The Synthesis Of Nickel-Cobalt-Sulfide/Carbon-nitrogen Composite And Its Application In Electrocatalysis

The growing demand from energy and environmental crisis has promoted worldwide research for advanced electrochemical energy storage technologies such as fuel cells and metal-air batteries.Rechargeable zinc-air batteries?ZABs?have emerged as a prospective energy conversion system due to the advantages of low-cost,high safety,environmental green,and high theoretical energy density?¹084 Wh Kg-1?compared to other chemical batteries.Oxygen reduction reaction?ORR?and oxygen evolution reaction?OER?are two important processes for the energy conversion efficiency of electrically rechargeable ZABs.At present,noble metals and their alloys have been recognized to be promising oxygen electrocatalysts.However,their poor stability and high cost bring great challenges for their widespread applications.Therefore,extensive effort has been devoted to the design and development of cost-competitive and earth-abundant materials with high catalytic activity and stability for oxygen electrocatalysis.Numerous studies have shown that a metal-nitrogen-carbon?Me-N-C,Me is mainly a transition metal?composite containing mechanism has good ORR catalytic potential,while transition metal sulfides have excellent OER activity due to their good electrical conductivity and rich in active sites.Transition sulfide carbon-nitrogen composites are expected to replace precious metal catalysts and be used in rechargeable zinc batteries.In this paper,we synthesized two transition metal sulfide carbon-nitrogen composite catalysts with higher activity and better stability.In the first work,we loaded nickel-cobalt-sulfur nanoparticles?NiCo₂S₄?on nitrogen-doped carbon nanotubes?NiCo₂S₄/N-CNT?,and the size of the supported NiCo₂S₄ nanoparticles can be controlled by changing the synthesis conditions.The electrocatalytic properties of the synthesized materials were investigated.In the second work,we synthesized a carbon nanotube?CNT?coated NiCo₂S₄@g-C₃N₄?NiCo₂S₄nanoparticle grown to g-C₃N₄?three-dimensional porous catalyst.We obtained a an self-supporting electrode with a certain mechanical strength using the entanglement between NiCo₂S₄@g-C₃N₄ and CNT by suction filtration.And further explore the interaction between CNT,NiCo₂S₄ and g-C₃N₄.It was found that there is an electron interaction between CNT,g-C₃N₄ and NiCo₂S₄,which causes the deflection of the electron cloud,further enhanced the catalytic performance towards.Furthermore,the prepared NiCo₂S₄/N-CNT and NiCo₂S₄@g-C₃N₄-CNT were applied to rechargeable zinc-air batteries?ZABs?and water-splitting system.When applied to rechargeable ZABs,NiCo₂S₄@g-C₃N₄-CNT exhibits a low overpotential?0.84 V?,high efficiency?60.6%?and a long charge and discharge cycle?330 cycles?.The NiCo₂S₄@g-C₃N₄-CNT Free-standing electrode also exhibits good battery performance when applied to a solid-state zinc-air battery,and still has stable performance under repeated bending conditions,basically satisfying the flexibility requirement of the battery.NiCo₂S₄@g-C₃N₄-CNT based ZABs can successfully illuminate the LED screen,the LED watch and charge the mobile phone.It is precisely because of the coupling between NiCo₂S₄ nanoparticles,g-C₃N₄ and CNT that the electron cloud changes and exposes more active sites,meanwhile the structure of the Free-standing electrode also provides a good channel for oxygen diffusion,thereby promoting The adsorption and desorption behavior during the catalytic process.