Thermodynamically controllable synthesis of ZIF-8 exposing different facets and their applications in single atom catalytic oxygen reduction reactions

The development of thermodynamically controllable synthetic strategy to manipulate the morphology of ZIF-8 without capping agent is essential to help understanding their facet effect and the structure-activity relationship of single atom catalysts derived from ZIF-8. Here, we prepared ZIF-8 with different morphologies (cube, truncated rhombododecahedral and rhombododecahedral) and thus area ratio of exposed {100}, {110} facets by a thermodynamically controllable synthetic strategy. When the reaction proceeds under room temperature (30 °C), the assembling of ZIF-8 followed an area-reducing layered growth mode, while switched to an integral layered growth mode at lower temperature –40 °C. Moreover, this strategy also works to obtain ZIF-8 encapsulated with metal precursors (Fe(acac)₃, Cu(acac)₂ and Co(acac)₂). Single Fe atom anchored on nitrogen doped carbon catalysts (SA-Fe/CN) derived from Fe-ZIF-8 retain their original morphologies and the unsaturated surface-active sites on {100} facet, which further displays different catalytic performance towards oxygen reduction reaction (ORR). This work not only reveals the different growth pattern of ZIF-8, but also points out a new direction for designing and synthesizing MOFs with different morphology rationally.