also observed in Co-PPD. The optimized Fe@NPC-2 material features uniform and well-dispersed 3-5 nm Fe nanoparticles embedded in two-dimensional ultrathin carbon nanosheets delivered excellent electrocatalytic performance (Eonset: 0.96 V vs RHE, E1/2: 0.84 V vs RHE), which very close to those of commercially available Pt/C (Eonset: 0.95 V vs RHE, E1/2: 0.84 V vs RHE) and its methanol tolerance and durability also better than that of Pt/C.