Exploring the structural dependence of metal-free carbon electrocatalysts on zinc-based metal-organic framework types

Metal-organic frameworks (MOFs) have been widely used as precursors to derive carbon-based electrocatalysts for the oxygen reduction reaction (ORR) due to their high porosity and tunable chemical composition/structure. However, the influence of MOF type on the structure and further ORR activity of derived metal-free carbon catalysts is still elusive. In the present work, a series of different Zn-based MOFs were employed as precursors to explore this issue. Meanwhile, prepare N-doped metal-free carbon catalysts were prepared for the ORR under the activation of sacrificial urea (which is effective to enhance the ORR activity of carbon-based catalysts). By analyzing the intermediates during pyrolysis, it is found that the decisive role of MOF types on the doped N and the morphology of derived carbon catalysts was played by the Zn coordination environment of MOFs and its reactivity with the decomposition intermediate of urea. Although the structure and porosity of derived carbon catalysts from different MOFs are very different, they all showed superior ORR activity and Zn-air battery performance up to 20 wt% Pt/C benchmark catalysts. From the above analyses, the combination of urea and compounded Zn is also a promising activation method for the preparation of highly-efficient metal-free carbon electrocatalysts.

Automated summary

Metal-organic frameworks (MOFs) have been used as precursors for carbon-based electrocatalysts. This study investigates the influence of MOF type on the structure and ORR activity of metal-free carbon catalysts derived from them. It is found that the coordination environment of Zn in MOFs and its reactivity with urea play a decisive role in the doped N and morphology of the derived carbon catalysts. Despite different structures and porosities, carbon catalysts derived from different MOFs exhibit superior ORR activity and Zn-air battery performance. The combination of urea and compounded Zn shows promise as an activation method for efficient metal-free carbon electrocatalysts.