MOF nanoleaves as new sacrificial templates for the fabrication of nanoporous Co-Nx/C electrocatalysts for oxygen reduction
Although traditional three-dimensional (3D) zeolitic-imidazolate framework (ZIF) particles have been explored as promising precursors for preparing carbon-based electrocatalyst for oxygen reduction reaction (ORR), their natural tendency to agglomerate impedes the exposure of the active sites and significantly reduces their ORR performance. Herein, novel Co/Zn-containing bimetallic ZIF nanoleaves are synthesized by the "shape-transforming method in an aqueous system", in which the nitrogen atoms in amines form hydrogen bonds with hydrogen atoms from H2O molecules, which induce the formation of sodalite layers to generate the ZIF nanoleaves. By directly pyrolyzing the ZIF nanoleaves, the obtained cobalt-embedded nitrogen-doped mesoporous carbon (Co-N/C) product possesses refined leaf-like two-dimensional (2D) morphologies. Moreover, the obtained 2D catalyst with a high mass loading of cobalt nanoparticles (31.17 wt%) shows an excellent electrocatalytic performance for the ORR in an alkaline electrolyte. The half-wave potential of the Co-N/C catalyst is 0.825 V versus the reversible hydrogen electrode, which is 14 mV more positive than that of the commercial Pt/C (0.811 V). In addition, the resulting zinc-air battery assembled using the Co-N/C air cathode with a liquid electrolyte exhibits both high open-circuit potential (1.446 V) and high energy density (837.5 W h kgzn-1).