Preparation Of Cobalt Nickel-based Compounds/nitrogen-doped Graphene Catalysts And Their Application In Zinc-air Batteries

As the oxygen electrode is regarded as the most important part of zinc air batteries,it plays a vital role in the performance of zinc air batteries.Therefore,non-precious metal catalysts of an oxygen electrode with high efficiency,robust stability and rich resources have become a research hot spot.Among the non-precious metal catalysts,the transition metal-carbon-based hybrid materials possess the advantages of the transition metal compound and carbon-based materials,the materials of the oxygen electrode that own good development prospects are obtained by the way which learning from each other.Consequently,the composite materials base on the combination of transition metal cobalt-nickel-based compounds and nitrogen-doped graphene,the structures and morphologies of hybrid materials are designed and optimized by the hydrothermal preparation methods in this paper.As a result,the catalysts have a large specific surface area of activity and high conductivity,which can expose more activity sites and accelerate the rate of charge transfer.These effects are benefit to the improvement with the catalytic activity of oxygen reduction reaction?ORR?and oxygen evolution reaction?OER?.Moreover,the materials are applied to as an oxygen electrode of zinc air batteries,which exhibit excellent electrochemical performance and superior stability.The specific work content of this work is as follows:?1?The hybrid catalyst material which combined Co?OH?₂-NiCo₂O₄ nanosheets compound with nitrogen-doped graphene?Co?OH?₂-NiCo₂O₄/N-rGO?was successfully prepared by a simple two-step hydrothermal method.The experimental results indicated that the Co?OH?₂-NiCo₂O₄/N-rGO hybrid catalyst possessed excellent performance of oxygen reduction reaction?ORR?and oxygen evolution reaction?OER?in alkaline media.Meanwhile,it also exhibited efficient performance for oxygen reduction reaction?ORR?in neutral media.Moreover,the Co?OH?₂-NiCo₂O₄/N-rGO catalyst had excellent electrochemical performance and robust stability as an oxygen electrode for zinc air batteries.These results are attributed to the architecture of the 2D nanosheets with Co?OH?₂-NiCo₂O₄ and N-rGO,the hybrid catalyst possesses a large surface specific area,which can expose more active sites.Additionally,owing to the high electrical conductivity of the N-rGO,the synergistic effect of the strongly coupling Co?OH?₂-NiCo₂O₄ with N-rGO contributes faster charge transfer rate for electrochemical process.?2?The Co₃O₄-NiCo₂O₄ heterostructure hybrid nanoparticles anchored in nitrogen doped graphene?Co₃O₄-NiCo₂O₄/N-rGO?was successfully synthesized by a simple one-step hydrothermal synthesis method.The experimental results manifested that the Co₃O₄-NiCo₂O₄/N-rGO catalyst displayed superior performance of oxygen reduction reaction?ORR?and oxygen evolution reaction?OER?in alkaline media.Meanwhile,the catalyst was used as an oxygen electrode of zinc-air battery,which also exhibited splendid electrochemical performance and superior stability.These results are ascribed to Co₃O₄-NiCo₂O₄nanoparticles dispersed uniformly on the N-rGO,leading to the catalyst owns a large active specific surface area,which can expose rich active sites.Additionally,the N-rGO nanosheets are provided with high conductivity and the heterostructure exists in Co₃O₄-NiCo₂O₄ hybrid nanoparticles,and the combination between Co₃O₄-NiCo₂O₄ nanoparticles and N-rGO nanosheets possesses synergistic effect,resulting in the rate of charge transfer and transport is accelerated during electrochemical process.