Controllable Preparation Of Nitrogen-doped Porous Carbon For Zinc-air Battery

Developing low-cost,environment-friendly,stable and efficient ORR/OER electrode catalysts is very important for the large-scale practical application of zinc-air batteries.Currently,Pt,Ru and Ir-based precious metal catalysts are widely used as the ORR/OER catalysts in zinc-air batteries.The disadvantages of these precious metal catalysts are high cost,easy poisoning,scarce resources and poor durability.Therefore,it is important to find non-precious metal catalysts with low cost and high efficiency to replace the precious metal catalysts for promoting the commercialization of zinc-air batteries.In this dissertation,the controllable preparation of nitrogen-doped porous carbon composites with transition metal active species was achieved by means of component control and optimization of preparation conditions.Graphene,melamine sponge,and polypyrrole were separately used as the carbon and nitrogen precursors to synthesize novel non-precious metal carbon-based electrochemical catalysts by the solid-gas reaction method.The as-prepared catalysts,including N-HGO,Co@CNT/MSC,Co/HMSC and Co/HNCPPy,exhibit high ORR/OER catalytic performance in alkaline electrolyte.In the study,XRD,SEM,TEM,XPS,Raman and other characterization methods were utilized to explore the affect factors on the formation of the material’s micro-morphology,and to reveal the formation mechanism of the materials.Combined with the electrochemical performance tests,the relationship between the ORR/OER performance and the structure of materials was analyzed.The as-prepared materials were assembled into the rechargeable zinc-air batteries,and the electrochemical performance and stability of the materials were evaluated by the power density,the specific discharge capacity,and the charge-discharge cycling stability of cells.The ORR/OER evaluations and the zinc-air battery tests reveal the following results:（1）N-HGO shows better ORR performance and low OER performance in alkaline electrolyte,with the E1/2 of 0.82 V andΔE（defined as EOER–EORR）of 0.98 V.N-HGO-based zinc-air battery has good rechargeable performance.After a continuous discharge-charge test at a current density of 10 mA cm^-2 for 33.3 hours（200 cycles）,its stability is slightly better than commercial Pt/C.（2）Both Co@CNT/MSC and Co/HMSC show significant ORR/OER performance.In particular,Co/HMSC has the E1/2 of 0.84 V,the OER overpotential of 396 mV,andΔE of 0.78 V.Co/HMSC-based zinc-air battery has excellent rechargeable performance.After a continuous discharge-charge test at a current density of 10 mA cm^-2 for 51.6 hours（310 cycles）,its stability is better than commercial Pt/C.（3）Co/HNCPPy has the excellent ORR/OER performance with E1/2 of 0.86 V,OER overpotential of 373 mV,andΔE of 0.74 V.Co/HNCPPy-based zinc-air battery has outstanding charge-discharge cycling stability and is superior to commercial Pt/C.This dissertation demonstrates a practical cost-effective way towards the design and construction of porous ORR/OER bifunctional electrocatalysts with high performance.It provides the following valuable conclusions:（1）The hierarchical porous structure of the material is conducive to improving the catalytic performance of the material.Micropores can significantly increase the specific surface area of the material to expose more active sites,while mesopores can be large pores to facilitate electrolyte conduction.（2）Appropriate carbon matrix can not only improve the electron transport ability of the catalysts,but also help to form a highly dispersed Co/CoNx active structure and to reduce the agglomeration of metal nanoparticles.（3）The synergy between Co/CoNx active structure and nitrogen-doped porous carbon can significantly improve the ORR/OER activity and stability of an electrochemical catalyst.