Application Of Transition Metal Based Materials In Zinc-Air Battery

The shortage of high efficiency,economical,and stable electrocatalysts is the bottleneck for both energy conversion and storage.Among the currently known energy storage devices,Zn-air batteries（ZABs）are being extensively investigated owing to their low cost,high capacity and long shelf life in comparison to other metal-air and ion batteries.However,their progress has been largely slowed down by the lack of high efficiency and stable air electrodes,as a result of the sluggish oxygen reduction and evolution reactions at the cathode（ORR and OER）.Pt or Ir-based nanomaterials are widely known as the most satisfied ORR or OER electrocatalysts.However,the high cost and inferior durability greatly impede their large-scale applications.Therefore,there is a timely urgency to explore high efficiency,economical,bifunctional ORR/OER electrocatalysts,derived from earth-abundance elements.Transition metal-based materials have been extensively studied due to their low cost,abundant reserves,and efficient oxygen reactions.The electrocatalytic performance of the electrocatalysts can be improved by adjusting the surface atoms,heteroatomic doping and surface interface structure.Hence,in this dissertation,the electrocatalytic performance of the electrocatalysts were regulated by adjusting the surface interface structure of the transition metal base material.The specific works are shown as belows:1.NiFe@N-C electrocatalysts were synthesized by one-step sintering method.Their core-shell structure guarantees Ni_0.5Fe_0.5@N-C with excellent electrocatalytic activity and stability towards.The liquid Zn-air battery shows a large open-circuit potential of 1.48 V,a small charge-discharge voltage gap of 0.12 V at 10 mA/cm²,together with excellent cycling stability even after 40 h at 20 mA/cm².Interestingly,the all-solid-like Zn-air battery shows the desired mechanical flexibility.The present study opens new an opportunity for the rational design of metal@N-graphite based catalysts of core-shell structures for electrochemical catalysts and renewable energy applications.2.CuCo@N-C electrocatalysts were synthesized by a one-step sintering method.The catalytic activity of CuCo@N-C is promoted by the co-decoration due to the strong electron transfer between Cu and Co.Accordingly,the aqueous ZAB assembled with CuCo@N-C as the air electrode exhibits a high voltage of 1.51 V,a maximum power density of 170 mW/cm²（1.48 V and 165 mW/cm² for Pt/C）,and excellent device cycling stability.The solid-like ZAB shows a low voltage gap of 0.76 V at 40 mA/cm²and high energy efficiency of 72%at 10 mA/cm² with an excellent cyclic stability（50h）.3.Fe/Fe₃C@N-C electrocatalysts were synthesized by a one-step sintering method.The phase structure and surface interface structure of the nanocomposite material were regulated by adjusting the ratio of Fe and Fe₃C.The electrocatalyst exhibits a low potential gaps(ΔE,ΔE=E_j=10-E_1/2)in pH-universal environment.The estimated values are about 0.70 V,1.07 V and 1.10 V in alkaline,neutral,and acidic media.Neutral ZAB is constructed by the Fe/Fe₃C@N-C composite as an air electrode,exhibiting a favorable performance in energy storage with an open-circuit potential of 1.42 V and the high power density of 80 mW/cm².The ZAB also has a superior cycling stability with only 0.5%decay more after 1200 charge-discharge cycles at 2 mA/cm².This work provides potential applications of Fe/Fe₃C@N-C as the air electrodes for advanced pH-universal media based on Zn-air batteries for future energy storage devices.4.MnO/Co@N-C electrocatalysts were synthesized by a one-step sintering method.The electrocatalyst exhibits a satisfactory OER overpotential of 1.42（at 10mA/cm²）under illumination,contrasting with the dark condition（overpotential of 1.52）.Importantly,the ZAB with the MnO/Co@N-C air cathode shows a maximum power densities of 189 mW/cm² under illumination（about 33.1%increment compare with the without illumination）.In addition,the open-circuit potential（OCP）of the MnO/Co@N-C is 1.48 V（about 2.1%increment）.What’s more,the MnO/Co@N-C based ZAB can not only enhance the round-trip efficiency from⁵5.6%to⁶4.1%,but also increase the cyclic stabilities（about 66.7%increment）.The study opens a new pathway for enhancing the OER and ORR bifunctional electrocatalysis and also provides a new strategy for improving the round-trip efficiency of ZAB.5.Porous Ni/NiO nanosheets were synthesized by a water bath method.Benefiting from the contributions of the Ni and NiO phases,the well-established pore channels for charge transport at the interface between the phases,and the enhanced conductivity due to oxygen-deficiency at the pore-edges,the porous Ni/NiO nanosheets show an outstanding OER and ORR performance.More significantly,a Zn–air battery employing the porous Ni/NiO nanosheets exhibit an initial charge-discharging voltage gap of 0.83 V（2 mA/cm²）and long-time cycling stability（120 h）.