| Facing the crisis of energy shortage,it is very important to develop efficient clean energy.Zinc-air battery has attracted much attention because of its high theoretical energy density.The main factor restricting its development is its slow oxygen reduction and oxygen evolution reaction.Therefore,it is necessary to develop efficient and stable bifunctional electrocatalysts to promote the reaction.In this paper,the preparation and electrocatalytic properties of cobalt-based carbon nanotube composites are studied in the following three aspects:1.Co Fe-coated carbon nanotubes(Co Fe/NO-CNT)were prepared in situ on carbon paper by hydrothermal method and CVD pyrolysis process,The effects of pyrolytic carbon sources(urea and dicyandiamide)used in the front section of tubular furnace on the N/O doping content and the electrocatalytic performance of OER/ORR of carbon nanotubes were compared,and the effects of single cobalt and cobalt-iron alloy on the electrocatalytic performance of nanotubes were also compared and analyzed,It is found that carbon nanotubes coated with cobalt-iron alloy prepared by using urea as pyrolytic carbon source have the best OER/ORR electrocatalysis performance and zinc-air battery performance,The overpotential is 180 m V when the OER current density is 10 m A/cm2,the limiting current density of oxygen reduction is 5.71 m A/cm2,the half-wave potential is 0.86 V,the specific capacity of zinc-air battery is803 m Ah/g Zn,and the peak power density is 139 m W/cm2,The excellent properties of this sample are attributed to:(i)the alloying effect of alloy Co Fe promotes the contribution of core-shell structure(M@C)species to ORR performance;(ii)Higher carbon-oxygen double bond functional group content promotes the adsorption of oxygen intermediates,which is beneficial to improve OER performance.2.The composite catalytic materials of manganese oxide and cobalt-iron alloy coated carbon nanotubes(Co Fe@CNT/Mn O)were prepared in situ on carbon paper by hydrothermal method and CVD pyrolysis process,It was found that the introduction of manganous oxide and trimanganese tetroxide improved the oxygen reduction performance and OER/ORR stability of the catalyst,It has an overpotential of 193 m V when the OER current density is 10 m A/cm2,a larger diffusion limit current density of 5.75 m A/cm2 and a half-wave potential(E1/2=0.85 V)under ORR,The assemble zinc-air battery shows high specific capacity(810 m Ah/g Zn)and peak pow density(164 m W/cm2),The reasons for its performance optimization are as follows:(i)Mn Ox supported on carbon nanotubes improves the ORR catalytic performance of the catalyst;(ii)Varying manganese oxides can protect and delay the oxidation damage of carbon materials,and promote the improvement of ORR/OER stability of the whole electrocatalytic material.3.the catalytic material(Co@CNT-2)of flaky multi-stage cathode carbon material was prepared by chemical bath deposition and CVD pyrolysis process,The effects of the amount of melamine used in the front end of tubular furnace on the morphology and structure of materials,the electrocatalysis performance of OER/ORR and the battery performance were comparatively studied,It was found that the flaky graded cobalt-carbon nanotube catalytic material prepared when the amount of melamine was 2 g had the best catalytic performance of OER/ORR battery and zinc-air battery,It has a low overpotential of 210 m V when the OER current density is 10m A/cm2,and a large diffusion limit current density of 5.13 m A/cm2 and a half-wave potential(E1/2=0.87 V)under ORR,The assembled zinc-air battery has specific capacity(771 m Ah/g Zn)and peak power density(167 m W/cm2),The optimization of its performance can be attributed to:(i)the carbon nanotube composite catalyst grown in situ on CFP has high conductivity;(ii)The graded carbon material structure is beneficial to electrolyte diffusion,gas precipitation,active site exposure and has larger electrochemical activity specific surface area. |
PDF Full Text Request