Porous carbon electrocatalyst with exclusive metal-coordinate active sites for acidic oxygen reduction reaction

A porous P-doped M/N/C electrocatalyst with high-surface-area (up to 1312 m² g⁻¹) was prepared by annealing a mixture of triphenylphosphine, polyaniline, phthalocyanine iron (II), and phthalocyanine cobalt (II). The synthesis involves hard templating with silica nanoparticles, followed by NH₃ activation. Along with low metal loading (Fe loading = 0.46 wt. %; Co loading = 0.26 wt. %), the resulting P-doped M/N/C exhibits an excellent ORR activity and durability in acidic media. The half-wave potential difference of the catalyst for ORR is only ∼53 mV negative relative to the benchmarked Pt/C (360 μg Pt) at the same loading. More importantly, transmission electron microscopy, X-ray absorption fine structure spectra, and electrochemical poisoning by SCN⁻ ion suggested that exclusive metal-coordinate catalytic active sites such as Fe-N₆ and Co-N₄, are involved in ORR. Moreover, as-prepared P-doped M/N/C catalysts with bimetallic catalytic active sites exhibit superior electrochemical performance compared to catalysts with single metal active sites. These results represent an important step towards rational design of high-performance ORR electrocatalysts for polymer exchange membrane fuel cells.