A hierarchically ordered porous nitrogen-doped carbon catalyst with densely accessible Co-Nx active sites for efficient oxygen reduction reaction

Reasonable design and construction of efficient and stable catalysts with abundant metal-N x active sites are the focus of oxygen reduction reaction (ORR) research. In this work, a type of catalyst with isolated single-atomic Co sites embedded in the ultra-thin pore walls of hierarchically ordered porous N-doped carbon (ISA-Co/HOPNC) by a simple single template pyrolysis strategy has been successfully synthesized. The interconnected macropores introduced by the silica colloidal crystal template (CCT) not only improve the mass transmission of molecules and ions to achieve the accessibility of internal Co-N x active sites, but also promote the complete removal of inactive Co species nanoparticles (NPs) inside the catalyst. Removal of inactive Co species NPs that form mesopores in the ultra-thin walls of the macropores increases the specific surface area to expose more active sites. In comparison with the commercial 20 wt% Pt/C, the optimal ISA-Co/HOPNC-0.3 catalyst shows comparable ORR activity, but much higher methanol tolerance and cycle stability. The remarkable ORR performance of ISA-Co/HOPNC-0.3 can be attributed to the numerous exposed single-atomic Co-N x active sites, as well as the high surface area and efficient mass transport from the 3D hierarchically ordered porous structure.