String of ZIF-derived hollow beaded nanocage embedded into carbon nanofiber with intensified exposed Co-Nx sites for efficient oxygen catalysis in various fuel cell devices

The rational control of Co-Nx active sites dispersion in nanomaterials is significant to construct efficient oxygen reduction reaction (ORR) electrocatalysts in fuel cells. Herein, a novel strategy for the scalable synthesis of carbon nanofiber supported hollow beaded nanocage with accessible Co-Nx sites in cavity wall (PAN-Co-ZIF-8-C-A and PAN-Co/ZIF-8-C-A) originated from zeolitic imidazolate frameworks (ZIFs) and polyacrylonitrile (PAN) is reported. Remarkably, the formed samples modified with Co-Nx sites exhibit superior ORR activity, which makes it promising ORR catalysts for microbial fuel cell (MFC) and direct methanol fuel cell (DMFC). Accordingly, the maximum power densities of MFC decorated with PAN-Co-ZIF-8-C-A and PAN-Co/ZIF-8-C-A achieve 869.6 and 888.3 mW cm-2, which are 1.17 and 1.19 times higher than that of Pt/C. In addition, the PAN-Co/ZIF-8-C-A modified DMFC exhibits comparable power density of 23.27 mW cm-2 close to Pt/C electrode (25.63 mW cm-2). Such commendable catalytic performances can be primarily attributed to the synergistic effect of hier-archical porosity for fast mass transport, high conductivity for electron migration, and well-tuned Co-Nx sites for oxygen reduction. This facile-effective optimization strategy may open a new avenue for exposing the catalytic centers of one-dimensional (1D) nanofiber and ZIFs-derived oxygen catalyst in fuel cells.