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Tuning the dual-active sites of ZIF-67 derived porous nanomaterials for boosting oxygen catalysis and rechargeable Zn-air batteries
Nano Research 2021, 14 (7): 2353-2362
Published: 05 July 2021
Downloads:49

The rational control of the active site of metal-organic frameworks (MOFs) derived nanomaterials is essential to build efficient bifunctional oxygen reduction/evolution reaction (ORR/OER) catalysts. Accordingly, through designing and constructing a Co3O4-Co heterostructure embedded in Co, N co-doped carbon polyhedra derived (Co3O4-Co@NC) from the in-situ compositions of ZIF-67 and cobalt nanocrystals synthesized by the strategy of in-situ NaBH4 reduction, the dual-active site (Co3O4-Co and Co-Nx) is synchronously realized in a MOFs derived nanomaterials. The formed Co3O4-Co@NC shows excellent bifunctional electrocatalytic activity with ultra-small potential gap (ΔE = Ej=10 (OER) - E1/2 (ORR)) of 0.72 V, which surpasses the commercial Pt/C and RuO2 catalysts. The theory calculation results reveal that the excellent bifunctional electrocatalytic activity can be attributed to the charge redistribution of Co of Co-Nx induced by the synergistic effects of well-tuned active sites of Co3O4-Co nanoparticle and Co-Nx, thus optimizing the rate-determining step of the desorption of O2* intermediate in ORR and OH* intermediate in OER. The rechargeable Zn-air batteries with our bifunctional catalysts exhibit superior performance as well as high cycling stability. This simple-effective optimization strategy offers prospects for tuning the active site of MOF derived bifunctional catalyst in electrochemical energy devices.

Research Article Issue
Defects enriched hollow porous Co-N-doped carbons embedded with ultrafine CoFe/Co nanoparticles as bifunctional oxygen electrocatalyst for rechargeable flexible solid zinc-air batteries
Nano Research 2021, 14 (3): 868-878
Published: 01 March 2021
Downloads:85

The construction and design of highly efficient and inexpensive bifunctional oxygen electrocatalysts substitute for noble-metal- based catalysts is highly desirable for the development of rechargeable Zn-air battery (ZAB). In this work, a bifunctional oxygen electrocatalysts of based on ultrafine CoFe alloy (4-5 nm) dispersed in defects enriched hollow porous Co-N-doped carbons, made by annealing SiO2 coated zeolitic imidazolate framework-67 (ZIF-67) encapsulated Fe ions. The hollow porous structure not only exposed the active sites inside ZIF-67, but also provided efficient charge and mass transfer. The strong synergetic coupling among high-density CoFe alloys and Co-Nx sites in Co, N-doped carbon species ensures high oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activity. First-principles simulations reveal that the synergistic promotion effect between CoFe alloy and Co-N site effectively reduced the formation energy of from O* to OH*. The optimized CoFe-Co@PNC exhibits outstanding electrocatalytic stability and activity with the overpotential of only 320 mV for OER at 10 mA·cm−2 and the half-wave potential of 0.887 V for ORR, outperforming that of most recent reported bifunctional electrocatalysts. A rechargeable ZAB constructed with CoFe-Co@PNC as the air cathode displays long-term cyclability for over 200 h and high power density (152.8 mW·cm−2). Flexible solid-state ZAB with our CoFe-Co@PNC as the air cathode possesses a high open circuit potential (OCP) up to 1.46 V as well as good bending flexibility. This universal structure design provides an attractive and instructive model for the application of nanomaterials derived from MOF in the field of sustainable flexible energy applications device.

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