In-Situ Preparation Of Nickel And Cobalt-Based Electrode Materials And Their Electrocatalytic And Energy Storage Properties

The development of high-performance and stable electrode materials is a key issue for the construction of high-performance water-based batteries.Finding efficient,green,and pollution-free materials has always been a key direction in the field of energy research.Based on the preparation and performance of nickel-cobalt-based transition metal compounds,this article takes alkaline zinc-air batteries and nickel-zinc batteries as the starting point,and studies their applications in devices.The specific content is as follows:(1)N and O co-doped helical carbon nanotubes encapsulated with Co Fe alloy(Co Fe@NO-CNT)were in situ prepared on carbon paper using ZIF67 as precursor through ion exchange and CVD pyrolysis methods.Comparative studies found that the heterogeneous catalysis of Co Fe alloy produced spiral carbon nanotubes,which had a much higher N and O doping content than conventional carbon nanotubes containing monometallic cobalt particles.On the basis of the advantages of in situ growth and 3D open structure of catalytic electrode,the helical carbon nanotubes with abundant N catalytic species,C=O functional groups and core-shell structure exhibit a larger diffusion-limited current density of 5.75 m A/cm² for ORR,low overpotential of 160 and 126 m V at the current density of 10 m A/cm² for OER and HER,respectively,and a small potential gap of 0.61 V between ORR and OER.The zinc-air battery(ZAB)and water electrolysis device based on Co Fe@NO-CNT electrodes showed peak power density(142 m W/cm²),specific capacity(819 m Ah/g _Zn),energy density(1037Wh/kg _Zn),low overall water splitting voltage(1.57 v@10 m A/cm²)and good stability.Two Co Fe@NO-CNT based zinc-air batteries in serial connection can efficiently drive the electrolyzer with two same Co Fe@NO-CNT/CFP electrodes as the anode and cathode to splite water and two quasi-solid state ZABs in series provid a peak power of 212 m W to light a red light-emitting diode(LED)indicator(1.5V).This work opens up an effective way for in-situ preparation of high performance multifunctional electrocatalysts with 3D open structures and high doping element content.(2)Using a simple hydrothermal method and coating preparation process,a polypyrrole(PPy)film was prepared on a carbon paper substrate to wrap the molybdenum-doped nickel hydroxide nanosheet array(Mo-Ni(OH)₂@PPy).Experiments show that molybdenum doping changes the phase of nickel hydroxide and significantly increases the electrode capacity.PPy as a protective shell structure can reduce the resistance of?-Ni(OH)₂ and improve the cycle stability.After modification,Mo-Ni(OH)₂@PPy has a specific capacity of 193m Ah/g when discharged at a current density of 0.86 A/g,and a specific capacity of 173m Ah/g when discharged at a current density of 5.16 A/g.After 600 cycles of testing,the capacity retention rate of Mo-Ni(OH)₂@PPy is 84.2%,which is higher than that of the Mo-Ni(OH)₂ electrode.This method is expected to provide direction and ideas for the preparation of new electrodes in high capacity and high stability energy storage technology.(3)Using ZIF67 as a template,P-Ni Co₂O₄ nanosheet arrays were prepared on a carbon paper substrate through ion exchange,oxidation,and phosphating processes,and used for energy storage performance research.Experiments have found that the phosphating temperature can affect the morphology and performance to varying degrees.When phosphating at 300?,a better structure is obtained and the electrochemical performance is the best.It is found by comparison that the phosphating process produces a large amount of oxygen vacancies in the nickel cobalt oxide,which reduces the interface resistance and significantly increases its capacity.A nickel-zinc battery is constructed with P-Ni Co₂O₄.At a discharge current density of 7.1 A/g,a high capacity of 272.4 m Ah/g can be obtained,and it has good rate performance.After a cyclic test of 2070 cycles,the capacity retention rate was87.8%.The energy density of the constructed P-Ni Co₂O₄//Zn battery is 540 Wh/kg,and the maximum power density is 11.8 k W/kg,which is superior to the previously reported nickel-zinc aqueous battery.This kind of high performance nickel-zinc battery has a broad application prospect in electric vehicles and intelligent devices.