MOF nanoleaves as new sacrificial templates for the fabrication of nanoporous Co-N_:X/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 kg_zn^-1).