Defect-Mediated In Situ CNT Growth in Hollow Porous Carbon From ZIF-8/ZIF-67 Bilayers for Efficient and Stable ORR Catalysis.

The rational design of carbon-based electrocatalysts with hierarchical porosity, graphitic domains, and optimized active sites is crucial for advancing the oxygen reduction reaction (ORR). Herein, a bilayer core-shell ZIF (PS@BCZ)-derived strategy is presented that enables the in situ growth of carbon nanotubes (CNTs) and uniform embedding of cobalt nanoparticles (Co NPs) within an N-doped hollow porous carbon matrix (CNT-Co/N-HPC). Sequential ZIF-8/ZIF-67 growth on polystyrene spheres, followed by pyrolysis, induces Zn sublimation from the ZIF-8 layer, generating structural defects that promote CNT formation and facilitate the uniform dispersion of Co catalytic sites. Molecular dynamics simulations reveal that Zn-induced defect environments are critical for triggering CNT growth in the presence of Co catalysts. The optimized CNT-Co/N-HPC(1/20) exhibited excellent ORR performance, achieving a half-wave potential of 0.864 V (vs RHE) and a diffusion-limited current density of 5.35 mA cm-2 in alkaline media, comparable to commercial Pt/C. The catalyst demonstrated outstanding long-term durability (98.9% retention after 10 h, and only a slight 8 mV negative shift in half-wave potential after 5000 potential cycles) and strong tolerance to methanol. This study elucidates the role of Zn-induced defects in directing CNT growth and highlights a tunable ZIF-derived strategy for engineering efficient carbon-based ORR catalysts.