Synergistic effects of Co/Fe bimetallic polymer catalysts for enhanced ORR/OER: Insights from thermodynamic and in-situ kinetic study

•A pyrolysis-free bifunctional electrocatalyst is firstly synthesized from heterometal phthalocyanines and redox active TPDA linker.•Co/Fe-TPDA-CP possess the excellent oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) bifunctional performances with halfwave potential of 0.88 V and overpotential (E10) of 340 mV.•Structural and thermodynamic analyses demonstrated that the high bifunctional activities of catalyst are due to the synergistic effect between the Co/Fe metals.•Dynamic analysis found that the enhanced ORR stability originated from the fast H2O2 decomposition catalyzed by Co-N4 site.•The Zn-air battery with Co/Fe-TPDA-CP electrodes exhibited a high peak power density (97 mW cm−2), specific capacity (780 mA h g−1) and long-term discharge-charge stability. Bifunctional catalysts for oxygen reduction reaction and oxygen evolution reaction in Zinc-air batteries have been long pursued for the development of clean energy transformation devices. Yet, the underlying mechanism of the promoted electrocatalytic performance is still vague. Herein, a pyrolysis-free Co/Fe bimetallic phthalocyanine coordination polymer Co/Fe-TPDA-CP is firstly synthesized using heterometal tetra-aminophthalocyanines (MTAPcs, M=Co/Fe) as structural model and N,N,N’,N’-tetra(4-folmylphenyl)-p-phenylenediamine (TPDA) as linker. The Co/Fe-TPDA-CP exhibits the high oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activities with low ΔE of 692 mV, superior to monometallic Fe-TPDA-CP and Co-TPDA-CP polymers. Density functional theory (DFT) calculation and thermodynamic analysis find that ORR and OER happened separately on Fe and Co sites, in which the presence of second metal modulates the d-band center and optimizes the intermediates adsorption, thereby improving the ORR/OER synergistically. Moreover, dynamic analysis explains that the enhanced ORR stability originated from the fast H2O2 decomposition catalyzed by Co-N4 sites. Furthermore, the Zn-air battery with Co/Fe-TPDA-CP electrode also exhibits a high peak power density (97 mW cm−2) and specific capacity (780 mA h g−1). Through the proof-of-concept bifunctional electrocatalyst with clear structure and synergistic mechanism, this work paves the way for future molecular oxygen electrocatalyst design. [Display omitted] Schematic illustration of Two birds with one stone strategy in Co/Fe-TPDA-CP catalyst.