Preparation And Application Of Dual Function Oxygen Electrocatalysts Based On Titanium Dioxide Fibers

So far,carbon materials have been widely chosen as carriers for metal electrocatalysts due to their high electrical conductivity and large specific surface area.However,these carbon carrier catalysts may deteriorate in performance after long-term operation due to carrier corrosion or agglomeration of catalyst particles.Therefore,the development of stable and corrosion-resistant catalyst carriers is imperative for any catalytic system.Titanium dioxide(TiO2),as a transition metal oxide,has received much attention because of its structural stability,high chemical stability,high reactivity,environmental friendliness and low cost.The development of titanium dioxide materials with porous properties as catalyst carriers has become an important goal.Based on this,this paper selects TiO2 as the catalyst carrier material,designs and prepares Co3O4@TiO2 nanofibers and CoFe2O4@TiO2 nanofibers,investigates their catalytic performance of oxygen precipitation reaction(OER)and oxygen reduction reaction(ORR),and assembles these two catalyst materials into zincair batteries to study the energy density and charge/discharge stability of the batteries.The performance of these two catalysts was studied.The main work conducted and the conclusions obtained in this paper include the following:(1)TiO2 precursor fibers were prepared by sol-gel method combined with electrostatic spinning method using polyvinylpyrrolidone(PVP)as polymer template,ethanol as solvent and tetrabutyl titanate(TBT)as titanium source,and titanium dioxide nanofibers(TiO2 NFs)with mesoporous structure were generated after high temperature thermal annealing.The main parameters in the spinning process and thermal annealing process were studied comparatively.Since TiO2 NFs need to be used as catalyst carrier fibers,their diameter size will directly affect the loading of the subsequent catalyst and thus the catalytic performance of the subsequent materials,so the TiO2 precursor fibers need to have a uniform and coarse diameter.It was found that the diameter of TiO2 precursor fibers obtained by electrostatic spinning reached 558 nm at a PVP concentration of 10 wt%,a TBT concentration of 18 wt%,and a spinning voltage of 15 kV,the TiO2 precursor fibers obtained by electrostatic spinning reached a diameter of 558 nm with a standard deviation of 51.9 nm,and the dispersion was relatively small,indicating that the fiber thickness was relatively uniform..The TiO2 precursor fibers were warmed up to 600 ℃ and held for 3 h at a heating rate of 2 ℃/min,and anatase TiO2 NFs with a diameter of 384 nm,a specific surface area of 66.81 m2/g,and an average pore size of 5.62 nm were obtained.(2)Co3O4@TiO2 NFs were prepared by electrostatic spinning combined with thermal annealing using cobalt acetylacetonate(Co(acac)2)as the cobalt source,and the Co3O4@TiO2 NFs were characterized by XRD and specific surface area with a spinel-like crystalline structure and mesoporous structure in the fibers.After the oxygen evolution reaction(OER)and oxygen reduction reaction(ORR)tests,it was found that the fibers have high initial potential(0.84 V),low overpotential gap(0.85 V),low overpotential(382 mV)and high ultimate current density(5.30 mA·cm-2)at the cobalt:titanium atomic ratio of 1:10,and the Co3O4@TiO2-10 NFs have good durability and cycling stability.(3)Since there is still a large gap between the ORR and OER catalytic activities of Co3O4@TiO2-10 NFs and commercial Pt/C and IrO2/C catalysts,Fe(acac)3 was also introduced into the spinning solution of Co3O4@TiO2 NFs as an iron source to obtain a bimetallic spinel structure to improve its bifunctional catalytic activity.The spinel-type CoFe2O4 structure was found to be obvious in the Co1Fe1@TiO2 NFs with a molar ratio of 1:1 by XRD tests.In the specific surface area test,it was found that the structure of large pores around 13 nm appeared in Co1Fe1@TiO2 NFs.Compared with other prepared fibers,Co1Fe1@TiO2 NFs have high initial potential(0.88 V),low overpotential(284 mV),high ultimate current density(6.40 mA·cm-2)and low overpotential gap(0.72 V)during the catalytic process.In addition,Co1Fe1@TiO2 NFs have good durability,cycling stability and bifunctional catalytic properties.Co3O4@TiO2-10 NFs and Co1Fe1@TiO2 NFs were assembled as catalyst materials to form a zinc-air battery(ZAB)and tested for the relevant performance of the battery.It was found that the open-circuit voltage of Co1Fe1@TiO2 NFsbased ZAB is low but the discharge time is long,about 1.16 times that of Pt/C&IrO2/Cbased cells.The specific capacity is as high as 1021.4 mAh g-1,which almost reaches the theoretical energy density of primary ZABs.In summary,different spinel oxide loaded TiO2 NFs were prepared by electrostatic spinning method combined with thermal annealing as catalyst materials for oxygen electrode reaction.The prepared transition metal oxide catalysts showed good catalytic activity and stability for both OER and ORR.Therefore,this topic is instructive in the development of non-precious metal bifunctional catalysts.