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[Display omitted] • A weak-strong coetching strategy is developed for metal–organic frameworks. • Hollow nanopompoms structure is obtained and can be maintained upon pyrolysis. • Pyrolyzed nanopompoms allow for efficient electron transfer applications. • Heterophases increase active sites and promotes electrocatalytic performance. • Nanopompoms catalyst has desirable bifunctional performance for Zn-air batteries. The rational structure and composition design of bifunctional electrocatalysts for oxygen evolution reactions (OER) and oxygen reduction reactions (ORR) is crucial for rechargeable metal–air batteries. Here, we report controlled structural transitions of metal–organic frameworks through a weak-strong competitive coordination strategy for high-performance electrocatalysts. Upon the introduction of potassium ferricyanide (PF) and/or phosphomolybdic acid (POM), cubic zeolitic-imidazole framework-67 (Cube-67) undergoes both chemical and macroscopic morphology changes, i.e., from nanocubes to hollow nanopompoms, where PF and POM act as the weak chelator (i.e., for finer structures) and the strong chelator (i.e., shape-directing agent), respectively. After calcination, the hierarchically structured nanopompoms display tunable and high-performance OER and ORR catalytic activities suitable for Zn–air batteries that display a long-term charge–discharge cycling stability. This work not only holds promise for clean-energy applications but provides a design principle for engineering advanced electrocatalysts by effectively tuning their structural and chemical properties. [ABSTRACT FROM AUTHOR]

[Display omitted] • A weak-strong coetching strategy is developed for metal–organic frameworks. • Hollow nanopompoms structure is obtained and can be maintained upon pyrolysis. • Pyrolyzed nanopompoms allow for efficient electron transfer applications. • Heterophases increase active sites and promotes electrocatalytic performance. • Nanopompoms catalyst has desirable bifunctional performance for Zn-air batteries. The rational structure and composition design of bifunctional electrocatalysts for oxygen evolution reactions (OER) and oxygen reduction reactions (ORR) is crucial for rechargeable metal–air batteries. Here, we report controlled structural transitions of metal–organic frameworks through a weak-strong competitive coordination strategy for high-performance electrocatalysts. Upon the introduction of potassium ferricyanide (PF) and/or phosphomolybdic acid (POM), cubic zeolitic-imidazole framework-67 (Cube-67) undergoes both chemical and macroscopic morphology changes, i.e., from nanocubes to hollow nanopompoms, where PF and POM act as the weak chelator (i.e., for finer structures) and the strong chelator (i.e., shape-directing agent), respectively. After calcination, the hierarchically structured nanopompoms display tunable and high-performance OER and ORR catalytic activities suitable for Zn–air batteries that display a long-term charge–discharge cycling stability. This work not only holds promise for clean-energy applications but provides a design principle for engineering advanced electrocatalysts by effectively tuning their structural and chemical properties. [ABSTRACT FROM AUTHOR]

[Display omitted] • NiFe-LDH were grown vertically on the surface of BTO which provided more active sites. • t-BTO@NiFe-LDH has excellent OER property due to the self-polarized ferroelectric t-BTO. • Interface tension between BTO and NiFe-LDH made BTO easily self-polarize, causing band tilting. • The superior OER activity results from the active sites and the optimized d-band center. • The design of a ferroelectric OER electrocatalyst based on self-polarization is provided. A flower-like core–shell heterostructured oxygen evolution reaction (OER) electrocatalyst based on tetragonal BaTiO 3 nanoparticles (t-BTO NPs) and NiFe-layered double hydroxide (NiFe-LDH) nanoarrays was prepared in this study. The influence from the self-polarization effect of t-BTO on the OER performance of NiFe-LDH is reported. Intriguingly, the OER activity of the t-BTO@NiFe-LDH heterojunctions in an alkaline media (1.0 M KOH) exhibited a low overpotential of 186 mV at 10 mA/cm2 and a low Tafel slope of 38.3 mV dec-1, which were far superior to those of the component materials: NiFe-LDH (267 mV and 94.8 mV dec-1) and t-BTO NPs (517 mV and 132.4 mV dec-1). Density functional theory (DFT) calculations revealed that the effective electronic modulation between t-BTO NPs and NiFe-LDH nanoplatelets narrowed the bandgap, promoted the electric conductivity, moderately raised Ed (i.e., energy level of the d-band center), optimized the adsorption ability of the oxygen-containing intermediates (*O, *OH, and *OOH), and induced an apparent reduction in the free energy barrier for the transformation from O* to OOH* in the t-BTO@NiFe-LDH heterojunctions. The PDOS result confirmed that t-BTO in the heterojunctions was easier to polarize, which can cause the rapid electron transfer in the OER process. In these heterostructures, the interface tension between BTO NPs and NiFe-LDH endowed BTO with easier self-polarization, thus leading to greater band tilting and faster electron transfer. Multiple synergistic effects of the flower-like core–shell t-BTO@NiFe-LDH heterojunctions enabled them with higher electrocatalytic activity. This work provides an in-depth understanding of the rational design of a high-efficiency, noble metal-free ferroelectric OER electrocatalyst based on the self-polarization of t-BTO NPs. [ABSTRACT FROM AUTHOR]