CMP-on-MOF bimetallic hybrids derived sheet-on-rod heterostructure as bifunctional oxygen electrocatalyst for rechargeable Zn-air batteries

Abstract

As a simple but effective approach to engineer the simultaneous geometric structure and composition diversity into one nano-material, hybrids have geared great research attention, recently. Here, a N-decorated sheet-on-rod heterostructure with hierarchical porosity, as well as homogeneously dispersed Co5.47N, Co0.7Fe0.3, and Fe/Co-Nx species on the phase interface, was developed via pyrolysis of a CMP-on-MOF bimetal hybrid, to achieve the bifunctional oxygen electrocatalytic activity. Conjugated microporous polymers (CMPs) are an emerging class of multifunctional materials combining the features of conventional conjugated polymers and porous materials, simultaneously. CMP-on-MOF was prepared via the assembly of Co-phthalocyanine-CMP (Co-CMP) on the surface of Fe-MIL-88B (Fe-MOF) through a solid-phase synthesis method. The optimized catalyst (PM-900), namely the product of hybrid pyrolysis, is obtained by finely regulating the composition of hybrid (mCMP to mMOF of 1:1) and pyrolysis temperature (900 °C) on the hybrid, simultaneously. The abundant Co5.47N, Co0.7Fe0.3, and atomically dispersed Fe/Co-Nx species are highly catalytically active, and the hierarchical porous structure provides easily accessible pathway for active sites, and the sheet-on-rod structure ensures a high electrical conductivity which is conducive for the catalysis. As a result, the optimum electrocatalyst, denoted as PM-900, presents a superb bifunctional electrocatalytic activity for both the oxygen reduction (ORR) and oxygen evolution reaction (OER) under alkaline conditions. Additionally, a home-made Zn–air battery (ZAB) comprising PM-900 catalyst presents prominent charge-discharge property even outperforms the mixture of Pt/C (20 wt%) and IrO2. The hybrid strategy paves a new avenue for the rational design and synthesis of advanced bifunctional catalysts with intricate and unprecedented porous superstructures for reversible energy storage and conversion applications.