ZIF-CoO@ZIF-Derived Urchin-Like Hierarchically Porous Carbon as Efficient Bifunctional Oxygen Electrocatalysts.

CoO nanoparticles were sandwiched into interlayers between ZIF-8 and ZIF-67 to form ZIF-CoO@ZIF precursors. Pyrolysis of ZIF-CoO@ZIF yielded an urchin-like hierarchically porous carbon (Co@CNT/NC), the thorns of which were carbon nanotubes embedded Co nanoparticles. With large specific surface area and hierarchically porous structure, as-prepared Co@CNT/NC exhibited excellent bifunctional oxygen electrocatalytic performances. It has good ORR performance with E of 0.85 V, which exceeds the Pt/C half-wave potential (E=0.83 V). In addition, Co@CNT/NC has an OER performance close to that of RuO. To further demonstrate the effect of Co modifying on the properties, the samples were subjected to acid washing treatment. Co-based nanoparticles were proved to After acid washing, there was obvious loss of Co particles in Co@CNT/NC, resulting in poor oxygen electrocatalysis. So, the pyrolysis products of ZIF-8-CoO@ZIF-67 retained large specific surface area and porous structure can be retained, and on the other hand, the carbon tube structure and original polyhedron framework. Besides, existence of Co nanoparticle@carbon nanotube provided more active sites and improved the ORR and OER performances.